Chapter 15: The Autonomic Nervous System

Overview

Part of the efferent portion of the nervous system.
Motor output from the brain to the body.
Involves involuntary control of the body’s internal environment through different effector organs.

Effector Organs: Skeletal muscles.
Control: Voluntary (intentional movements).
Pathway: Upper motor neurons from the primary motor cortex descend, synapse with lower motor neurons in the ventral gray horn or cranial nerve nuclei.

Effector Organs: Smooth muscle, cardiac muscle, glands, adipocytes.
Control: Involuntary.
Pathway: Involves visceral motor neurons.
- Preganglionic Neuron: Leaves the CNS.
- Synapse: Occurs in a ganglia.
- Postganglionic Neuron: Synapses with the target tissue.
Distinction: Always two neurons between the CNS and target tissue.

Origin: Lateral gray horn, thoracolumbar (T1-L2).
Ganglia: Near CNS/spinal cord.
Pathways:
- Short preganglionic, long postganglionic fibers.
- Patterns:
  - Pattern 1: To skin, arms, legs (via spinal nerves).
  - Pattern 2: To head/thoracic cavity (via sympathetic nerves).
  - Pattern 3: To abdominal/pelvic viscera (via splanchnic nerves).
  - Adrenal Medulla: Direct sympathetic innervation.
  - Pelvic variant: Sacral splanchnic nerves.

Origin: Craniosacral; cranial nerves 3, 7, 9, 10, and sacral nerves.
Ganglia: Near or on the target organs (terminal ganglia).
Pathways:
- Long preganglionic, short postganglionic fibers.
- Cranial Nerves:
  - CN III: Oculomotor to ciliary ganglion.
  - CN VII: Facial to pterygopalatine and submandibular ganglia.
  - CN IX: Glossopharyngeal to otic ganglion.
  - CN X: Vagus nerve to thoracic and abdominal organs.
- Pelvic splanchnic nerves to pelvic organs.

Most target tissues receive both sympathetic and parasympathetic inputs.
Typically results in opposite physiological effects (e.g., dilation vs. constriction).
Sympathetic activation: Fight or flight response.