Gross Anatomy
Spinal cord disease results from multiple diverse pathologic processes. Trauma is the most common cause of spinal cord injury. Depending on its pathogenesis, spinal cord disease can manifest with variable impairment of motor, sensory, or autonomic function. This review focuses on spinal cord anatomy. Basic clinical descriptions of common patterns of spinal cord involvement are related to essential aspects of spinal cord anatomy.
The spinal cord is located inside the vertebral canal, which is formed by the foramina of 7 cervical, 12 thoracic, 5 lumbar, and 5 sacral vertebrae, which together form the spine. The spinal cord extends from the foramen magnum down to the level of the first and second lumbar vertebrae (at birth, down to second and third lumbar vertebrae). See the image below.
Spine, anterior view.
The spinal cord is composed of the following 31 segments:
8 cervical (C) segments
12 thoracic (T) segments
5 lumbar (L) segments
5 sacral (S) segments
1 coccygeal (Co) segment – mainly vestigial
The spinal nerves consist of the sensory nerve roots, which enter the spinal cord at each level, and the motor roots, which emerge from the cord at each level. The spinal nerves are named and numbered according to the site of their emergence from the vertebral canal. C1-7 nerves emerge above their respective vertebrae. C8 emerges between the seventh cervical and first thoracic vertebrae. The remaining nerves emerge below their respective vertebrae. See the image below.
Spine, lateral view.
The dorsal rami of C1-4 are located in the suboccipital region. C1 participates in the innervation of neck muscles, including the semispinalis capitis muscle. C2 carries sensation from the back of the head and scalp, along with motor innervation to several muscles in the neck. C3-C5 contribute to the formation of the phrenic nerve and innervate the diaphragm. C5-T1 provide motor control for the upper extremities and related muscles.
The thoracic cord has 12 segments and provides motor control to the thoracoabdominal musculature. The lumbar and sacral portions of the cord have 5 segments each. L2-S2 provide motor control to lower extremities and related muscles.
The conus medullaris is the cone-shaped termination of the caudal cord. The pia mater continues caudally as the filum terminale through the dural sac and attaches to the coccyx. The coccyx has only 1 spinal segment. The cauda equina (Latin for horse tail) is the collection of lumbar and sacral spinal nerve roots that travel caudally prior to exiting at their respective intervertebral foramina. The cord ends at vertebral levels L1-L2.