Lecture on Spinal Nerves and Spinal Cord

Overview

• Focus on spinal nerves, spinal cord, and their interaction with the peripheral nervous system.
• Builds on concepts from previous lectures on the brain and cranial nerves.

Spinal Cord Function and Structure

• Vital Link: Connects brain and body.
  • Functions independently for some reflex actions.
  • Sensory info travels to the brain; motor info leaves the brain.
• External Surface:
  • Posterior Median Sulcus: Located on the posterior side.
  • Anterior Median Fissure/Sulcus: Located on the anterior side.

Spinal Cord Regions and Nerves

• Regions & Nerves:

  • Cervical Region: 8 spinal nerves (C1-C8)
  • Thoracic Region: 12 spinal nerves (T1-T12)
  • Lumbar Region: 5 spinal nerves (L1-L5)
  • Sacral Region: 5 spinal nerves (S1-S5)
  • Coxal Region: 1 pair at the base

• Note: Spinal cord is shorter than vertebral canal.

Important Structures

• Conus Medullaris: Cone-like tapering end of the spinal cord.
• Cauda Equina: Axons running to the legs.
• Filum Terminale: Anchors spinal cord to coccyx.

Meninges and Spaces

• Layers (Outer to Inner):
  • Vertebra > Epidural Space > Dura Mater > Subdural Space > Arachnoid Mater > Subarachnoid Space > Pia Mater

Gray & White Matter

• Gray Matter:

  • Internal, H-shaped (butterfly appearance).
  • Divisions: Anterior, Lateral, Posterior horns.
  • Gray Commissure: Connects two sides.

• White Matter:

  • Surrounds gray matter, opposite of brain arrangement.
  • Divisions: Anterior, Lateral, Posterior funiculi.

Spinal Nerves

• Bundles of Motor and Sensory Axons:

  • Connected via anterior (motor) and posterior (sensory) roots.

• Dermatome Map:

  • Skin segments associated with specific spinal nerves.
  • Most nerves innervate skin except C1.

Nerve Plexuses

• Branching Network of Nerves:
  • Principal Plexuses: Cervical, Brachial, Lumbar, Sacral

Reflexes

• Definition: Automatic, involuntary responses.

• Properties: Occur rapidly, same way every time, do not require intent or awareness.

• Types of Reflex Arcs:

  • Ipsilateral: Receptor and effector on the same side.
  • Contralateral: Opposite sides.
  • Monosynaptic: One synapse, e.g., stretch reflexes.
  • Polysynaptic: Multiple synapses, more complex.

Neural Pathways

• Sensory and Motor Pathways:

  • Sensory (Ascending): Carry info to CNS.
  • Motor (Descending): Carry motor commands from CNS.

• Components: Tracts (axons) and nuclei (neuron cell bodies).

• Decussation: Crossing over of pathways in CNS; common.

Brain Hemisphere Functions

• Left Hemisphere: Language, analytical reasoning (math/science).

• Right Hemisphere: Visual-spatial skills, imagination, and patterns.

• Communication: Constant through corpus callosum.