MMT: Introduction to the ANS Flashcards
Break down the nervous system, starting with the two major divisions and branching out
Briefly describe the role of the autonomic nervous system in our bodies
The ANS innervates almost every organ/tissue in the body and helps maintain homeostasis in response to changing environments
What are the main targets of autonomic nervous system?
Cardiac muscle, smooth muscle, and glands
Most tissues in the body are dually innervated by sympathetic and parasympathetic nervous systems. What are the big exceptions?
Blood vessels and sweat glands are only innervated by the sympathetic nervous system
compare the organization of the SNS and PSNS
In the PSNS, the long preganglionic fibers synapse onto an autonomic ganglion near the effector organ. The short postganglionic fiber leaves the ganglion and travels to the effector organ.
In the SNS, the short preganglionic fiber synapses onto an autonomic ganglion in the sympathetic trunk. A long postganglionic fiber leaves the ganglion and travels to the effector organ.
What is another name for the parasympathetic nervous system? Why?
Craniosacral; preganglionic fibers originate from the brainstem or sacral region of the spinal cord
What is another name for the sympathetic nervous system? Why?
Thoracolumbar; preganglionic fibers originate from the thoracic or lumbar spine (T1-L2/3)
identify the neurotransmitters released by fibers in the SNS and PSNS
PSNS: preganglionic and postganglionic both release acetylcholine
SNS: preganglionic releases acetylcholine, postganglionic releases norepinephrine
What ion channels are involved in action potentials moving along preganglionic fibers, and the fiber synapsing onto a ganglion?
In a preganglionic fiber, signals are propagated via voltage gated sodium channels. The preganglionic fibers able to synapse due to voltage gated calcium channels.
Which division of the nervous system is considered all or nothing? Why?
Sympathetic; one preganglionic fiber can synapse on multiple postganglionic fibers
Which division of the nervous system is considered to have discrete output? Why?
The PSNS; most of the ganglia are set up in a 1:1 ratio, meaning one preganglionic fiber synapses on one postganglionic fiber.
In what instance does the sympathetic nervous system utilize acetylcholine in postganglionic fibers?
When it is targeting the adrenal medulla or sweat glands.
What is released by the adrenal medulla in response to sympathetic innervation?
Epinephrine (hormone) and some norepinephrine (neurotransmitter) into the bloodstream
What are major control points of the ANS?
Hypothalamus and medulla
How does the body measure volume in vessels?
Via the stretching and mechano and chemosensory receptors; in response to stretch or lack thereof, these receptors send signals to the brain and ultimately impact activity of the SNS
What is the primary neurotransmitter used at the neuromuscular junction?
acetylcholine
Cholinergic drugs target ___ receptors in the ___
acetylcholine; PSNS
adrenergic drugs target ___ receptors in the ___
NE; SNS
What are the two major classes of cholinergic receptors? What are their methods of action?
Muscarinic: GPCRs
Nicotinic: ion channels that are permeable to cations, particularly Na.
What are the two primary subtypes associated with nicotinic receptors
Nn: neuronal nicotinic that are present in ganglia
Nm: neuromuscular nicotinic present in neuromuscular junction
Describe where muscarinic receptors will be found
All PSNS effector sites, CNS, and some SNS effector sites
Describe where nicotinic receptors will be found
All ANS ganglia, adrenal medulla, neuromuscular junction, and CNS
What receptor type will always be found at the synapse between the preganglionic fiber and the ganglion? Why?
Nicotinic acetylcholine receptors; they’re ligand-gated ion channels that allow for depolarization of the membranes and thus further synapsing onto a postganglionic fiber
Describe basic impacts of the SNS
Raised epinephrine
raised heart rate, conduction velocity, contractility, and cardiac output
increased blood flow to skeletal muscle
dilation of pupils
dilation of bronchioles
relaxed bladder and tightened sphincter to inhibit urination
lowered GI motility and digestion
increased blood glucose
increased sweating
Describe the basic impacts of the PSNS
lowered heart rate, conduction velocity, contractility, and cardiac output
increased blood flow to GI tract
contraction of pupils
constriction of airways
increased bladder tone and loosened sphincter to allow urination
raised GI motility and digestion
increased salivation
stimulated tear production
