Peripheral nervous system

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Peripheral nervous system
Nervous system diagram-en.svg
The human nervous system. Sky blue is PNS; yellow is CNS.
Identifiers
Acronym(s)PNS
MeSH D017933
TA98 A14.2.00.001
TA2 6129
FMA 9093
Anatomical terms of neuroanatomy

The peripheral nervous system (PNS) is one of two components that make up the nervous system of bilateral animals, with the other part being the central nervous system (CNS). The PNS consists of nerves and ganglia, which lie outside the brain and the spinal cord. [1] The main function of the PNS is to connect the CNS to the limbs and organs, essentially serving as a relay between the brain and spinal cord and the rest of the body. [2] Unlike the CNS, the PNS is not protected by the vertebral column and skull, or by the blood–brain barrier, which leaves it exposed to toxins. [3]

Contents

The peripheral nervous system can be divided into the somatic nervous system and the visceral nervous system. Each of these have a sensory and a motor division. The visceral motor division is known as the autonomic nervous system. [4] In the somatic nervous system, the cranial nerves are part of the PNS with the exceptions of the olfactory nerve and epithelia and the optic nerve (cranial nerve II) along with the retina, which are considered parts of the central nervous system based on developmental origin. The second cranial nerve is not a true peripheral nerve but a tract of the diencephalon. [5] Cranial nerve ganglia, as with all ganglia, are part of the PNS. [6] The autonomic nervous system exerts involuntary control over smooth muscle and glands. [7] The connection between CNS and organs allows the system to be in two different functional states: sympathetic and parasympathetic.

Structure

The peripheral nervous system is divided into the somatic nervous system, and the autonomic nervous system. The somatic nervous system is under voluntary control, and transmits signals from the brain to end organs such as muscles. The sensory nervous system is part of the somatic nervous system and transmits signals from senses such as taste and touch (including fine touch and gross touch) to the spinal cord and brain. The autonomic nervous system is a "self-regulating" system which influences the function of organs outside voluntary control, such as the heart rate, or the functions of the digestive system.

Somatic nervous system

The somatic nervous system includes the sensory nervous system and the somatosensory system and consists of sensory nerves and somatic nerves, and many nerves which hold both functions.

In the head and neck, cranial nerves carry somatosensory data. There are twelve cranial nerves, ten of which originate from the brainstem, and mainly control the functions of the anatomic structures of the head with some exceptions. One unique cranial nerve is the vagus nerve, which receives sensory information from organs in the thorax and abdomen. The other unique cranial nerve is the accessory nerve which is responsible for innervating the sternocleidomastoid and trapezius muscles, neither of which are located exclusively in the head.

For the rest of the body, spinal nerves are responsible for somatosensory information. These arise from the spinal cord. Usually these arise as a web ("plexus") of interconnected nerves roots that arrange to form single nerves. These nerves control the functions of the rest of the body. In humans, there are 31 pairs of spinal nerves: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal. These nerve roots are named according to the spinal vertebrata which they are adjacent to. In the cervical region, the spinal nerve roots come out above the corresponding vertebrae (i.e., nerve root between the skull and 1st cervical vertebrae is called spinal nerve C1). From the thoracic region to the coccygeal region, the spinal nerve roots come out below the corresponding vertebrae. This method creates a problem when naming the spinal nerve root between C7 and T1 (so it is called spinal nerve root C8). In the lumbar and sacral region, the spinal nerve roots travel within the dural sac and they travel below the level of L2 as the cauda equina.

Cervical spinal nerves (C1–C4)

The first 4 cervical spinal nerves, C1 through C4, split and recombine to produce a variety of nerves that serve the neck and back of head.

Spinal nerve C1 is called the suboccipital nerve, which provides motor innervation to muscles at the base of the skull. C2 and C3 form many of the nerves of the neck, providing both sensory and motor control. These include the greater occipital nerve, which provides sensation to the back of the head, the lesser occipital nerve, which provides sensation to the area behind the ears, the greater auricular nerve and the lesser auricular nerve.

The phrenic nerve is a nerve essential for our survival which arises from nerve roots C3, C4 and C5. It supplies the thoracic diaphragm, enabling breathing. If the spinal cord is transected above C3, then spontaneous breathing is not possible.[ citation needed ]

Brachial plexus (C5–T1)

The last four cervical spinal nerves, C5 through C8, and the first thoracic spinal nerve, T1, combine to form the brachial plexus, or plexus brachialis, a tangled array of nerves, splitting, combining and recombining, to form the nerves that subserve the upper-limb and upper back. Although the brachial plexus may appear tangled, it is highly organized and predictable, with little variation between people. See brachial plexus injuries.

