Biology 449 - Animal Physiology

Spring 2002

Midterm 2 - Key

Multiple choice:   As always, choose the best answer for each multiple-choice question.  Answer on your scantron form.  Each question (except #1) is worth 3 points.

1. Fill in your scantron form:  (1 point)

· Write and bubble in your name in the upper left (last name first).

· If you wish to retrieve your exam score through the course web site, write and bubble in a secret code (i.e. a password) in the “Special Codes” section.  Be sure you remember it!

· Follow any additional instructions provided in class.

· Sign your form in the upper right.

a. As you command.

b. – e.  This was definitely not covered in lecture.

2. Smooth muscle would most likely be found

a. in the wall of the small intestine.

b. in the heart.

c. in the biceps.

d. a and b.

e. b and c.

3. The thin filaments of the myofibril consist mainly of

a. actin.

b. myosin.

c. myofibrin.

d. troponin.

e. tropomyosin.

4. When referring to muscles, the term “contraction” will always mean

a. the muscle is getting shorter.

b. the muscle is producing force.

c. the muscle is exhibiting cross-bridge cycling.

d. Two of the above. (b and c)

e. All of the above.

5. Which of the following is not part of the sequence of events that occurs during excitation-contraction coupling?

a. An action potential arriving at the axon terminal of the motor neuron triggers the release of acetylcholine.

b. Acetylcholine triggers the opening of channels that allow increased Na⁺ influx, depolarizing the sarcolemma (muscle fiber membrane).

c. An action potential is triggered in the sarcolemma and travels along the cell surface and down the T-tubules.

d. Ca²⁺ is released from the T-tubules into the cytoplasm of the muscle fiber.

e. Ca²⁺ diffuses into the myofibril, allowing cross-bridge cycling to occur.

6. Which molecule blocks the site of cross-bridge formation in a muscle at rest?

a. Actin

b. Myosin

c. Tropomyosin

d. Troponin

e. ATP

7. During cross-bridge cycling in a muscle, what is the first result of ATP binding with myosin?

a. The myosin head is energized, changing from a low-energy to a high-energy conformation.

b. The myosin head moves from high- to low-energy conformation, powering muscular contraction.

c. The myosin head dissociates from actin.

d. The myosin head forms a cross-bridge with actin.

e. ATP does not bind with myosin.

8. A tetanic contraction

a. involves a single sustained action potential, and force production that lasts longer but is no greater than a twitch contraction.

b. involves a single sustained action potential, and force production that lasts longer and is greater than a twitch contraction.

c. involves multiple action potentials, and force production that lasts longer but is no greater than a twitch contraction.

d. involves multiple action potentials, and force production that lasts longer and is greater than a twitch contraction.

e. None of the above.

9. The graph below shows the force production of a muscle during a single twitch contraction.  If a 2.0 newton weight was attached to the muscle and a twitch was elicited, when would muscle shortening begin?

a. 5 ms

b. 10 ms

c. 20 ms

d. 40 ms

e. The muscle would not shorten.

10. In humans, which of the following is true?

a. Fast glycolytic fibers can become fast oxidative fibers and vice-versa.

b. Fast oxidative fibers can become slow oxidative fibers and vice-versa.

c. Fast oxidative fibers can become slow oxidative fibers but not the reverse.

d. a and b.

e. a and c.

11. A “motor unit” refers to

a. an entire muscle.

b. all the fibers of a single type in a muscle.

c. all the fibers innervated by a single neuron.

d. all the sarcomeres in a single muscle fiber.

e. a single sarcomere.

12. One-way valves are found in

a. arteries.

b. capillaries.

c. veins.

d. the heart.

e. Two of the above.

13. For its oxygen supply, the heart relies on blood traveling through

a. the subclavian arteries.

b. the iliac arteries.

c. the coronary arteries.

d. the carotid arteries.

e. The heart is oxygenated by blood as it passes through the atria and ventricles.

14. Major regions of the heart tend to contract fairly synchronously because

a. adjacent myocardial cells communicate using chemical messengers.

b. adjacent myocardial cells are connected electrically.

c. a single motor neuron innervates large numbers of myocardial cells.

d. multiple motor neurons carry a coordinated signal to the myocardial cells.

e. myocardial cells are simultaneously stimulated by released hormones.

15. During a heartbeat, the atrio-ventricular valve opens when (for the left side of the heart)

a. the blood pressure in the atrium first exceeds pressure in the ventricle.

b. the blood pressure in the ventricle first exceeds pressure in the atrium.

c. the blood pressure in the aorta first exceeds pressure in the ventricle.

d. the blood pressure in the ventricle first exceeds pressure in the aorta.

e. The atrio-ventricular valve is not part of the left side of the heart.

