3.1.5. Autonomic Neurotransmitters Flashcards

1
Q

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

A

Acetylcholine (ACh)

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2
Q

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

A

Acetylcholine (ACh)

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3
Q

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

A

Norepinephrine (NE)

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4
Q

What is the parasympathetic response in the heart?

A

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

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5
Q

What is the parasympathetic response in blood vessels?

A

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

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6
Q

What is the parasympathetic response in bronchioles?

A

Increased contraction

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7
Q

What is the parasympathetic response in the iris?

A

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

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8
Q

What is the parasympathetic response in the GI tract?

A

Increase in motility and tone.

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9
Q

What is the parasympathetic response in sweat glands?

A

Slight increase in localized secretion.

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10
Q

What is the sympathetic response in the heart?

A

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

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11
Q

What is the sympathetic response in blood vessels?

A

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

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12
Q

What is the sympathetic response in bronchioles?

A

Increased relaxation.

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13
Q

What is the sympathetic response in the iris?

A

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

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14
Q

What is the sympathetic response in the GI tract?

A

Decreased motility and tone.

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15
Q

What is the sympathetic response in sweat glands?

A

Decreased sweat secretion.

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16
Q

What are two subtypes of cholinergic receptors?

A

Muscarinic and Nicotinic

17
Q

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

A

Nicotinic receptor

18
Q

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

A

Muscarinic receptor

19
Q

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

A

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

20
Q

What is the mechanism of action of the nicotinic receptor?

A

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.

21
Q

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

A

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).

22
Q

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

A

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

23
Q

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

A

B1 (beta 1).

24
Q

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

A

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

25
Q

M2 receptor activation results in what?

A

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

26
Q

The a1 receptor results in what?

A

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

27
Q

Discuss effect of isoproterenal on BP and HR

A

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

28
Q

Discuss the effect of norepinephrine on BP and HR

A

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

29
Q

Discuss the effect of epinephrine on BP and HR

A

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