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- Describe the structures found in the PNS
- Distinguish between somatic and autonomic structures, including the special peripheral structures of the enteric nervous system
- Name the twelve cranial nerves and explain the functions associated with each
- Describe the sensory and motor components of spinal nerves and the plexuses that they pass through
The PNS is not as contained as the CNS because it is defined as everything that is not the CNS. Some peripheral structures are incorporated into the other organs of the body. In describing the anatomy of the PNS, it is necessary to describe the common structures, the nerves and the ganglia, as they are found in various parts of the body. Many of the neural structures that are incorporated into other organs are features of the digestive system; these structures are known as the enteric nervous system and are a special subset of the PNS.
A ganglion is a group of neuron cell bodies in the periphery. Ganglia can be categorized, for the most part, as either sensory ganglia or autonomic ganglia, referring to their primary functions. The most common type of sensory ganglion is a dorsal (posterior) root ganglion. These ganglia are the cell bodies of neurons with axons that are sensory endings in the periphery, such as in the skin, and that extend into the CNS through the dorsal nerve root. The ganglion is an enlargement of the nerve root. Under microscopic inspection, it can be seen to include the cell bodies of the neurons, as well as bundles of fibers that are the posterior nerve root (Figure 1). The cells of the dorsal root ganglion are unipolar cells, classifying them by shape. Also, the small round nuclei of satellite cells can be seen surrounding—as if they were orbiting—the neuron cell bodies.
Another type of sensory ganglion is a cranial nerve ganglion. This is analogous to the dorsal root ganglion, except that it is associated with a cranial nerve instead of a spinal nerve. The roots of cranial nerves are within the cranium, whereas the ganglia are outside the skull. For example, the trigeminal ganglion is superficial to the temporal bone whereas its associated nerve is attached to the mid-pons region of the brain stem. The neurons of cranial nerve ganglia are also unipolar in shape with associated satellite cells. The other major category of ganglia are those of the autonomic nervous system, which is divided into the sympathetic and parasympathetic nervous systems.
The sympathetic chain ganglia constitute a row of ganglia along the vertebral column that receive central input from the lateral horn of the thoracic and upper lumbar spinal cord. Superior to the chain ganglia are three paravertebral ganglia in the cervical region. Three other autonomic ganglia that are related to the sympathetic chain are the prevertebral ganglia, which are located outside of the chain but have similar functions. They are referred to as prevertebral because they are anterior to the vertebral column. The neurons of these autonomic ganglia are multipolar in shape, with dendrites radiating out around the cell body where synapses from the spinal cord neurons are made. The neurons of the chain, paravertebral, and prevertebral ganglia then project to organs in the head and neck, thoracic, abdominal, and pelvic cavities to regulate the sympathetic aspect of homeostatic mechanisms.
Another group of autonomic ganglia are the terminal ganglia that receive input from cranial nerves or sacral spinal nerves and are responsible for regulating the parasympathetic aspect of homeostatic mechanisms. These two sets of ganglia, sympathetic and parasympathetic, often project to the same organs—one input from the chain ganglia and one input from a terminal ganglion—to regulate the overall function of an organ. For example, the heart receives two inputs such as these; one increases heart rate, and the other decreases it.
The terminal ganglia that receive input from cranial nerves are found in the head and neck, as well as the thoracic and upper abdominal cavities, whereas the terminal ganglia that receive sacral input are in the lower abdominal and pelvic cavities. Terminal ganglia below the head and neck are often incorporated into the wall of the target organ as a plexus. A plexus, in a general sense, is a network of fibers or vessels. This can apply to nervous tissue (as in this instance) or structures containing blood vessels (such as a choroid plexus). For example, the enteric plexus is the extensive network of axons and neurons in the wall of the small and large intestines. The enteric plexus is actually part of the enteric nervous system, along with the gastric plexuses and the esophageal plexus. Though the enteric nervous system receives input originating from central neurons of the autonomic nervous system, it does not require CNS input to function. In fact, it operates independently to regulate the digestive system.
View the University of Michigan WebScope to explore the tissue sample in greater detail. If you zoom in on the dorsal root ganglion, you can see smaller satellite glial cells surrounding the large cell bodies of the sensory neurons. From what structure do satellite cells derive during embryologic development?
Bundles of axons in the PNS are referred to as nerves. These structures in the periphery are different than the central counterpart, called a tract. Nerves are composed of more than just nervous tissue. They have connective tissues invested in their structure, as well as blood vessels supplying the tissues with nourishment. The outer surface of a nerve is a surrounding layer of fibrous connective tissue called the epineurium. Within the nerve, axons are further bundled into fascicles, which are each surrounded by their own layer of fibrous connective tissue called perineurium. Finally, individual axons are surrounded by loose connective tissue called the endoneurium (Figure 3).
These three layers are similar to the connective tissue sheaths for muscles. Nerves are associated with the region of the CNS to which they are connected, either as cranial nerves connected to the brain or spinal nerves connected to the spinal cord.
View the University of Michigan WebScope to explore the tissue sample in greater detail. With what structures in a skeletal muscle are the endoneurium, perineurium, and epineurium comparable?
The nerves attached to the brain are the cranial nerves, which are primarily responsible for the sensory and motor functions of the head and neck (one of these nerves targets organs in the thoracic and abdominal cavities as part of the parasympathetic nervous system). There are twelve cranial nerves, which are designated CNI through CNXII for “Cranial Nerve,” using Roman numerals for 1 through 12. They can be classified as sensory nerves, motor nerves, or a combination of both, meaning that the axons in these nerves originate out of sensory ganglia external to the cranium or motor nuclei within the brain stem. Sensory axons enter the brain to synapse in a nucleus. Motor axons connect to skeletal muscles of the head or neck. Three of the nerves are solely composed of sensory fibers; five are strictly motor; and the remaining four are mixed nerves.
Learning the cranial nerves is a tradition in anatomy courses, and students have always used mnemonic devices to remember the nerve names. A traditional mnemonic is the rhyming couplet, “On Old Olympus’ Towering Tops/A Finn And German Viewed Some Hops,” in which the initial letter of each word corresponds to the initial letter in the name of each nerve. The names of the nerves have changed over the years to reflect current usage and more accurate naming. An exercise to help learn this sort of information is to generate a mnemonic using words that have personal significance. The names of the cranial nerves are listed in Table 1 along with a brief description of their function, their source (sensory ganglion or motor nucleus), and their target (sensory nucleus or skeletal muscle).
Figure 5 shows where the nerves are located in the brain. The olfactory nerve and optic nerve are responsible for the sense of smell and vision, respectively. The oculomotor nerve is responsible for eye movements by controlling four of the extraocular muscles. It is also responsible for lifting the upper eyelid when the eyes point up, and for pupillary constriction. The trochlear nerve and the abducens nerve are both responsible for eye movement, but do so by controlling different extraocular muscles. The trigeminal nerve is responsible for cutaneous sensations of the face and controlling the muscles of mastication. The facial nerve is responsible for the muscles involved in facial expressions, as well as part of the sense of taste and the production of saliva. The vestibulocochlear nerve is responsible for the senses of hearing and balance. The glossopharyngeal nerve is responsible for controlling muscles in the oral cavity and upper throat, as well as part of the sense of taste and the production of saliva. The vagus nerve is responsible for contributing to homeostatic control of the organs of the thoracic and upper abdominal cavities. The spinal accessory nerve is responsible for controlling the muscles of the neck, along with cervical spinal nerves. The hypoglossal nerve is responsible for controlling the muscles of the lower throat and tongue.
|Table 1. Cranial Nerves|
|Mnemonic||#||Name||Function (S/M/B)||Central connection (nuclei)||Peripheral connection (ganglion or muscle)|
|On||I||Olfactory||Smell (S)||Olfactory bulb||Olfactory epithelium|
|Old||II||Optic||Vision (S)||Hypothalamus/thalamus/midbrain||Retina (retinal ganglion cells)|
|Olympus||III||Oculomotor||Eye movements (M)||Oculomotor nucleus||Extraocular muscles (other 4), levator palpebrae superioris, ciliary ganglion (autonomic)|
|Towering||IV||Trochlear||Eye movements (M)||Trochlear nucleus||Superior oblique muscle|
|Tops||V||Trigeminal||Sensory/motor—face (B)||Trigeminal nuclei in the midbrain, pons, and medulla||Trigemal|
|A||VI||Abducens||Eye movements (M)||Abducens nucleus||Lateral rectus muscle|
|Finn||VII||Facial||Motor—face, Taste (B)||Facial nucleus, solitary nucleus, superior salivatory nucleus||Facial muscles, Geniculate ganglion, Pterygopalatine ganglion (autonomic)|
|And||VIII||Auditory (Vestibulocochlear)||Hearing/balance (S)||Cochlearn nucleus, Vestibular nucleus/cerebellum||Spiral ganglion (hearing), Vestibular ganglion (balance)|
|German||IX||Glossopharyngeal||Motor—throat Taste (B)||Solitary nucleus, inferior salivatory nucleus, nucleus ambiguus||Pharyngeal muscles, Geniculate ganglion, Otic ganglion (autonomic)|
|Viewed||X||Vagus||Motor/sensory—viscera (autonomic)||Medulla||Terminal ganglia serving thoracic and upper abdominal organs (heart and small intestines)|
|Some||XI||Spinal Accessory||Motor—head and neck (M)||Spinal accessory nucleus||Neck muscles|
|Hops||XII||Hypoglossal||Motor—lower throat (M)||Hypoglossal nucleus||Muscles of the larynx and lower pharynx|
Three of the cranial nerves also contain autonomic fibers, and a fourth is almost purely a component of the autonomic system. The oculomotor, facial, and glossopharyngeal nerves contain fibers that contact autonomic ganglia. The oculomotor fibers initiate pupillary constriction, whereas the facial and glossopharyngeal fibers both initiate salivation. The vagus nerve primarily targets autonomic ganglia in the thoracic and upper abdominal cavities.
