ch 14

Overview of the Spinal Cord

  • The spinal cord functions as the information highway of the body.

  • It serves as a pathway for information transmission (sensory and motor).

  • Key concepts include:

    • Afferent: Sensory information going to the brain.

    • Efferent: Motor information going from the brain.

  • Spinal reflexes mediate rapid responses to stimuli.

Types of Paralysis

  • Quadriplegia: Paralysis from the neck down.

  • Paraplegia: Paralysis from the waist down.

  • Hemiplegia: Paralysis affecting one side of the body.

Structure of the Spinal Cord

  • The spinal cord extends from the foramen magnum at the base of the skull to the L1-L2 vertebrae.

  • Beyond L1-L2, the spinal cord continues as a collection of nerves known as the cauda equina.

    • Meaning "horse's tail," as it resembles tail hairs.

  • The spinal cord is shorter than the vertebral canal, indicating early developmental growth halting before the vertebrae fully form.

Surface Anatomy

  • Regions of the Spinal Cord:

    • Cervical, thoracic, lumbar, sacral.

  • Two major enlargements:

    • Cervical enlargement (C3 - T2): Responsible for upper limb innervation.

    • Lumbar enlargement (T7 - T11): Responsible for lower limb innervation.

  • The medullary cone marks the transition into the cauda equina.

Understanding Spinal Nerves

  • There are 31 pairs of mixed spinal nerves (both sensory and motor).

    • Distinction between cranial nerves, which arise from the brain, and spinal nerves.

Protective Layers of the Spinal Cord

  • Meninges consist of three layers encasing the spinal cord and brain:

    1. Dura Mater: Tough, outer layer.

    2. Arachnoid Mater: Web-like middle layer.

    3. Pia Mater: Delicate inner layer, directly covering the spinal cord.

Pathways for Information

  • Gray Matter (unmyelinated): Contains:

    • Cell bodies of neurons and synaptic connections.

    • Organized in an H-shape (butterfly shape) with:

      • Dorsal (Posterior) Horn: Receives sensory inputs.

      • Ventral (Anterior) Horn: Sends motor signals to skeletal muscles.

      • Lateral Horn (only in thoracic/lumbar regions): Contains sympathetic nervous system neurons.

  • White Matter (myelinated): Surrounds gray matter and carries signals between brain and body.

    • Divided into funiculi (columns): posterior, lateral, anterior.

Ascending and Descending Tracts

  • Ascending Tracts: Convey sensory information to the brain.

    • Example: Spinothalamic tract (pain, temperature).

  • Descending Tracts: Relay motor commands from the brain:

    • Example: Corticospinal tract (controls voluntary movements).

  • Decussation: The crossing over of tracts from one side of the body to the other, leading to contralateral effects in brain injuries.

Reflexes and Sensory Pathways

  • Reflex Arcs: Automatic responses with minimal brain involvement, involving both sensory (afferent) and motor (efferent) pathways through the spinal cord.

  • Dorsal Root Ganglion: Contains cell bodies of sensory neurons entering the spinal cord.

Additional Concepts

  • Denticulate Ligaments: Extensions of pia mater that help anchor the spinal cord in place.

  • Cerebrospinal Fluid Buildup: Important for cushioning and nutrient provision in the subarachnoid space.

  • Lumbar Puncture: Procedure to collect cerebrospinal fluid, typically performed between L3 and L4 vertebrae.

Summary of Key Functions and Structures

  • Gray Horns:

    • Posterior Horn: Contains sensory neurons.

    • Anterior Horn: Contains motor neurons for skeletal muscles.

    • Lateral Horn: Sympathetic autonomic functions.

  • Cerebrospinal Fluid: Circulated for cushioning, protection, and nutrient transport.

  • Recognizing structures through histology helps understand the anatomy and functions of the spinal cord.