Lumbosacral plexus (L1–Co1)

The anterior divisions of the lumbar nerves, sacral nerves, and coccygeal nerve form the lumbosacral plexus, the first lumbar nerve being frequently joined by a branch from the twelfth thoracic. For descriptive purposes this plexus is usually divided into three parts:

3D Medical Animation still shot of Lumbosacral Plexus 3D Medical Animation of Lumbosacral Plaxus.jpg
3D Medical Animation still shot of Lumbosacral Plexus

Autonomic nervous system

The autonomic nervous system (ANS) controls involuntary responses to regulate physiological functions. [8] The brain and spinal cord of the central nervous system are connected with organs that have smooth muscle, such as the heart, bladder, and other cardiac, exocrine, and endocrine related organs, by ganglionic neurons. [8] The most notable physiological effects from autonomic activity are pupil constriction and dilation, and salivation of saliva. [8] The autonomic nervous system is always activated, but is either in the sympathetic or parasympathetic state. [8] Depending on the situation, one state can overshadow the other, resulting in a release of different kinds of neurotransmitters. [8]

Sympathetic nervous system

The sympathetic system is activated during a "fight or flight" situation in which mental stress or physical danger is encountered. [8] Neurotransmitters such as norepinephrine, and epinephrine are released, [8] which increases heart rate and blood flow in certain areas like muscle, while simultaneously decreasing activities of non-critical functions for survival, like digestion. [9] The systems are independent to each other, which allows activation of certain parts of the body, while others remain rested. [9]

Parasympathetic nervous system

Primarily using the neurotransmitter acetylcholine (ACh) as a mediator, the parasympathetic system allows the body to function in a "rest and digest" state. [9] Consequently, when the parasympathetic system dominates the body, there are increases in salivation and activities in digestion, while heart rate and other sympathetic response decrease. [9] Unlike the sympathetic system, humans have some voluntary controls in the parasympathetic system. The most prominent examples of this control are urination and defecation. [9]

Enteric nervous system

There is a lesser known division of the autonomic nervous system known as the enteric nervous system. [9] Located only around the digestive tract, this system allows for local control without input from the sympathetic or the parasympathetic branches, though it can still receive and respond to signals from the rest of the body. [9] The enteric system is responsible for various functions related to gastrointestinal system. [9]

Disease

Diseases of the peripheral nervous system can be specific to one or more nerves, or affect the system as a whole.

Any peripheral nerve or nerve root can be damaged, called a mononeuropathy. Such injuries can be because of injury or trauma, or compression. Compression of nerves can occur because of a tumour mass or injury. Alternatively, if a nerve is in an area with a fixed size it may be trapped if the other components increase in size, such as carpal tunnel syndrome and tarsal tunnel syndrome. Common symptoms of carpal tunnel syndrome include pain and numbness in the thumb, index and middle finger. In peripheral neuropathy, the function one or more nerves are damaged through a variety of means. Toxic damage may occur because of diabetes (diabetic neuropathy), alcohol, heavy metals or other toxins; some infections; autoimmune and inflammatory conditions such as amyloidosis and sarcoidosis. [8] Peripheral neuropathy is associated with a sensory loss in a "glove and stocking" distribution that begins at the peripheral and slowly progresses upwards, and may also be associated with acute and chronic pain. Peripheral neuropathy is not just limited to the somatosensory nerves, but the autonomic nervous system too (autonomic neuropathy). [8]

See also

Related Research Articles

<span class="mw-page-title-main">Ganglion</span> Clusters of neurons in the peripheral nervous system

A ganglion is a group of neuron cell bodies in the peripheral nervous system. In the somatic nervous system, this includes dorsal root ganglia and trigeminal ganglia among a few others. In the autonomic nervous system, there are both sympathetic and parasympathetic ganglia which contain the cell bodies of postganglionic sympathetic and parasympathetic neurons respectively.

<span class="mw-page-title-main">Nerve</span> Enclosed, cable-like bundle of axons in the peripheral nervous system

A nerve is an enclosed, cable-like bundle of nerve fibers in the peripheral nervous system.

