3.1.5. Autonomic Neurotransmitters Flashcards
In the parasympathetic nervous system, which neurotransmitter is released by the pre- and postganglionic fibers?
Acetylcholine (ACh)
In the sympathetic nervous system, which neurotransmitter is released by preganglionic fibers?
Acetylcholine (ACh)
In the sympathetic nervous system, which neurotransmitter is released by postganglionic fibers?
Norepinephrine (NE)
What is the parasympathetic response in the heart?
Decreased heart rate, decreased atrial and nodal automaticity, decreased conduction velocity, and little effect on the contractile force.
What is the parasympathetic response in blood vessels?
Dilation (drugs can act on M3 receptors, but there is no parasympathetic innervation).
What is the parasympathetic response in bronchioles?
Increased contraction
What is the parasympathetic response in the iris?
There is increased contraction in the sphincter muscle (miosis). Causes pupils to constrict.
What is the parasympathetic response in the GI tract?
Increase in motility and tone.
What is the parasympathetic response in sweat glands?
Slight increase in localized secretion.
What is the sympathetic response in the heart?
Increased heart rate, increased atrial and nodal automaticity, increased conduction velocity, and increased contractile force.
What is the sympathetic response in blood vessels?
Increased constriction and increased dilation (in select vascular beds like skeletal muscle and the liver).
What is the sympathetic response in bronchioles?
Increased relaxation.
What is the sympathetic response in the iris?
Increased contraction of the radial muscle (mydriasis). Causes the pupils to dilate.
What is the sympathetic response in the GI tract?
Decreased motility and tone.
What is the sympathetic response in sweat glands?
Decreased sweat secretion.
What are two subtypes of cholinergic receptors?
Muscarinic and Nicotinic
In the parasympathetic system, ACh released from the PREganglionic fiber acts on which type of receptor on the POSTganglionic fiber?
Nicotinic receptor
In the parasympathetic system, ACh released from the POSTganglionic fiber acts on which type of receptor on the end organs?
Muscarinic receptor
In the sympathetic system, ACh released from PREganglionic fibers acts on which type of receptor on POSTganglionic fibers?
Nicotinic receptor (OR adrenal medullary cells of the adrenal gland).
What is the mechanism of action of the nicotinic receptor?
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.
What are the 5 subtypes of muscarinic receptors and in general terms, what do they do?
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).
What is the most important mechanism for the termination of the action of NE?
Active reuptake into the nerve terminal via NET (norepinephrine transporter).
In the sympathetic nervous system, NE released by postganglionic fibers on the heart acts on which type of adrenergic receptor?
B1 (beta 1).
What happens when we block reuptake of NE by the membrane transporter (NET)?
There is an exaggerated effect of the transmitter. Drugs that act as reuptake blockers include cocaine, tricyclic antidepressants and methylphenidate.
M2 receptor activation results in what?
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
The a1 receptor results in what?
increase in BP via vasoconstriction with a reflex decrease in HR. NE activates it in the sympathetic system primarily via vascular smooth muscle.
Discuss effect of isoproterenal on BP and HR
BP decreases due to b2 activation. HR increases due to b1 activation
Discuss the effect of norepinephrine on BP and HR
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
Discuss the effect of epinephrine on BP and HR
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
