Flashcards in L14 – Neural Control of the Cardiovascular System Deck (101):
What is the lowest order/ level of CVS control?
What is the medulla responsible for? Give one example of its action.
keep BP, HR constant when asleep
What are the two divisions of the medulla?
Dorsal motor vagal nucleus
What are the two main functions of medullary cardiovascular centre?
1. Receives & integrates inputs from all CVS receptors
2. Maintains sympathetic tone on blood vessels, heart
What is another name for medullary cardiovascular centre?
What are the two parts of the medullary cardiovascular centre? Location of each?
Pressor region (lateral)
Depressor region (caudal)
Which of the two regions of the cardiovascular center has direct contact with the CVS?
Pressor region has direct contact via axons down to CVS
depressor region doesnt
What is the difference in functionality/ anatomical grouping between pressor/depressor and dorsal motor vagal nucleus/ vagus nerve?
pressor/depressor are functionally grouped but anatomically separated
Dorsal motor vagal nucleus and vagus nerve are both functionally and anatomically grouped
What is the function of the pressor region?
1) Tonically active (always generate AP)
2) Gives rises to sympathetic adrenergic nerves supplying the blood vessels, heart
How does the depressor region function to reduce level of sympathetic tone?
1) Inhibiting tonic activity of the pressor region
2) Inhibiting sympathetic nerves within the spinal cord
What does the depressor region connect to?
No axons down to CVS, but connects with cells in pressor area
What originates from the Dorsal motor vagal nucleus? Nature of the nerve to heart?
parasympathetic nerve supply of the heart
What is the dorsal motor vagal nucleus closely related to?
Closely coordinated with cardiovascular centre
What is the function of the dorsal motor vagal nucleus? How does it relate to the pressor region?
RECIPROCAL activation of the cardiac sympathetic and parasympathetic nerves
When pressor region is activated, DMVN is inactivated> sympathetic activity > raise BP
When DMVN is activated, pressor region is not > parasym. action > lower BP
How is the dorsal motor vagal nucleus activated?
Not tonically active; relies on inputs from CVS receptors
Where is the Dorsal motor vagal nucleus located?
group of cells at the back of medulla
What is the next higher level of control above medulla?
How is the hypothalamus controlled? How does it control medullary CV centre? When is it active?
No direct tonic influence on CVS
Assumes control by manipulating medullary CV Centre
only during physiological stress
How might the hypothalamus alter the medullary CV centre?
Med. CV centre maintains sympathetic tone on blood vessels and heart
Hypothalamus can increase or decrease sympathetic tone by: stimulating the pressor or depressor regions/DMVN
What three physiological stresses can activate the hypothalamus?
(e.g. redirect blood flow to exercising muscle)
ii. Temperature control
(e.g. lose heat by sweating or insulate by vasoconstriction)
iii. Defence reaction
Why is hypothalamus activated under stress? Is psychological stress also a trigger?
To adapt to surrounding environment
What is higher in order than Medulla and Hypothalamus?
Motor cortex and higher centres
What is the motor cortex an origin of? How does that differ from the DMVN?
Motor cortex origin of sympathetic Cholinergic nerves
DMVN is origin of Vagus
What do the motor cortex sympathetic cholinergic nerves go through and bypass?
Goes through the hypothlalmus
Bypass the medullary centres to directly reach blood vessels
What do the nerves from motor cortex use as neurotransmitter?
Is the action of motor cortex sympathetic cholinergic nerves vasodilation or constriction? Is this way of control common?
No. Only very small number of vessels receive this input
What is the highest order of CVS control? On top of medullary CV centre, hypothalamus and motor cortex?
Higher centres/ Limbic system
What is limbic system?
parts of brain concerned with “emotional” responses)
What does the higher centre control?
hypothalamus and medulla CV centre
What can the higher centre override?
override motor cortex, hypothalamus, and normal reflex regulation
Why is the motor cortex sympathetic cholinergic nerve special?
Only sympathetic nerve to use Ach but not Noradrenaline
Action is UNLIKE other sympathetic nerves that cause vasoCONtriction
Motor cortex nerves are for vasoDILATION
What does pressor region sympathetic nerves innervate?
Heart and Blood Vessels
Which is the only parasympathetic efferent nerve in all of the control levels?
Dorsal motor vagal nucleus, parasympathetic cholinergic
Which two of the control levels use Ach as the neurotransmitter?
DNVM (parasymp.) and Motor cortex (symp.)
Which part of the heart does sympathetic cholinergic reach?