<span class="mw-page-title-main">Vagus nerve</span> Main nerve of the parasympathetic nervous system

The vagus nerve, also known as the tenth cranial nerve, cranial nerve X, or simply CN X, is a cranial nerve that carries sensory fibers that create a pathway that interfaces with the parasympathetic control of the heart, lungs, and digestive tract.

<span class="mw-page-title-main">Autonomic nervous system</span> Division of the nervous system supplying internal organs, smooth muscle and glands

The autonomic nervous system (ANS), sometimes called the visceral nervous system and formerly the vegetative nervous system, is a division of the nervous system that operates internal organs, smooth muscle and glands. The autonomic nervous system is a control system that acts largely unconsciously and regulates bodily functions, such as the heart rate, its force of contraction, digestion, respiratory rate, pupillary response, urination, and sexual arousal.

<span class="mw-page-title-main">Parasympathetic nervous system</span> Division of the autonomic nervous system

The parasympathetic nervous system is one of the three divisions of the autonomic nervous system, the others being the sympathetic nervous system and the enteric nervous system. The enteric nervous system is sometimes considered part of the autonomic nervous system, and sometimes considered an independent system.

<span class="mw-page-title-main">Sympathetic nervous system</span> Part of the autonomic nervous system which stimulates fight-or-flight responses

The sympathetic nervous system is one of the three divisions of the autonomic nervous system, the others being the parasympathetic nervous system and the enteric nervous system. The enteric nervous system is sometimes considered part of the autonomic nervous system, and sometimes considered an independent system.

<span class="mw-page-title-main">Spinal nerve</span> Nerve that carries signals between the spinal cord and the body

A spinal nerve is a mixed nerve, which carries motor, sensory, and autonomic signals between the spinal cord and the body. In the human body there are 31 pairs of spinal nerves, one on each side of the vertebral column. These are grouped into the corresponding cervical, thoracic, lumbar, sacral and coccygeal regions of the spine. There are eight pairs of cervical nerves, twelve pairs of thoracic nerves, five pairs of lumbar nerves, five pairs of sacral nerves, and one pair of coccygeal nerves. The spinal nerves are part of the peripheral nervous system.

<span class="mw-page-title-main">Somatic nervous system</span> Part of the peripheral nervous system

The somatic nervous system (SNS), also known as voluntary nervous system, is a part of the peripheral nervous system (PNS) that links brain and spinal cord to skeletal muscles under conscious control, as well as to sensory receptors in the skin. The other part complementary to the somatic nervous system is the autonomic nervous system (ANS).

<span class="mw-page-title-main">Nerve plexus</span> Network of nerve fibres

A nerve plexus is a plexus of intersecting nerves. A nerve plexus is composed of afferent and efferent fibers that arise from the merging of the anterior rami of spinal nerves and blood vessels. There are five spinal nerve plexuses, except in the thoracic region, as well as other forms of autonomic plexuses, many of which are a part of the enteric nervous system. The nerves that arise from the plexuses have both sensory and motor functions. These functions include muscle contraction, the maintenance of body coordination and control, and the reaction to sensations such as heat, cold, pain, and pressure. There are several plexuses in the body, including:

<span class="mw-page-title-main">General visceral efferent fiber</span> Autonomic nervous system nerve fiber

General visceral efferent fibers (GVE), visceral efferents or autonomic efferents are the efferent nerve fibers of the autonomic nervous system that provide motor innervation to smooth muscle, cardiac muscle, and glands through postganglionic varicosities.

<span class="mw-page-title-main">Sympathetic ganglia</span> Ganglia of the sympathetic nervous system

The sympathetic ganglia, or paravertebral ganglia, are autonomic ganglia of the sympathetic nervous system. Ganglia are 20,000 to 30,000 afferent and efferent nerve cell bodies that run along on either side of the spinal cord. Afferent nerve cell bodies bring information from the body to the brain and spinal cord, while efferent nerve cell bodies bring information from the brain and spinal cord to the rest of the body. The cell bodies create long sympathetic chains that are on either side of the spinal cord. They also form para- or pre-vertebral ganglia of gross anatomy.

<span class="mw-page-title-main">Lateral grey column</span> One of three columns of grey matter in the spinal cord

The lateral grey column is one of the three grey columns of the spinal cord ; the others being the anterior and posterior grey columns. The lateral grey column is primarily involved with activity in the sympathetic division of the autonomic motor system. It projects to the side as a triangular field in the thoracic and upper lumbar regions of the postero-lateral part of the anterior grey column.

