Intro to Autonomic NS Flashcards
A 14-year-old boy enters the yard of his school friend only to be confronted by a large fierce-looking
dog. The boy is frightened by the dog and runs away. His autonomic nervous system is activated and this
results in which of the following effects?
A. Constriction of bronchiolar smooth muscle
B. Relaxation of gastrointestinal intestinal wall smooth muscle
C. Contraction of the ciliary muscle
D. Decrease in force of contraction of the heart
E. Decrease in heart rate
Answer: B
Explanation: The “Fight or Flight” response (as depicted in this scenario) causes activation of the
sympathetic nervous system which would: relax, not constrict bronchiolar smooth muscle (A); relax, not
contract the ciliary muscle to the lens (C); increase, not decrease the force of contraction of the heart
(D); and increase, not decrease heart rate.
Activation of M3 muscarinic acetylcholine receptors (mAChRs) results in activation of which of the following signaling systems? A. Adenylate cyclase B. Gi C. Gq D. Gs
Answer: C
Explanation: M3 muscarinic acetylcholine receptors primarily activate Gq which then in turn activates
phospholipase C (PLC) and increases intracellular Ca2+. Adenylate cyclase (A) is activated by Gs which is
in turn activated by beta adrenoceptors. Gi (B) is activated by M2 and M4 muscarinic acetylcholine
receptors (mACHRs) and alpha 2 adrenoceptors and inhibits adenylate cyclase, decreasing cAMP production.
Gs (D) is activated by beta-adrenoceptors.
Which of the following statements about the myenteric plexus is correct?
A. It controls movements in the upper limb
B. It regulates gastrointestinal tractmotility
C. It regulates gastrointestinal blood flow
D. It regulates heart rate
Answer: B
Explanation: The myenteric plexus is part of the enteric nervous system (ENS) that regulates GI tract
motility (B). The brachial plexus innervates the upper limb (A) but has nothing to do with the myenteric
plexus. The submucosal plexus, not the myenteric plexus, regulates gastrointestinal blood flow (C).
Heart rate (D) is regulated by the sympathetic and parasympathetic nervous system.
Increasing the activity of the parasympathetic branch of the autonomic nervous system results in all
of the following responses, expect which one?
A. Accommodation for near vision
B. Bronchiolar dilation
C. Increased gastrointestinal glandular secretion of fluids and electrolytes
D. Penile erection
E. Pupillary constriction
Answer: B
Explanation: Activation of the parasympathetic (Rest and Digest) would stimulate contraction the ciliary
muscle allowing accommodation for near vision (A); constrict, not dilate bronchiolar smooth muscle (B);
increase GI tract secretions (C); stimulate penile endothelial cells to secrete nitric oxide (NO) which then
causes relaxation of penile smooth muscle and vasodilation leading to erection (D); stimulates
contraction of the sphincter pupillae causing pupil constriction (E).
The sympathetic response in a “fight or flight” reaction causes a decrease in which of the following? A. Airway resistance B. Aqueous humor production C. Force of contraction of the heart D. Heart Rate E. Pupil diameter
Answer: A
Explanation: The “Fight or Flight” response causes activation of the sympathetic nervous system which
would: relax the bronchiolar smooth muscle, decreasing airway resistance (A); stimulate not decrease
aqueous humor production (B); increase not decrease cardiac force of contraction (C); increase, not
decrease heart rate (D); cause contraction of the dilator pupillae muscle, causing pupil dilation and thus
increased pupil diameter (E).
Which of the following synapses does not have acetylcholine as its primary neurotransmitter?
A. Synapse of a postganglionic parasympathetic neuron onto a heart cell
B. Synapse of a postganglionic sympathetic neuron onto a smooth muscle cell
C. Synapse of a preganglionic sympathetic neuron onto a postganglionic neuron
D. Synapse of a somatic neuron onto a skeletal muscle cell
E. Synapse of a preganglionic sympathetic neuron onto chromaffin cells
Answer: B
Explanation: Acetylcholine (ACh) is the neurotransmitter at all ANS preganglionic synapses (C, E), target
tissues of the parasympathetic division (A) and is the primary neurotransmitter released by somatic
motor neurons at the neuromuscular junction (D). Norepinephrine is the primary neurotransmitter
released from sympathetic postganglionic neurons innervating smoothmuscle cells. The sympathetic
division primarily uses norepinephrine as the signaling molecule at target tissues (C). The only exception
to this rule is sympathetic post-ganglionic innervation of the sweat glands, where ACh is the
neurotransmitter (sympathetic cholinergic neurons).
