MSP PROBLEM SET 3

1)A) Match the following condition with its ECG

1. Atrial Fibrillation

2. Ventricular Fibrillation

3. Third-Degree Heart Block

A.

B.

C.1

B) Explain why atrial fibrillation is not typically immediately fatal while ventricular fibrillation can cause sudden death.

C) Explain why atrial fibrillation produces an irregularly irregular pulse while complete heart block often produces a regular slow rhythm.

2)A) Due to your exhaustive college research project obtaining a standard deviation for the number of nephrons in the guinea pig kidney and due to your current and future medical school studies you have failed to hear any news of the modern world much less see the light of day for the past 6 years. Thus, little do you know that cardiac transplantation is a viable and common wonder of modern medical science. However, while mulling over the curious nature of the Electrocardiogram a thought strikes you - what if we could replace a failing heart by removing its diseased ventricles and suturing the posterior right atria and left and right ventricles from a donor heart, all while preventing rejection with powerful immunosuppressive drugs (which you will have to discover next). However, in the midst of your idea you realize that such a transplant might markedly change the ECG of the heart recipient when at rest. What changes from normal of the following might you expect? (HINT: A wave of depolarization cannot pass through the suture line that lies between the native recipient left and right atrium and the donor posterior right atrium and left and right ventricles; two posterior right atrial walls are present; a transplanted heart has a tachycardic basal rate.)

P wave:

PR interval:

QRS complex:

T wave:

Interbeat Interval:

Sinus Arrhythmia:

3) You then become concerned how the heart will function during exercise since it now needs to overcome two problems: first, hear rate needs to increase to match physiological need but no sympathetic innervation is present; and second, once the heart increases there is no sympathetic innervation to compensate for decreased diastolic filling time. However, you breathe a sigh of relief when you realize that remaining mechanisms exist to obtain sufficient cardiac output during exercise in a dennervated heart. What are they?

4)

A) Epinephrine is a potent bronchodilator, because the smooth muscle of the bronchioles contain many beta2-receptors. However, smooth muscle differs from striated muscle in that contraction is not regulated by control of the thin filaments. How, then does epinephrine relax the bronchiole?

B) What do you think the effects on smooth muscle contraction would be with a phosphodiesterase inhibitor?

5) Norepinephrine is stored in vesicles and is released in quantized fashion to the extracellular space in response to the depolarization of the presynaptic membrane and the accompanying rise in presynaptic terminal [Ca2+]. This neurotransmitter can be a culprit in severe hypertensive episodes. Devise three different antihypertensive drug strategies targeting the adrenergic pre-synaptic membrane.

6) The neuromuscular junctions (NMJ) of smooth muscle do not have a precise distance relationship and therefore, unlike skeletal muscle, the coupling between a presynaptic nerve terminal action potential and cell response is not 1:1. It can be as inefficient as 100:1. Describe two types of innervation of the smooth muscle?

7)

A) The contractile state of VSM is greatly affected by ion-conducting channels in the cell membrane, because these influence membrane potential and intracellular calcium concentration. Why do the resting VSM cells have a negative intracellular potential of Ð70mv to Ð50mv instead of a fixed value of -90mv found in most other cells.

B) How can small depolarizations of the resting potential produce significant increases in the intracellular concentration of Ca in the VSM cytoplasm?

C) There are many subtypes of K+ channels. List them and their major role in smooth muscle contraction.

8)All about the autonomic nervous system.

A)Fill in the chart:

Nerve / Neurotransmitter released / Receptor Type that neurotransmitter binds to
Preganglionic sympathetic fibers
Preganglionic parasympathetic fibers
Postganglionic sympathetic fibers (except for sweat glands)
Postganglionic sympathetic fibers to sweat glands
Postgangioninc parasympathetic fibers
Motor fiber to skeletal muscle (somatic nervous system)

B)Explain how it is possible that epinephrine acts as a vasodilator at physiologic

(relatively low) doses, but acts as a vasoconstrictor at pharmacologic (high) doses?

C)Describe the details of the sympathetic Òfight or flightÓ response. Specifically, how does your

body change, and how do these changes help you to adapt to frightening/threatening situations?

9)Unlike cardiac and skeletal muscle, smooth muscle does not rely PRIMARILY on a changing

membrane potential or extracellular calcium to produce contraction. How is this possible?

10)Provide an explanation for why smooth muscle force does not decrease over a period of

continued stimulation, even though ATPase activity and shortening velocity decrease over time? (See Figure 13)

11) You and a friend decide to take a half-day off from school in order to play a quick nine holes down at the pitch and putt. When you get ready to tee off on the 7th, you notice a commotion halfway down the fairway. Even thought itÕs only about 36 F outside, you decide to run down to see whatÕs going on. When you get to the commotion, you realize thereÕs been a freak golfing accident. The man lying below you has half of a graphite shaft sticking up through his lower jaw. Luckily you donÕt see any exit point on top of his scalp. Strangely, his feet, hands, and nose are completely red, yet his trunk and head are whitish and dry. WhatÕs going on? HINT: If you could get an MRI of the accident, the shaft is lodged directly in the hypothalamus.

12) Your friend starts freaking out when he sees the blood dribbling down this poor golferÕs chin. You look at your buddy and think to yourself, ÒIt looks like heÕs going into a panic attack.Ó The next thing you know heÕs on the floor next to the golfer. What (exactly) happened?

13) A month later, you and your buddy decide to play hookie again. But this time you decide that biking might be a bit safer. You are tearing up towards the Santa Monica mountains when your buddy turns and fires a barrage of questionsÉ

A) Are we sympathetically or parasympathetically stimulating our systems?

B) Does that type of stimulation usually cause vasoconstriction or vasodilation at rest?

C) So, if weÕre vasoconstricting our vessels as weÕre biking, how are we getting blood to the muscles in our legs to pump the bikes?