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MBBS I CPRS > L14 – Neural Control of the Cardiovascular System > Flashcards

L14 – Neural Control of the Cardiovascular System Flashcards

(101 cards)

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1
Q

What is the lowest order/ level of CVS control?

A

Medulla

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2
Q

What is the medulla responsible for? Give one example of its action.

A

basic reflex

keep BP, HR constant when asleep

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3
Q

What are the two divisions of the medulla?

A

Cardiovascular centre

Dorsal motor vagal nucleus

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4
Q

What are the two main functions of medullary cardiovascular centre?

A
  1. Receives & integrates inputs from all CVS receptors

2. Maintains sympathetic tone on blood vessels, heart

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5
Q

What is another name for medullary cardiovascular centre?

A

vasomotor centre

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6
Q

What are the two parts of the medullary cardiovascular centre? Location of each?

A

Pressor region (lateral)

Depressor region (caudal)

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7
Q

Which of the two regions of the cardiovascular center has direct contact with the CVS?

A

Pressor region has direct contact via axons down to CVS

depressor region doesnt

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8
Q

What is the difference in functionality/ anatomical grouping between pressor/depressor and dorsal motor vagal nucleus/ vagus nerve?

A

pressor/depressor are functionally grouped but anatomically separated

Dorsal motor vagal nucleus and vagus nerve are both functionally and anatomically grouped

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9
Q

What is the function of the pressor region?

A

1) Tonically active (always generate AP)

2) Gives rises to sympathetic adrenergic nerves supplying the blood vessels, heart

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10
Q

How does the depressor region function to reduce level of sympathetic tone?

A

When activated:

1) Inhibiting tonic activity of the pressor region
2) Inhibiting sympathetic nerves within the spinal cord

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11
Q

What does the depressor region connect to?

A

No axons down to CVS, but connects with cells in pressor area

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12
Q

What originates from the Dorsal motor vagal nucleus? Nature of the nerve to heart?

A

Vagus nerve

parasympathetic nerve supply of the heart

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13
Q

What is the dorsal motor vagal nucleus closely related to?

A

Closely coordinated with cardiovascular centre

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14
Q

What is the function of the dorsal motor vagal nucleus? How does it relate to the pressor region?

A

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

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15
Q

How is the dorsal motor vagal nucleus activated?

A

Not tonically active; relies on inputs from CVS receptors

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16
Q

Where is the Dorsal motor vagal nucleus located?

A

group of cells at the back of medulla

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17
Q

What is the next higher level of control above medulla?

A

Hypothalamus

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18
Q

How is the hypothalamus controlled? How does it control medullary CV centre? When is it active?

A

No direct tonic influence on CVS

Assumes control by manipulating medullary CV Centre

only during physiological stress

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19
Q

How might the hypothalamus alter the medullary CV centre?

A

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

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20
Q

What three physiological stresses can activate the hypothalamus?

A

i. Exercise
(e. g. redirect blood flow to exercising muscle)

ii. Temperature control
(e. g. lose heat by sweating or insulate by vasoconstriction)

iii. Defence reaction

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21
Q

Why is hypothalamus activated under stress? Is psychological stress also a trigger?

A

To adapt to surrounding environment

No

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22
Q

What is higher in order than Medulla and Hypothalamus?

A

Motor cortex and higher centres

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23
Q

What is the motor cortex an origin of? How does that differ from the DMVN?

A

Motor cortex origin of sympathetic Cholinergic nerves

DMVN is origin of Vagus

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24
Q

What do the motor cortex sympathetic cholinergic nerves go through and bypass?

