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CVS > Central neural control of CNS > Flashcards

Central neural control of CNS Flashcards

1
Q

What local influences occur in the heart, arterioles and veins?

A

Heart - intrinsic beating, Starling’s law
Arterioles - Endothelial, myogenic and metabolic influences for resistance
Veins - Gravity, respiratory pump and muscle pump for capacitence

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2
Q

What does the central control do?

A

Modulates reflexes by altering the sensitivity of receptors or can initiate a response without the need for a receptor

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3
Q

How do afferent nerve fibres enter the CNS?

A

At the spinal level, following spinal pathways or into a CN

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4
Q

What is the course of efferent parasympathetic fibres and what is their action?

A

CN X travels to SAN to DECREASE HR

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5
Q

What is the course of efferent sympathetic fibres and what is their action?

A

The fibres follow the descending pathways in the spinal cord and travel to the heart and vessels from T1-L2. They INCREASE HR, CONTRACTILITY and vasoCONSTRICT

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6
Q

What is involved in the reflex evoked by sympathetic?

A

Catecholamines, ADH and RAS

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7
Q

What are integrated areas of the midbrain?

A

Areas that are connected for altering a response. The areas integrate factors including exercise, satiety, alert/defence, thermoregulation and reproduction.

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8
Q

What are cortical influences and give two examples?

A

Cortical influences are higher brain functions from the forebrain e.g. emotion and volition/will.

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9
Q

What will be lost from damage above T1 and why?

A

There is no sympathetic control above T1 so will lose the ability to alter HR, BP and contractility.

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10
Q

What is the baroreceptor reflex?

A

A homeostatic regulation of ABP to keep pressure constant for supply to the brain and body.

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11
Q

Where are the baroreceptors located?

A

Within the carotid sinus at the CCA bifurcation and at the arch of the aorta.

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12
Q

What is the innervation of the receptors in the carotid sinus?

A

Afferents travel via Sinus N to join CN IX.

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13
Q

What is the innervation of the receptors at the aortic arch?

A

Afferents travel via Aortic N to join CN X.

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14
Q

What type of receptors are the baroreceptors?

A

Stretch receptors - respond to magnitude of stretch and the rate of change

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15
Q

Where does the afferent activity travel to?

A

NTS

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16
Q

Why are the fibres tonically active?

A

To allow a decrease in activity if BP falls

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17
Q

What is the difference between the receptors at the carotid sinus and those at the aortic arch?

A

Each receptor has its own individual threshold >60mmHg.

The carotid are more sensitive and have a lower threshold, 60-140mmHg.

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18
Q

What is the response of the reflex when BP rises?

A

The increase in stretch, increases afferent activity to the NTS to excite NA and INHIBIT tonic excitatory input
reducing sympathetic - reduce HR, vasodilation
increasing parasympathetic - reduce HR
Results in DECREASED CO and TPR

19
Q

What happens if BP falls below 60mmHg?

A

This is the minimum threshold and so receptors would be silent.

20
Q

What is the response of the reflex if BP falls?

A

Receptor activity decreases, reduced excitation of NA and RVLM so LESS INHIBITION of sympathetic activity
Increase sympathetic = increased HR, contractility, SV, vasoconstriction of venous and arteriole
Decreased parasympathetic = Increase HR
= INCREASED CO and TPR.

21
Q

What changes occur to raise BP when it has fallen?

A

Decreased parasympathetic = Increase HR
Increase sympathetic = Increased contractility and therefor SV (ESV)
= venous constriction to increase SV (EDV)
= Arteriole constriction to increase TPR and reduce capillary hydrostatic pressure for increased absorption to increase SV (EDV).

22
Q

What happens when capillary hydrostatic pressure falls and what causes it to fall?

A

Arteriole constriction causes it to fall, and fluid will be reabsorbed from the interstitium to increase blood volume and therefore VR.

23
Q

What is the function of NA?

A

Main regulator of Parasympathetic.
Increased activity to NTS activates the excitatory fibres to NA. NA will INCREASE PARASYMPATHEITC activity to the heart.

