Autonomic Nervous System (ANS)

Jul 5, 2024

Autonomic Nervous System (ANS)

Overview

  • Autonomic Nervous System (ANS): Controls involuntary actions.
    • Includes sympathetic, parasympathetic, and enteric systems.
  • Central Nervous System (CNS): Brain and spinal cord.
  • Peripheral Nervous System (PNS): Divided into sensory and motor systems.
    • Motor System: Further divided into somatic motor (voluntary) and visceral motor (autonomic, involuntary).

Somatic vs. Autonomic Nervous System

  • Somatic Nervous System:
    • One motor neuron directly from spinal cord (anterior/ventral gray horn) to the skeletal muscles.
    • Neurotransmitter: Acetylcholine (binds to nicotinic receptors).
  • Autonomic Nervous System:
    • Requires two motor neurons to reach the effector organ: preganglionic and postganglionic.
    • Sympathetic and parasympathetic systems discussed.

Sympathetic Nervous System

  • Function: Fight or flight response; uses energy during stress.
  • Location: T1 to L2 spinal cord segments (thoracolumbar outflow).
  • Ganglia:
    • Preganglionic neurons: Short.
    • Postganglionic neurons: Long.
    • Chain Ganglia/ Paravertebral Ganglia: Located along the spinal column.
      • Can ascend, descend, or synapse at the same level.
      • White Ramus Communicans: Path for preganglionic (myelinated) neurons.
      • Gray Ramus Communicans: Path for postganglionic (unmyelinated) neurons.
      • Synapse can occur at the ganglia or pass through to another ganglia.
    • Prevertebral/Collateral/Subdiaphragmatic Ganglia: Located in front of the vertebral column, primarily around the aorta.
      • Preganglionic neurons pass through chain ganglia without synapsing.
  • Neurotransmitters:
    • Preganglionic: Acetylcholine (cholinergic).
    • Postganglionic: Norepinephrine (adrenergic), except sweat glands (acetylcholine).
      • Note: Direct pathway to adrenal medulla, releases epinephrine (acts as a hormone).

Parasympathetic Nervous System

  • Function: Rest and digest; conserves energy.
  • Location: Brainstem (cranial nerves III, VII, IX, X) and sacral spinal cord segments (S2-S4).
    • Craniosacral Outflow: Combination of cranial and sacral outflow.
  • Ganglia:
    • Preganglionic neurons: Long.
    • Postganglionic neurons: Short, located near or within the target organs.
    • Terminal/Intramural Ganglia: Near or inside the target organs.
  • Neurotransmitters:
    • Both preganglionic and postganglionic: Acetylcholine (cholinergic).

Summary of Differences

  • Sympathetic vs Parasympathetic
    • Sympathetic:
      • Short preganglionic, long postganglionic.
      • Thoracolumbar outflow.
      • Norepinephrine at target tissues, except sweat glands.
    • Parasympathetic:
      • Long preganglionic, short postganglionic.
      • Craniosacral outflow.
      • Acetylcholine at all synapses.

Upcoming Topics

  • Detailed exploration of cranial sacral outflow, muscarinic, and nicotinic receptors.
  • Further details on sympathetic ganglia, splanchnic nerves, and adrenergic receptors.