Lecture 21- Autonomic nervous system III

Question 1

Where did we get to?

Answer 1

• cortex (thought) going down, some excitatory and inhibitory
• now: -two differently coloured neurons (red and blue)

Question 2

What is the working heart-brainstem preparation and what is it used for?

Answer 2

• everything from pons onwards is taken out
• so insensate as there is no hypothalamus
• no blood in either -bring it back to life by perfusing it with CSF
• now medulla, pons and spinal cord intact that we can measure
• everything for breathing is here
• can measure perfusion pressure as a measur eof arterial pressue and activity of different nerves
• all the circuitry for sympathetic circuitry and breathing is here

Question 3

Where does the phrenic nerve come from and what does it do?

Answer 3

• comes from upper spinal cord (cervical) (indicator of breathing)
• innervates the diaphragm, when active it constricts the diaphragm= reduces pressure and draws air into the lung (inspiration) in between is expiration

Question 4

What is the relationship between breathing and sympathetic activity? (sympathetic respiratory coupling)

Answer 4

• the respiratorymodulation of sympathetic nerve activity= each time animal breaths in there is shortly after a burst of sympathetic activity
• there is a component of this that is afferent, the pressure in thorax decreases as you breath in, venous blood supply returns at a higher level= causes momentary increase in cardiac pressure= activate baroreceptor reflex
• so every time you breath in, you get some activation of the baroreceptor reflex that then has some influence on sympathetic activity
• but in the preparation= coupling between phrenic activity an dthe sympathetic control this respiratory sympathetic coupling has effects, if stop animal breathing and then make it breath again, as bringing breathing again the sympathetic activity and perfusion pressure increases= gives you a measure of the relative influence on the contribution hoe much of the blood
• 25% of sympathetic activity is driven by this coupling -link between respiration and

Question 5

What is the state of the sympathetic respiratory coupling in a hypertensive rat?

Answer 5

-in a hypertensive rat the relationship between the sympathetic activity and breathing, they think it is causal and a research project to see if it could

Question 6

What is the interaction between the breathing generator and the sympathetic control system?

Answer 6

• there is an interaction between the breathing generator and the sympathetic control system
• this is very important for basal pressure and ability to respond for some behaviour
• breathing is essential and entirely dependent on the CNS
• phrenic nerve control diapragm tp breathe in (skeletal motor neuron)
• it is also the muscles below the rib cage= consrtrict so air comes in
• lungs are sponges, the air come sin only due to teh decrease in pressure
• the lungs expand with the chest wall -also intercostal motor neuron
• also abdominal motor neurons= project to rectus abdominus, don’t do much when breathing quitely but once exercise then you use these

Question 7

What is the central pattern generator?

Answer 7

• somatic neurons that control expiration and inspiration
• those are controlled by a complex network of neurons of the CNS (together forming the central pattern generator)
• the central pattern generator has output that activates the neurons and then stops them (to breathe out)
• if stressed= breath faster -so controlled by higher centers
• if you are eating, drinking, talking then you alter the breathing pattern
• also a reflex= chemoreceptor reflexes that change your breathing pattern

Question 8

What are the medullary locations of the respiratory centres?

Answer 8

• columns of neurons controlling the breathing:
• there is a ventral group in the medulla and dorsal
• present in a column

Question 9

What is this?

Answer 9

• RVLM projects to spinal cord, and CVLM the barorecpetor= these togetehr are the sympathetic column= the column of sympathetic control group
• then the ventral respiratory column is the green/blue = if recording from RVLM neurons you will be recording from Botzinger neurons at the same time as they are intermingled (the breathing and sympathetic neurons are intermingled= so sth going on here)
• BotC= Botzinger complex, pre-Botc= pre Botzinger complex rVRG= ventral respiratory group and cVRG= caudal part of the respiratory group
• cVRG are the output to the spinal cord
• when breathing, nostrils flare up= to allow the air in and then muscles constrict to not make a noise and let the air out
• if recording, so know that output is cVRG but if don’t have the prebotzinger complex= the curinal the pacemaker that drives breathing!