Visit this site to read about a man who wakes with a headache and a loss of vision. His regular doctor sent him to an ophthalmologist to the vision loss. The ophthalmologist recognizes a greater problem and immediately sends him to the emergency room. Once there, the patient undergoes a large battery of tests, but a definite cause cannot be found. A specialist recognizes the problem as meningitis, but the question is what caused it originally. How can that be cured? The loss of vision comes from swelling around the optic nerve, which probably presented as a bulge on the inside of the eye. Why is swelling related to meningitis going to push on the optic nerve?
Another important aspect of the cranial nerves that lends itself to a mnemonic is the functional role each nerve plays. The nerves fall into one of three basic groups. They are sensory, motor, or both (see Table 1). The sentence, “Some Say Marry Money But My Brother Says Brains Beauty Matter More,” corresponds to the basic function of each nerve.
The first, second, and eighth nerves are purely sensory: the olfactory (CNI), optic (CNII), and vestibulocochlear (CNVIII) nerves. The three eye-movement nerves are all motor: the oculomotor (CNIII), trochlear (CNIV), and abducens (CNVI). The spinal accessory (CNXI) and hypoglossal (CNXII) nerves are also strictly motor. The remainder of the nerves contain both sensory and motor fibers. They are the trigeminal (CNV), facial (CNVII), glossopharyngeal (CNIX), and vagus (CNX) nerves.
The nerves that convey both are often related to each other. The trigeminal and facial nerves both concern the face; one concerns the sensations and the other concerns the muscle movements. The facial and glossopharyngeal nerves are both responsible for conveying gustatory, or taste, sensations as well as controlling salivary glands. The vagus nerve is involved in visceral responses to taste, namely the gag reflex. This is not an exhaustive list of what these combination nerves do, but there is a thread of relation between them.
The nerves connected to the spinal cord are the spinal nerves. The arrangement of these nerves is much more regular than that of the cranial nerves. All of the spinal nerves are combined sensory and motor axons that separate into two nerve roots. The sensory axons enter the spinal cord as the dorsal nerve root. The motor fibers, both somatic and autonomic, emerge as the ventral nerve root. The dorsal root ganglion for each nerve is an enlargement of the spinal nerve.
There are 31 spinal nerves, named for the level of the spinal cord at which each one emerges. There are eight pairs of cervical nerves designated C1 to C8, twelve thoracic nerves designated T1 to T12, five pairs of lumbar nerves designated L1 to L5, five pairs of sacral nerves designated S1 to S5, and one pair of coccygeal nerves. The nerves are numbered from the superior to inferior positions, and each emerges from the vertebral column through the intervertebral foramen at its level. The first nerve, C1, emerges between the first cervical vertebra and the occipital bone. The second nerve, C2, emerges between the first and second cervical vertebrae. The same occurs for C3 to C7, but C8 emerges between the seventh cervical vertebra and the first thoracic vertebra. For the thoracic and lumbar nerves, each one emerges between the vertebra that has the same designation and the next vertebra in the column. The sacral nerves emerge from the sacral foramina along the length of that unique vertebra.
Spinal nerves extend outward from the vertebral column to enervate the periphery. The nerves in the periphery are not straight continuations of the spinal nerves, but rather the reorganization of the axons in those nerves to follow different courses. Axons from different spinal nerves will come together into a systemic nerve. This occurs at four places along the length of the vertebral column, each identified as a nerve plexus, whereas the other spinal nerves directly correspond to nerves at their respective levels. In this instance, the word plexus is used to describe networks of nerve fibers with no associated cell bodies. Of the four nerve plexuses, two are found at the cervical level, one at the lumbar level, and one at the sacral level (Figure 6).
The cervical plexus is composed of axons from spinal nerves C1 through C5 and branches into nerves in the posterior neck and head, as well as the phrenic nerve, which connects to the diaphragm at the base of the thoracic cavity. The other plexus from the cervical level is the brachial plexus.
Spinal nerves C4 through T1 reorganize through this plexus to give rise to the nerves of the arms, as the name brachial suggests. A large nerve from this plexus is the radial nerve from which the axillary nerve branches to go to the armpit region. The radial nerve continues through the arm and is paralleled by the ulnar nerve and the median nerve. The lumbar plexus arises from all the lumbar spinal nerves and gives rise to nerves enervating the pelvic region and the anterior leg. The femoral nerve is one of the major nerves from this plexus, which gives rise to the saphenous nerve as a branch that extends through the anterior lower leg.
The sacral plexus comes from the lower lumbar nerves L4 and L5 and the sacral nerves S1 to S4. The most significant systemic nerve to come from this plexus is the sciatic nerve, which is a combination of the tibial nerve and the fibular nerve. The sciatic nerve extends across the hip joint and is most commonly associated with the condition sciatica, which is the result of compression or irritation of the nerve or any of the spinal nerves giving rise to it.
These plexuses are described as arising from spinal nerves and giving rise to certain systemic nerves, but they contain fibers that serve sensory functions or fibers that serve motor functions. This means that some fibers extend from cutaneous or other peripheral sensory surfaces and send action potentials into the CNS. Those are axons of sensory neurons in the dorsal root ganglia that enter the spinal cord through the dorsal nerve root. Other fibers are the axons of motor neurons of the anterior horn of the spinal cord, which emerge in the ventral nerve root and send action potentials to cause skeletal muscles to contract in their target regions. For example, the radial nerve contains fibers of cutaneous sensation in the arm, as well as motor fibers that move muscles in the arm. Spinal nerves of the thoracic region, T2 through T11, are not part of the plexuses but rather emerge and give rise to the intercostal nerves found between the ribs, which articulate with the vertebrae surrounding the spinal nerve.
Anosmia is the loss of the sense of smell. It is often the result of the olfactory nerve being severed, usually because of blunt force trauma to the head. The sensory neurons of the olfactory epithelium have a limited lifespan of approximately one to four months, and new ones are made on a regular basis. The new neurons extend their axons into the CNS by growing along the existing fibers of the olfactory nerve. The ability of these neurons to be replaced is lost with age. Age-related anosmia is not the result of impact trauma to the head, but rather a slow loss of the sensory neurons with no new neurons born to replace them.
Smell is an important sense, especially for the enjoyment of food. There are only five tastes sensed by the tongue, and two of them are generally thought of as unpleasant tastes (sour and bitter). The rich sensory experience of food is the result of odor molecules associated with the food, both as food is moved into the mouth, and therefore passes under the nose, and when it is chewed and molecules are released to move up the pharynx into the posterior nasal cavity.
Anosmia results in a loss of the enjoyment of food. As the replacement of olfactory neurons declines with age, anosmia can set in. Without the sense of smell, many sufferers complain of food tasting bland. Often, the only way to enjoy food is to add seasoning that can be sensed on the tongue, which usually means adding table salt. The problem with this solution, however, is that this increases sodium intake, which can lead to cardiovascular problems through water retention and the associated increase in blood pressure.
Adrenomedullin: an important participant in neurological diseases
Adrenomedullin, a peptide with multiple physiological functions in nervous system injury and disease, has aroused the interest of researchers. This review summarizes the role of adrenomedullin in neuropathological disorders, including pathological pain, brain injury and nerve regeneration, and their treatment. As a newly characterized pronociceptive mediator, adrenomedullin has been shown to act as an upstream factor in the transmission of noxious information for various types of pathological pain including acute and chronic inflammatory pain, cancer pain, neuropathic pain induced by spinal nerve injury and diabetic neuropathy. Initiation of glia-neuron signaling networks in the peripheral and central nervous system by adrenomedullin is involved in the formation and maintenance of morphine tolerance. Adrenomedullin has been shown to exert a facilitated or neuroprotective effect against brain injury including hemorrhagic or ischemic stroke and traumatic brain injury. Additionally, adrenomedullin can serve as a regulator to promote nerve regeneration in pathological conditions. Therefore, adrenomedullin is an important participant in nervous system diseases.
Keywords: adrenomedullin brain injury glia mechanism morphine tolerance neural regeneration neuroprotective effect pathological pain regeneration sensitization target.
Conflict of interest statement
Summary schematic of the involvement…
Summary schematic of the involvement of adrenomedullin in pathological pain. Peripheral noxious stimuli…
Summary schematic of the involvement…
Summary schematic of the involvement of adrenomedullin in morphine tolerance. Chronic morphine administration…
Summary schematic of potential applications…
Summary schematic of potential applications of adrenomedullin for neuropathological diseases. Potential applications of…
Clonal Recognition in Anemones
Sea anemones compete for space on rocks or large shells, engaging in territorial battles using their stinging cells. Because asexual reproduction by fission is common in anemones, adjacent anemones are likely to be clonemates. Aggression is reduced or absent among clonemates, and intense between unrelated anemones. This self/nonself recognition system seems to function analogously to the vertebrate MHC system: internal identification of tissues is extended to an external phenotype that shapes aggressive interactions.
A fascinating thread that runs through the vertebrate kin recognition literature is in the intimate linkage between MHC variation and recognition phenotypes. This association between MHC and recognition draws an obvious inference that the recognition of self extends from the internal immune identification of tissue and organs to the external environment. Given this inference, it is unsurprising that MHC differences among animals correlate with urinary odorants.
