Lecture on Nervous System Pathways

Types of Pathways

• Autonomic Pathway

  • Begins in the brain's gray matter or spinal cord's gray matter, near lateral gray horns.
  • Involves two motor neurons:
    • Preganglionic Neuron (myelinated): First motor neuron.
    • Postganglionic Neuron (unmyelinated): Second motor neuron.
  • Neurotransmitter release:
    • Preganglionic neuron releases Acetylcholine (ACH).
    • Postganglionic neuron can release either ACH or Norepinephrine (NE).
  • Effectors: Smooth muscle, glands, cardiac muscle.
  • Generally involuntary, can be excitatory or inhibitory.

• Somatic Pathway

  • Begins in the gray matter of the brain or spinal cord, in the anterior gray horns.
  • Involves a single motor neuron (myelinated).
  • Neurotransmitter release:
    • Always releases Acetylcholine (ACH).
  • Effectors: Skeletal muscles.
  • Voluntary and always excitatory, causing muscle contraction.

Integration Process

• Sensory receptors detect stimuli and send inputs via sensory neurons to the spinal cord.
• Integration occurs in the gray matter, potentially involving interneurons.
• Motor output is delivered via:
  • Somatic Pathway: Directly to skeletal muscle through one neuron.
  • Autonomic Pathway: Through two neurons to effectors like cardiac and smooth muscles.

Exception in Autonomic Pathway

• While typically involving two motor neurons, the autonomic pathway has an exception:
  • Adrenal Gland Exception:
    • Preganglionic neuron goes directly to the adrenal medulla.
    • Chromaffin cells in the medulla act as postganglionic neurons.
    • Releases ACH into the medulla.

Summary

• Autonomic vs. Somatic:
  • Autonomic: Two neurons, can release ACH or NE, involuntary, multiple effectors.
  • Somatic: One neuron, releases ACH, voluntary, effects skeletal muscle only.
• Somatic pathways are always excitatory, while autonomic can be both excitatory and inhibitory.
• Location of first motor neuron: Gray matter of the brain or spinal cord.
• Exception in autonomic pathway occurs with the adrenal medulla.

This summary captures the essential differences and characteristics of the autonomic and somatic nervous pathways, emphasizing their structure, neurotransmitter behavior, and effects.