Question 10

What are the two types of neurons in the RVLM and what are their functions?

Answer 10

• in RVLM have two groups of neurons
• C1 cells that make catecholamines (have all the enzymes to make adrenaline etc.)
• non C1 cells (don’t make catecholamines)
• which ones transmit the info about breathing?
• use viruses to introduce molecules into cells, one of the molecules allowing inhibition is latostatin
• breathing activity, then put latostatin, inhibit only C1 neurons= then there is a change, the red ones= the C1 are the ones affecting sympathetic activty of breathing
• C1 cells are the ones causing the coupling
• blood pressure completely tracks the number of C1 cells, as you lose C1 cells you lower your blood pressure as you are losing the respiratory coupling
• the breathing input comes in and drives the C1 neurons to drive a component of sympathetic activity

Question 11

Why is sympathetic respiratory coupling important?

Answer 11

• perfusion pressure in a muscle, stimulated electronically, if you make the activation irregular= get greater preser response, if do 20x/s and then wait for 9s = like what happens in the sympathetic activity get much greater constriction of the vasculature
• this patterning gives you more efficient constriction of the vasculature and changes the amount of the neurotransmitter that comes out!
• when the bursts= get more noradrenaline, and neuropeptide Y (NPY) produced by postganglionic neurons, normally not much comes out but now it does
• so changing even the composition of the neurotransmitters, ATP is also regulated this way
• so these neurons can affect what and how much is released onto the smooth muscle depending on the patterning

Question 12

What is the connection between sympathetic activity and exercise/food?

Answer 12

• activation of sympathetic activity in some vascular beds and inhibited in others, eg. after food activate around the gut and more likely to be sleepy at rest= cardiac output around 5 l a minute
• with exercise= solid exercise= proportion of teh blood flow going to the skeletal muscle is dramatically increased
• to the heart doesn’t change, kidney less, bone less, all the maintaining bits get less
• increase your cardiac output 5 times, to 26 l, the brain is getting the same amount of blood! cannot reduce that -decrease flow to tissues by activating sympathetic activity to the tissues (eg kidney)
• sympathetic activity also increases during exercise to muscles so how is there more blood?: sympatholysis, it becomes less effective, the loacal build up in metabolites accumulates in muscle
• skin: sympatehtic activity to the skin decreases during exercise, so you can dilate the skin and get rid of heat -sympathetic activity during exercise increases to some beds and some decreases
• there is a link between sympathetic activity and exercise, as increase the oxygen needed in exercise, need to have it distributed and need more in and out of the lungs, as increase breathing increase sympathetic activity

Question 13

What happens with exercise? (increase/decrease of activity)

Answer 13

-skin there it doesn’t increase

Question 14

What happens in a dehydrates animal?

Answer 14

• response to injection of hypertonic saline, it’s a bit like a trick to make you think you are dehydrated, one thing to intake more fluid and remove the sodium thriugh the kidneys, when decrease sympathetic activity to kidney you dump the sodium, there is increase in blood pressure and in the kidney it will decrease so to get rid of the sodium
• the dotted line is the response to the same stimulus when paraventricular nucleus is inhibited= so it is produced by paraventricular nucleus of teh thalamus
• cardiac not changed, and kidney decreases
• pvn= paraventricular nucleus in the hypothalamus

Question 15

What happens when the dorsomedial hypothalamus is activated?

Answer 15

• dorsomedial hypothalamus activation, = increase in blood pressure, increase in heart rate, increase in renal sympathetic activity and breathing
• so all activation! -when activate dorsomedial hypothalamus= widespread activation of sympatehtic activity, kidney, muscle etc.
• according to need sympathetic activity to different beds can be dialed up
• DMH and PVN hypothalamus = the hypothalamus is the leader of teh orchestar, leader

Question 16

What is this?

Answer 16

-dorsomedial hypothalamus and paraventricular hypothalamus

Question 17

Where did we get to?

Answer 17

-now hypothalamus coming in and orchestrating different patetrns of sympatehtic activity