Atria, ventricles, nodal tissues
What happens when pressor region is activated?
Increase HR, Force = increase cardiac output
Does the pressor region efferent nerves reach all blood vessels?
All vascular smooth muscle except capillaries
The action of motor cortex on blood vessels is the same as which control level?
Dorsal motor vagal nucleus
What is the difference between the amount of blood vessels that motor cortex nerves reach compared to DMVN?
Motor cortex= Arterioles in muscle, skin only
DMVN= Very few vessels
What is the difference between DMVN's action on heart and Motor Cortex?
Motor cortex doesnt innervate heart
What is the action DMVN has on heart? Which parts of the heart does it reach compared to pressor region?
Atria, nodal tissues only, whereas pressor region innervate ventricles also
What is the consequence of DMVN' innervation on heart on the force of contraction?
not innervate ventricles = no influence on force
How is BP mainly changed? How come only this pathway of innervation is used?
Changed mainly by increasing / decreasing sympathetic noradrenergic action
Much of CVS has no parasympathetic innervation
What makes up the great majority of all sympathetic nerves ?
Sympathetic noradrenergic nerves
Is sympathetic noradrenergic nerves always active?
Innervate all vascular smooth muscle
sympathetic tone is always present
What is the most important mechanism for nerual control of blood vessels?
Sympathetic noradrenergic nerves
How does Sympathetic noradrenergic nerves work to achieve its action? What is released...etc?
Release noradrenaline at terminal > interacts with α-receptors on vascular smooth muscle > contract
How can sympathetic noradrenergic nerves alter BP?
increase/ decrease level of sympathetic tone > alter the degree of vascular smooth muscle contraction > change vascular resistance
What happens if all sympathetic noradrenergic nerves cease action on vessels?
Complete withdrawal of sympathetic tone > vessels dilate passively due to pressure of blood
within > BP drop to a very low level
What is the difference in the vascular smooth muscles between arterioles and veins?
Arteriole SM is circular and can change diameter
Vein SM is longitudinal and can change compliance
How is reflex changes in vascular resistance achieved mainly?
Increase noradrenergic tone on arterioles > increase vascular resistance
What happens with increased noradrenergic tone on veins?
Increase noradrenergic tone on veins (longitudinal muscle)
> decrease compliance
> increase venous pressure
Sympathetic cholinergic* efferent nerves originate from where again? What for?
What receptor is involved in motor cortex efferent nerves ?
Sympathetic cholinergic nerves:
Release acetylcholine as their neurotransmitter
Under what circumstance is sympathetic cholinergic nerves active?
Not involved in day-to-day reflex regulation of BP
FIGHT, FRIGHT, FLIGHT
How is sympathetic cholinergic nerve activation different from that of hypothalamus?
Hypothalamus activated by physiological stress not psychological stress
What is the consequence of sympathetic cholinergic nerve activation on blood flow?
Vasodilation > rapidly increase muscle blood flow > can alter overall vascular resistance
Why does sympathetic cholinergic nerves only innervate the skin and muscle arterioles?
skin, muscle receive large blood supply: ~25%
Parasympathetic nerves are found in which control centre?
Dorsal motor vagal nucleus
What neurotransmitter does DMVN use?
Release acetylcholine as their neurotransmitter
Give two examples of the small number of vessels that DMVN innervates. (2 divisions)
Cranial division: facial skin > blushing
Sacral division: external genitalia (e.g. sexual responses), bladder, large bowel
Does DMVN alter vascular resistance?
No, Only produces localised responses – does not alter vascular resistance
What is the primary action of DMVN when activated?
vagus activation > decrease heart rate
What part of the heart has pacemaker potential and is for starting heart beat?
Sinoatrial node has pacemaker potential
(Slow response AP cell)
What is the intrinsic activity rate of SA node?
activity at intrinsic rate of 100 bts/min
How can HR be changed via the SA node?
Nerves act on sinoatrial node > modify myogenic activity > change heart rate
What is the SA node normally under control of? (At resting HR)
SA node is normally under parasympathetic control (DMVN, vagus) > resting HR ~70 bpm
Recall the curve for slow response AP cells. If HR is to increase, what slope is changed?
Change slope of pacemaker potential (alter rate of decline in potassium conductance)
Reach threshold for AP quicker (-40mV)
What other way can HR be changed via the SA node apart from changing slope of pacemaker potential?
