Intro to ANS Function Flashcards
The sympathetic nervous system activates which of the following target tissue receptors to produce the indicated effect?
Answer: A
Explanation: The sympathetic nervous system releases norepinephrine which: activates b1 adrenoceptors (C) but this increases heart rate; activates a1 adrenoceptors (B) but this does not enhance peristalsis; it does, however, cause pupil dilation (A). Norepinephrine does not activate muscarinic acetylcholine receptors (D, E).
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 bronchiolar smooth muscle
relax contract the ciliary muscle to the lens
increase the force of contraction of the heart
increase heart rate
decrease peristalsis
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 is activated by Gs which is in turn activated by b- adrenoceptors.
Gi is activated by M2 and M4 muscarinic acetylcholine receptors (mACHRs) and a2 adrenoceptors and inhibits adenylate cyclase, decreasing cAMP production.
Gs is activated by b-adrenoceptors.
Which of the following statements about the myenteric plexus is correct?
A. It controls movements in the upper limb
B. It regulates gastrointestinal tract motility
C. It regulates gastrointestinal blood flow
D. It regulates heart rate
The myenteric plexus is part of the enteric nervous system (ENS) that regulates GI tract motility.
The brachial plexus innervates the upper limb.
The submucosal plexus regulates gastrointestinal blood flow.
Heart rate 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
B
Explanation: Activation of the parasympathetic (Rest and Digest) would stimulate contraction the ciliary muscle allowing accommodation for near vision (A); constrict bronchiolar smooth muscle (B); increase GI tract secretions (C); stimulate penile endothelial cells to secrete nitric o xide (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
A
Explanation: The “Fight or Flight” response causes activation of the sympathetic nervous system which would:
relax the bronchiolar smooth muscle, decreasing airway resistance;
stimulate aqueous humor production
increase cardiac force of contraction
increase heart rate
cause contraction of the dilator pupillae muscle, causing pupil dilation and thus increased pupil diameter
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
Norepinephrine is the primary neurotransmitter released from sympathetic postganglionic neurons innervating smooth muscle cells.
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
Norepinephrine (NE) acting through alpha 1 adrenoceptors activates Gq stimulating PLC and increasing intracellular Ca2+, thereby stimulating smooth muscle contraction.
Activation of which autonomic receptor stimulates release of epinephrine from the 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 inn ervate the adrenal medulla. Here, ACh stimulates release 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 chromaffincells.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.
A 21-year-old male presents to his physician with complaints of profound anxiety and profuse sweatingwheneverspeakinginpublic. From the attached table, which of the following combinations of autonomic nervous system division, neurotransmitter released from post-ganglionic fiber, and target tissue receptor are most likely responsible for the abundant sweating in this patient?
Sympathetic - Acetylcholine - Muscarinic acetylcholine receptor
Sweating is under sympathetic cholinergic control. Sympathetic post-ganglionic cholinergic nerves release ACh which binds to muscarinic cholinergic (ACh) receptors at sweat glands stimulating increased sweat production.
Which adrenergic receptor produces its stimulatory effects via formation of inositol 1,4,5- trisphosphate (IP3) and an increase in intracellular [Ca2+]?
A. a1 receptors
B. a2 receptors
C.b1 receptors
D.b2 receptors
E. Muscarinic receptors
F. Nicotinic receptors
Answer: A
Explanation: a1 adrenergic receptors produce physiologic actions by stimulating the formation of IP3 and causing a subsequent increase in intracellular calcium concentration.
Both b1 and b2 receptors act by stimulating adenylate cyclase and increasing production of cAMP.
a2 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 a1 receptors
B. Adrenergic b1 receptors
C. Adrenergic b2 receptors
D. Cholinergic muscarinic receptors
E. Cholinergic nicotinic receptors
Answer: B
Explanation:Heart rate is increased by the stimulatory effect of norepinephrine on b1 receptors on the SA node.
