What is the Peripheral Nervous System?

It consists of neural stem, plexus, ganglion, and nerve terminal device composed of perinuclear bodies and nerve fibers. Anatomically, it is often divided into three parts: brain nerve, spinal nerve and autonomic nerve. Its function is to connect peripheral receptors to the central nervous system.

Chinese name: Peripheral nervous system
Foreign name: Peripheral nervous system

Explanation: All nerve structures except the brain and spinal cord
Classification: Spine, brain, and splanchnic nervous system

Peripheral nervous system

Connected to the brain, a total of 12 pairs, in accordance with the order of access to the cranial cavity, that is, the olfactory nerve, optic nerve, oculomotor nerve, pulley nerve, trigeminal nerve, abductor nerve, facial nerve, auditory nerve, glossopharyngeal nerve, vagus nerve, accessory nerve and sublingual Each pair of nerves. Except that the olfactory nerve is connected to the brain's olfactory bulb and the optic nerve is connected to the mesencephalic optic cross, the remaining 10 pairs are connected to the brain stem. Among the 12 pairs of brain nerves, the olfactory nerve, optic nerve, and auditory nerve are pure sensory components that transmit the olfactory, visual, and auditory impulses to the center. The oculomotor nerve, the pulley nerve, the abductor nerve, the accessory nerve, and the hypoglossal nerve are motor components that transmit central information to the receptors. The trigeminal nerve, facial nerve, glossopharyngeal nerve, and vagus nerve have both sensory and motor components. They are mixed nerves. The motor nerves control the eye muscles, tongue muscles, masticatory muscles, expression muscles, and throat muscles, as well as smooth muscles. Of the heart and glands. Cerebral nerve damage can cause many disorders.

The olfactory nerve (CN), located in the middle of the face, resembles a nasal septum, suggesting that the olfactory area at the top of the nasal cavity is rich in olfactory cells that receive olfactory stimulation. Among them, the axon is gathered into more than 20 olfactory filaments, which are connected to the olfactory bulb through the sieve and conduct Smell.

Optic nerve (CN), located in the middle of the eye, resembles a pupil or "black eyeball". The optic nerve is related to optics and visual conduction.

The oculomotor nerve (CN) is located above the eye and looks like an eyelid. The oculomotor nerve governs the movement of the main extraocular muscles such as the levator levator and the superior rectus muscle.

The trochlear nerve (CNIV) is located on the inner side of the eye. The trochlear nerve innervates the superior oblique muscle, which can turn the pupil downward and outward.

The trigeminal nerve (CN) is located in the front, and the trigeminal nerve senses the feeling of the face.

The abductor nerve (CN) is located on the outer side of the eye. The abductor nerve innervates the external rectus muscle and can turn the pupil to the outside.

The facial nerve (CN) mirrors left and right in the face to form the contour of the face.

The vestibular snail nerve (CN), located at the lateral edge of the middle face, looks like the auricle (Guo). The vestibular snail nerve is related to the ear, and it senses hearing and position.

The glossopharyngeal nerve (CN) is located in the center of the mouth and looks like uvula (sacral). The glossopharyngeal nerve governs most of the pharyngeal muscles and feels the general feeling and taste of the back 1/3 of the tongue.

The vagus nerve (CNXX) is located in the middle of the neck and looks like a laryngeal knot. The vagus nerve is closely related to the larynx in the neck, which controls the laryngeal muscles and conducts the sensation of the laryngeal mucosa.

The accessory nerve (CN), located on the outer side of the neck, resembles the sternocleidomastoid muscle and is dynamic. The accessory nerve innervates the sternocleidomastoid and trapezius muscles and is related to the movement of the neck.

The hypoglossal nerve (CN), located in the front of the mouth, resembles the tongue and tongue protruding out of the mouth. The hypoglossal nerve innervates the external and internal tongue muscles, which can extend the tongue and change its shape.

Peripheral nervous system spinal nerve

There are a total of 31 pairs, and each pair of spinal nerves is formed by the convergence of the anterior and posterior roots connected to the spinal cord in the intervertebral foramen. The anterior root is mainly motor fibers, composed of motor fibers located in the anterior horn cells of the gray matter of the spinal cord, lateral horns, and internal sympathetic visceral motor fibers. Parasympathetic visceral motor fibers from the spinal gray matter intermediate zone cells are located in the anterior roots of the second, third, and fourth phrenic nerves. The axons of the anterior horn cells are distributed to the skeletal muscle, and the axons of the lateral horns and the crotch sympathetic and parasympathetic cells are distributed to the viscera, myocardium, vascular smooth muscle and glands. Some people think that there is also a sensory fiber in the anterior root of the spinal nerve. This fiber comes from cells in the spinal ganglion. Its central process passes through the anterior root into the spinal cord and transmits pain. The posterior root is a sensory fiber consisting of the central processes of spinal ganglion pseudomonopolar neurons. The spinal ganglia is an enlarged part of the posterior root on the inner surface of the intervertebral foramen. It is composed of the cell bodies of pseudomonopolar neurons. Among them, the axon constitutes the posterior root and enters the spinal cord. , Muscles, joints and viscera, the body and visceral sensations are transmitted to the center. Therefore, each pair of spinal nerves formed by the anterior and posterior roots are all mixed fibers.

