Integration of Reflexes

Question 1

Why is the HR and TPR response to the chemoreflex variable?

Answer 1

Chemoreflex = bradyycardia, vasoconstriction and an increase in ventilation.

But the increase in VE can activate SAR which cause a vasodilation and a tachycardia.

Question 2

How can two reflexes interact?

Answer 2

Change operating point, curve shifts to right. This may alter sensitivity at the extremes due to maximal stimulation and extreme inhibition at either ends respectively. Should always look at responses in mid-range.

Change sensitivity.

Shift curve up = no change in one variable despite an increase in the other.

Question 3

What is respiratory sinus arrhythmia?

Answer 3

Lung afferents inhibit CVMN -> decrease HR

Large stretch of lung -> activate HB reflex -> inhibiton of respiratory drive -> lack of inhibition of CVMN -> increase in HR

Question 4

What are the probable sites for respiratory modulation of central respiratory drive?

Answer 4

1. Pre-synaptic inhibition of baro-R afferents
2. NTS neurones
3. inhibition of excitatory interneurones to CVMs
4. the CVMs

Question 5

What is the evidence against pre-synpatic inhibition of Baro-R afferents

Answer 5

Their membrane potentials dont show resp modulation

Question 6

Evidence against inhibition of NTS neurones?

Answer 6

Little convergence of neurones which show both cardiac and respiratory rhythm

Question 7

Evidence against inhibition of excitatory neurons to CVM/inhibition of CVM itself

Answer 7

Apply excitatory AA DLH to CVM. Causes response to CSN stimulation even during inspiration. Therefore Baro-R is still reaching CVM, so gating cannot be earlier in that path.

Question 8

Where is the main site of respiratory modulation of CVM?

Answer 8

At the CVM itself due to input from inspiratory drive. Input is ACh, as atropine abolishes resp modulation of CVM discharge.

Some gating by pulmonary SARs

Question 9

Who first demonstrated the dive reflex?

Answer 9

Bert, 1870

Bradycardia of breath holding more profound with head immersion in water than in air

Question 10

What nerve supplies the R on the face which are activated by the dive reflex?

Answer 10

V1, V2

Question 11

Dive reflex?

Answer 11

Apnoea
Bradycardia
Reduced CO
Widespread vasoconstrcition
? small rise in BP in man

Question 12

What maintains the bradycardia?

Answer 12

Activation of CB due to hypoxia/hypercapnia. Hyperoxic blood prevented the bradycardia.

Question 13

What happens to BP and blood flow?

Answer 13

BP stays the same in the seal.

Blood flow pretty much stops in aorta and renal circulation. Brain only area preserved.

Question 14

What does the apnoea do?

Answer 14

Maintains bradycardia. The chemo-R would otherwise cause an increase in ventilation, stimulate lung receptors and cause a tachycardia.

Question 15

Any effect on the spleen during diving?

Answer 15

Yes. Contracts. Supply RBCs? HCT and Hb concentration seen to fall following dive

Question 16

What is the effect of breath holding in expiration?

Answer 16

Greater bradycardia. Lack of central insp drive or pulm receptor stimulation inhibitng CVMs

Question 17

Is the dive reflex oxygen conserving in man?

Answer 17

Facial immersion decreased the falli n oxygen saturation in trained breath-hold divers (Andersson 2002)

Question 18

Stimulus and response of the defence/alerting response?

Answer 18

Stimulus = anything unexpected, novel, noxious. Species and individual specific. Hypoxia

Behavioural response - ear pricking to hissing and full blown rage
CV response - tachycardia, increase contractility, vasoconstriction skin, kidney, gut, vasodilation of skeletal muscle.
Other- pupil dilation, piloerection, increased respiration

Question 19

What areas of the brain are involved?

Answer 19

Amygdala, hypothalamus, periaqueductal grey of midbrain and medulla

Question 20

Mechanism of vasodilation?

Answer 20

Reduced symp, adrenergic vasoconstriction

circulating adrenaline