Young salmonid fish swim in schools that are predominantly full sibs. Later in life, territorial interactions among adults can occur between highly related fish that have settled on adjacent territories. The cues used in maintaining sib associations are MHC related. The prevailing argument in studies of these fish is that MHC-related phenotype matching allows territorial fish to modulate their aggression to close relatives, resulting in inclusive fitness benefits to the fish.
One of the earliest areas of exploration of kin associations was schooling tadpoles. Larvae of many species of amphibia, including frogs, toads, and salamanders, preferentially school with close kin. The underlying ecological and evolutionary benefit of kin schooling in amphibia has been elusive. As in salmonid fish, kin associations may lead to modulation of competitive interactions among related animals. Alternatively, kin selection benefits from shared vigilance and predation risk may be important. In salamanders that develop cannibalistic morphs under food deprivation, cannibals avoid consuming close relatives. This is a clear example of kin recognition facilitating a kin-selected evolutionary response.
Rodent studies, using a wide variety of species, have provided key clues to the mechanisms and function of social recognition in mammals. Classic studies in mice link the cues used in phenotypic matching to the MHC complex. Mice that differ only at MHC loci can be discriminated using phenotypic matching mechanisms. Generally speaking, rodents show strong abilities to discriminate kin from nonkin using phenotype matching. This ability is important as many rodent populations may contain previously unmet close relatives both nepotistic (aid-giving) and mating decisions can reflect information concerning kinship. Enough is known about rodent kin recognition to reveal that expression of phenotype matching as a source of kinship information in behavioral decisions is very much affected by life history. A 2003 review of rodent kin recognition by Mateo shows that while recognition by familiarity (presumably individual recognition) is nearly universal in rodents, phenotypic matching is more restricted. Hypothetically, phenotype matching is used by those species the life histories of which are likely to bring previously unmet relatives together ( Figure 2 ).
Figure 2 . Mammals, such as this coati (Nasua narica), often have variable color patterns that might be used in making individual discriminations within social groups. Their highly developed olfactory senses could provide a platform for social recognition, as well. While individual recognition is often assumed with mammalian social groups, rigorous tests of this hypothesis are only available for a few species.
Human social biology is largely structured around individual recognition and classification. Familial similarity, at least in visual cues, provides at best weak evidence of relatedness, with the notable exception of monozygotic twins. The hypothesis that kin information, including possible phenotypic matching, operates at subconscious levels and shapes human social interactions is relatively unexplored.
Unlike all of the other animals discussed in this article, birds appear not to use olfactory information in social recognition. Studies of cooperatively breeding and communally nesting birds demonstrate that social recognition via distinctive calls, such as the contact call of the long-tailed tit, carry individually distinctive information that can be learned. Thus, kin are identified by association, but as yet there is no evidence for kin recognition by phenotypic matching in birds.
Nestmate recognition in eusocial insects usually relies on phenotype matching. Colony-specific cues are learned by young workers and that information is used in social interactions, particularly in excluding nonnestmates from the colony. Transfers among colonies of larvae or newly emerged adults are usually fully tolerated, suggesting that the cues are acquired from the surrounding environment rather than distinct productions of each worker. A key early finding was that recognition cues in social wasps are usually transmitted among workers via the colony’s nesting material. In honeybees, fatty acids that serve as strengtheners in the comb wax give all workers in the colony the same odor because of contact of the workers with the comb. Some ants use compound sequestration of hydrocarbons in the postpharyngeal gland as a method of establishing a colony-level recognition odor. These collective, or gestalt, labels simplify the recognition process in colonies that may have hundreds or thousands of members.
In eusocial insects, significant progress has been made in identifying the chemical compounds composing the recognition phenotype. Numerous studies show that young workers learn phenotypes, typically odors, of other workers in the colony. Most often the odors are metabolic products of the insects themselves as discussed earlier, the products of colony members typically combine to form a colony-level recognition signature. The most commonly used compounds are waxy materials secreted as waterproofing on the surface of the insect. These compounds are typically alkanes, methyalkanes, and alkenes, with chain lengths from 21 to 37 carbons. In some species, though, odors acquired from the environment contribute to nestmate recognition cues. Chemical analyses of surface extracts of insects often yield 20 or more compounds, but the presence of a compound does not automatically translate in the use of that compound in recognition. Experimental studies suggest that alkanes are used less as signals, perhaps because alkanes lack an easily perceived functional group or conformational feature. Multivariate analyses of gas chromatographic results can easily separate colonies, but offer no proof of which compounds are used in discriminations by the insects. Bioassays of putative recognition cues have implicated alkenes and methylalkanes (in ants and wasps), fatty acids (in honeybees), and macrocyclic lactones (in halictid bees) as recognition cues.
Phenotypic variation among colonies in the relative proportion of these compounds (correlated with genotypic variation among colonies) provides the information needed to make discriminations. In most species, young workers learn the phenotype of their colony and use this to make nestmate/nonnestmate discriminations. Young workers are flexible enough to learn the phenotype of the colony in which they emerge, even if they are not genetic members of the colony. This extends to an ability to integrate into colonies of other species: a mechanism that facilitates slave-making in ants and other types of social parasitism.
A notable exception to the use of odors in nestmate recognition is the discovery that some eusocial wasps use interindividual variation in surface markings in individual recognition and as the basis for social classifications.
Explorations of differential nepotism within colonies have generally yielded negative results. The most intensely explored question is whether honeybee queen larvae, which may be either full- or half-sisters to the workers that tend them, are preferentially treated by full-sisters. While some experiments suggest the existence of such preferential treatment, others show no such effect. The opportunity for differential nepotism exists in many species of eusocial insect, either because the colony’s queen mates several times, as in the honeybee, or because the colony has several queens. Worker policing mechanisms, in which competition among worker subgroups counterbalances possible nepotism, may prevent the emergence of measurable nepotistic biases.
List of Changes
Many thanks to reviewers of this text for their comments, suggestions, and corrections, most of which were incorporated throughout this new edition of Human Biology.
A thorough copy edit has improved the overall quality of the entire text.
As in the previous edition, the contributions of each organ system to maintaining homeostasis are emphasized throughout. A new homeostasis icon (scale) is used to identify homeostatic functions in the systems chapters, chapter 4 through chapter 16.
All statistics have been updated for this edition.
New Bioethical Focus readings present pros and cons on particular bioethical issues. Students are challenged to develop and defend his or her own opinions on the issues.
Chapter 4 - New title: Organization and Regulation of Body Systems. This was chapter 3, Introduction to Homeostasis, in the previous edition. The title was changed to better reflect the content of the chapter. Homeostasis was expanded and rewritten to provide better coverage of this topic.
Chapter 13: Nervous System has been extensively reorganized and rewritten. The discussion of the central nervous system now precedes that of the peripheral nervous system.
Chapter 19: Chromosomal Inheritance (previously chapter 18). This chapter has been reorganized. The human life cycle, including mitosis and meiosis, now begins the chapter. The chapter ends with a discussion of chromosomal inheritance abnormalities.
Chapter 23: Human Evolution (previously chapter 22: Evolution) has been completely rewritten and expanded. More detailed information on the origin of life and human evolution is given. This chapter contains many new, interesting, and helpful illustrations and photographs.
Chapter 24: Ecosystems and Human Interferences (previously chapter 23: Ecosystems). This chapter was rewritten and reorganized, and combines the material previously found in chapters 23 and 24.
Chapter 25: Conservation of Biodiversity is a completely new chapter, which discusses the current biodiversity crises including why we should care, the root causes, and how to preserve species and prevent extinctions.
e-Learning Connection is new to this edition, and gives access information to new learning technologies.
Chapter 1: A Human Perspective
This was the Introduction chapter in the previous edition.
1.2 The Process of Science includes an expanded explanation and summary of the scientific method.
New Bioethical Focus: Animals in the Laboratory
1.5 Flow diagram for the scientific method
Chapter 2: Chemistry of Life
This was chapter 1 in the previous edition.
2.6 Lipids. The discussion of soap was replaced by a discussion of emulsifiers.
New Bioethical Focus: Organic Pollutants
2.12 The pH scale 2.18 Glycogen structure and function
Chapter 3: Cell Structure and Function
This was chapter 2 in the previous edition.
3.3 Cellular Metabolism. The discussion of cellular respiration has been simplified. The phrase aerobic cellular respiration has been changed to cellular respiration for clarity.
New Bioethical Focus: Stem Cells
3.3 Animal cell 3.5 Tonicity 3.7 The nucleus and the nuclear envelope 3.9 The Golgi apparatus 3.12 Sperm cells 3.14 Cellular respiration
Chapter 4: Organization and Regulation of Body Systems
This was chapter 3, Introduction to Homeostasis, in the previous edition. The title was changed to better reflect the content of the chapter. Homeostasis was expanded and rewritten to provide better coverage of this topic.
4.1 Types of Tissues. As in the previous edition, this section covers the tissues, cavities, membranes, and organ systems of the human body. The term fiber (with regard to nerves) is explained. The phrase neuroglial cell has been changed to neuroglia throughout.
4.3 Organ Systems. This section has been reorganized so that the discussions of the Integumentary System and Regions of the Skin are kept together. The Working Together box has been moved to section 4.4 Homeostasis.
4.4 Homeostasis. The entire section has been rewritten and reorganized to give more emphasis on this topic. Negative and positive feedback mechanisms are more clearly explained in this edition. Regulation of Body Temperature has been moved to this section and rewritten. Homeostasis and Body Systems is new to this section.
