spinal nerves

 Spinal nerve

There are 31 pairs of spinal nerves that leave the vertebral canal and they are named according to vertebrae with which they are associated.

1. 8 cervical

2. 12 thoracic

3. 5 lumber

4. 5 sacral

5. 1 coccygeal

All spinal nerves are mixed, containing both sensory and motor fibers.

Each nerve has a ventral (efferent) root and dorsal (afferent root), after leaving spinal cord to form single mixed.

1. 8 cervical nerve

Sensory function

Sensation in neck, upper limbs and sometimes in lower limbs also.

Motor function

Voluntary activities (somatic) of neck, upper limbs and sometimes lower limbs. (Skeletal muscle)

2. 12 thoracic nerve

Sensory function

Sensation in back, chest and trunk.

Motor function

1. Somatic (voluntary)

Voluntary activities of torso; trunk muscle like bending (torso skeletal muscle).

2. Autonomic 

Sympathetic and parasympathetic

3. 5 lumbar function

Sensory function

Sensation in hip and lower limbs

Motor function

Skeletal muscle contraction and relaxation of hip and lower limbs.

4. Sacral nerve

Sensory function

Sensation in lower limbs.

Motor function

Contraction of skeletal muscle of lower limbs.

5. 1 Coccygeal nerve

It is responsible for activities in reproductive track and genital area, perineal area.

Branches of Spinal Nerve


Dorsal and ventral root joint together to form spinal nerve proper, nerve divided into several branches called rami.

These branches are-

Dorsal ramus

Ventral ramus

Ganglion of autonomus nervous system

Ramus communicantes


A plexus is interconnection of fibers which form new combinations. Each plexuses give rise to new combination of fibers as peripheral nerve.

Where nerve fibers are regrouped and rearranged before proceeding to supply skin, bone, muscles and joints of particular area.

There are four plexuses-

1. Cervical plexus

2. Brachial plexus

3. Lumbar plexus

4. Secral plexus

1. Cervical plexus

Cervical plexus is composed of ventral rami of spinal nerve (C1-C4). 

Superficial branches- supply the structure at back and side of the head and the skin of the front of neck to level of sternum.

Deep branches- supply muscles to neck.

Phrenic nerve- Passes downward through thoracic cavity supply to diaphragm initiating respiration.

2. Brachial plexus

C5-C8, T1, brachial plexus is made up of ventral rami of C5-C8, T1 spinal nerve.

Brachial plexus give rise to number of nerves to upper limb, which supply skin and muscles of upper limb and some of chest muscle.

Five major mixed nerve emerge from brachial plexus, which are-

1. Axillary nerve C5-C6; supply deltoid muscle, shoulder joint and upper arm skin.

2. Musculocutaneous nerve C5-C7; supplies muscles of upper arm and skin of forearm.

3. Radial nerve; C5-C8,T1; supply to wrist and finger joint, radial side skin.

4. Median nerve; C5-C8, T1; supply muscle of front of forearm, muscle of palm of hand and skin.

5. Ulnar nerve; C7-C8, T1; supply to ulnar side of hand.

3. Lumbar plexus

(L1-L4) Lumbar plexus is composed of ventral rami of L1-L4 nerves. It supplies anterior and lateral abdominal wall, external genitals and thigh.

Main branches of lumbar plexus are-

1. Femoral nerve

2. Genitofemoral nerve

4. Secral plexus (L3-S3); secral plexus is composed of fibers of ventral rami of spinal nerves.

Supply muscles and skin of pelvic floor, muscles around hip joint and pelvic organs, leg, foot and toes, heel, ankle.

Main branches of secral plexus are-

1. Sciatica nerve

2. Tibial nerve

5. Coccygeal plexus

Formed by ventral rami of S4-Co1 nerves.

Supply skin in area of coccyx and muscles of pelvic floor.


Dermatome is an area of skin that mainly supplied by single spinal nerve. The area of skin that provides sensory input to CNS via one pair of spinal nerve.

The nerve from the-

C2-C4 ; supply the skin of neck

C5-T1; nerve supply arms

T2 to L2; nerve supply chest and abdomen

L3-S1; nerve supply skin of leg

S1-S4; nerve go to groin

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