Spinal Cord Overview

• The spinal cord is a vital part of the central nervous system, responsible for coordinating motor, sensory, and reflex functions.

• Positioned within the spinal canal, it extends from the base of the medulla (C1) to the conus medullaris (between L1 and L2). 

• The cord can be categorized into gray matter at its center and white matter at its periphery, a reversal of the brain's organization. 

• The gray matter comprises the anterior (ventral) horn, containing motor neuron cell bodies; the posterior (dorsal) horn, housing sensory neuron cell bodies; and the lateral horn, home to preganglionic sympathetic neuron cell bodies. 

• The white matter contains both descending and ascending tracts, transmitting motor signals to the body and sensory signals to the brain, respectively. 

• Blood supply to the spinal cord comes from branches of the vertebral artery and drains into the vertebral veins. 

• 31 pairs of peripheral spinal nerves originate segmentally from the spinal cord, conveying autonomic, motor, sensory, and reflex signals between the central nervous system and the body. 

• Dermatomes are specific areas of skin innervated by a single spinal nerve or cord level. Evaluating strength, sensation, and reflexes in a particular dermatome can help identify the level of a spinal cord injury (as shown in the image below).

Regional Spinal Cord Differences:

• The cervical region between C5-T1 is the largest part of the spinal cord because it contains all the nerve tracts that will later form the brachial plexus.  A cross-section of the cervical region shows large anterior horns, absent lateral horns, and both dorsal columns (gracile fasciculus and cuneate fasciculus).

• The thoracic region (T1-T12) does not have an enlargement. A cross-section shows lateral horns, small anterior horns, both dorsal columns above T5, but only the gracile fasciculus below T6.

• The lumbar region is enlarged between L2-S3 due to the nerve tracts that eventually form the lumbar and sacral plexuses, which innervate the lower limbs. A cross-section of the lumbar region shows a large anterior horn, absent lateral horn, and a single dorsal column (gracile fasciculus).

Spinal Nerve Overview

• There are 31 pairs of peripheral spinal nerves, categorized into 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal pairs. Each pair emerges from the spinal cord through spaces between adjacent vertebrae, known as intervertebral foramina.

• Spinal nerves play a crucial role in transmitting information between the brain and the body. They carry motor signals from the brain to muscles and glands (efferent pathways) and sensory signals from the body to the brain (afferent pathways). Additionally, they participate in the autonomic nervous system, regulating involuntary bodily functions.

• Each spinal nerve is formed by the union of two roots: the ventral (anterior) root and the dorsal (posterior) root. The ventral root contains motor fibers originating from the anterior horn, controlling voluntary muscle movements. In contrast, the dorsal root contains sensory fibers originating from the posterior horn, which carry information about touch, temperature, pain, and proprioception from the body to the spinal cord.

• Compression of spinal nerve roots, often caused by conditions such as herniated intervertebral discs or osteophytes (bone spurs), can lead to radicular pain. This type of pain radiates along the path of the affected nerve, causing symptoms such as numbness, tingling, or weakness in the corresponding body area.

• Each dorsal root contains a swelling called the dorsal root ganglion, which houses the cell bodies of sensory neurons. These neurons transmit sensory information from the body to the spinal cord, where it is processed and relayed to the brain.

• Upon exiting the intervertebral foramina, spinal nerves divide into ventral and dorsal rami. The ventral rami supply the anterior aspects of the body, including the muscles and skin of the trunk and limbs, while the dorsal rami innervate the muscles and skin of the posterior trunk.

• The conus medullaris is the tapering, cone-shaped end of the spinal cord, located at the level of the first or second lumbar vertebra. It contains both upper and lower motor neurons, which contribute to motor control and coordination.

• Below the conus medullaris, the spinal cord tapers into a bundle of nerve roots resembling a horse's tail, known as the cauda equina. These nerve roots continue to convey sensory and motor signals to and from the lower extremities and pelvic organs.

• The filum terminale is a thin, fibrous strand extending from the conus medullaris to the coccyx. It is a remnant of the embryonic spinal cord and serves to anchor the spinal cord within the vertebral canal, providing stability and preventing excessive movement or traction.