Reduced activity to NTS, INHIBITS excitatory fibres to NA. Inhibition of NA, INHIBITS an increase in parasympathetic.

24
Q

What is the function of RVLM?

A

Main regulator of sympathetic.
Increased activity to NTS, sends INHIBITORY signals to RVLM to INIHIBIT SYMPATHETIC.

Decreased activity to NTS, prevents firing of inhibitory fibres to RVLM so there is less inhibition of sympathetic activity.

25
Q

What receptors are involved in producing responses to sym and parasym innervation?

A 
alpha1 = Vasoconstriction (NAd)
beta1 = increased HR and contractility (NAd)
beta2 = vasodilation (Ad)
M2 = reduce HR by hyperpolarising (ACh)
26
Q

Under what condition causes increased activity to NTS?

A

Raised BP = increased receptor firing to NTS = inhibits RVLM to inhibit sympathetic and excites NA for parasympathetic activity.

27
Q

Which arterioles are affected most by the baroreceptor reflex?

A

Strongest influence on GIT (25%) and Skeletal muscle (20%) to alter 45% of TPR.

28
Q

When will influences in the skin not occur?

A

If hot, as cutaneous vessels respond to thermoreceptors for BP control.

29
Q

Will the kidneys be affected by the baroreceptor reflex?

A

Kidneys have myogenic dilation when blood pressure falls to maintain flow. But if the decrease is large, the reflex is elicted and renal vasoconstriction occurs with renin release for Ang11 production.

30
Q

Will the brain respond to the baroreceptor reflex?

A

The brain always maintains myogenic vasodilation to maintain CBF even when BP falls. The reflex has no influence over cerebral flow.

31
Q

What response occurs within the myogenic muscle that is not part of the baroreceptor reflex?

A

As the reflex tries to increase sympathetic activity and increase HR, CO and TPR, the coronary circulation undergoes FUNCTIONAL HYPERAEMIA. The circulation dilates to increase O2 supply to the muscle.

32
Q

What happens to ADH levels as BP rises?

A

ADH levels decrease to prevent further absorption of water and therefore reducing plasma volume.

33
Q

What is the autoregulatory range of BP?

A

60-180mmHg

70-120mmHg in the kidney

34
Q

What is the purpose of the autoregulatory range? What happens when ABP changes?

A

Ensures a constant CBF.
If ABP increases, cerebral vessels constrict to prevent excess flow and reduce risk of haemorrhagic stroke. Constriction will increase the resistance to reduce flow.
If ABP falls, vessels dilate to reduce resistance and increase flow to reduce risk of fainting.

35
Q

Name three situations in which the reflex will act with a rise in ABP.

A

Cough/sneeze
Static exercise
Stressors

36
Q

Name three situations in which the reflex will act with a fall in ABP.

A

Standing up
Dehydration
Haemorrhage

37
Q

What is the volume receptor reflex?

A

Stretch receptors in the right atrium detect CVP to regulate BP longterm by adjusting sympathetic activity to the kidney and ADH release.

38
Q

How is this reflex different to the baroreceptor reflex?

A

Volume reflex is slower and regulates BP longterm.

Volume reflex uses CVP but baroreceptor uses BP directly.

39
Q

What is the innervation to the volume receptors?

A

Afferents fire via CN X to the NTS and onto PVS.

40
Q

What is the difference between a real and distributed change in volume?

A

A real change is a change in blood volume due to inputs and outputs of fluid.
A change in distribution of the volume.

41
Q

When are the receptors stimulated and what is the process that it results in?

A

Stimulated with increased volume.
Induces Bainbridge reflex - increase sympathetic to heart for increased HR to prevent overfilling
Reduces sympathetic to the kidney for increased renal perfusion (Dilation)
Decreased ADH release from pituitary to reduce H2O retention.
Increase urine production

42
Q

What would a decrease in blood volume result in?

A

No bainbridge.

Increased sympathetic activity to kidney, increased ADH and reduced urine.

43
Q

In what situations will the atrium become less distended?

A

Standing
Dehydration
Haemorrhage

44
Q

In what situations will the atrium become more distended?

A

Supine
Large fluid intake
Over transfusion

CVS (15 decks)

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