Norepinephrine stimulates contraction of which of the following smooth muscles? A. Bronchiolar B. Ciliary muscle C. Gastrointestinal blood vessels D. Skeletal muscle blood vessels E. Sphincter pupillae
Answer: C
Explanation: Norepinephrine (NE) acting through alpha 1 adrenoceptors activates Gq stimulating PLC
and increasing intracellular Ca2+, thereby stimulating smooth muscle contraction. This occurs in GI blood
vessels causing constriction and diverting blood away from the gut (C). Norepinephrine acting through
beta 2 adrenoceptors activates Gs, which in turn activates adenylate cyclase and increases cAMP
production. cAMP relaxes smooth muscle. This is the mechanism of dilation of blood vessels in the
skeletal muscle and facilitates increased blood flow to skeletal muscle during the fight or flight response
(D). Activation of beta 2 adrenoceptors stimulates relaxation of bronchiolar smooth muscle permitting
more air to enter the lungs (A) and relaxation of ciliary muscle in the lens permitting far vision (B). The
sphincter pupillae has M3 muscarinic receptors and ACh stimulates its contraction via increased Ca 2+
leading to pupil constriction. The sphincter pupillae is not affected by norepinephrine.
Another(potentially easier) way to reason your way through answering this type of question is to think
about the situation where norepinephrine is increased (sympathetic/fight or flight response) and what
your body wants to achieve by activating this branch of the ANS (i.e. run or fight!). Contraction of
bronchiolar smooth muscle will decrease air entry – not good when trying to run away. Ciliary muscle
contraction permits accommodation for focusing on close up objects –useful for reading, not useful if
looking out for danger. Constriction of blood vessels to the skeletal muscle will limit blood supply, thus
reducing delivery of oxygen and nutrients –again not useful if trying to run away from danger as in a
classic fight or flight response. Contraction of the sphincter pupillae leads to pupil constriction,
restricting light entry into the eye –again, not useful if looking out for danger. Contraction of the GI
blood vessels limits blood flow to the GI tract, diverting blood elsewhere in the body. In a fight or flight
response, digestive processes are not a priority, thus norepinephrine stimulated contraction of GI blood
vessels is the only effect that makes sense under these circumstances, and as such is the correct answer.
Activation of which autonomic receptor stimulates release of epinephrine fromthe adrenal medulla? A. Adrenergic α receptors B. Adrenergic β1 receptors C. Adrenergic β2 receptors D. Cholinergic muscarinic receptors E. Cholinergic nicotinic receptors
Answer: E
Explanation: Acetylcholine is the neurotransmitter released from all autonomic nervous system
preganglionic neurons including the preganglionic sympathetic neurons which innervate the adrenal
medulla. Here, ACh stimulatesrelease of epinephrine (and norepinephrine) from the chromaffin cells
(also called pheochromocytes). The adrenal medulla is considered a modified ganglion. ACh released
here binds to nicotinic ACh receptors, opening sodium channels and causing depolarization in the
chromaffin cells. This opens voltage-gated calcium channels in the chromaffin cell membrane.
Intracellular calcium levels increase stimulating the movement of vesicles containing norepinephrine
and epinephrine to the cell membrane. The vesicles fuse with the cell membrane and empty their
contents (by exocytosis) into the blood stream.
Atropine is a muscarinic acetylcholine antagonist and prevents(or blocks) the action of acetylcholine
on smooth muscles, glands and the heart. Which of the following effects would you expect after
administration of a physiologic dose of atropine to a patient?
A. Decrease heart rate
B. Bronchoconstriction
C. Contraction of GI smooth muscle
D. Erection
E. Pupil dilation
Answer: E
Explanation: Acetylcholine (ACh) causes pupil constriction –blocking its action would cause pupil
dilation. At the heart, ACh reduces heart rate - blocking this effect would cause heart rate to increase.
ACh causes contraction of bronchiolar smooth muscle –blocking this effect would cause
bronchodilation. ACh stimulates contraction of GI smooth muscle –blocking this effect would cause
relaxation of GI smooth muscle. Erection is mediated by ACh release from parasympathetic nerves
innervating the penis –blocking ACh action would act to inhibit erection.
Which adrenergic receptor produces its stimulatory effects via formation of inositol 1,4,5- trisphosphate (IP3) and an increase in intracellular [Ca2+]? A. Alpha 1 receptors B. Alpha 2 receptors C. Beta 1 receptors D. Beta 2 receptors E. Muscarinic receptors F. Nicotinic receptors
Answer: A
Explanation; alpha 1 adrenergic receptors produce physiologic actions by stimulating the formation of IP3
and causing a subsequent increase in intracellular calcium concentration. Both beta 1 and beta 2 receptors act
by stimulating adenylate cyclase and increasing production of cyclic adenosine monophosphate (cAMP).
Alpha 2 receptors inhibit adenylate cyclase and decrease cAMP levels. Muscarinic and nicotinic receptors are
cholinergic, not adrenergic.
Stimulation of which autonomic receptor mediates an increase in heart rate? A. Adrenergic alpha 1 receptors B. Adrenergic beta 1 receptors C. Adrenergic beta 2 receptors D. Cholinergic muscarinic receptors E. Cholinergic nicotinic receptors
Explanation: Heart rate is increased by the stimulatory effect of norepinephrine on beta1 receptors on the
SA node.