A

Goes through the hypothlalmus

Bypass the medullary centres to directly reach blood vessels

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25
What do the nerves from motor cortex use as neurotransmitter?
Ach
26
Is the action of motor cortex sympathetic cholinergic nerves vasodilation or constriction? Is this way of control common?
Vasodilation No. Only very small number of vessels receive this input
27
What is the highest order of CVS control? On top of medullary CV centre, hypothalamus and motor cortex?
Higher centres/ Limbic system
28
What is limbic system?
parts of brain concerned with “emotional” responses)
29
What does the higher centre control?
hypothalamus and medulla CV centre
30
What can the higher centre override?
override motor cortex, hypothalamus, and normal reflex regulation
31
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
32
What does pressor region sympathetic nerves innervate?
Heart and Blood Vessels
33
Which is the only parasympathetic efferent nerve in all of the control levels?
Dorsal motor vagal nucleus, parasympathetic cholinergic
34
Which two of the control levels use Ach as the neurotransmitter?
DNVM (parasymp.) and Motor cortex (symp.)
35
Which part of the heart does sympathetic cholinergic reach?
Atria, ventricles, nodal tissues
36
What happens when pressor region is activated?
Increase HR, Force = increase cardiac output | Vasoconstriction
37
Does the pressor region efferent nerves reach all blood vessels?
All vascular smooth muscle except capillaries
38
The action of motor cortex on blood vessels is the same as which control level?
Dorsal motor vagal nucleus Vasodilation
39
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
40
What is the difference between DMVN's action on heart and Motor Cortex?
Motor cortex doesnt innervate heart
41
What is the action DMVN has on heart? Which parts of the heart does it reach compared to pressor region?
Decrease HR Atria, nodal tissues only, whereas pressor region innervate ventricles also
42
What is the consequence of DMVN' innervation on heart on the force of contraction?
not innervate ventricles = no influence on force
43
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
44
What makes up the great majority of all sympathetic nerves ?
Sympathetic noradrenergic nerves | Pressor region
45
Is sympathetic noradrenergic nerves always active?
Innervate all vascular smooth muscle | sympathetic tone is always present
46
What is the most important mechanism for nerual control of blood vessels?
Sympathetic noradrenergic nerves
47
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 (vasoconstriction)
48
How can sympathetic noradrenergic nerves alter BP?
increase/ decrease level of sympathetic tone > alter the degree of vascular smooth muscle contraction > change vascular resistance
49
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
50
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
51
How is reflex changes in vascular resistance achieved mainly?
Increase noradrenergic tone on arterioles > increase vascular resistance
52
What happens with increased noradrenergic tone on veins?
Increase noradrenergic tone on veins (longitudinal muscle) > decrease compliance > increase venous pressure
53
Sympathetic cholinergic* efferent nerves originate from where again? What for?
Motor Cortex VasoDILATION
54
What receptor is involved in motor cortex efferent nerves ?
Sympathetic cholinergic nerves: Release acetylcholine as their neurotransmitter muscarinic receptors
55
Under what circumstance is sympathetic cholinergic nerves active?
Not involved in day-to-day reflex regulation of BP FIGHT, FRIGHT, FLIGHT
56
How is sympathetic cholinergic nerve activation different from that of hypothalamus?
Hypothalamus activated by physiological stress not psychological stress
57
What is the consequence of sympathetic cholinergic nerve activation on blood flow?
Vasodilation > rapidly increase muscle blood flow > can alter overall vascular resistance
58
Why does sympathetic cholinergic nerves only innervate the skin and muscle arterioles?
skin, muscle receive large blood supply: ~25%
59
Parasympathetic nerves are found in which control centre?
Dorsal motor vagal nucleus
60
What neurotransmitter does DMVN use?
Release acetylcholine as their neurotransmitter
61
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
62
Does DMVN alter vascular resistance?
No, Only produces localised responses – does not alter vascular resistance
63
What is the primary action of DMVN when activated?
Heart: | vagus activation > decrease heart rate
64
What part of the heart has pacemaker potential and is for starting heart beat?
Sinoatrial node has pacemaker potential | Slow response AP cell
65
What is the intrinsic activity rate of SA node?
produces myogenic | activity at intrinsic rate of 100 bts/min
66
How can HR be changed via the SA node?
Nerves act on sinoatrial node > modify myogenic activity > change heart rate
67
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
68
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)
69
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
70
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
71
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)
72
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
73
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
74
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
75
What is the full name of the channel critical to Vagus nerve action on decreasing HR?
IKAch = Acetylcholine-activated potassium channel
76
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
77
What is the consequence of lowering pacemaker potential?
= takes more time to reach threshold for depolarization
78
Which two phases of AP is IKAch open for?
Repolarization and Pacemaker phases
79
What nerve works in opposite action to vagus?
Cardiac sympathetic nerves (nodal tisues, atria, ventricles)
80
What are the differences in action between left and right cardiac sympathetic nerve? (Pressor)
 Right sympathetic nerve innervates nodal tissues, atria = affects heart rate  Left sympathetic nerve innervates ventricles = affects force of contraction
81
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
82
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
83
What are Lf funny channels activate by? What does it need to open?
 Hyperpolarization-activated |  Cyclic nucleotide-gated (need cAMP to open)
84
What is the result of cAMP binding to Lf channels?
binding shifts | voltage dependence to more positive value
85
What 4 reflexes change HR? (BBPL)
Baroreflex Bainbridge reflex Peripheral chemoreceptors Lung stretch receptors
86
What receptors do Baroreflex and Bainbridge reflex involve?
``` Baroreflex= Baroreceptors (= arterial pressure receptors) ``` Bainbridge reflex= Atrial volume receptors
87
Where are baroreflex baroreceptors located at? | What do they detect?
 Carotid sinus  Aortic arch Detect blood pressure
88
What is the action of Baroreceptor on heart if BP drops?
Drop BP Signal to cardiovascular centre in medulla (pressor) reflex = increase by increasing force (Left sympathetic cardiac nerve)= increase cardiac output
89
What is the action of baroreceptor on vascular system if BP drop?
Signal to cause Peripheral vasoconstriction (via pressor region) > increase total peripheral resistance
90
Where are receptors for bainbridge reflex located ?
Atrial volume receptors @ | Atrial wall
91
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
92
How is bainbridge reflex activated?
Atrial volume receptors More AP if stretched Detect stretch of atrium (e.g. increase blood volume, filling of heart)
93
What does the bainbridge reflex protect?
Reflex increase HR to protect atria from over-stretch, thus stroke volume is reduced
94
What is the other action of bainbridge reflex?
Increase urine production > eliminate excess volume
95
Where are peripheral chemoreceptors located?
 Carotid bodies |  Aortic bodies
96
What are peripheral chemoreceptors stimulated by? (3)
Low oxygen High CO2 Low pH
97
What are the two responses of activated peripheral chemoreceptors?
1. Primary response = increase respiration / ventilation | 2. Increase heart rate
98
Why are there two responses by peripheral chemoreceptors?
ventilation - perfusion | matching: increase blood flow through lungs to transport more O2 to body
99
What are lung stretch receptors?
mechanoreceptors in | interstitium of lung
100
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
101
Respiratory Sinus Arrhythmia is a normal physiological response. Explain its action (how HR and breathing relate here).
Low HR in early expiration High HR in early inspiration

MBBS I CPRS (78 decks)

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