Lecture 17: Autonomic Nervous System 2 Flashcards
What do all blood vessels have a certain level of? What will this determine?
a certain level of tone
will determine blood flow through the vessel
What types of control influence the tone of blood vessels?
local, hormonal and sympathetic control
What is tonic activity? What is this dictated by in blood vessels?
the basal level of activity that is present
the level of ongoing activity in the sympathetic nerves
What does tonic activity in blood vessels allow for?
dilation and constriction of blood vessels on the basis of changing activity in the sympathetic neuron
What happens when there is an increase in activity of the sympathetic neuron?
constriction
What happens when there is a decrease in activity of the sympathetic neuron?
dilation
What do pupillary constrictor muscles form and what happens when they contract?
form a series of concentric circles around the pupil
the diameter of the pupil decreases
Where do pupillary dilator muscles extend and what happens when they contract?
extend radially away from the edge of the pupil
enlarges pupil
What causes pupil dilation?
decreased light intensity and increased sympathetic stimulation
What causes pupil constriction?
increased light intensity and increased parasympathetic stimulation
What is the route for innervation of pupil constrictor muscles in the iris?
Edinger-Westphal nucleus -> III nerve -> ciliary ganglia -> pupil constrictor muscles in the iris
What is the route for innervation of pupil dilator muscles in the iris?
hypothalamus -> superior cervical sympathetic ganglion -> internal carotid artery -> ciliary ganglion -> short ciliary nerve -> pupil dilator muscle in the iris
How is heart rate increased?
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
How is heart rate decreased?
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
What is the role of Gby in decreasing heart rate?
opens K+ channels which increases the magnitude of hyperpolarisation (AP starts from a more hyperpolarised state AND takes longer to reach threshold again)
The control of resistance blood vessel diameter is accomplished through…
innervation by sympathetic neurons alone
What does the SNS influence in the circulatory system?
total peripheral resistance, stroke volume and heart rate
What does the PNS influence in the cardiovascular system?
heart rate
What influences cardiac output?
stroke volume and heart rate
What influences arterial pressure?
cardiac output and total peripheral resistance
What happens when blood pressure falls?
cardiac sensitive nerve activity increases and as a result heart rate increases
What occurs in response to a fall in blood pressure?
increase in sympathetic drive to the heart, increase in sympathetic drive to resistance blood vessels and decrease in parasympathetic drive to the heart
How does an increase in sympathetic drive increase blood pressure?
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
What do most blood vessels receive input from?
only receive input from the SNS
What is one of the drivers that leads to increase in cardiac output and heart rate?
feedback from the exercising muscle
Where does ongoing activity in sympathetic nerves supplying the vasculature originate?
from centres “above” the spinal cord
What is the role of sensory neurons in the large blood vessels supplying the brain?
send information about brain perfusion
What is the role of integrating circuits in the circulatory system?
compare sensory information with behavioural requirements (e.g. maintaining higher blood flow if required during exercise)
What is the role of efferent autonomic pathways in the circulatory system?
regulate blood vessel diameter (sympathetic) and cardiac output (sympathetic and parasympathetic)
What is the role of all systems in the circulatory system?
maintain blood pressure homeostasis and dampen potentially deleterious swings in blood pressure
How are we able to maintain visceral function in the face of behavioural change?
the autonomic nervous system, in concert with visceral sensory function, enables this to occur
