Spinal Cord

Spinal Cord Overview

  • The spinal cord extends from the foramen magnum to the level of the disc between vertebrae L1 and L2 in adults.

  • In neonates, the spinal cord extends approximately to vertebra L3 but can reach as low as vertebra L4.

Conus Medullaris

  • At the L2 vertebral level, the spinal cord tapers off, forming the cone-shaped distal end known as the conus medullaris.

Cauda Equina

  • The spinal nerves that arise from the end of the spinal cord bundle together to form the structure known as the cauda equina.

Cauda Equina Syndrome

  • Cauda equina syndrome arises from compression of the nerve bundles of the cauda equina, located in the subarachnoid space.

  • Causes include:

    • Intervertebral disc prolapse

    • Primary cord tumors

    • Spinal stenosis

    • Trauma

    • Abscess formation

Regions of the Spinal Cord

  • The spinal cord is divided into five regions, each synonymous with the vertebral regions:

    • Cervical

    • Thoracic

    • Lumbar

    • Sacral

    • Coccygeal

Spinal Enlargements

  • Cervical Enlargement:

    • Occurs in the region of spinal nerves C5 to T1, innervating the upper limbs.

  • Lumbosacral Enlargement:

    • Occurs in the region of spinal nerves L1 to S3, innervating the lower limbs.

External Surface of Spinal Cord

  • The external surface has several fissures and sulci:

    • Anterior Median Fissure: Extends the length of the anterior surface.

    • Posterior Median Sulcus: Extends along the posterior surface.

    • Posterolateral Sulcus: Marks where the posterior roots of spinal nerves enter the cord.

Internal Features of Spinal Cord

  • Contains a small central canal surrounded by gray and white matter:

    • Gray Matter: Rich in neuronal cell bodies, forms longitudinal columns, appears H-shaped in the central regions.

    • White Matter: Surrounds gray matter, contains neuronal cell processes forming ascending and descending tracts that carry information to and from the brain.

Spinal Meninges

  • Comprised of three layers:

    • Dura Mater: Outer layer; separates the vertebral canal from bones by an extradural space.

    • Arachnoid Mater: Thin delicate membrane, not adherent to the dura, and separated from the pia mater by the subarachnoid space.

    • Pia Mater: Innermost vascular membrane that adheres to the spinal cord's surface and forms denticulate ligaments.

Filum Terminale

  • Forms a strand of fibrous tissue at the distal end of the meninges, anchoring the spinal cord to the coccyx.

Epidural Space

  • Located between the bone of the vertebral canal and dura mater.

  • Contains:

    • Blood vessels

    • Fat

    • Areolar tissue

  • Used clinically for epidural anesthesia, particularly during childbirth and pelvic surgeries.

Subdural Space

  • A potential space between the dura and arachnoid mater.

Subarachnoid Space

  • Contains cerebrospinal fluid (CSF), lies between the arachnoid and pia mater, and is continuous with the subarachnoid space of the brain.

  • Largest in the lower lumbar region, where it surrounds the cauda equina.

  • Accessible during spinal anesthesia and lumbar punctures.

Lumbar Puncture

  • Also known as spinal tap, performed at the intervertebral disc between L3 and L4.

  • Used to draw CSF for diagnosing conditions like meningitis, leukemia, and encephalitis.

Spinal Nerves

  • Total: 31 pairs:

    • Cervical: 8

    • Thoracic: 12

    • Lumbar: 5

    • Sacral: 5

    • Coccygeal: 1

Formation and Fate of Spinal Nerves

  • Formed by two roots:

    • Ventral (motor) root

    • Dorsal (sensory) root

  • After emerging from the intervertebral foramen, each spinal nerve divides into a ventral and dorsal ramus:

    • The ventral ramus supplies limbs and the anterior and lateral body wall.

    • The dorsal ramus supplies back muscles and the skin covering them.

Spinal Tracts - Basic Concepts

  • Composed of three-neuron systems:

    • Ascending tracts are sensory.

    • Descending tracts are motor.

  • Naming indicates the direction and type of fiber involved.

Spinal Cord Injuries

  • Fractures of the atlas (C1) and axis (C2) can cause severe spinal cord injuries, potentially leading to death or paralysis due to brainstem damage affecting cardiac and respiratory centers.

Spinal Cord Infarction

  • Refers to the death of nervous tissue due to interrupted arterial supply, resulting in muscle weakness and paralysis with loss of reflexes.

Paraplegia & Tetraplegia

  • Tetraplegia: Injury to the cervical spinal cord causing varying degrees of sensory and motor impairment in all four limbs.

    • Upper cervical injuries can be fatal due to diaphragm innervation loss.

  • Paraplegia: Results from lower cervical injuries affecting only the lower limbs.

Fun Facts

  • The spinal cord extends to the intervertebral disc between L1 and L2 in adults and to L3 in neonates.

  • The cauda equina consists of nerve roots from L3 to L5 and S1 to S3.

  • The epidural space is clinically significant for epidural anesthesia.

  • Lumbar puncture is performed between L3 and L4 in the subarachnoid space.

  • There are 31 pairs of mixed spinal nerves, with nerve plexuses formed always by the ventral ramus.