Which rami form plexuses

The sacral plexus is formed by the ventral rami of L4-S3, with parts of the L4 and S4 spinal nerves. It is located on the posterior wall of the pelvic cavity. The coccygeal plexus serves a small region over the coccyx and originates from S4, S5, and Co1 spinal nerves.

It is interconnected with the lower part of sacral plexus. Brachial plexus : Cervical C5—C8 and thoracic T1 nerves comprise the brachial plexus, which is a nerve plexus that provides sensory and motor function to the shoulders and upper limbs. Lumbar plexus : The lumbar plexus is comprised of the ventral rami of the lumbar spinal nerves L1—L5 and a contribution from thoracic nerve T The posterior green and anterior yellow divisions of the lumbar plexus are shown in the diagram. Learning Objectives Describe nerve plexuses in the peripheral nervous system.

Key Points Nerve plexuses throughout the body tend to be named after the area in which the plexus occurs and the organs, limbs, and tissues it serves. Examples include the cervical, brachial, lumbar, sacral, celiac, and coccygeal plexuses.

The brachial plexus serves the chest, shoulders, arms and hands and is formed by the ventral rami of C5, C8, and T1 spinal nerves, and the lower and upper halves of the C4 and T2 spinal nerves. Key Terms nerve plexus : A network of intersecting nerves. It proceeds through the neck, the axilla armpit region , and into the arm. It is located on the posterior wall of the pelvic cavity. The coccygeal plexus serves a small region over the coccyx and originates from S4, S5, and Co1 spinal nerves.

It is interconnected with the lower part of sacral plexus. Brachial plexus : Cervical C5—C8 and thoracic T1 nerves comprise the brachial plexus, which is a nerve plexus that provides sensory and motor function to the shoulders and upper limbs. Lumbar plexus : The lumbar plexus is comprised of the ventral rami of the lumbar spinal nerves L1—L5 and a contribution from thoracic nerve T The posterior green and anterior yellow divisions of the lumbar plexus are shown in the diagram.

The intercostal nerves are part of the somatic nervous system and arise from anterior divisions rami anteriores, ventral divisions of the thoracic spinal nerves T1 to T The intercostal nerves are distributed chiefly to the thoracic pleura and abdominal peritoneum. Intercostal nerves : An image of the intercostal brachial nerves.

They differ from the anterior divisions of the other spinal nerves in that each pursues an independent course without plexus formation. These are limited in their distribution to the parietes wall of the thorax. The anterior divisions of the second, third, fourth, fifth, and sixth thoracic nerves, and the small branch from the first thoracic, are confined to the walls of the thorax and are named thoracic intercostal nerves.

Near the sternum, they cross in front of the internal mammary artery and transversus thoracis muscle, pierce the intercostales interni, the anterior intercostal membranes, and pectoralis major, and supply the integument of the front of the thorax and over the mamma, forming the anterior cutaneous branches of the thorax. The branch from the second nerve unites with the anterior supraclavicular nerves of the cervical plexus. The seventh intercostal nerve terminates at the xyphoid process, at the lower end of the sternum.

The anterior divisions of the seventh, eighth, ninth, tenth, and eleventh thoracic intercostal nerves are continued anteriorly from the intercostal spaces into the abdominal wall; hence they are named thoraco-abdominal nerves or thoracicoabdominal intercostal nerves. Unlike the nerves from the autonomic nervous system that innervate the visceral pleura of the thoracic cavity, the intercostal nerves arise from the somatic nervous system. This enables them to control the contraction of muscles, as well as provide specific sensory information regarding the skin and parietal pleura.

This explains why damage to the internal wall of the thoracic cavity can be felt as a sharp pain localized in the injured region. Damage to the visceral pleura is experienced as an unlocalized ache. A dermatome is an area of skin that is supplied by a single spinal nerve, and a myotome is a group of muscles that a single spinal nerve root innervates.

A dermatome is an area of skin that is supplied by a single spinal nerve. There are eight cervical nerves, twelve thoracic nerves, five lumbar nerves and five sacral nerves. Each of these nerves relays sensation, including pain, from a particular region of the skin to the brain.

Dermatomes : Dermatomes are areas of skin supplied by sensory neurons that arise from a spinal nerve ganglion. Dermatomes and the associated major cutaneous nerves are shown here in a ventral view.

Along the thorax and abdomen, the dermatomes are like a stack of discs, with each section supplied by a different spinal nerve. Along the arms and the legs, the pattern is different. The dermatomes run longitudinally along the limbs, so that each half of the limb has a different dermatome. Although the general pattern is similar in all people, the precise areas of innervation are as unique to an individual as fingerprints.

Dermatomes have clinical significance, especially in the diagnosis of certain diseases. Symptoms that follow a dermatome, such as pain or a rash, may indicate a pathology that involves the related nerve root. Examples include dysfunction of the spine or a viral infection. Viruses that remain dormant in nerve ganglia, such as the varicella zoster virus that causes both chickenpox and shingles, often cause either pain, rash, or both in a pattern defined by a dermatome.

Shingles rash : The shingles rash appears across a dermatome. In this patient, one of the dermatomes in the arm is affected, restricting the rash to the length of the back of the arm. Shingles is one of the only diseases that causes a rash in a dermatomal pattern, and as such, this is its defining symptom. The rash of shingles is almost always restricted to a specific dermatome, such as on the chest, leg, or arm caused by the residual varicella zoster virus infection of the nerve that supplies that area of skin.

Shingles typically appears years or decades after recovery from chickenpox. A myotome is the group of muscles that a single spinal nerve root innervates. The myotome is the motor equivalent of a dermatome.

