April, Bill, Grace, Tommy #TeamBernard Cardiovascular System April, Bill, Grace, Tommy #TeamBernard

Questions: What is the dive reflex? Data for the dive reflex. Draw a reflex arc for this response. What is the mechanism causing this response? Why would humans, who are typically not diving animals, retain this reflex?

What is a dive reflex? aka diving response set of reflexes activated under several conditions enables body to manage and tolerate lower levels of oxygen

Dive Reflex Data breath-hold over water 60 sec recovery from submerging

The Dive Reflex Arc

Dive Reflex Arc Once upon a time, you put your face in the water. The receptors on our face are actually in our nose. It feels cold and wet.

Dive Reflex Arc

Dive Reflex Arc

Dive Reflex Arc

Dive Reflex Arc During Apnea, there is no movement of the respiratory muscles. So an individual doesn’t breathe. Volume in lungs remains unchanged. Initial stimulus is inhibiting the respiratory system.

Dive Reflex Arc At the same time, there are other receptors that react to the cold water and these are the arterial chemoreceptors. These arterial chemoreceptors detect the decrease in O2.

Dive Reflex Arc

Dive Reflex Arc

Dive Reflex Arc Bradycardia is slowing down of the heart rate

What is the mechanism causing this response? Trigeminal skin receptors on the nose sense cold water, the signal is sent to medulla. In medulla, the cardiovascular control system coordinates the dive response by: Increasing the parasympathetic stimulus to the cardiac pacemaker in order to decrease heart rate. Increasing the sympathetic stimulus to arterioles in extremities stopping circulation in those areas

Why would humans, who are typically not diving animals, retain this reflex? Diving reflex is a shared trait among all mammals Some mammals use the reflex to dive for extended periods of time (seals, dolphins, etc) Humans, however, retained the reflex in order to survive drowning in extreme circumstances We can assume that drowning was a common enough cause of death in human evolution as to affect reproductive success

Have a safe Halloween! (: