Lecture Notes on the Spinal Cord

Overview

• Spinal Cord Function: Acts as a communication gateway between the brain and spinal nerves.
• Structure: A long, thin tube of nervous tissue, enclosed in 3 membranes of the meninges, protected by the vertebral column.

Spinal Nerves

• Pairs: 31 pairs of spinal nerves arise from the spinal cord.
• Emergence: Nerves emerge from the vertebrae.
• Extension: Extends from the brainstem to the upper lumbar vertebrae.
• Cauda Equina: Formed by descending nerve roots in lower lumbar and sacral regions.

Nervous Tissue

• Gray Matter:
  • Butterfly-shaped central core.
  • Contains cell bodies and dendrites of neurons.
  • Site of synapses and information transmission.
• White Matter:
  • Contains bundles of axons.
  • Conducts information up and down the cord.
  • Organized into specific groups, forming spinal tracts.

Spinal Tracts

• Function: Conduct information between spinal cord and brain.
• Types:
  • Ascending Tracts: Conduct sensory information to the brain.
  • Descending Tracts: Convey motor instructions down the cord.
• Contralateral Transmission: Some tracts cross sides to transmit information.
• Ipsilateral Transmission: Tracts that stay on the same side.

Spinal Nerves Composition

• Mixed Nerves: Contain both sensory and motor fibers.
• Sensory Fibers: Enter via dorsal root.
• Motor Fibers: Exit via ventral root.

Sensory Pathways

• Neurons Involved:
  • First-order Neurons: Detect stimuli, transmit signals to the spinal cord.
  • Second-order Neurons: Ascend tracts to the brainstem or thalamus.
  • Third-order Neurons: Conduct information to the sensory cortex.

Motor Pathways

• Neurons Involved:
  • Upper Motor Neuron: Starts in motor cortex or brainstem.
  • Lower Motor Neuron: Continues from brainstem or spinal cord.
  • Function: Conduct motor instructions down along descending tract.

Reflexes

• Somatic Reflexes: Fast, involuntary responses of skeletal muscles.
• Reflex Arc Components: Somatic receptor, sensory neuron, interneuron, motor neuron, and effector muscle.
• Complex Reflexes: Require contralateral pathways and central coordination from the brain.
• Example: Response to stepping on something sharp, involving multiple muscles and pathways.