The Spinal Cord: Lecture Review

The Spinal Cord

Module 1, Part 2

Function of the Spinal Cord

  • Sensations (Afferent)

    • Sensations such as touch and pain must pass through the spinal cord to reach the brain, where they are perceived.

  • Voluntary Movements (Efferent)

    • Commands for voluntary movement must travel through the spinal cord to reach spinal nerves that innervate appropriate muscles.

  • Consequences of Damage

    • Damage to the spinal cord may result in the loss of general sensations and paralysis of voluntary movements in their respective parts of the body supplied by spinal nerves.

Spinal Cord Anatomy

  • Location

    • The spinal cord is located within the vertebral canal.

  • Beginning

    • It begins at the foramen magnum, the large opening at the base of the skull.

  • Ending

    • The spinal cord ends at the conus medullaris, typically at the L1-L2 vertebral level.

  • Vertebral Segment Count

    • 7 cervical vertebrae

    • 12 thoracic vertebrae

    • 5 lumbar vertebrae

    • 5 fused sacral vertebrae

  • Spinal Nerve Count

    • 8 cervical spinal nerves

    • 12 thoracic spinal nerves

    • 5 lumbar spinal nerves

    • 5 sacral spinal nerves

  • Nerve Exit Points

    • C1-C7 nerves exit above their corresponding vertebrae.

    • Below the C7 vertebra, spinal nerves exit below their respective vertebrae.

Structures Associated with the Spinal Cord

  • Conus Medullaris

    • Tip of the conus medullaris marks the end of the spinal cord.

  • Cauda Equina

    • Collection of spinal nerves and nerve roots extending from the lower end of the spinal cord.

  • Filum Terminale Internum

    • A fibrous extension of the pia mater, anchoring the spinal cord to the coccyx.

Clinical Connection

  • Lumbar Punctures

    • A procedure used to withdraw cerebrospinal fluid (CSF) for diagnostic or therapeutic purposes.

    • Can also be used to inject anesthetics (nerve blocks) or therapeutic agents such as steroids.

    • Punctures are performed below the L2-L3 space in adults to minimize complications.

    • Contraindications

    • Lumbar punctures are contraindicated in patients with elevated intracranial pressure due to conditions such as trauma or stroke.

Meningeal Layers of the Spinal Cord

  • Three Meningeal Layers

    • Pia Mater

    • The innermost layer, delicate and adherent to the spinal cord.

    • Arachnoid Mater

    • The middle layer, web-like in structure, situated between the pia and dura mater.

    • Dura Mater

    • The outermost tough layer, protective in nature.

  • Denticulate Ligament

    • A structure that stabilizes the spinal cord within the vertebral canal.

  • Nerve Roots

    • Dorsal Root

    • Sensory nerve roots entering the spinal cord.

    • Ventral Root

    • Motor nerve roots exiting the spinal cord.

  • Dorsal Root Ganglion (DRG)

    • A collection of nerve cell bodies located in the dorsal root of a spinal nerve.

  • Spinal Nerve

    • Formed by the joining of the dorsal and ventral roots.

Spinal Nerves

  • Structure at Each Spinal Level

    • Each spinal nerve features:

    • (2) Ventral Rootlets

      • Forming the anterior root, responsible for motor outputs.

    • (2) Dorsal Rootlets

      • Forming the posterior root, responsible for sensory inputs.

    • Dorsal root ganglion (DRG) houses the cell bodies of sensory neurons.

    • Components include: Rootlets, Roots, Vertebral Foramen, and Spinal Nerve.

    • Anterior Median Fissure

    • A deep groove that houses the anterior spinal artery, significant for blood supply to the anterior part of the spinal cord.

Internal Structure of the Spinal Cord

  • White Matter

    • Located in the external area of the spinal cord and consists mainly of myelinated axons.

    • Divisions

    • Divided into three areas or “funiculi”:

      • Posterior Funiculi

      • Lateral Funiculi

      • Anterior Funiculi

    • White matter is essential because it includes nerve tracts functioning as an elevator system for signals going up and down the spinal cord.

  • Gray Matter

    • Found in the internal area of the spinal cord, primarily consisting of unmyelinated axons and nerve cell bodies.

    • Divisions

    • Divided into four main parts:

      1. Posterior/Dorsal Horns

      • Associated with sensory function, primarily containing ascending tracts.

      1. Anterior/Ventral Horns

      • Associated with motor function for voluntary movements and containing descending tracts.

      1. Intermediate Zones

      • Contains mostly interneurons, facilitating connections within the spinal cord, acting as the “association” area for reflexes and integration.

      1. Lateral Horns

      • Contains preganglionic neurons of the sympathetic nervous system; found only from T1-T12 and L1-L2.

Spinal Cord Injury

  • Acute Injuries

    • Examples include stroke or trauma that result from instant or prolonged vascular or compression injuries to the spinal cord.

    • Such injuries may present immediate signs & symptoms (S/S).

    • If both trauma and vascular insult occur simultaneously, they can bruise or create a contusion of the spinal cord.

    • Contusions can lead to vascular insufficiency and necrosis, referred to as a physiologic transection.

  • Chronic Injuries

    • Caused by ongoing conditions such as infections, inflammation, tumors, genetic disorders, and chronic compression of spinal cord structures.