What type of sensory info can trigger autonomic reflexes?
Somatic and visceral sensory info can trigger autonomic reflexes; however, the ANS only regulates the activity of visceral effectors.
What are the functions of the ANS?
- Self-governed motor control of visceral effectors (glands, cardiac muscle, smooth muscle)
- Involuntary control of cariovascular, respiratory, digestive, urinary system, etc.
- Ultimately, maintains homeostasis
Compare and contrast the SNS and ANS.
SNS:
- voluntary control
- Effectors–skeletal muscle
- CNS motor neuron synapses directly with effector
- One division
- All neurons release ACh and effect is always excitatory
ANS:
- Involuntary control
- Effectors-cardiac and smooth muscle, glands
- CNS motor neuron first synapses with autonomic ganglion
- Two divisions (sympathetic and parasympathetic)
- Various neurotransmitters released and effect may be excitatory or inhibitory
Where are the cell bodies of the preganglionic neurons (ANS) located? Where do the preganglionic fibers travel and where do they synapse with the postganglionic neurons?
The cell bodies of the preganglionic neurons are housed in the brain stem of spinal cord of the CNS. The myelinated axons of the pregnaglionic neurons then leave the CNS via cranial or spinal nerves and synapse with the postganglionic neurons in the autonomic ganglion.
Where are the cell bodies of the postganglionic neurons located? Where do they travel from there? Where do they synapse?
The cell bodies of the postganglionic neurons are housed in the autonomic ganglia (because of this, they are sometimes called ganglionic neurons). The unmyelinated axons of the postganglionic neurons travel to visceral effectors where they synapse with cardiac muscle, smooth muscle or glands.
What are varicosities?
Varicosities are a collection of modified synaptic terminals that are found at the synapse of the postganglionic neuron and the effector. They resemble beads on a string and form a network around the effector. Neurotransmitters often get reabsorbed by varicosities and reused or broken down by extracellular enzymes.
Describe the two divisions of the ANS.
Sypathetic:
“fight or flight”
primarily excitatory
thoracolumbar division
Parasympathetic:
“rest and digest”
primarily inhibitory (but excitatory of digestion)
craniosacral division
- These two divisions are primarily antagonistic to each other
- Usually some effect of both divisions at the same time. This is known as autonomic tone.
- Some structures are only innervated by one division.