4.2 Epithelial tissue 4.4 Connective tissue examples 4.6 Muscular tissue 4.11 Homeostasis 4.12 Negative feedback 4.13 Homeostasis and body temperature regulation 4.14 Regulation of tissue fluid composition
Part 2: Maintenance of the Human Body
Chapter 5: Digestive System and Nutrition
This was chapter 4 in the previous edition.
5.5 Nutrition. In the discussion of calcium, the usefulness of vitamin D and other vitamins in preventing osteoporosis is presented. The Health Focus "Weight Loss the Healthy Way" has been revised to improve clarity.
5.3 Swallowing 5.7 Hormonal control of digestive gland secretions
Chapter 6: Composition and Function of Blood
This was chapter 5 in the previous edition.
6.2 The White Blood Cells. Colony-stimulating factors (CSFs) are introduced.
6.3 Blood Clotting has been reorganized and rewritten.
6.5 Action of erythropoietin 6.8 Capillary exchange
Chapter 7: Cardiovascular System
This was chapter 6 in the previous edition. Throughout the chapter and entire text, the terms "O2-rich" and "O2-poor" replace the phrases "high in oxygen" and oxygenated" and "low in oxygen" or "deoxygenated."
7.4 The Vascular Pathways. The path of blood to and from the lower legs has been corrected and now includes the femoral artery, lower leg capillaries, and femoral vein.
7.6 Homeostasis. The end of the chapter has been repaged so that The Working Together page does not interrupt the end matter.
7.5 Internal view of the heart 7.6 Stages in the cardiac cycle 7.7 Conduction system of the heart
Chapter 8: Lymphatic and Immune Systems
This was chapter 7, Lymphatic System and Immunity, in the previous edition. The introductory story was revised to better introduce the immune system and its functions.
8.4 Induced Immunity. The immunization schedule for infants and young children has been updated to contain the latest requirements. In Cytokines and Immunity, the explanation of the technique to activate cytotoxic T cells to destroy cancer cells has been clarified. The explanation of the delayed allergic response has been simplified.
8.6 Clonal selection theory as it applies to B cells 8.8 Clonal selection theory as it applies to T cells 8.10b (updated Immunization table)
8.1 immunization table in Figure 8.10
Chapter 9: Respiratory System
This was chapter 8 in the previous edition.
9.3 The introductory paragraph was rewritten to emphasize the contribution of gas exchange to homeostasis.
9.5 Homeostasis has been rewritten and clearly explains how the respiratory system regulates pH and immunity.
9.1 The path of air(caption) 9.2 The respiratory tract 9.6 Vital capacity 9.8 Inspiration and expiration
Chapter 10: Urinary System and Excretion
This was chapter 9 in the previous edition.
10.1 has been revised to introduce the urinary system and the path of urine right away, before discussing the urinary organs. Some reorganization of heads allows the discussion of the role of kidneys in maintaining homeostasis to logically lead to a discussion of salt-water balance and acid-base balance.
10.7 Problems with Kidney Function. Replacing a kidney is a new topic to this edition.
New Bioethical Focus: Organ Transplants
10.1 Taking a drink of water 10.5 Nephron anatomy 10.7 Steps in urine formation 10.11 An artificial kidney machine
Part 3: Movement and Support in Humans
Chapter 11: Skeletal System
This was chapter 10 in the previous edition.
11.1 Tissues of the Skeletal System. The opening paragraph now introduces bone, cartilage, and connective tissues before discussing each in depth.
11.3 Bones of the Skeleton. The discussions of the pectoral girdle and arm have been rewritten, and the rotator cuff is mentioned.
11.4 Articulations has been revised - the discussion of arthritis has been expanded and was moved to the end of the section. The text for Figure 11.12 Joint Movements now more closely follows the illustration. The Working Together illustration now follows 11.5 Homeostasis, so it does not break up the text.
11.7 The vertebral column 11.8 Thoracic vertebrae and the rib cage 11.9 Bones of the pectoral girdle and arm 11.12 Joint movements, 11.13 Hip prosthesis
Chapter 12: Muscular System
This was chapter 11 in the previous edition.
12.4 Energy for Muscle Contraction introductory paragraphs have been rewritten for clarity. The discussion entitled Muscular Disorders is completely new and discusses muscle spasms and cramps, tendonitis, tetanus, muscular dystrophy, and myasthenia gravis.
12.7 Neuromuscular junction 12.12 Myasthenia gravis.
Part 4: Integration and Coordination in Humans
Chapter 13: Nervous System
This was chapter 12 in the previous edition. This chapter has been extensively reorganized. Many sections and topics have been rewritten. The central nervous system, limbic system, memory, language, and speech are discussed before the peripheral nervous system. Homeostasis ends the chapter.
13.1 Nervous Tissue was previously entitled Neurons and How They Work. Neuron Structure and Myelin Sheath have been rewritten. Synaptic Integration now follows the discussion of transmission across a synapse.
13.2 The Central Nervous System is discussed next in the logical sequence of spinal cord and brain. Functions of the Spinal Cord has been rewritten and now discusses the role the spinal cord plays in regulating internal organs in addition to the skeletal muscles. Parts of the brain are discussed in more depth.
13.3 The Limbic System and Higher Mental Functions contains discussions of the limbic system, memory and learning, and language and speech. (The discussion of Alzheimer disease has been moved to the end of the chapter).
13.4 The Peripheral System. The organization and content of this section remains essentially the same as in the last edition.
13.6 Homeostasis has been expanded to include discussions of two degenerative nervous system diseases, Alzheimer disease and Parkinson disease. The Alzheimer disease discussion has been updated with the newest information, and the Parkinson disease discussion is new to this chapter.
13.1 Organization of the nervous system 13.3 Myelin sheath 13.4 Resting and action potential 13.5 Synapse structure and function 13.6 Integration 13.7 Organization of the nervous system 13.9 The human brain 13.10 The cerebral cortex 13.12 The limbic system 13.13 Long-term memory circuits 13.15 Cranial and spinal nerves 13.16 A reflex arc 13.18 Drug actions at a synapse 13.19 Drug use 13.20 Alzheimer disease.
This was chapter 13 in the previous edition.
14.1 Sensory Receptors. Table 14.1 Exteroceptors is new and replaces Table 13.1 Special Sense Organs. Discussions of sensory receptors have been revised. How Sensation Occurs has been revised to include the influence of the reticular activating system, and how sensory receptors contribute to homeostasis.
14.2 Proprioceptors and Cutaneous Receptors. New A head title identifies and focuses the discussion of these topics. The topics Cutaneous Receptors and Pain Receptors were revised.
14.6 Sense of Equilibrium. Terminology has been changed. The term dynamic equilibrium has been changed to rotational equilibrium, and the term static equilibrium has been changed to gravitational equilibrium. The Health Focus reading Protecting Vision and Hearing now follows the discussion of hearing and is found at end of the chapter.
14.2 Sensation 14.10 Structure and function of the retina 14.15 Mechanoreceptors for equilibrium
14.1 Exteroceptors is new and replaces Table 13.1 Special Sense Organs
Chapter 15: Endocrine System
This was chapter 14 in the previous edition. The chapter has been reorganized, and some heads have changed. The chapter now ends with Chemical Signals (previously called Environmental Signals), instead of beginning with it. The introductory story is new. Terminology change: contrary hormone has been changed to antagonistic hormone. As before, each gland is discussed in turn with an emphasis on medical disorders caused by too much or too little hormones.
15.1 Endocrine Glands introduces and defines endocrine glands and hormones in general, and discusses the contribution of hormones to homeostasis. Table 15.1 logically ends this section.
15.4 Adrenal Glands. Glucocorticoids has been revised it now precedes the discussion of mineralocorticoids.
15.7 Chemical Signals. The information in this section has been reorganized and rewritten, and includes the discussion of steroid and peptide hormones. Hormonal versus Neural Signals includes the material formerly discussed in Environmental Signals.
New Health Focus: melatonin
New Bioethical Focus: Fertility Drugs
15.1 Puberty 15.9 Adrenal glands 15.14 Glucose tolerance test 15A Melatonin production 15.16 Cellular activity of hormones 15.17 Chemical signals 15B Higher-order multiple births
Part 5: Reproduction in Humans
The AIDS supplement and chapter 17 regarding STDs have been rewritten to include the latest research, techniques, and information.
Chapter 16: Reproductive System
This was chapter 15 in the previous edition. Development of Male and Female Sex Organs has been moved to chapter 18 Development and Agin.
16.1 Male Reproduction System. The discussion of sperm production and movement has been rewritten.
16.2 Female Reproduction System. The discussions of external genitals and orgasm in females has been rewritten.
16.3 Female Hormone Levels. The discussion of follicle development has been rewritten.
16.4 Control of Reproduction. Information about the "male pill" has been updated. Infertility is redefined. New to this section are discussions of fertility drugs, higher-order births, and vasectomy reversals. The terminology Assisted Reproductive replaces the terminology Alternative Methods of Reproduction in the previous edition. A new procedure called Intracytoplasmic Sperm Injection (ICSI) is covered in this section.
New Bioethical Focus: Assisted Reproductive Technologies.
16.3 Testis and sperm 16.9 Female hormone levels 16.10 Implantation 16.12 In vitro fertilization 16B Couples and children
Chapter 17: Sexually Transmitted Diseases
This was chapter 16 in the previous edition. The chapter has been revised to include non-sexually transmitted infectious diseases caused by viruses, bacteria, fungi, and other animals. Statistics of new cases of AIDS and other STDs have been updated to reflect the most current information from the Centers of Disease Control.
