Spinal Nerve

The human body consists of several nerves that help the body in performing several functions. One of the major nerves in the body is the spinal nerves that are peripheral nerves and play a key role in motor, sensory, and other critical functions of the body. The number of spinal nerves in the body is 31 pairs and they are found at the thoracic, cervical, sacral, lumbar, and coccygeal levels.

When the spinal nerves are affected by certain medical disorders, it can lead to weakness, pain, and /or a decreased sensation in the body. One of the most common spinal nerve disorders is the pinched nerve. In this case, there is pressure or compression on the spinal nerves which leads to pain. 

The primary spinal nerves function is to transmit messages between the spinal cord and the rest of the body like the muscles, internal organs, and the skin. Each spinal nerve is dedicated to a different region of the body. 

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Spinal Cord and Nerves Anatomy

The formation of a typical spinal nerve happens by the merging of a sensory nerve root and a motor nerve root. These nerve roots come from the spinal cord: the motor nerve roots from the front of the spinal cord and the sensory nerve roots from the back. Together they form the spinal nerves on the sides of the spinal cord.

The tiny nerves located in areas such as the bones, skin, and internal organs, send sensory messages to the spinal nerves. These spinal nerves give sensory messages to the sensory roots, and then to the sensory fibres present in the posterior (back or dorsal) part of the spinal cord.

The anterior (front or ventral) part of the spinal cord sends nerve messages to the motor roots that further send nerve messages to the spinal nerves. The motor nerves also send nerve messages to small nerve branches for activating muscles in the legs, arms, and other parts of the body.

Location of the Spinal Nerves

Spinal cord nerves are spread evenly along the spine and the spinal cord. The spine is made up of a column of vertebral bones that surround and protect the spinal cord. Each spinal nerve emerges from the spine through the foramen. These are openings on the left and right sides of the vertebral bones of the spine. The spinal nerves are present on each side of the spine within a few centimeters. 

When a group of nerves combines with each other, they form a plexus. While some groups of spinal nerves merge with each other to form a large plexus, some divide into smaller branches and do not form a plexus.

The Spinal Nerves Form Five Main Plexi:

• Cervical Plexus: 

Formed by the merging of spinal nerves C1 through 5. The cervical plexus further gets divided into smaller nerves. The function of these nerves is to carry sensory messages and to provide motor control to the neck and shoulders muscles.

• Brachial Plexus: 

Formed by the merging of spinal nerves C5 through T1, the Brachial plexus splits into nerves whose function is to carry sensory messages and to provide motor control to the arm and upper back muscles.

• Lumbar Plexus: 

Formed by the converging of spinal nerves L1 through L4, the lumbar plexus branches into nerves that carry sensory messages and provide motor control to the abdominal and leg muscles.

• Sacral Plexus: 

Formed by the merging of spinal nerves L4 through S4 together, the Sacral plexus branches out into nerves that carry sensory messages and provide motor control to the leg muscles.

• Coccygeal Plexus: 

Formed by the merging of nerves S4 through Co1, the function of the Coccygeal plexus is to supply motor and sensory control to the genitalia and to the muscles that control defecation.

Functions of the Spinal Nerves

The brain produces the motor messages that are sent to the spinal nerves. The motor strip (also known as homunculus) in the brain gives out the muscle control command. The nerve impulses send this command to the spine. Thereafter, it travels through the motor root to the spinal nerve.

There are small motor and sensory branches in the spinal nerves. Each spinal nerve is responsible for functions corresponding to a particular area or part of the body. These functions include sensation, muscle movement, and autonomic functions like the control of internal organs.

• Sensory Function: 

The small nerves in the skin, joints, muscles, and internal organs of the body send messages to the spinal nerves. These include touch, position, temperature, pain, and vibration.

• Autonomic Functions: 

The autonomic function of spinal nerves corresponds to the body’s internal organs, such as the intestines and the bladder.

• Motor Functions: 

These are one of the most important functions of the spinal nerves. The motor strip (homunculus) in the brain initiates the muscle control command which is sent to the spine through nerve impulses. It then travels through the motor root to the spinal nerve.