<span class="mw-page-title-main">Head and neck anatomy</span> Structure of the human head and neck

This article describes the anatomy of the head and neck of the human body, including the brain, bones, muscles, blood vessels, nerves, glands, nose, mouth, teeth, tongue, and throat.

Pelvic splanchnic nerves or nervi erigentes are splanchnic nerves that arise from sacral spinal nerves S2, S3, S4 to provide parasympathetic innervation to the organs of the pelvic cavity.

<span class="mw-page-title-main">Outline of human anatomy</span> Overview of and topical guide to human anatomy

The following outline is provided as an overview of and topical guide to human anatomy:

Body reactivity is usually understood as an organism's functional ability of its body to react adequately in response to influence the environment. It is not to be confused with resistance, which is its physiological stability against the influence of pathogenic factors. The body reactivity can range from homeostasis to a fight or flight response. Ultimately, they are all governed by the nervous system.

<span class="mw-page-title-main">Outline of the human nervous system</span> Overview of and topical guide to the human nervous system

The following diagram is provided as an overview of and topical guide to the human nervous system:

<span class="mw-page-title-main">Classification of peripheral nerves</span>

The classification of peripheral nerves in the peripheral nervous system (PNS) groups the nerves into two main groups, the somatic and the autonomic nervous systems. Together, these two systems provide information regarding the location and status of the limbs, organs, and the remainder of the body to the central nervous system (CNS) via nerves and ganglia present outside of the spinal cord and brain. The somatic nervous system directs all voluntary movements of the skeletal muscles, and can be sub-divided into afferent and efferent neuronal flow. The autonomic nervous system is divided primarily into the sympathetic and parasympathetic nervous systems with a third system, the enteric nervous system, receiving less recognition.

<span class="mw-page-title-main">Roots of the ciliary ganglion</span>

The ciliary ganglion is a parasympathetic ganglion located just behind the eye in the posterior orbit. Three types of axons enter the ciliary ganglion but only the preganglionic parasympathetic axons synapse there. The entering axons are arranged into three roots of the ciliary ganglion, which join enter the posterior surface of the ganglion.

References

  1. ↑ Alberts, Daniel (2012). Dorland's illustrated medical dictionary (32nd ed.). Philadelphia, PA: Saunders/Elsevier. p. 1862. ISBN   9781416062578.
  2. ↑ "Slide show: How your brain works - Mayo Clinic". mayoclinic.com. Retrieved 17 June 2016.
  3. ↑ Aspromonte, John (2019). ADHD : the ultimate teen guide. Lanham. p. 51. ISBN   978-1-5381-0039-4. OCLC   1048014796.{{cite book}}: CS1 maint: location missing publisher (link)
  4. ↑ Saladin, Kenneth (2024). Anatomy & Physiology: The Unity of Form and Function (10th ed.). New York, NY: McGraw Hill. p. 1076. ISBN   9781266041846.
  5. ↑ Board Review Series: Neuroanatomy, 4th Ed., Lippincott Williams & Wilkins, Maryland 2008, p. 177. ISBN   978-0-7817-7245-7.
  6. ↑ James S. White (21 March 2008). Neurobioscitifity. McGraw-Hill Professional. pp. 1–. ISBN   978-0-07-149623-0 . Retrieved 17 November 2010.
  7. ↑ Campbell biology. Lisa A. Urry, Michael L. Cain, Steven Alexander Wasserman, Peter V. Minorsky, Rebecca B. Orr, Neil A. Campbell (12th ed.). New York, NY. 2021. ISBN   978-0-13-518874-3. OCLC   1119065904.{{cite book}}: CS1 maint: location missing publisher (link) CS1 maint: others (link)
  8. 1 2 3 4 5 6 7 8 9 Laight, David (September 2013). "Overview of peripheral nervous system pharmacology". Nurse Prescribing. 11 (9): 448–454. doi:10.12968/npre.2013.11.9.448. ISSN   1479-9189.[ permanent dead link ]
  9. 1 2 3 4 5 6 7 8 Matic, Agnella Izzo (2014). "Introduction to the Nervous System, Part 2: The Autonomic Nervous System and the Central Nervous System". AMWA Journal: American Medical Writers Association Journal (AMWA J). ISSN   1075-6361.[ permanent dead link ]
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