17.1 Viral Infectious Diseases (previously Viral in Origin) has been rewritten and the discussion of the typical DNA animal virus life cycle has been simplified for better understanding Figure 17.3 illustrating this life cycle has also been simplified. The discussion of HIV infections summarized and identifies types and subtypes of HIV found in Africa and in the United States. HIV infections and AIDS are covered in detail in the AIDS supplement.
17.2 Bacterial Infectious Diseases (previously Bacterial in Origin). All statistics have been updated.
17.3 Other Infectious Diseases (previously Other Sexually Transmitted Diseases) has been rewritten and includes a more detailed introduction to kingdoms Protista, Fungi, and Animalia, and how these organisms transmit infectious diseases. Several diseases caused by protozoa are discussed. There is a new topic on infectious diseases caused by fungi. The topic on infectious diseases caused by animals discusses head lice and parasitic worms, as well as pubic lice.
New Bioethical Focus: HIV Vaccine Testing in Africa
17.3 Life cycle of an animal DNA virus 17.4 Genital warts 17.5 Genital herpes 17.8 Chlamydial infection 17.10 Gonorrhea 17.12 Syphilis 17A AIDS in Africa 17.13 Organisms that cause vaginitis 17.14 Sexually transmitted animal
17.1 Infectious Diseases Caused by Viruses (revised) 17.2 Infectious Diseases Caused by Bacteria (revised) 17.3 Infectious Diseases Caused by Protozoa, Fungi, and Animals (new).
All sections of The AIDS Supplement have been rewritten and updated with the latest research, information, and statistics. The new introduction identifies the types and subtypes of HIV. The prevalence of AIDS in Africa and other less-developed countries is presented in the introductory story and reinforced in Figure S.2 and in Section S.1, which has been extensively rewritten.
S.2 Phases of an HIV Infection identifies HIV-1B as the prevalent subtype in the U.S. The definitions of the three categories remain the same. The discussions of the HIV structure and life cycle have been simplified for better understanding Figure S.5 illustrating the reproduction of HIV has also been simplified. The discussion of drug therapy and vaccines have been revised, reflecting the latest information on therapies now in use, in trials, and undergoing research.
A new Health Focus reading, Preventing Transmission of HIV, gives more emphasis to this information, which was contained in section S.4 in the previous edition.
S.2 Global HIV prevalence rates in adults at the end of 1999 S.5 Reproduction of HIV.
Chapter 18: Development and Aging
This was chapter 17 in the previous edition.
18.1 Fertilization has been completely rewritten and clearly shows the steps of fertilization. Figure 18.2 has been corrected.
18.2 Development Before Birth. The topic Gastrulation has been reorganized, rewritten, and clarified. The difference between embryonic development and fetal development is made clear in the discussion of embryonic development. New to this section, the discussion of the first month of embryonic development introduces stem cells and the controversy over using embryonic stem cells to cure human conditions. Much of the information in the First Month has been rewritten. Includes 18.3 Development of Male and Female Sex Organs (previously in the reproduction chapter).
18.4 Birth has been rewritten and explains the positive feedback mechanism in relation to the onset and continuation of labor.
There is a new discussion of the benefits of breast feeding to the mother and child under female breast and lactation.
New Bioethical Focus: Maternal Health Habits
18.2 Fertilization 18.3 Human development before implantation 18.4 Early developmental stages in cross section 18.7 Fetal circulation and the placenta 18.9 Human embryo at five weeks 18.10 A three- to four-month-old fetus 18.11 A six- to seven-month-old fetus 18B Health habits
Part 6: Human Genetics
Chapter 19: Chromosomal Inheritance
This was chapter 18 in the previous edition. The chapter has been reorganized. The human life cycle, including mitosis and meiosis, now begins the chapter. The chapter ends with a discussion of chromosomal inheritance abnormalities.
19.2 Mitosis contains a new topic Cytokinesis, which discusses cytokinesis and formation of a cleavage furrow.
19.4 Chromosomal Inheritance. The discussion of nondisjunction now precedes an expanded explanation of nondisjunction, how it occurs, and its resulting chromosomal abnormalities. Down syndrome and other syndromes caused by abnormalities in chromosome makeup follow the discussion of nondisjunction. The term triplo-X syndrome has been changed to poly-X syndrome.
New Bioethical Focus: Cloning in Humans
19.1 Life cycle of humans 19.8 Spermatogenesis and oogenesis 19.9 Human karyotype preparation
19.1 Meiosis I Versus Mitosis 19.2 Meiosis II Versus Mitosis These new tables help summarize the information given in the chapter.
Chapter 20: Genes and Medical Genetics
This was chapter 19 in the previous edition. This chapter has been fewer A heads. The new section 20.3 Beyond Simple Inheritance Patterns includes polygenic inheritance, multiple allelic traits, and incompletely dominant traits. Four sets of Practice Problems have been added.
20.2 Dominant/Recessive Traits. Recessive Disorders are now discussed before dominant disorders. Pedigree Charts makes it clear that with recessive genetic disorders, when both parents are affected, all children are affected (and why) and with dominant genetic disorders, two affected parents can have an unaffected child (and why). This information will help the student be able to understand and successfully answer the related practice problems.
20.3 Beyond Simple Inheritance Patterns includes polygenic inheritance, multiple allelic traits, and incompletely dominant traits.
New Bioethical Focus: Genetic Profiling
20.2 Genetic inheritance 20.9 Autosomal recessive pedigree chart 20.10 Autosomal dominant pedigree chart 20.12 Inheritance of blood type 20.13 Incomplete dominance 20.14 Cross involving an X-linked allele 20.15 X-linked recessive pedigree chart 20A Genetic profiling
Chapter 21: DNA and Biotechnology
This was chapter 20 in the previous edition. Most main sections and topics were rewritten for clarity.
21.1 DNA and RNA Structure and Function. Most topics in this section were rewritten for clarity.
21.2 Gene Expression. The DNA Code and Transcription topics were rewritten for clarity.
21.3 Biotechnology. Polymerase Chain Reaction was rewritten for clarity. Cloning of Transgenic Animals was updated, and the diagram (Fig. 21.18) that illustrates this procedure has been simplified for better understanding. The Human Genome Project discussion was updated to include recent achievements in that area. Gene sequencing of diseases or afflictions found on chromosome 17 is illustrated in new Figure 21.19. The Gene Therapy discussion has been updated and greatly expanded. It gives new information on gene therapy treatments for cystic fibrosis and for children with SCID using bone marrow stem cells. It also discussed the possibilities for the use of gene therapy to treat other illnesses, such as hemophilia, AIDS, cancer, and heart disease.
New Health Focus: Organs for Transplant
New Bioethical Focus: Transgenic Plants
21.2 DNA location and structure 21.9 Function of introns 21.16 Polymerase chain reaction 21.18 Genetically engineered animals 21.19 Genetic map of chromosome 17 Colors have been made consistent in all DNA/RNA illustrations.
21.2 Some DNA Codes and RNA Codons has been expanded.
This was chapter 21 in the previous edition. Statistics have been updated.
22.2 Origin of Cancer. Regulation of the Cell Cycle has been reorganized and rewritten for better understanding of the stimulatory and inhibitory pathways involved in the action of proto-oncogenes and tumor-suppressor genes. Apoptosis has been rewritten and contains new information on caspases and how they work to bring about apoptosis.
22.4 Diagnosis and Treatment. Future Therapies, which ends the section and the chapter has been updated and includes new information and a new illustration regarding cancer vaccine therapy and inhibitory drug therapy (previously called chemoprevention).
The Health Focus and Bioethical Focus readings have been moved to the end of the chapter so text is not interrupted.
New Bioethical Focus: Tobacco and Alcohol Use
22.3 Origin of cancer 22.4 Function of p53 22.5 Industrial chemicals 22.7 Treatment of cancer 22.8 Cancer vaccine
Part 7: Human Evolution and Ecology
Part 7 contains a new part introduction. Chapter 25 Conservation of Biodiversity is a completely new chapter.
Chapter 23: Human Evolution
This was chapter 22, Evolution, in the previous edition. The entire chapter has been completely rewritten and expanded to include more detailed information on the origin of life and human evolutionary events. This chapter contains many new, interesting, and helpful illustrations and photographs. The chapter has a new introductory story.
23.1 Origin of Life (previously 22.3 Organic Evolution). This section has been rewritten in more detail and Miller's experiment is explained. Taxonomy has been moved to 23.3 Humans are Primates. Only the classification of humans is examined.
23.2 Biological Evolution includes evidences of evolution - common descent and natural selection. The entire section has been rewritten. Each topic goes into more detail than previously.
23.3 Humans are Primates. This section has been completely rewritten. Characteristics of primates and the primate evolutionary tree are examined.
23.4 Evolution of Australopithecines. This new section gives details about the discoveries of australopithecine fossils in Southern and Eastern Africa.
23.5 Evolution of Humans. This entire section has been rewritten and has much more information and detail than in the previous edition.
New Bioethical Focus: The Theory of Evolution.
23.1 Chemical evolution 23.2 Fossils 23.3 Mechanism of evolution 23.4 Primate evolutionary tree 23.5 Australopithecus africanus 23.6 Human evolution 23.7 Homo erectus 23.8 Origin of modern humans 23.9 Neanderthals 23.10 Cro-Magnons 23A Australopithecus africanus skull
23.1 Evolution and Classification of Humans
Chapter 24: Ecosystems and Human Interferences
This was chapter 23 Ecosystems in the previous edition. This chapter has been rewritten and reorganized, and combines the material previously found in chapters 23 and 24.
