Lecture 17: Autonomic Nervous System 2

Question 1

What do all blood vessels have a certain level of? What will this determine?

Answer 1

a certain level of tone

will determine blood flow through the vessel

Question 2

What types of control influence the tone of blood vessels?

Answer 2

local, hormonal and sympathetic control

Question 3

What is tonic activity? What is this dictated by in blood vessels?

Answer 3

the basal level of activity that is present

the level of ongoing activity in the sympathetic nerves

Question 4

What does tonic activity in blood vessels allow for?

Answer 4

dilation and constriction of blood vessels on the basis of changing activity in the sympathetic neuron

Question 5

What happens when there is an increase in activity of the sympathetic neuron?

Answer 5

constriction

Question 6

What happens when there is a decrease in activity of the sympathetic neuron?

Answer 6

dilation

Question 7

What do pupillary constrictor muscles form and what happens when they contract?

Answer 7

form a series of concentric circles around the pupil

the diameter of the pupil decreases

Question 8

Where do pupillary dilator muscles extend and what happens when they contract?

Answer 8

extend radially away from the edge of the pupil

enlarges pupil

Question 9

What causes pupil dilation?

Answer 9

decreased light intensity and increased sympathetic stimulation

Question 10

What causes pupil constriction?

Answer 10

increased light intensity and increased parasympathetic stimulation

Question 11

What is the route for innervation of pupil constrictor muscles in the iris?

Answer 11

Edinger-Westphal nucleus -> III nerve -> ciliary ganglia -> pupil constrictor muscles in the iris

Question 12

What is the route for innervation of pupil dilator muscles in the iris?

Answer 12

hypothalamus -> superior cervical sympathetic ganglion -> internal carotid artery -> ciliary ganglion -> short ciliary nerve -> pupil dilator muscle in the iris

Question 13

How is heart rate increased?

Answer 13

noradrenaline released by sympathetic terminals binds to beta-1 adrenoceptors -> activates Gas -> increases production of cAMP which opens Na+ and Ca2+ channels -> return from hyperpolarisation to threshold is much quicker in APs

Question 14

How is heart rate decreased?

Answer 14

acetylcholine released by parasympathetic terminals binds to muscarinic receptors -> activates Gai -> decreases production of cAMP which leads to Na+ and Ca2+ channels closing -> return from hyperpolarisation to threshold is much slower in APs

Question 15

What is the role of Gby in decreasing heart rate?

Answer 15

opens K+ channels which increases the magnitude of hyperpolarisation (AP starts from a more hyperpolarised state AND takes longer to reach threshold again)

Question 16

The control of resistance blood vessel diameter is accomplished through…

Answer 16

innervation by sympathetic neurons alone

Question 17

What does the SNS influence in the circulatory system?

Answer 17

total peripheral resistance, stroke volume and heart rate

Question 18

What does the PNS influence in the cardiovascular system?

Answer 18

heart rate

Question 19

What influences cardiac output?

Answer 19

stroke volume and heart rate

Question 20

What influences arterial pressure?

Answer 20

cardiac output and total peripheral resistance

Question 21

What happens when blood pressure falls?

Answer 21

cardiac sensitive nerve activity increases and as a result heart rate increases

Question 22

What occurs in response to a fall in blood pressure?

Answer 22

increase in sympathetic drive to the heart, increase in sympathetic drive to resistance blood vessels and decrease in parasympathetic drive to the heart

Question 23

How does an increase in sympathetic drive increase blood pressure?

Answer 23

increases total peripheral resistance, stroke volume and heart rate
an increase in stroke volume and heart rate leads to an increase in cardiac output which leads to an increase in arterial pressure

Question 24

What do most blood vessels receive input from?

Answer 24

only receive input from the SNS

Question 25

What is one of the drivers that leads to increase in cardiac output and heart rate?

Answer 25

feedback from the exercising muscle

Question 26

Where does ongoing activity in sympathetic nerves supplying the vasculature originate?

Answer 26

from centres “above” the spinal cord

Question 27

What is the role of sensory neurons in the large blood vessels supplying the brain?

Answer 27

send information about brain perfusion

Question 28

What is the role of integrating circuits in the circulatory system?

Answer 28

compare sensory information with behavioural requirements (e.g. maintaining higher blood flow if required during exercise)

Question 29

What is the role of efferent autonomic pathways in the circulatory system?

Answer 29

regulate blood vessel diameter (sympathetic) and cardiac output (sympathetic and parasympathetic)

Question 30

What is the role of all systems in the circulatory system?

Answer 30

maintain blood pressure homeostasis and dampen potentially deleterious swings in blood pressure

Question 31

How are we able to maintain visceral function in the face of behavioural change?

Answer 31

the autonomic nervous system, in concert with visceral sensory function, enables this to occur