The testing of myotomes provides the clinician with information about the level in the spine where a lesion may be present. During testing, the clinician looks for muscle weakness of a particular group of muscles. Results may indicate lesions to the spinal cord nerve root, or intervertebral disc herniation that presses on the spinal nerve roots. The peripheral nervous system PNS consists of the nerves and ganglia outside of the brain and spinal cord. Unlike the CNS, the PNS is not protected by the bones of the spine and skull, or by the blood —brain barrier, leaving it exposed to toxins and mechanical injuries.

The peripheral nervous system is divided into the somatic nervous system and the autonomic nervous system. Spinal nerve : This diagram indicates the formation of a typical spinal nerve from the dorsal and ventral roots.

Numbers indicate the types of nerve fibers: 1 somatic efferent, 2 somatic afferent, 3—5 sympathetic efferent, 6—7 sympathetic afferent. The peripheral nervous system includes 12 cranial nerves and 31 pairs of spinal nerves that provide communication from the CNS to the rest of the body by nerve impulses to regulate the functions of the human body. The term spinal nerve generally refers to a mixed spinal nerve, which carries motor, sensory, and autonomic signals between the spinal cord and the body.

Each pair of spinal nerves roughly correspond to a segment of the vertebral column: 8 cervical spinal nerve pairs C1—C8 , 12 thoracic pairs T1—T12 , 5 lumbar pairs L1—L5 , 5 sacral pairs S1—S5 , and 1 coccygeal pair. The anterior divisions of the lumbar, sacral, and coccygeal nerves 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: lumbar plexus, sacral plexus, and pudendal plexus. The sympathetic division typically functions in actions that need quick responses.

The parasympathetic division functions with actions that do not require immediate reaction. The sympathetic system is often considered the fight or flight system, while the parasympathetic system is often considered the rest and digest or feed and breed system. Autonomic nervous sytem : The functions of the parasympathetic and sympathetic nervous systems are detailed.

The somatic nervous system consists of afferent and efferent nerves and is associated with the voluntary control of skeletal muscle movements. The afferent nerves are responsible for relaying sensations from the body to the central nervous system CNS , while the efferent nerves are responsible for sending out commands from the CNS to the body to stimulate muscle contraction. Upper motor neurons release acetylcholine.

Acetylcholine is released from the axon terminal knobs of alpha motor neurons and received by postsynaptic receptors nicotinic acetylcholine receptors of muscles, thereby relaying the stimulus to contract muscle fibers. Privacy Policy. Skip to main content. Peripheral Nervous System. Search for:. Spinal Nerves. Overview of the Spinal Nerves Spinal nerves, a part of the peripheral nervous system PNS , are mixed nerves that send motor, sensory, and autonomic signals between the CNS and the body.

Learning Objectives Describe spinal nerves of the peripheral nervous system. Key Takeaways Key Points Afferent sensory axons bring sensory information from the body to the spinal cord and brain; they travel through the dorsal roots of the spinal cord. Efferent motor axons bring motor information from the brain to the body; they travel through the ventral roots of the spinal cord. All spinal nerves—except the first pair—emerge from the spinal column through an opening between vertebrae, called an intervertebral foramen.

The spinal nerves are typically labeled by their location in the body: thoracic, lumbar, or sacral. Key Terms ventral root : Also called the anterior root, it is the efferent motor root of a spinal nerve.

Branches of Spinal Nerves The spinal nerves branch into the dorsal ramus, ventral ramus, the meningeal branches, and the rami communicantes. Learning Objectives Describe branches of the peripheral nervous system. Key Takeaways Key Points The dorsal and ventral rami contain nerves that provide visceral motor, somatic motor, and sensory information, with the dorsal ramus feeding the dorsal trunk skin and muscles of the back , and the ventral ramus feeding the ventral trunk and limbs through the ventrolateral surface.

The meningeal branches supply nerve function to the vertebrae themselves, including the ligaments, dura, blood vessels, intervertebral discs, facet joints, and periosteum. The rami communicantes contain autonomic nerves that carry visceral motor and sensory information to and from the visceral organs. Key Terms nerve plexus : A branching network of intersecting nerves. They are also referred to as the dorsal rami. They are directed backwards and—with the exceptions of those of the first cervical, the fourth and fifth sacral, and the coccygeal—divide into medial and lateral branches for the supply of the muscles and skin of the posterior part of the trunk.

They then re-enter the intervertebral foramen, and innervate the facet joints, the annulus fibrosus of the intervertebral disk, and the ligaments and periosteum of the spinal canal, carrying pain sensation.

Outside the vertebral column, the spinal nerves divide into branches. The dorsal ramus: Contains nerves that serve the dorsal portions of the trunk carrying visceral motor, somatic motor, and sensory information to and from the skin and muscles of the back. The ventral ramus: Contains nerves that serve the remaining ventral parts of the trunk and the upper and lower limbs carrying visceral motor, somatic motor, and sensory information to and from the ventrolateral body surface, structures in the body wall, and the limbs.

Some ventral rami merge with adjacent ventral rami to form a nerve plexus, a network of interconnecting nerves. Nerves emerging from a plexus contain fibers from various spinal nerves, which are now carried together to some target location. Major plexuses include the cervical, brachial, lumbar, and sacral plexuses. The meningeal branches recurrent meningeal or sinuvertebral nerves : These branch from the spinal nerve and re-enter the intervertebral foramen to serve the ligaments, dura, blood vessels, intervertebral discs, facet joints, and periosteum of the vertebrae.

The rami communicantes: Contain autonomic nerves that carry visceral motor and sensory information to and from the visceral organs. Plexuses A nerve plexus is a network of intersecting nerves that serve the same part of the body. Learning Objectives Describe nerve plexuses in the peripheral nervous system.

Key Takeaways Key Points Nerve plexuses throughout the body tend to be named after the area in which the plexus occurs and the organs, limbs, and tissues it serves.