24.2 Energy Flow and Chemical Cycling is now a main head, which emphasizes its importance. The content is the same as in the previous edition.
24.3 Global Biogeochemical Cycles. The order of the cycles has been changed to this: water cycle, carbon cycle, nitrogen cycle, and phosphorus cycle.
The discussion of the carbon cycle has been reorganized and rewritten. The topic Carbon Dioxide and Global Warming is new and contains information and statistics on global warming.
The discussion of the nitrogen cycle has been reorganized and rewritten. The topic Nitrogen and Air Pollution is new and contains information about acid rain, smog, and thermal inversions.
In the discussion of the phosphorus cycle, the Phosphorus and Water Pollution is new and contains information on eutrophication, biological magnification, and pollution of coastal regions and the seas.
New Health Focus: Stratospheric Ozone Depletion Threatens the Biosphere.
New Bioethical Focus: Preserving Ecosystems Abroad
24.2 Example of primary succession 24.5 Nature of an ecosystem 24A Ozone shield depletion 24B preserving ecosystems
Chapter 25: Conservation of Biodiversity
Chapter 25 Conservation of Biodiversity is a completely new chapter, which discusses the current biodiversity crises including why we should care, the root causes, and how to preserve species and prevent extinctions.
Transcriptional regulation of the peripheral nervous system in Ciona intestinalis
The formation of the sensory organs and cells that make up the peripheral nervous system (PNS) relies on the activity of transcription factors encoded by proneural genes (PNGs). Although PNGs have been identified in the nervous systems of both vertebrates and invertebrates, the complexity of their interactions has complicated efforts to understand their function in the context of their underlying regulatory networks. To gain insight into the regulatory network of PNG activity in chordates, we investigated the roles played by PNG homologs in regulating PNS development of the invertebrate chordate Ciona intestinalis. We discovered that in Ciona, MyT1, Pou4, Atonal, and NeuroD-like are expressed in a sequential regulatory cascade in the developing epidermal sensory neurons (ESNs) of the PNS and act downstream of Notch signaling, which negatively regulates these genes and the number of ESNs along the tail midlines. Transgenic embryos mis-expressing any of these proneural genes in the epidermis produced ectopic midline ESNs. In transgenic embryos mis-expressing Pou4, and MyT1 to a lesser extent, numerous ESNs were produced outside of the embryonic midlines. In addition we found that the microRNA miR-124, which inhibits Notch signaling in ESNs, is activated downstream of all the proneural factors we tested, suggesting that these genes operate collectively in a regulatory network. Interestingly, these factors are encoded by the same genes that have recently been demonstrated to convert fibroblasts into neurons. Our findings suggest the ascidian PNS can serve as an in vivo model to study the underlying regulatory mechanisms that enable the conversion of cells into sensory neurons.
Riveting hammer vibration damages mechanosensory nerve endings
Danny A. Riley, PhD, 13701 Evergreen Way, Austin, TX 78737.
Cell Biology, Neurobiology and Anatomy, Medical College of Wisconsin, Milwaukee, Wisconsin, USA
Cell Biology, Neurobiology and Anatomy, Medical College of Wisconsin, Milwaukee, Wisconsin, USA
Plastic Surgery, Medical College of Wisconsin, Milwaukee, Wisconsin, USA
Material Manufacturing, Swerea IVF, Mölndal, Sweden
Material Manufacturing, Swerea IVF, Mölndal, Sweden
Cell Biology, Neurobiology and Anatomy, Medical College of Wisconsin, Milwaukee, Wisconsin, USA
Danny A. Riley, PhD, 13701 Evergreen Way, Austin, TX 78737.
Part of the research material was presented in abstract form at the 7th American Conference on Human Vibration, Seattle, WA on June 13, 2018.
Funding information: National Institute for Occupational Safety and Health, Grant/Award Number: R01OH003493 Sweden's Innovation Agency Plastic Surgery Foundation Wisconsin Space Grant Consortium Research Fellowship
Hand-arm vibration syndrome (HAVS) is an irreversible neurodegenerative, vasospastic, and musculoskeletal occupational disease of workers who use powered hand tools. The etiology is poorly understood. Neurological symptoms include numbness, tingling, and pain. This study examines impact hammer vibration-induced injury and recoverability of hair mechanosensory innervation. Rat tails were vibrated 12 min/d for 5 weeks followed by 5 week recovery with synchronous non-vibrated controls. Nerve fibers were PGP9.5 immunostained. Lanceolate complex innervation was compared quantitatively in vibrated vs sham. Vibration peak acceleration magnitudes were characterized by frequency power spectral analysis. Average magnitude (2515 m/s 2 , root mean squared) in kHz frequencies was 109 times that (23 m/s 2 ) in low Hz. Percentage of hairs innervated by lanceolate complexes was 69.1% in 5-week sham and 53.4% in 5-week vibration generating a denervation difference of 15.7% higher in vibration. Hair innervation was 76.9% in 5-weeks recovery sham and 62.0% in 5-week recovery vibration producing a denervation difference 14.9% higher in recovery vibration. Lanceolate number per complex (18.4 ± 0.2) after vibration remained near sham (19.3 ± 0.3), but 44.9% of lanceolate complexes were abnormal in 5 weeks vibrated compared to 18.8% in sham. The largest vibration energies are peak kHz accelerations (approximately 100 000 m/s 2 ) from shock waves. The existing ISO 5349-1 standard excludes kHz vibrations, seriously underestimating vibration injury risk. The present study validates the rat tail, impact hammer vibration as a model for investigating irreversible nerve damage. Persistence of higher denervation difference after 5-week recovery suggests repeated vibration injury destroys the capability of lanceolate nerve endings to regenerate.
15.7: The Peripheral Nervous System - Biology
The Peripheral Nervous System
Peripheral nervous system overview: The PNS is the communication network between the CNS and the rest of the body.
Organization and function: The peripheral nervous system (PNS) includes all neural tissue excluding the brain and the spinal cord.
- PNS specific neurons: Unipolar Sensory Neurons: large myelinated neurons with the cell body off to one side of the single dendritic-axon process. Multipolar Motor Neurons: large myelinated neurons that have many dendrites off the cell body and an axon that may branch to effect many effectors.
- Signal transmission: electrical signals are transmitted in 3 steps: (1) Neurotransmitters released from one neuron bind to and activate the dendrites of the next neuron. (2) If the signal is strong enough, an action potential is propagated down the axon. (3) Which causes the release of neurotransmitters from that neuron.
- Action potential: When another neuron sends a sufficiently strong signal to the next neuron, the neuron excites to a threshold potential. Transporters on the cell membrane let positive ions into the cell, causing a change in potential, which spreads down the axon. This electrical propagation is called the action potential.
Glial cells of the PNS
- Satellite Cells: The cell bodies of several sensory neurons form structures called Ganglia. Satellite cells are the glial cells that surround each ganglion.
- Schwann Cells: Like Oligodendrocytes in the CNS, Schwann cells wrap themselves around neurons in the PNS to form the myelin sheath. Unlike Oligodendrocytes, which myelinate several neurons, a single Schwann cell forms a segment of myelin sheath.
Proprioception: involve sensors that keep track of where the body is in space. The five senses: The sensory nervous system includes sensory organs, which receive information from the environment, and sends it to the CNS.
- Skin: detects temperature, touch, and painful stimuli. Three separate kinds of nerves detect sensation on the skin
- Mechanoreceptors: Detect pressure and tension on the skin
- Thermoreceptors: Detect the temperature of the
- Nociceptors: Detect painful stimuli.
- Spinal Nerve Anatomy: There are 31 nerves exiting the spinal cord, dorsal connections bring sensory information to the CNS, ventral motor connections send commands to the periphery.
- Reflexes: For painful stimuli, involuntary withdrawal (like a hand from a flame) occurs without input from the brain. This very simple nervous pathway is called a reflex arc.
- Autonomic nervous system: directly controls automatic body functions (involuntary movements). The autonomic system has two opposing parts: the sympathetic and parasympathetic nervous systems.
- This tutorial is all about the peripheral nervous system and its functions. Specific details about the signal transmission through the peripheral nervous system are discussed. The cell types unique to the peripheral nervous system will be presented and their function discussed.
- The afferent and efferent neurons that transmit the initial information to the spinal cord and then transmit the information from the brain will also be presented.
Specific Tutorial Features:
Animated diagrams showing the five sensory organs and their mode of actions.
- Concept map showing inter-connections of new concepts in this tutorial and those previously introduced.
- Definition slides introduce terms as they are needed.
- Visual representation of concepts
- Examples given throughout to illustrate how the concepts apply.
- A concise summary is given at the conclusion of the tutorial.
Peripheral nervous system overview
Organization and function
PNS specific neurons
The five senses:
Spinal Nerve Anatomy
Autonomic nervous system
See all 24 lessons in Anatomy and Physiology, including concept tutorials, problem drills and cheat sheets: Teach Yourself Anatomy and Physiology Visually in 24 Hours
What is Peripheral Nervous System
The peripheral nervous system (PNS) is the other part of the nervous system in vertebrates, which send sensory signals to the CNS and response of the body to the effector organs. The PNS is composed of neurons and neuron clusters called ganglia. The PNS can be divided into two as somatic nervous system and autonomic nervous system.