Increase potassium permeability during repolarisation phase
= repolarize to a lower potential closer to EK
= takes longer time = slower HR
How can changing the threshold level for SA nodal cell depolarization cause change in HR?
Higher threshold (e.g. induced by drug) = takes more time to reach threshold for depolarization = slower HR
Summarize the three ways that HR can be altered through changing the electrical activity of SA node.
1) change in slope of pacemaker potential (+/- HR)
2)Change threshold for spontaneous depolarization (raise threshold = lower HR)
3)Increase potassium permeability during polarization (repolarize to lower potential, more time to reach threshold= lower HR)
Parasympathetic and sympathetic fibres can change HR. What channel is critical to the parasympathetic nerve action?
IKACh channels open
Additional K+ channel open causes Vm to become more negative (closer to EK) and hyperpolarize
What three changes to the SA node electrical activity curve by Vagus nerve lead to decreased HR?
1. Shorter action potential (quicker repolarization)
2. Hyperpolarisation (more negative)
3. Decrease slope of pacemaker potential
What is the result of Vagus nerve decreasing AV conduction activity?
Vagus normally keeps HR at 70bpm
More time for blood to fill ventricles = keep systole and diastole separate by sustaining delay between 2 phases
What is the full name of the channel critical to Vagus nerve action on decreasing HR?
IKAch = Acetylcholine-activated potassium channel
What is the pathway of Vagus on lowering HR?
DMVN > Vagus > Ach > muscarinic receptor > increase K+ permeability by opening IKAch > Shorten AP, cause Hyperpolarisation and lower slope of pacemaker potential > decrease HR
What is the consequence of lowering pacemaker potential?
= takes more time to reach threshold for depolarization
Which two phases of AP is IKAch open for?
Repolarization and Pacemaker phases
What nerve works in opposite action to vagus?
Cardiac sympathetic nerves (nodal tisues, atria, ventricles)
What are the differences in action between left and right cardiac sympathetic nerve? (Pressor)
Right sympathetic nerve innervates nodal tissues, atria = affects heart
Left sympathetic nerve innervates ventricles = affects force of
Walk through the pathway that Cardiac sympathetic nerves (from pressor) causes an increase in HR
Medullary CV pressor region > noradrenaline > b- receptors in heart > release of cAMP > funny channels open earlier before pacemaker potential at lower Vm > increase slope of pacemaker potential> increase HR
How does increase in slope of pacemaker potential cause change in K+ potential during pacemaker phase?
Increase slope of pacemaker potential =
faster decrease of potassium conductance during pacemaker phase
What are Lf funny channels activate by? What does it need to open?
Cyclic nucleotide-gated (need cAMP to open)
What is the result of cAMP binding to Lf channels?
voltage dependence to more positive value
What 4 reflexes change HR? (BBPL)
Lung stretch receptors
What receptors do Baroreflex and Bainbridge reflex involve?
(= arterial pressure receptors)
Bainbridge reflex= Atrial volume receptors
Where are baroreflex baroreceptors located at?
What do they detect?
Detect blood pressure
What is the action of Baroreceptor on heart if BP drops?
Signal to cardiovascular centre in medulla (pressor)
reflex = increase by increasing force (Left sympathetic cardiac nerve)= increase cardiac output
What is the action of baroreceptor on vascular system if BP drop?
Signal to cause Peripheral vasoconstriction (via pressor region) > increase total peripheral resistance
Where are receptors for bainbridge reflex located ?
Atrial volume receptors @
What action does bainbridge reflex include? Does it change cardiac output?
Reflex = increase heart rate
Overall no change in cardiac output because of
lower stroke volume
How is bainbridge reflex activated?
Atrial volume receptors
More AP if stretched
Detect stretch of atrium (e.g. increase blood volume, filling of heart)
What does the bainbridge reflex protect?
Reflex increase HR to protect atria from over-stretch, thus stroke volume is reduced
What is the other action of bainbridge reflex?
Increase urine production > eliminate excess volume
Where are peripheral chemoreceptors located?
What are peripheral chemoreceptors stimulated by? (3)
What are the two responses of activated peripheral chemoreceptors?
1. Primary response = increase respiration / ventilation
2. Increase heart rate
Why are there two responses by peripheral chemoreceptors?
ventilation - perfusion
matching: increase blood flow through lungs to transport more O2 to body
What are lung stretch receptors?
interstitium of lung
When is lung stretch receptor activated by? What are its 2 actions?
Lung inflation e.g. at end of inspiration
1. Initiate expiration (regulate breathing)
2. Reflex = decrease heart rate