Autonomic Nervous System Flashcards
Autonomic fibers:
VE - visceral efferent (motor)
VA - visceral afferent (sensory)
There are 4 types of functional nerve fibers in a typical spinal nerve:
SA - somatic afferent (sensory)
VA - visceral afferent (sensory)
SE - somatic efferent (motor)
VE - visceral efferent (motor)
The ANS regulates visceral functions by way of:
A two (pre- and post-ganglionic) neuron chain circuit. The cell body of the preganglionic neuron is always located in the CNS, the postganglionic neuron is in the autonomic ganglion. The postganglionic neuron goes to either: smooth muscle, cardiac muscle, or glands.
Paravertebral ganglia:
Sympathetic chain, found lateral to vertebral bodies along the entire length of the vertebral column, 24-25 pairs (3 cervical, 11-12 thoracic, 4 lumbar, 5 sacral) - all attached in ladder fashion by the sympathetic trunk
Prevertebral ganglia:
Called sympathetic collateral, found in front of (ventral to) the vertebral bodies, often next to major branches of the abdominal aorta (celiac, superior mesenteric etc)
Terminal ganglia:
Most are parasympathetic, found within the wall of the viscera
Sympathetic (SS) and parasympathetic (PS) divisions are based on:
- Site of origin
- Location of their ganglia
- Neurotransmitter content (NE or ACh)
- Action on target (ANS is subdivided into SS and PS divisions)
Most viscera are innervated by both SS and PS with the exceptions of:
Blood vessels, sweat glands, and the adrenal medulla - all primarily controlled by the SS
Thoracolumbar outflow:
Sympathetic
Functions to spend energy stores throughout the body:
SS (as in the stress syndrome)
Craniosacral outflow:
Parasympathetic division
Functions to conserve and store energy:
PS (as in digestion)
Parasympathetic cranial nerve targets:
CN3 - eye
CN7 - salivary glands, secretion of tears
CN9 - salivary glands, secretion of tears
CN10 - long trajectory fibers to the heart, stomach, small intestine, and large intestine (thoracic and abdominal viscera)
Parasympathetic sacral nerve targets:
S2-S4: called pelvic splanchnics - main function is to empty the bladder and the colon
Preganglionic axons follow pelvic splanchnic nerves to terminal ganglia in the wall of pelvic viscera
SS innervation of skin, blood vessels, sweat glands, and arrector pili muscles:
- These targets are not innervated by PS
- SS preganglionic axon enters the sympathetic chain ganglia (SCG) by way of white (myelinated) communicating ramus and synapses with the postganglionic neuron in SCG
- SS postganglionic axon follows the gray (unmyelinated) communicating ramus, joins a spinal nerve and courses to its target in the body wall