Ventral rami innervate which muscles

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 brain sends impulses to the spinal cord that relay the message.

This is imperative in understanding that the left hemisphere of the brain controls the RIGHT side of the body, while the right hemisphere of the brain controls the LEFT side of the body. The signals cross in the medulla oblongata, and this process is also known as decussation. The primary purpose of the corticospinal tract is to maintain voluntary motor control of the body and limbs. However, connections to the somatosensory cortex suggest that the pyramidal tracts are also responsible for modulating sensory information from the body.

Some of these connections cross the midline; therefore, each side of the brain is responsible for controlling muscles for the limbs on opposite sides of the body.

However, control of trunk muscles is on the same side of the body. Fortunately, they can re-learn some crude, basic motions, but not fine movements. This implies that the connections to these tracts are crucial for fine movement, and only partial recovery is possible if they are damaged.

Privacy Policy. Skip to main content. Peripheral Nervous System. Search for:. Distribution of Spinal Nerves. Cervical Plexus The cervical plexus is the plexus of the ventral rami of the first four cervical spinal nerves. Learning Objectives Describe the cervical plexus and its function. Key Takeaways Key Points The cervical plexus describes the plexus of the ventral rami of the first four cervical spinal nerves that arise from the cervical spinal column in the neck.

The cervical spinal nerves that form the cervical plexus are located laterally farther from the median line to the transverse processes of the prevertebral skeletal muscles of the neck from the medial side, and vertebral closer to the vertebral column to these muscles from the lateral side. The cervical plexus forms an anastomosis, a connection, with the accessory nerve, the hypoglossal nerve, and the sympathetic trunk.

The cervical plexus is located in the neck, internal to the sternocleidomastoid, an anterior neck muscle. Key Terms sympathetic trunk : Also called the sympathetic chain or gangliated cord, these are a paired bundle of nerve fibers that run from the base of the skull to the coccyx. They are located laterally to the transverse processes of the prevertebral muscles from the medial side and vertebral scalenus, levator scapulae, splenius cervicis muscles from the lateral side.

Cervical plexus : Diagram of the cervical plexus. Brachial Plexus The brachial plexus is formed by the four lower cervical spinal nerves and the first thoracic spinal nerve. Learning Objectives Describe the brachial plexus.

Key Takeaways Key Points The nerve bundles of the brachial plexus pass through the cervico-axillary canal to serve the axilla armpit , brachium arm , antebrachium forearm , and hand.

The brachial plexus provides cutaneous skin and muscular innervations for the upper limbs, excluding the trapezius muscle and an area of skin near the axilla that are innervated by the spinal accessory nerve and the intercostobrachial nerve, respectively. Key Terms spinal accessory nerve : A nerve that controls specific muscles of the shoulder and neck.

Lumbar Plexus The lumbar plexus is formed by the subcostal nerve and divisions of the first four lumbar nerves that arise from the middle to lower back. Learning Objectives Describe the lumbar plexus. Key Takeaways Key Points The lumbar plexus passes through the psoas major muscle and innervates the skin and muscles of the abdominal wall, thigh, and external genitalia.

The largest nerve that forms part of the lumbar plexus is the femoral nerve, which innervates the anterior thigh muscles and some of the skin distal to the inguinal ligament. The ilioinguinal nerve pierces the lateral abdominal wall and runs medially at the level of the inguinal ligament.

It supplies motor branches to both transversus abdominis and sensory branches to the skin over the pubic symphysis and the lateral aspect of the labia majora or scrotum. The genital branch of the genitofemoral nerve courses differently in females and males. Key Terms lumbosacral plexus : The anterior divisions of the lumbar nerves, sacral nerves, and coccygeal nerve form this plexus, the first lumbar nerve being frequently joined by a branch from the twelfth thoracic nerve.

Its anatomy is very important for operating on hernia patients. Sacral and Coccygeal Plexuses The sacral plexus is the plexus of the three sacral spinal nerves S2—S4 that arise from the lower back just above the sacrum. Learning Objectives Distinguish between the sacral and coccygeal plexuses. Key Takeaways Key Points The sacral plexus, together with the lumbar plexus, forms the lumbosacral plexus. The largest nerve in the sacral plexus is the sciatic nerve that innervates the thigh, lower leg, and the foot.

The coccygeal plexus consists of the coccygeal nerve and the fifth sacral nerve, which innervate the skin in the coccygeal region, around the tailbone called the coccyx. Key Terms sacral plexus : A nerve plexus that provides motor and sensory nerves for the posterior thigh, most of the lower leg, the entire foot, and part of the pelvis.

Sensory and Motor Tracts The spinothalamic tract is a somatosensory tract and the corticospinal tract is a motor tract.

The smaller part of the fourth joins with the fifth to form the lumbosacral trunk, which assists in the formation of the sacral plexus.

The fourth nerve is named the furcal nerve, from the fact that it is subdivided between the two plexuses. There are five paired sacral nerves, half of them arising through the sacrum on the left side and the other half on the right side. Each nerve emerges in two divisions: one division through the anterior sacral foramina and the other division through the posterior sacral foramina.

The sacral nerves have both afferent and efferent fibers, thus they are responsible for part of the sensory perception and the movements of the lower extremities of the human body. The pudendal nerve and parasympathetic fibers arise from S2, S3, and S4.

They supply the descending colon and rectum, urinary bladder, and genital organs. These pathways have both afferent and efferent fibers. The coccygeal nerve is the 31st pair of spinal nerves and arises from the conus medullaris. Its anterior root helps form the coccygeal plexus. The spinal nerves branch into the dorsal ramus, ventral ramus, the meningeal branches, and the rami communicantes.

Course and branches of thoracic spinal nerve : This diagram depicts the course and branches of a typical thoracic spinal nerve. The posterior division dorsal ramus is labeled at the top right. A nerve plexus is a network of intersecting nerves; multiple nerve plexuses exist in the body. Nerve plexuses are 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 cervical plexus is formed by the ventral rami of the upper four cervical nerves and the upper part of fifth cervical ventral ramus. The network of rami is located deep within the neck. The brachial plexus is formed by the ventral rami of C5—C8 and the T1 spinal nerves, and lower and upper halves of the C4 and T2 spinal nerves.

The plexus extends toward the armpit axilla. The lumbar plexus is formed by the ventral rami of L1—L5 spinal nerves with a contribution of T12 form the lumbar plexus. This plexus lies within the psoas major muscle. 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. 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.