Spinal Cord Overview

Spinal Cord

• The spinal cord is the second major component of the CNS, serving as a communication link between the brain and the peripheral nervous system (PNS).
• In adults, the spinal cord measures between 42 and 45 cm in length. It extends inferiorly from the brain through the foramen magnum and the vertebral canal, terminating at the level of the L1 vertebra.
• The spinal cord is shorter than the vertebral column due to its slower rate of growth during development.
• The spinal cord gives rise to 31 pairs of spinal nerves, exiting the vertebral column via intervertebral and sacral foramina.
• The spinal cord is divided into four regions: cervical, thoracic, lumbar, and sacral. The coccygeal part is the inferior tip of the spinal cord.
• The cervical part is the superiormost region, continuous with the medulla oblongata.
• The thoracic part lies inferior to the cervical part.
• The lumbar part is a relatively shorter segment.
• The sacral part is another region of the spinal cord.

Spinal Cord Enlargements

• Two prominent enlargements are visible externally on the spinal cord.
• The cervical enlargement is located between the third cervical and second thoracic vertebrae, serving the upper extremities.
• The lumbar enlargement is situated between the ninth and twelfth thoracic vertebrae, supplying the lower extremities.
• Inferior to the lumbosacral enlargement, the spinal cord tapers into a cone-shaped structure called the conus medullaris, marking the inferior end of the spinal cord.
• Below the conus medullaris, a collection of axons known as the cauda equina is present.
• The filum terminale, an extension of the pia mater, extends inferiorly, fusing with the arachnoid and dura mater and anchoring the spinal cord to the coccyx.

Spinal Cord Sections

• A transverse section of the spinal cord reveals white matter surrounding a core of gray matter.
• The gray matter has a butterfly or H shape. It contains neuron cell bodies, dendrites, unmyelinated axons, and neuroglia.
• Projections of the gray matter are called horns (posterior, anterior, and lateral) and are named based on their direction of projection.
• Posterior horns contain interneurons and incoming sensory axons.
• Anterior horns contain somatic motor nuclei.
• Lateral horns contain autonomic motor nuclei.
• The gray commissure is the crossbar of the H-shaped gray matter, containing the central canal. The central canal is filled with cerebrospinal fluid and continuous with the fourth ventricle.

Spinal Cord Columns

• The spinal cord's white matter is organized into six columns called funiculi, named based on their relative positions.
• The anterior funiculi are located between the anterior horns.
• The posterior funiculi are located between the posterior horns.
• Two lateral funiculi are located between the anterior and posterior horns.

Spinal Nerves

• Spinal nerves are communication pathways between the spinal cord and specific body regions.
• There are 31 pairs of spinal nerves, including 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal.
• A spinal nerve is a mixed nerve, composed of both sensory (posterior root) and motor (anterior root) fibers.
• The posterior root ganglion contains the cell bodies of sensory neurons.
• The anterior root consists of axons of motor neurons that carry impulses away from the CNS.

Spinal Nerve Rami

• After exiting the intervertebral foramen, spinal nerves branch into rami.
• Rami contain three types: anterior, posterior, and rami communicantes.
• Anterior rami distribute to the anterior and lateral portions of the trunk, upper and lower limbs; in the thoracic region, they form intercostal nerves to innervate intercostal muscles and skin.
• Posterior rami innervate deep back muscles and the skin of the back.
• Rami communicantes are associated with the autonomic nervous system, connecting the spinal nerve to the sympathetic trunk ganglion.

Spinal Plexuses

• Spinal nerves (except T2-T12) form networks called plexuses.

• Principal plexuses include cervical, brachial, lumbar, and sacral.

• The anterior rami of T2-T12 form intercostal nerves.

• Plexus nerves are named based on the structure they innervate.

• The cervical plexus lies lateral to the first four cervical vertebrae.

• The brachial plexus is positioned next to the last four cervical and first thoracic vertebrae.

• The lumbar plexus is positioned next to the first four lumbar vertebrae.

• The sacral plexus is positioned immediately inferior to the lumbar plexus.

• The lumbar and sacral plexuses are sometimes described jointly as the lumbosacral plexus.

• The sciatic nerve, the largest nerve in the body, arises from the sacral plexus. It is composed of the tibial and common fibular nerves.

Explore the anatomy and function of the spinal cord, the vital communication link between the brain and the peripheral nervous system. This quiz covers its length, regions, and the number of spinal nerves it gives rise to. Test your knowledge on this essential component of the central nervous system.