Spinal Cord Anatomy

• Focuses on the spinal cord, gray and white matter, nerve roots, ganglia, and various nerve plexuses.
• Details the location, components, and functions of these structures.

Spinal Cord

• The spinal cord extends from the foramen magnum to the 2nd lumbar vertebra, terminating as the conus medullaris.
• The dura and arachnoid mater extend to the 2nd sacral vertebra.

Gray Matter

• Dorsal horns feature posterior projections, composed mostly of interneurons and sensory neuron axons.
• Ventral anterior horns contain anterior projections, specifically the cell bodies of somatic motor neurons and interneurons.
• Lateral horns are exclusive to thoracic and lumbar regions, housing cell bodies of motor neurons of the autonomic nervous system (ANS).
• The gray commissure surrounds the central canal, which is continuous with the ventricles of the brain.

Roots/Ganglion

• Dorsal root rootlets extend from the posterior spinal cord, containing axons of sensory neurons.
• The dorsal root ganglion contains cell bodies of sensory neurons.
• Ventral root contains ventral rootlets from the anterior spinal cord, comprising axons of motor neurons.
• Spinal nerves are formed by the merging of ventral and dorsal roots and are mixed nerves.

White Matter

• The ventral median fissure is an anterior, more open fissure.
• The dorsal median sulcus is a posterior, shallower groove.
• Columns are also known as funiculi, classified as dorsal, lateral, and ventral.

Spinal Nerves

• There are 31 pairs of spinal nerves.
• 8 Cervical spinal nerves emerge above their corresponding vertebrae.
• The 8th cervical nerve emerges below the 7th cervical vertebrae.
• 12 Thoracic spinal nerves emerge below their corresponding vertebrae and do not form plexuses.
• 5 Lumbar spinal nerves emerge below their corresponding vertebrae.
• 5 Sacral spinal nerves emerge below their corresponding vertebrae.
• 1 Coccygeal spinal nerve.
• The brachial plexus serves the arm.
• Spinal nerves split into dorsal and ventral rami after leaving the vertebrae.
• Dorsal rami supply the skin and muscles they emerge by.
• Ventral rami of thoracic vertebrae (T2-T12) form the intercostal nerves.
• Other ventral rami form plexuses, which are complex networks of nerves.

Cervical Plexus

• The cervical plexus arises from the rami of C1 through C5.
• It serves the shoulder and neck.
• The major motor branch, C3-C4, is the phrenic nerve, which passes into the thoracic cavity to innervate the diaphragm.
• A broken neck could lead to the cessation of breathing.
• The phrenic nerve then continues down into the abdomen, to innervate the diaphragm

Brachial Plexus

• Spans from C5 to C8/T1.
• Divides into 5 major nerves.
• The axillary nerve supplies the muscle and skin of the shoulders
• The radial nerve serves the posterolateral surface of the arm and exterior muscles of the arm, forearm, and hand; a crutch can injure this nerve.
• The median nerve supplies the anteriomedial flexor muscles in the forearm and muscles in the hand.
• The musculocutaneous nerve supplies the arm muscles that flex the forearm and the lateral surface of the skin.
• The ulnar nerve supplies the posteromedial surface, running past the medial epicondyle of the humerus, serving flexor carpi ulnaris and intrinsic muscles of the hand not served by the median nerve; hitting this nerve results in "hitting the funny bone."

Lumbar Plexus

• Arises from the rami of L1 to L4.
• Serves the lower abdominopelvic region and anterior thigh.
• The femoral nerve is the largest in the plexus, innervating the anterior thigh muscles.
• Branches (cutaneous) supply anteromedial skin of the lower thigh.
• Plexus travels down to innervate the lower abdomen and anterior thigh muscles.

Sacral Plexus

• Arises from the rami of L4 to S4, serving the buttock, posterior thigh, and sensory/motor neurons of the leg and foot.
• Innervates posterior butt region, posterior thigh (hamstrings) and soleus (calf)
• The sciatic nerve is the largest on the body, serving the posterior thigh.
• The sciatic nerve splits into the common fibular and tibial nerves, which serve the leg balance muscles.

Other Notable Nerves

• Auricular nerve serves skin of the ear (C2 to C3).
• Cervical nerve serves skin on the anterior and lateral aspect of the neck (C2, C3).
• Obturator nerve (L2 to L4) functions in motor control (adductor magnus, gracilis, longus, brevis) and sensation of the skin of the hip, medial thigh, and knee.
• Ilioinguinal nerve (L1) serves the skin of the external genitalia, proximal medial aspect of the thigh, and inferior abdominal muscles.
• Genitofemoral nerve (L1, L2) serves the scrotum in males and labia majora in females.
• Pudendal nerve (S2 to S4) serves the skin and muscles of the perineum.