Somatic Nervous System
The somatic nervous system (SONS) controls actions of the body via voluntary movements and reflexes. The afferent fibers of the PNS carry sensory signals from the external stimuli. The sensory organs, which are connected by the afferent nerve fibers are eye, nose, tongue, ear, and skin. The efferent nerve fibers carry instructions from the CNS to the effector organs. The reflexes have no integration with the CNS for the response. The monosynaptic reflexes contain a single synapse between sensory and motor neuron and polysynaptic reflexes contain as least a single interneuron between the sensory and motor neurons.
Autonomic Nervous System
The autonomic nervous system (ANS) controls the unconscious or involuntary muscular movements. The ANS controls the functioning of the internal organs, breathing, heartbeat, and digestion. The two complementary parts of the ANS are sympathetic and parasympathetic nervous systems. The sympathetic nervous system prepares the body for fight-or-flight response under stressful conditions by raising the heartbeat, blood pressure, and dilating the pupil. The parasympathetic nervous system keeps the body at rest. The secretion and digestion are stimulated by the parasympathetic nervous system. The third component of the ANS is the enteric nervous system, which is capable of directly controlling the digestive system of the body. The nervous system of the body in humans is shown in figure 2.
Figure 2: Nervous System in Humans
Peripheral nervous system
Our nervous system is divided in two components: the central nervous system (CNS), which includes the brain and spinal cord, and the peripheral nervous system (PNS), which encompasses nerves outside the brain and spinal cord. These two components cooperate at all times to ensure our lively functions: we are nothing without our nervous system!
Unlike the brain and the spinal cord of the central nervous system that are protected by the vertebrae and the skull, the nerves and cells of the peripheral nervous system are not enclosed by bones, and therefore are more susceptible to trauma.
If we consider the entire nervous system as an electric grid, the central nervous system would represent the powerhouse, whereas the peripheral nervous system would represent long cables that connect the powerhouse to the outlying cities (limbs, glands and organs) to bring them electricity and send information back about their status.
Image credit: Alessandra Donato
Basically, signals from the brain and spinal cord are relayed to the periphery by motor nerves, to tell the body to move or to conduct resting functions (like breathing, salivating and digesting), for example. The peripheral nervous system sends back the status report to the brain by relaying information via sensory nerves (see above image).
As with the central nervous system, the basic cell units of the peripheral central nervous system are neurons. Each neuron has a long process, known as the axon, which transmits the electrochemical signals through which neurons communicate.
Axons of the peripheral nervous system run together in bundles called fibres, and multiple fibres form the nerve, the cable of the electric circuit. The nerves, which also contain connective tissue and blood vessels, reach out to the muscles, glands and organs in the entire body
Nerves of the peripheral nervous system are classified based on the types of neurons they contain - sensory, motor or mixed nerves (if they contain both sensory and motor neurons), as well as the direction of information flow – towards or away from the brain.
The afferent nerves, from the Latin "afferre" that means "to bring towards", contain neurons that bring information to the central nervous system. In this case, the afferent are sensory neurons, which have the role of receiving a sensory input – hearing, vision, smell, taste and touch - and pass the signal to the CNS to encode the appropriate sensation.
The afferent neurons have also another important subconscious function. In this case, the peripheral nervous system brings information to the central nervous system about the inner state of the organs (homeostasis), providing feedback on their conditions, without the need for us to be consciously aware. For example, afferent nerves communicate to the brain the level of energy intake of various organs.
The efferent nerves, from the Latin "efferre" that means "to bring away from", contain efferent neurons that transmit the signals originating in the central nervous system to the organs and muscles, and put into action the orders from the brain. For example, motor neurons (efferent neurons) contact the skeletal muscles to execute the voluntary movement of raising your arm and wiggling your hand about.
Peripheral nervous system nerves often extend a great length from the central nervous system to reach the periphery of the body. The longest nerve in the human body, the sciatic nerve, originates around the lumbar region of the spine and its branches reach until the tip of the toes, measuring a meter or more in an average adult.
Importantly, injuries can occur at any point in peripheral nerves and could break the connection between the "powerhouse" and its "cities", resulting in a loss of function of the parts of the body that nerves reach into. So, it of great interest for scientists to understand how the nerves, or even how the axonal structure within the nerves, are protected from the constant mechanical stresses exerted on them. Work in this area of biology is carried out by Dr. Sean Coakley, in the laboratory of A/Prof Massimo Hilliard.
The peripheral nervous system can be divided into somatic, autonomic and enteric nervous systems, determined by the function of the parts of the body they connect to.
Author: Alessandra Donato from the Hilliard Lab
Top image credit: OpenStax Anatomy and Physiology / Wikimedia
Journal of the Peripheral Nervous SystemThe Journal of the Peripheral Nervous System is the official journal of the Peripheral Nerve Society. Founded in 1996, it is the scientific journal of choice for clinicians, clinical scientists and basic neuroscientists interested in all aspects of biology and clinical research of peripheral nervous system disorders. The Journal of the Peripheral Nervous System is a peer-reviewed journal that publishes high quality articles on cell and molecular biology, genomics, neuropathic pain, clinical research, trials, and unique case reports on inherited and acquired peripheral neuropathies. Original articles are organized according to the topic in one of four specific areas: Mechanisms of Disease, Genetics, Clinical Research, and Clinical Trials. The journal also publishes regular review papers on hot topics and Special Issues on basic, clinical, or assembled research in the field of peripheral nervous system disorders. Authors interested in contributing a review-type article or a Special Issue should contact the Editorial Office to discuss the scope of the proposed article with the Editor-in-Chief. Join the conversation about this journal
The set of journals have been ranked according to their SJR and divided into four equal groups, four quartiles. Q1 (green) comprises the quarter of the journals with the highest values, Q2 (yellow) the second highest values, Q3 (orange) the third highest values and Q4 (red) the lowest values.
Category Year Quartile Medicine (miscellaneous) 1999 Q1 Medicine (miscellaneous) 2000 Q2 Medicine (miscellaneous) 2001 Q1 Medicine (miscellaneous) 2002 Q1 Medicine (miscellaneous) 2003 Q1 Medicine (miscellaneous) 2004 Q1 Medicine (miscellaneous) 2005 Q1 Medicine (miscellaneous) 2006 Q1 Medicine (miscellaneous) 2007 Q1 Medicine (miscellaneous) 2008 Q1 Medicine (miscellaneous) 2009 Q1 Medicine (miscellaneous) 2010 Q1 Medicine (miscellaneous) 2011 Q1 Medicine (miscellaneous) 2012 Q1 Medicine (miscellaneous) 2013 Q1 Medicine (miscellaneous) 2014 Q1 Medicine (miscellaneous) 2015 Q1 Medicine (miscellaneous) 2016 Q1 Medicine (miscellaneous) 2017 Q1 Medicine (miscellaneous) 2018 Q1 Medicine (miscellaneous) 2019 Q1 Medicine (miscellaneous) 2020 Q1 Neurology (clinical) 1999 Q2 Neurology (clinical) 2000 Q3 Neurology (clinical) 2001 Q2 Neurology (clinical) 2002 Q2 Neurology (clinical) 2003 Q1 Neurology (clinical) 2004 Q1 Neurology (clinical) 2005 Q2 Neurology (clinical) 2006 Q2 Neurology (clinical) 2007 Q2 Neurology (clinical) 2008 Q1 Neurology (clinical) 2009 Q1 Neurology (clinical) 2010 Q2 Neurology (clinical) 2011 Q2 Neurology (clinical) 2012 Q1 Neurology (clinical) 2013 Q1 Neurology (clinical) 2014 Q2 Neurology (clinical) 2015 Q2 Neurology (clinical) 2016 Q2 Neurology (clinical) 2017 Q2 Neurology (clinical) 2018 Q2 Neurology (clinical) 2019 Q2 Neurology (clinical) 2020 Q2 Neuroscience (miscellaneous) 1999 Q3 Neuroscience (miscellaneous) 2000 Q3 Neuroscience (miscellaneous) 2001 Q3 Neuroscience (miscellaneous) 2002 Q3 Neuroscience (miscellaneous) 2003 Q2 Neuroscience (miscellaneous) 2004 Q2 Neuroscience (miscellaneous) 2005 Q2 Neuroscience (miscellaneous) 2006 Q2 Neuroscience (miscellaneous) 2007 Q2 Neuroscience (miscellaneous) 2008 Q2 Neuroscience (miscellaneous) 2009 Q2 Neuroscience (miscellaneous) 2010 Q2 Neuroscience (miscellaneous) 2011 Q2 Neuroscience (miscellaneous) 2012 Q2 Neuroscience (miscellaneous) 2013 Q2 Neuroscience (miscellaneous) 2014 Q2 Neuroscience (miscellaneous) 2015 Q2 Neuroscience (miscellaneous) 2016 Q2 Neuroscience (miscellaneous) 2017 Q2 Neuroscience (miscellaneous) 2018 Q2 Neuroscience (miscellaneous) 2019 Q2 Neuroscience (miscellaneous) 2020 Q2
The SJR is a size-independent prestige indicator that ranks journals by their 'average prestige per article'. It is based on the idea that 'all citations are not created equal'. SJR is a measure of scientific influence of journals that accounts for both the number of citations received by a journal and the importance or prestige of the journals where such citations come from It measures the scientific influence of the average article in a journal, it expresses how central to the global scientific discussion an average article of the journal is.
Year SJR 1999 0.558 2000 0.347 2001 0.429 2002 0.505 2003 0.821 2004 1.063 2005 0.679 2006 0.807 2007 0.930 2008 1.201 2009 1.183 2010 0.968 2011 1.029 2012 1.142 2013 1.357 2014 1.079 2015 1.158 2016 0.967 2017 1.092 2018 1.079 2019 1.075 2020 1.000
Evolution of the number of published documents. All types of documents are considered, including citable and non citable documents.
