Central Nervous System Anatomy

Central Nervous System (CNS)

• The CNS is organized into gray and white matter, differing in color tone due to the presence of myelinated nerve processes and neuroglia.
• Gray matter consists of nerve cell bodies embedded in neuroglia, appearing grayish in color.
• White matter consists of nerve processes (axons) and blood vessels embedded in neuroglia, appearing white and glistening due to myelinated nerve processes.
• In the spinal cord, gray matter forms an H-shaped (or butterfly-shaped) pattern with paired posterior, anterior, and lateral gray horns.
• A central canal containing cerebrospinal fluid runs along the internal length of the CNS.

Meninges

• The CNS is surrounded by three membranes: dura mater (outer), arachnoid mater (middle), and pia mater (innermost).
• The meninges serve to protect, anchor, and stabilize the CNS, and contain a surrounding sac of cerebrospinal fluid.

Peripheral Nervous System

• The peripheral nervous system consists of cranial and spinal nerves and their associated ganglia.
• A ganglion is a cluster of neuron cell bodies located outside the CNS.
• Cranial and spinal nerves appear as grayish white cords made up of bundles of neuron processes (axons) supported by delicate areolar tissue.

Cranial Nerves

• There are 12 pairs of cranial nerves that branch off the brain and upper spinal cord and pass through openings (foramina) in the skull.
• All cranial nerves are distributed in the head and neck except CN X (vagus nerve), which also supplies structures in the thorax and abdomen.

Spinal Nerves

• There are 31 pairs of spinal nerves that leave the spinal cord and pass through intervertebral foramina in the vertebral column.
• Spinal nerves are named according to the region of the vertebral column with which they are associated: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal.