COMPONENTS:
I. SPINAL NERVES
II. CRANIAL NERVES

PNS CONSISTS OF:
1. NERVES - group of nerve fibers outside the CNS.
2. PLEXUSES - group of nerves outside the CNS.
3. GANGLIA - group of cell bodies outside the CNS.

I. SPINAL NERVES: 31 pairs

- Arise from the spinal cord within the vertebral canal and pass out through the intervertebral foramina.
- C1 to C7 nerve roots leave the spinal cord through the intervertebral foramina above the corresponding vertebra.
- C8 emerge from the intervertebral foramina formed by C7 vertebra and T1 vertebra.
- T1 to Co emerge from the intervertebral foramina beneath the vertebra of the same number.

Connective tissue covering of the Spinal Nerve:
    Endoneurium - tissue covering individual axons.
    Perineurium - tissue-covering groups of axons, called FASCICLES.
    Perineurium - tissue covering the entire nerve.

ROOTS OF SPINAL NERVES:
1. VENTRAL ROOT - Anterior or Motor Root

- Emerges from the ventrolateral sulcus of the spinal cord.
- Fibers are efferent (motor fibers), derived from the cell bodies that lie in the ventral horn (Anterior Horn) of the spinal cord.

2. DORSAL ROOT - Psterior or Sensory Root

- Attached along the dorsolateral sulcus of the spinal cord.
- Fibers are sensory and arise from the cell bodies of the spinal (Dorsal Root Ganglion) Ganglia.
** The Dorsal and Ventral Roots unite immediately beyond the spinal ganglia to form the SPINAL NERVE.

DIVISIONS OF THE SPINAL NERVE:
    RAMI - These are several branches of the spinal nerve after passing through the intervertebral foramina.

1. POSTERIOR (DORSAL) RAMUS - Supplies the deep muscles of the skin of the dorsal surface of the trunk.
2. ANTERIOR (VENTRAL) RAMUS - Supplies the muscles and structures of the UE and LE and the skin of the lateral and ventral surfaces of the trunk.

ADDITIONAL BRANCH:
MENINGEAL BRANCH - Reenters the vertebral canal through the intervertebral foramen and supplies the vertebrae, vertebral ligaments, blood vessels of the spinal cord, and the meninges.

PLEXUSES: CERVICAL, BRACHIAL, LUMBAR AND SACRAL PLEXUS (COCCYGEAL PLEXUS is also present)

1. CERVICAL PLEXUS - Formed from the ventral rami of C1 to C4 spinal nerves.

- Supplies the skin and the muscles of the head, neck, and superior portion of the shoulders and chest.
    PHRENIC NERVE - arise from the C3  - C5 nerve roots.

2. BRACHIAL PLEXUS - derived from the ventral rami of C4 to T1 spinal nerves.

- Supplies the upper extremities.
MAJOR BRANCHES:
A. AXILLARY NERVE - C5 and C6
- Supplies the Deltoid and Teres Minor muscles.

B. MUSCULOCUTANEOUS NERVE - C6 to C7
- Supplies the coracobrachialis, Biceps Brachii, and Brachialis Muscle
- Lesion results to weakness of flexion and supination of forearm.

C. RADIAL NERVE - C5 to T8
- Supplies the muscles of the posterior arm and forearm.
- Frequently injured in fracture of the humerus.
- Injury results to WRIST DROP.
D. MEDIAN NERVE - C5 to T1
- Supplies most of the muscles of the anterior forearm and some of the muscles of the hand.
- Injury results to CARPAL TUNNEL SYNDROME.

E. ULNAR NERVE - C8 to T1
- Supplies the anteromedial muscles of the forearm and most of the muscles of the hand.
- Injury results to CLAW HAND.

INJURY OF THE BRACHIAL PLEXUS:
A. ERB - DUCHENNE SYNDROME
- Involves the muscles supplied by C5 and C6 such as: deltoid, biceps brachii, brachialis, brachioradialis, supinator, teres major, teres minor, and infraspinatus.
- There is difficulty in elevation and external rotation of the arm, accompanied by loss of elbow flexion and forearm supination.

B. DEJERINE - KLUMPKE SYNDROME
- Relatively rare and affects small muscles of the hand innervated by C8 and T1.
- Chief disabilities are in the fingers and wrist.

3. LUMBAR PLEXUS - Formed from the ventral rami of L1 to L4.

-     Supplies the anterolateral abdominal wall, external genitals, and part of the LE.
MAJOR BRANCH:
    FEMORAL NERVE - largest nerve arising from the lumbar plexus.

   
4. SACRAL PLEXUS - Formed from the ventral rami of spinal nerves L4 - L5 and S1 to S4.

- Supplies the buttocks, perineum and lower limbs.
MAJOR BRANCH:
    SCIATIC NERVE - largest nerve in the body.
- At the lower third of the thigh, it divides into the TIBIAL and COMMON PERONEAL NERVES.
TIBIAL NERVE -

COMMON PERONEAL NERVE -

II. CRANIAL NERVES:

- 12 pairs of cranial nerves
- Some carry only sensory input (I, II, VIII)
- Some carry only motor output (III, IV, VI, XI, XII)
- Others carry both sensory and motor information (V, VII, IX, X)
- The olfactory and optic nerves are the only ones connected to the brain.