Autonomic Nervous System Overview

Autonomic Nervous System

• The autonomic nervous system (ANS) controls involuntary actions, such as cardiac muscle, smooth muscle, and glands.
• It occupies both the central nervous system (CNS) and the peripheral nervous system (PNS).
• The ANS pathway from the CNS to an effector organ consists of two neurons, except for the adrenal medulla.
• The first neuron is located in the CNS; its axon is called the preganglionic fiber.
• The first neuron synapses with the second neuron in an autonomic ganglion.
• The second neuron's axon, called the postganglionic fiber, innervates the effector organ.

Anatomical Divisions of ANS

• Cranial: originates from cranial nerve nuclei (III, VII, IX, X)
• Thoracic-lumbar: originates from the lateral horn cells of the thoracic and upper lumbar segments.
• Sacral: originates from the lateral horn cells of the sacral segments.

Physiological Divisions of ANS

• Sympathetic system: thoracolumbar
• Parasympathetic system: craniosacral

Autonomic Ganglia

• Definition: collections of nerve cells outside the CNS, where preganglionic fibers synapse with postganglionic fibers.
• Types:
  • Lateral (paravertebral): bilaterally along the vertebral column (3 cervical, 10-12 thoracic, 4 lumbar, 4 sacral, 1 coccygeal), for sympathetic relay only.
  • Collateral (prevertebral or preaortic): anterior to the aorta and vertebral column (celiac, mesenteric, renal, and hypogastric ganglia); relay for sympathetic and some parasympathetic relay.
  • Terminal: in the wall of organs; relay for parasympathetic fibers only.

Properties of Autonomic Ganglia

• One-way transmission: impulses travel in one direction (preganglionic to postganglionic)
• One relay: nerve impulses pass only once through the autonomic ganglia.
• One chemical transmitter: acetylcholine
• Delay: due to chemical transmission

Modes of Autonomic Action

• Reciprocal action: one system stimulates while the other system inhibits.
• Antagonistic action: systems exert opposite actions on an organ.
• Complementary action: two systems together complete an action.
• Same action: both systems act similarly.
• Single innervation: only one system affects an organ.

Horner's Syndrome

• Occurs from lesions in cervical sympathetic nerves.
• Symptoms: miosis, ptosis, enophthalmos, anhidrosis, and vasodilation of cutaneous blood vessels on the affected side.

Sympathetic System Features

• Preganglionic neurons leave the spinal cord via ventral roots, and enter white rami communicantes to sympathetic chain ganglia.
• Postganglionic neurons travel to a target organ.
• Distribution of fibers depends on the location of target organs.

Parasympathetic System Features

• Preganglionic neurons originate from cranial nerves (III, VII, IX, X) or sacral spinal cord segments.
• Postganglionic neurons originate in terminal ganglia near or within the target organ.
• Target organs are primarily visceral organs regulating involuntary functions.

Neurotransmitters

• Acetylcholine, released by cholinergic neurons, affecting nicotinic and muscarinic receptors.
• Catecholamines (adrenaline and noradrenaline), affect alpha and beta receptors.

This quiz covers the autonomic nervous system (ANS), detailing its control over involuntary actions and its anatomical and physiological divisions. You will learn about the pathways made up of two neurons, the cranial and thoracic-lumbar sections, as well as differences between the sympathetic and parasympathetic systems.