Central neural control of CNS

Question 1

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

Answer 1

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

Question 2

What does the central control do?

Answer 2

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

Question 3

How do afferent nerve fibres enter the CNS?

Answer 3

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

Question 4

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

Answer 4

CN X travels to SAN to DECREASE HR

Question 5

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

Answer 5

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

Question 6

What is involved in the reflex evoked by sympathetic?

Answer 6

Catecholamines, ADH and RAS

Question 7

What are integrated areas of the midbrain?

Answer 7

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

Question 8

What are cortical influences and give two examples?

Answer 8

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

Question 9

What will be lost from damage above T1 and why?

Answer 9

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

Question 10

What is the baroreceptor reflex?

Answer 10

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

Question 11

Where are the baroreceptors located?

Answer 11

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

Question 12

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

Answer 12

Afferents travel via Sinus N to join CN IX.

Question 13

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

Answer 13

Afferents travel via Aortic N to join CN X.

Question 14

What type of receptors are the baroreceptors?

Answer 14

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

Question 15

Where does the afferent activity travel to?

Answer 15

NTS

Question 16

Why are the fibres tonically active?

Answer 16

To allow a decrease in activity if BP falls

Question 17

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

Answer 17

Each receptor has its own individual threshold >60mmHg.

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

Question 18

What is the response of the reflex when BP rises?

Answer 18

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

Question 19

What happens if BP falls below 60mmHg?

Answer 19

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

Question 20

What is the response of the reflex if BP falls?

Answer 20

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.

Question 21

What changes occur to raise BP when it has fallen?

Answer 21

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).

Question 22

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

Answer 22

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

Question 23

What is the function of NA?

Answer 23

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.

Question 24

What is the function of RVLM?

Answer 24

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.

Question 25

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

Answer 25

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

Question 26

Under what condition causes increased activity to NTS?

Answer 26

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

Question 27

Which arterioles are affected most by the baroreceptor reflex?

Answer 27

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

Question 28

When will influences in the skin not occur?

Answer 28

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

Question 29

Will the kidneys be affected by the baroreceptor reflex?

Answer 29

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.

Question 30

Will the brain respond to the baroreceptor reflex?

Answer 30

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

Question 31

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

Answer 31

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.

Question 32

What happens to ADH levels as BP rises?

Answer 32

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

Question 33

What is the autoregulatory range of BP?

Answer 33

60-180mmHg | 70-120mmHg in the kidney

Question 34

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

Answer 34

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.

Question 35

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

Answer 35

Cough/sneeze Static exercise Stressors

Question 36

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

Answer 36

Standing up Dehydration Haemorrhage

Question 37

What is the volume receptor reflex?

Answer 37

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

Question 38

How is this reflex different to the baroreceptor reflex?

Answer 38

Volume reflex is slower and regulates BP longterm. | Volume reflex uses CVP but baroreceptor uses BP directly.

Question 39

What is the innervation to the volume receptors?

Answer 39

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

Question 40

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

Answer 40

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

Question 41

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

Answer 41

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

Question 42

What would a decrease in blood volume result in?

Answer 42

No bainbridge. | Increased sympathetic activity to kidney, increased ADH and reduced urine.

Question 43

In what situations will the atrium become less distended?

Answer 43

Standing Dehydration Haemorrhage

Question 44

In what situations will the atrium become more distended?

Answer 44

Supine Large fluid intake Over transfusion