Integration of Cardiorespiratory Reflexes.

Question 1

Explain how multiple reflexes interact.

Answer 1

Different reflex paths are often stimulated simultaneously and individual reflexes may be integrated in complex ways - the net effect is not simply the sum of the parts and stimulation of one set of receptors may bring about reflex effects which in turn stimulate another set of receptors initiating a second set of reflex effects.

Stimulation of A might enhance or impair the transmission of reflex B.

Question 2

Explain the arterial baroreceptor reflex.

Answer 2

Increase BP.
Increase stretch receptor in carotid sinus/aortic baroreceptor.
Glossopharyngeal nerve (via carotid sinus nerve) and vagus.
Nucleus tractus solitarius (dorsomedial medulla)
Other areas of the medulla (RVLM, NA, DVN) and hypothalamus
Sympathetic vagal - bradycardia
Sympathetic - vasodilation, decrease contractility, venodilation.

Question 3

Explain gain (with reference to the baroreceptor reflex).

Answer 3

Gain = change in Sympathetic nerve activity / change in carotid sinus pressure.

Exercise resets the point of the baroreceptor reflex and changes gain.

Question 4

Explain the lung inflation reflex.

Answer 4

Lung stretch.
Slowly adapting pulmonary stretch receptors
Vagus
NTS
Other areas of medulla and hypothalamus.
Phrenic - inhibits expiration.
Vagus, sympathetic - tachycardia and vasodilation.

Question 5

Arterial chemoreceptor reflex.

Answer 5

Decrease arterial pO2, increase pCO2 and or increase [H+].
Chemoreceptors in carotid body and aortic bodies.
Glossopharyngeal nerve (via CSN) and vagus.
NTS.
Other areas of medulla and hypothalamus.
Phrenic - increase ventilation (lung receptors - vasodilation and tachycardia)
Sympathetic vagus - vasoconstriction and bradycardia.

Question 6

Explain the diving response.

Answer 6

Breath holding leads to bradycardia and vasoconstriction but these responses are more intense if breath holding takes palce with immersion in water - in particular facial immersion.

Receptors in skin of face supplied by opthalmic and maxillary divisions of the trigeminal.
Stimulus: water (esp v cold)

(Normally chemoreceptor stimulation causes tachycardia but when breath holding = bradycardia).

Question 7

Explain the outcome of the diving response.

Answer 7

Decrease CO.
Increase TPR.
Decrease BF.

Apnoea
Bradycardia
Vasoconstriction (except brain)
Contraction of spleen to increase haemocrit
~ increase BP.

Question 8

Explain the defense/alerting response.

Answer 8

Stimulus: anything unexpected, novel or noxious or hypoxia

Repsonse:

• Behavioural: ear pricking, hissing, full blown rage!
• CV - tachycardia, increase contractility, vasoconstrict skin, kidney and gut, vasodilate skeletal muscle.
• Other aspects - pupil dilation, piloerection and inceased respiration.

Question 9

Features of the alerting response?

Answer 9

graded depending on intensity of stimuli
Can be conditioned
May outlast the stimulus
May show habituation or sensitisation - some aspect of response more affects than others.

Muscle vasodilation…decrease symp adrenegeric venoconstriction

Question 10

Explain the neural pathway for the alerting response.

Answer 10

Central long axis - amygdala, hypothalamus, PAG, medulla - modulated by frontal cortex.

CV component may be blocked by anaesthetic

Question 11

What happens to the gain in defence reflex?

Answer 11

Moves operating point of baroreceptor reflex to a higher pressure and reduces gain.

Question 12

What happens to operating point and gain in exercise?

Answer 12

Operating point of baroreceptor reflex is changed - but gain is unchanged.