Spinal Region Anatomy and Reflexes

Spinal Region Anatomy and Function

  • Objective: Learn the Anatomy of the Spinal Cord and Spinal Nerves, and about spinal reflexes.

Introduction

  • Main Functions of the Spinal Cord:
    • Conveys information between neurons connecting peripheral structures to the brain.
    • Processes information in some cases.
  • Structure:
    • Encased in the vertebral column.
    • Continuous with the foramen magnum and terminates at L1-L2 intervertebral column.
    • Contains 31 pairs of spinal nerves emerging from the spinal cord.

Anatomy of Spinal Region

  • Meninges:

    • Protective membranes of the brain and spinal cord, continuous with cranial meninges.
    • Layers of Meninges:
    • Dura Mater: Tough outermost layer.
    • Epidural Space: Between dura mater and vertebral column; filled with adipose tissue for cushioning and blood vessels.
    • Subdural Space: Between dura mater and arachnoid mater.
    • Arachnoid Mater: Middle layer with a spider web-like appearance.
    • Subarachnoid Space: Between arachnoid and pia mater, filled with Cerebrospinal Fluid (CSF).
    • Pia Mater: Innermost layer tightly attached to the spinal cord.

  • Gray Matter:

    • Central Gray Matter:
    • Has a butterfly or ‘H’ shape, appears gray due to neuron cell bodies and unmyelinated axons.
    • Divided into dorsal, lateral, and ventral horns:
      • Dorsal Horns: Process sensory information.
      • Lateral Horns: Process autonomic information.
      • Ventral Horns: Process motor information.
    • Gray Commissure: Connects lateral areas of gray matter.

  • White Matter:

    • Surrounds the gray matter and appears white due to myelinated axons.
    • Contains ascending and descending tracts for sensory and motor information and is divided into:
    • Dorsal Columns
    • Lateral Columns
    • Anterior (Ventral) Columns.

  • Central Canal:

    • Continuously connects with the brain's ventricles for CSF flow.

Spinal Nerves

  • Function:
    • Carry both motor and sensory axons for spinal segments.
  • Dorsal and Ventral Roots:
    • Join briefly to form spinal nerves.
    • Dorsal Root: Enlarged section contains the dorsal root ganglion with sensory neuron cell bodies.
    • Ventral Root: Transmits motor information to effectors.
    • Spinal nerves exit the vertebral column and split into dorsal and ventral rami.

Spinal Tracts

  • Definitions:
    • Spinal Tracts: Bundles of axons with a common origin and termination.
    • Ascending Tracts: Carry sensory information from receptors to the brain.
    • Descending Tracts: Convey motor information from the brain to effectors.
Ascending Tracts Include:
  • Dorsal Fasciculus Gracilis
  • Fasciculus Cuneatus
  • Posterior Spinocerebellar Tract
  • Anterior Spinocerebellar Tract
  • Lateral Spinothalamic Tract
  • Anterior Spinothalamic Tract
Descending Tracts Include:
  • Lateral Corticospinal Tract
  • Anterior Corticospinal Tract
  • Lateral Reticulospinal Tract
  • Medial Reticulospinal Tract
  • Rubrospinal Tract
  • Vestibulospinal Tract
  • Tectospinal Tract.

Spinal Reflexes

  • Stretch Reflex:

    • Involuntary responses to stimuli, does not involve the brain.
    • Example: Patellar Reflex (knee jerk) and Achilles Reflex.
    • The simplest reflex involves a single sensory neuron synapsing with a single motor neuron (monosynaptic).

  • Withdrawal Reflex:

    • Protects the body by removing a part from a damaging stimulus.
    • Coordinates flexor muscle contraction and extensor muscle relaxation.
    • Involves a reflex arc: Receptor (Stimulus) > Sensory Neuron > (Interneuron) > Motor Neuron > Effector.

Disorders Associated with Spinal Region

  • Meningomyelocele: Failure of neuropore to close leading to an open spinal cord and possible loss of bowel/bladder control.
  • Spastic Cerebral Palsy: Muscle stiffness and jerky movements due to a congenital brain disorder.
  • Multiple Sclerosis: Autoimmune attack on CNS myelin, leading to numbness, weakness, and gait problems.
  • Spinal Region Tumors: Abnormal tissue growth affecting the spinal cord; symptoms vary.
  • Myelopathy due to Cervical Spondylosis: Degenerative joint disease leading to nerve compression, pain, and coordination issues.
  • Lumbar Stenosis: Narrowing of the lumbar spinal canal; leads to nerve and blood vessel compression.
  • Syringomyelia: Fluid-filled cyst in the spinal cord, leading to weakness and loss of sensation.