Lab 7: Mammalian Dive Reflex

Question 1

What is the mammalian dive relfex?

Answer 1

An adaptation for surving prolonged bouts of cold-water submersion. The reflex allows the body to reduce the negative side effects associated with a decreased oxygen supply to the vital organs. This reflex involves peripheral vasoconstriction and bradycardia.

Question 2

What nervous system is the mammalian dive reflex controlled by?

Answer 2

It is mediated by both branches of the ANS (SNS and PSNS).

Question 3

Describe the sequence of events that occur during the mammalian dive relfex.

Answer 3

• When the face is submerged in cold water, receptors sensitve to cold in the face become excited and relay information via the opthalmic branch (cranial nerver V1) of the trigemnial nerve.
• this information is integrated by the respitory center in the medulla oblongata resulting in inhibition of respiratory muscles
• the respiratory center relays information to the cardiovascular center in the medulla resutling in activation of the ANS

Question 4

How does the SNS contribute to the mammalian dive reflex?

Answer 4

Activation of the SNS during the MDR results in vasoconstriction of arterioles supplying the limbs, skin, intestine, & kidney.

Question 5

What is the molecular process that leads to vasoconstriction?

What kind of receptors?

Answer 5

1. Release of Norep increases
2. Norep binds to metabotropic alpha-adrenergic receptors altering levels of calcium in the cytoplasm of the smooth muscle cells through activation of second messenger signaling pathways
3. Muscle cells become more active and arteroles constrict

Question 6

If increased Ca2+ leads to vasoconstriction,

how does decreased Ca2+ lead to vasodilation?

Answer 6

Decreased levels of cytoplasmic Ca2+ lead to less activation of myosin light-chain kinase and vasodilation of blood vessels.

Question 7

During the MDR what does widespread peripheral vasoconstriction result in?

Answer 7

Increased mean arterial pressure with decreased pulse pressure measured in the periphery

Question 8

How does the PSNS contribute to the mammalian dive reflex?

Answer 8

Activation of the parasympathetic branch of the ANS during MDR results in bradycardia.

Question 9

If the SNS is activated during the dive reflex,

why doesn’t heart rate increase?

Answer 9

The vasomotor center of the medulla activates SNS neurons that stimulate smooth muscle of arterioles supplyingl non-essential organs, while the cardiac parasympathetic center causes activation of the heart via the vagus nerve

Question 10

What is the molecular process that allows the PSNS to regulate heart rate?

Answer 10

Post-ganglionic PSNS neurons release AcH onto autorhytmic cells of the heart that produce pacemaker potentials and regulate heart rate.

Question 11

What kinds of receptors does AcH interact with on authorythmic cells?

Answer 11

• Muscarinic
• Cholinergic

Question 12

What does an ECG represent?

Answer 12

The ECG represents the sum of all electrical activity occuring in the autorhythmic and contractile cells of the heart.

* Not a recording of a single cardiac action potential

Question 13

What do the 3 leads represent in an ECG?

Answer 13

1. The difference in electrical activity across the top of the heart
2. the difference in electrical activity along the right border of the heart
3. The difference in electrical activity along the left border of the heart