The spinal nerve is divided into 8 pairs of cervical nerves, 12 pairs of thoracic nerves, 5 pairs of lumbar nerves, 5 pairs of sacral nerves, and 1 pair of tail nerves, a total of 31 pairs. The spinal nerve exits the spinal canal through the intervertebral foramen, of which the upper 7 pairs of cervical nerves exit from above the corresponding cervical spine, and the 8th pair of cervical nerves exit from between the 7th cervical spine and the 1st thoracic spine. The following spinal nerves are in this order, penetrating the intervertebral foramen between the vertebra of this section and the next. The position of the spinal nerve in the foramen: the front is adjacent to the intervertebral disc and the vertebral body, and there are articular processes and ligaments at the rear. When these structures suffer from sports injuries, they often involve the spinal nerves, which can cause symptoms such as sensory and motor disorders.

Peripheral nervous system autonomic nerve

Includes sympathetic and parasympathetic nerves.

Peripheral nervous system sympathetic nerve

Part of the autonomic nervous system (autonomic nervous system). The preganglionic neurons are emitted from the gray medial lateral column of the spinal thoracic 1 to lumbar 2 segments, pass through the anterior root of the spinal cord, enter the paravertebral sympathetic nerve chain from the white branch of the corresponding segment, and go up or down in the chain, and Postganglionic neurons within or outside the ganglion synapse synapses. Postganglionic neurons follow the corresponding spinal nerves to the periphery, dominating the heart blood vessels, abdominal viscera, smooth muscles, and glands to regulate the functions of these tissues and organs. activity. Stimulation of the sympathetic nerves can lead to increased myocardial contractility, accelerated heartbeat, abdominal viscera, constriction of peripheral blood vessels, hypermetabolism, dilated pupils, and increased working capacity of tired skeletal muscles. Most tissues and organs in the human body are dominated by the sympathetic and parasympathetic nerves. They have functional antagonism. On the whole, they coordinate and promote visceral activities under the management of the cerebral cortex.

Parasympathetic nerve

Part of the autonomic nervous system (autonomic nervous system). Preganglionic neurons are emitted by certain nucleus of the brainstem and the middle and lateral column of the gray matter of the spinal cord, mixed with the brain nerves (mainly the facial nerve, glossopharyngeal nerve, and vagus nerve) or the spinal nerves to reach the organs or near the organs. Synaptic connections occur with the postganglionic neurons in the parasympathetic ganglia, which are then distributed in internal organs, smooth muscles, and glands, and regulate their functional activities. Stimulation of parasympathetic nerves can cause slow heartbeat, enhanced gastrointestinal motility, sphincter relaxation, pupil shrinkage, and increased glandular secretion. Most tissues and organs in the human body are dominated by parasympathetic nerves and sympathetic nerves. They function as antagonists. On the whole, they coordinate and promote visceral activities under the management of the cerebral cortex.

Histological characteristics of the peripheral nervous system

The peripheral nervous system consists of nerve fibers and neuronal cell bodies outside the central nervous system. There is a fibrous connection between the peripheral nervous system and the central nervous system. The neurons of the peripheral nervous system constitute a bridge connecting the central nervous system to the peripheral structure. Bundles of nerve fibers (axons) in the peripheral nervous system are wrapped by connective tissue envelopes to form a single peripheral nerve. When observed in vivo, it was a strong and whitish cord-like structure. Neurons outside the central nervous system accumulate in ganglia, such as the spinal ganglia.

The first 11 pairs of brain nerves originate from the brain. The first pair of brain nerves mostly originate from the upper part of the spinal cord. All the brain nerves pass through the holes in the skull and crack the skull. Thirty-one pairs of spinal nerves (neck, chest, lumbar, sacral, and tail nerves) originate from the spinal cord and emanate from the intervertebral foramen of the spine. The peripheral nervous system is a continuation of the structure and function of the central nervous system. Its afferent fibers (or sensory fibers) transfer impulses from sensory organs (such as the eye) and receptors in different parts of the body (such as the skin) into the central nervous system. The nervous impulses of the system travel to the effector organs (muscles and glands).

The composition of the peripheral nerve fibers of the peripheral nervous system includes:

1 axon;

2 Myelin sheath: There are two forms of myelin sheath, from which two types of nerve fibers can be distinguished.

(1) Myelin sheath of myelinated nerve fibers is formed by sequential Schwann cells arranged in sequence and wrapping a single axon;

(2) Myelin sheath cells do not produce sphingomyelin. Most nerve fibers located in the skin are unmyelinated.

3 Endometrium composed of connective tissue:

Because nerve fibers are supported and protected by three layers of connective tissue membrane, peripheral nerves are relatively strong and elastic. The 3-layer film includes:

(1) A thin layer of loose connective tissue membrane surrounding the inner membrane of myelin cells and axons;

(2) Nerve bundle membrane encloses connective tissue membranes of each bundle of nerve fibers, and has a barrier effect on substances entering and exiting peripheral nerve fibers;

(3) A thick and loose connective tissue membrane surrounding the outer nerve bundles of the outer nerve membrane, which constitutes the outermost layer of the nerve and contains adipose tissue, blood vessels and lymphatic vessels.

Peripheral nerves are much like electrical cables. An axon is a separate telephone wire. The myelin sheath and the endoneurium envelope provide insulation around the axon. The nerve bundle membrane wraps these insulated wires into bundles. These bundles are then wrapped in an orderly manner by the outer nerve membrane (like the outer cover of a "cable").