3.1.5. Autonomic Neurotransmitters

Question 1

In the parasympathetic nervous system, which neurotransmitter is released by the pre- and postganglionic fibers?

Answer 1

Acetylcholine (ACh)

Question 2

In the sympathetic nervous system, which neurotransmitter is released by preganglionic fibers?

Answer 2

Acetylcholine (ACh)

Question 3

In the sympathetic nervous system, which neurotransmitter is released by postganglionic fibers?

Answer 3

Norepinephrine (NE)

Question 4

What is the parasympathetic response in the heart?

Answer 4

Decreased heart rate, decreased atrial and nodal automaticity, decreased conduction velocity, and little effect on the contractile force.

Question 5

What is the parasympathetic response in blood vessels?

Answer 5

Dilation (drugs can act on M3 receptors, but there is no parasympathetic innervation).

Question 6

What is the parasympathetic response in bronchioles?

Answer 6

Increased contraction

Question 7

What is the parasympathetic response in the iris?

Answer 7

There is increased contraction in the sphincter muscle (miosis). Causes pupils to constrict.

Question 8

What is the parasympathetic response in the GI tract?

Answer 8

Increase in motility and tone.

Question 9

What is the parasympathetic response in sweat glands?

Answer 9

Slight increase in localized secretion.

Question 10

What is the sympathetic response in the heart?

Answer 10

Increased heart rate, increased atrial and nodal automaticity, increased conduction velocity, and increased contractile force.

Question 11

What is the sympathetic response in blood vessels?

Answer 11

Increased constriction and increased dilation (in select vascular beds like skeletal muscle and the liver).

Question 12

What is the sympathetic response in bronchioles?

Answer 12

Increased relaxation.

Question 13

What is the sympathetic response in the iris?

Answer 13

Increased contraction of the radial muscle (mydriasis). Causes the pupils to dilate.

Question 14

What is the sympathetic response in the GI tract?

Answer 14

Decreased motility and tone.

Question 15

What is the sympathetic response in sweat glands?

Answer 15

Decreased sweat secretion.

Question 16

What are two subtypes of cholinergic receptors?

Answer 16

Muscarinic and Nicotinic

Question 17

In the parasympathetic system, ACh released from the PREganglionic fiber acts on which type of receptor on the POSTganglionic fiber?

Answer 17

Nicotinic receptor

Question 18

In the parasympathetic system, ACh released from the POSTganglionic fiber acts on which type of receptor on the end organs?

Answer 18

Muscarinic receptor

Question 19

In the sympathetic system, ACh released from PREganglionic fibers acts on which type of receptor on POSTganglionic fibers?

Answer 19

Nicotinic receptor (OR adrenal medullary cells of the adrenal gland).

Question 20

What is the mechanism of action of the nicotinic receptor?

Answer 20

The nicotinic receptor is made up of 5 subunits that form a channel. When ACh binds to the receptor, the channel opens up and Na+ and Ca2+ flow into the cell and K+ flows out of the cell.

Question 21

What are the 5 subtypes of muscarinic receptors and in general terms, what do they do?

Answer 21

M1, M3, M5 increase IP3 and have a stimulatory effect.

M2 and M4 decrease cAMP and increase opening of K+ channels thus having an inhibitory effect (hyperpolarization).

Question 22

What is the most important mechanism for the termination of the action of NE?

Answer 22

Active reuptake into the nerve terminal via NET (norepinephrine transporter).

Question 23

In the sympathetic nervous system, NE released by postganglionic fibers on the heart acts on which type of adrenergic receptor?

Answer 23

B1 (beta 1).

Question 24

What happens when we block reuptake of NE by the membrane transporter (NET)?

Answer 24

There is an exaggerated effect of the transmitter. Drugs that act as reuptake blockers include cocaine, tricyclic antidepressants and methylphenidate.

Question 25

M2 receptor activation results in what?

Answer 25

As part of the parasympathetic reflex, M2 activation by ACh causes a decrease in HR and BP. M2 target tissues include myocardium, vascular smooth muscle, and presynaptic ganglia

Question 26

The a1 receptor results in what?

Answer 26

increase in BP via vasoconstriction with a reflex decrease in HR. NE activates it in the sympathetic system primarily via vascular smooth muscle.

Question 27

Discuss effect of isoproterenal on BP and HR

Answer 27

BP decreases due to b2 activation. HR increases due to b1 activation

Question 28

Discuss the effect of norepinephrine on BP and HR

Answer 28

systolic BP increases due to b1, diastolic BP increases due to a1. HR initially increases due to b1 and decreases due to m2 vagal response

Question 29

Discuss the effect of epinephrine on BP and HR

Answer 29

epi decreases BP due to b2, and increases HR due to b1 at low dose. At high dose it increases BP due to a1 and decreases HR due to m2