Year Documents 1999 23 2000 27 2001 23 2002 28 2003 31 2004 36 2005 53 2006 49 2007 37 2008 40 2009 40 2010 43 2011 67 2012 73 2013 47 2014 56 2015 36 2016 33 2017 41 2018 40 2019 62 2020 58
This indicator counts the number of citations received by documents from a journal and divides them by the total number of documents published in that journal. The chart shows the evolution of the average number of times documents published in a journal in the past two, three and four years have been cited in the current year. The two years line is equivalent to journal impact factor ™ (Thomson Reuters) metric.
Cites per document Year Value Cites / Doc. (4 years) 1999 1.229 Cites / Doc. (4 years) 2000 0.953 Cites / Doc. (4 years) 2001 1.110 Cites / Doc. (4 years) 2002 1.127 Cites / Doc. (4 years) 2003 1.822 Cites / Doc. (4 years) 2004 2.330 Cites / Doc. (4 years) 2005 2.356 Cites / Doc. (4 years) 2006 2.216 Cites / Doc. (4 years) 2007 2.124 Cites / Doc. (4 years) 2008 2.469 Cites / Doc. (4 years) 2009 2.855 Cites / Doc. (4 years) 2010 2.464 Cites / Doc. (4 years) 2011 2.850 Cites / Doc. (4 years) 2012 2.974 Cites / Doc. (4 years) 2013 3.193 Cites / Doc. (4 years) 2014 3.491 Cites / Doc. (4 years) 2015 2.560 Cites / Doc. (4 years) 2016 2.198 Cites / Doc. (4 years) 2017 2.314 Cites / Doc. (4 years) 2018 2.289 Cites / Doc. (4 years) 2019 2.533 Cites / Doc. (4 years) 2020 2.636 Cites / Doc. (3 years) 1999 1.229 Cites / Doc. (3 years) 2000 0.951 Cites / Doc. (3 years) 2001 1.013 Cites / Doc. (3 years) 2002 1.205 Cites / Doc. (3 years) 2003 1.923 Cites / Doc. (3 years) 2004 2.561 Cites / Doc. (3 years) 2005 2.105 Cites / Doc. (3 years) 2006 1.908 Cites / Doc. (3 years) 2007 2.130 Cites / Doc. (3 years) 2008 2.626 Cites / Doc. (3 years) 2009 2.587 Cites / Doc. (3 years) 2010 2.496 Cites / Doc. (3 years) 2011 2.707 Cites / Doc. (3 years) 2012 2.920 Cites / Doc. (3 years) 2013 3.202 Cites / Doc. (3 years) 2014 2.701 Cites / Doc. (3 years) 2015 2.517 Cites / Doc. (3 years) 2016 2.338 Cites / Doc. (3 years) 2017 2.416 Cites / Doc. (3 years) 2018 2.236 Cites / Doc. (3 years) 2019 2.491 Cites / Doc. (3 years) 2020 2.601 Cites / Doc. (2 years) 1999 1.322 Cites / Doc. (2 years) 2000 1.058 Cites / Doc. (2 years) 2001 1.060 Cites / Doc. (2 years) 2002 1.240 Cites / Doc. (2 years) 2003 2.235 Cites / Doc. (2 years) 2004 2.407 Cites / Doc. (2 years) 2005 1.493 Cites / Doc. (2 years) 2006 1.876 Cites / Doc. (2 years) 2007 2.402 Cites / Doc. (2 years) 2008 2.081 Cites / Doc. (2 years) 2009 2.675 Cites / Doc. (2 years) 2010 2.350 Cites / Doc. (2 years) 2011 2.675 Cites / Doc. (2 years) 2012 2.818 Cites / Doc. (2 years) 2013 2.500 Cites / Doc. (2 years) 2014 2.367 Cites / Doc. (2 years) 2015 2.350 Cites / Doc. (2 years) 2016 2.293 Cites / Doc. (2 years) 2017 2.232 Cites / Doc. (2 years) 2018 2.108 Cites / Doc. (2 years) 2019 2.309 Cites / Doc. (2 years) 2020 2.539
Evolution of the total number of citations and journal's self-citations received by a journal's published documents during the three previous years.
Journal Self-citation is defined as the number of citation from a journal citing article to articles published by the same journal.
Cites Year Value Self Cites 1999 4 Self Cites 2000 4 Self Cites 2001 2 Self Cites 2002 7 Self Cites 2003 9 Self Cites 2004 11 Self Cites 2005 11 Self Cites 2006 16 Self Cites 2007 14 Self Cites 2008 22 Self Cites 2009 13 Self Cites 2010 21 Self Cites 2011 27 Self Cites 2012 18 Self Cites 2013 29 Self Cites 2014 26 Self Cites 2015 14 Self Cites 2016 14 Self Cites 2017 19 Self Cites 2018 18 Self Cites 2019 27 Self Cites 2020 30 Total Cites 1999 102 Total Cites 2000 78 Total Cites 2001 80 Total Cites 2002 88 Total Cites 2003 150 Total Cites 2004 210 Total Cites 2005 200 Total Cites 2006 229 Total Cites 2007 294 Total Cites 2008 365 Total Cites 2009 326 Total Cites 2010 292 Total Cites 2011 333 Total Cites 2012 438 Total Cites 2013 586 Total Cites 2014 505 Total Cites 2015 443 Total Cites 2016 325 Total Cites 2017 302 Total Cites 2018 246 Total Cites 2019 284 Total Cites 2020 372
Evolution of the number of total citation per document and external citation per document (i.e. journal self-citations removed) received by a journal's published documents during the three previous years. External citations are calculated by subtracting the number of self-citations from the total number of citations received by the journal’s documents.
Cites Year Value External Cites per document 1999 1.195 External Cites per document 2000 0.925 External Cites per document 2001 1.054 External Cites per document 2002 1.174 External Cites per document 2003 1.905 External Cites per document 2004 2.653 External Cites per document 2005 2.392 External Cites per document 2006 2.420 External Cites per document 2007 2.800 External Cites per document 2008 3.500 External Cites per document 2009 3.440 External Cites per document 2010 3.151 External Cites per document 2011 3.290 External Cites per document 2012 3.415 External Cites per document 2013 3.594 External Cites per document 2014 2.957 External Cites per document 2015 2.768 External Cites per document 2016 2.528 External Cites per document 2017 2.504 External Cites per document 2018 2.257 External Cites per document 2019 2.425 External Cites per document 2020 2.591 Cites per document 1999 1.229 Cites per document 2000 0.951 Cites per document 2001 1.013 Cites per document 2002 1.205 Cites per document 2003 1.923 Cites per document 2004 2.561 Cites per document 2005 2.105 Cites per document 2006 1.908 Cites per document 2007 2.130 Cites per document 2008 2.626 Cites per document 2009 2.587 Cites per document 2010 2.496 Cites per document 2011 2.707 Cites per document 2012 2.920 Cites per document 2013 3.202 Cites per document 2014 2.701 Cites per document 2015 2.517 Cites per document 2016 2.338 Cites per document 2017 2.416 Cites per document 2018 2.236 Cites per document 2019 2.491 Cites per document 2020 2.601
International Collaboration accounts for the articles that have been produced by researchers from several countries. The chart shows the ratio of a journal's documents signed by researchers from more than one country that is including more than one country address.
Year International Collaboration 1999 26.09 2000 14.81 2001 13.04 2002 25.00 2003 19.35 2004 2.78 2005 7.55 2006 24.49 2007 10.81 2008 20.00 2009 27.50 2010 23.26 2011 19.40 2012 15.07 2013 19.15 2014 19.64 2015 61.11 2016 30.30 2017 21.95 2018 35.00 2019 41.94 2020 36.21
Not every article in a journal is considered primary research and therefore "citable", this chart shows the ratio of a journal's articles including substantial research (research articles, conference papers and reviews) in three year windows vs. those documents other than research articles, reviews and conference papers.
Documents Year Value Non-citable documents 1999 1 Non-citable documents 2000 2 Non-citable documents 2001 5 Non-citable documents 2002 4 Non-citable documents 2003 4 Non-citable documents 2004 7 Non-citable documents 2005 16 Non-citable documents 2006 32 Non-citable documents 2007 38 Non-citable documents 2008 41 Non-citable documents 2009 35 Non-citable documents 2010 31 Non-citable documents 2011 30 Non-citable documents 2012 27 Non-citable documents 2013 28 Non-citable documents 2014 25 Non-citable documents 2015 21 Non-citable documents 2016 16 Non-citable documents 2017 12 Non-citable documents 2018 9 Non-citable documents 2019 8 Non-citable documents 2020 11 Citable documents 1999 82 Citable documents 2000 80 Citable documents 2001 74 Citable documents 2002 69 Citable documents 2003 74 Citable documents 2004 75 Citable documents 2005 79 Citable documents 2006 88 Citable documents 2007 100 Citable documents 2008 98 Citable documents 2009 91 Citable documents 2010 86 Citable documents 2011 93 Citable documents 2012 123 Citable documents 2013 155 Citable documents 2014 162 Citable documents 2015 155 Citable documents 2016 123 Citable documents 2017 113 Citable documents 2018 101 Citable documents 2019 106 Citable documents 2020 132
Ratio of a journal's items, grouped in three years windows, that have been cited at least once vs. those not cited during the following year.
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