16. During diastole, the pressure in the arteries

a. stays constant until the next heartbeat because flow stops during diastole.

b. increases significantly throughout most of diastole due to the contraction of smooth muscles in the arteries.

c. increases significantly throughout most of diastole due to vasoconstriction by the  arterioles.

d. drops to zero almost immediately because the arteries have absorbed all the pressure.

e. drops relatively slowly throughout most of diastole because of the elastic nature of the arteries.

17. In a typical human, maximal cardiac output, in comparison to cardiac output at rest

a. is about five times as great, with the change due to significant increases in both heart rate and stroke volume.

b. is about five times as great, with almost all of the change due to increased heart rate.

c. is about twenty times as great, with the change due to significant increases in both heart rate and stroke volume.

d. is about twenty times as great, with almost all of the change due to increased heart rate.

e. is enough to make your heart explode.

18. If cardiac output is five liters per minute, the amount of blood passing through all the systemic capillaries combined must be

a. less than five liters per minute.

b. five liters per minute.

c. more than five liters per minute.

d. zero.

e. It is impossible to tell without additional information.

19. Lymph formation would not occur if

a. hydrostatic pressure in the capillaries was significantly lower.

b. the osmotic concentration of the blood was significantly lower.

c. the capillary walls were water-tight.

d. Two of the above. (a and c)

e. All of the above.

20. Gas exchange in the lungs takes place in

a. bronchi.

b. bronchioles.

c. alveoli.

d. Two of the above.

e. All of the above.

21. During deep breathing, a pressure drop in the thorax is normally created by

a. contraction of the diaphragm.

b. contraction of the internal intercostals.

c. contraction of the external intercostals.

d. a and b.

e. a and c.

22. The pressure in the intrapleural fluid of the thoracic cavity is

a. zero.

b. always negative due to the tendency of the lungs to collapse while the ribcage tends to expand.

c. always positive due to the inward curvature of the diaphragm.

d. negative during inhalation and positive during exhalation.

e. always equal to the pressure inside the alveoli.

23. A hemoglobin molecule consists of

a. One heme and one globin, with one O₂ binding to the heme group.

b. One heme and one globin, with one O₂ binding to the globin.

c. Four hemes and four globins, with one O₂ binding to each heme group.

d. Four hemes and four globins, with one O₂ binding to each globin.

e. Four hemes and four globins, with one O₂ binding to entire hemoglobin molecule.

24. Of the total oxygen carrying capacity of normal blood, about what percentage is due to oxygen binding to hemoglobin?

a. 40%

b. 65%

c. 75%

d. 85%

e. 98%

25. During an exciting incident of explosive decompression while flying in a 747, you are exposed to air with such low P_Total that your alveolar P_O2 drops to 30 torr.  After a few minutes under these conditions, your tissue P_O2 levels have dropped to about 15 torr.  Compared to the amount of oxygen in 100% saturated blood, what percent O₂ would be unloaded at your tissues under these conditions?

a. 20%

b. 40%

c. 60%

d. 80%

e. 100%

26. The Bohr effect results from changes in blood

a. temperature.

b. pH.

c. CO₂ partial pressure.

d. O₂ partial pressure.

e. 2,3-DPG levels.

Short answer:   Write a concise answer to each of the following questions.  Your answers should fit in the spaces provided.  Each question is worth 4 points.

27. Describe the mechanism by which Ca²⁺ levels in the cytosol of a muscle fiber control cross-bridge cycling activity.

At rest, when Ca²⁺ is not present, the binding site on actin for the myosin head is blocked by tropomyosin, which spirals along the thin filament.  Another molecule, troponin, is attached to both the tropomyosin and the actin.  When Ca²⁺ enters the myofibril, it binds to troponin, causing a conformation change in the molecule, which pulls the attached tropomyosin away from the myosin binding site on the actin.  Cross-bridges can then form, and cross-bridge cycling occurs until Ca²⁺ levels drop again, returning the muscle to the resting state.

28. Describe the pattern of action potentials that occurs in the heart during a normal heartbeat cycle.  You do not need to discuss the particular channels or ions involved in changing membrane potentials.

During a normal heartbeat, action potentials are initiated by the spontaneous depolarization of the sino-atrial nodeof the heart.  AP’s spread from the SA node to the rest of the atrial muscle [causing atrial contraction] and to the atrio-ventricular node.  After a delay of about 0.1 seconds, the AV node responds by depolarizing itself, triggering a new wave of AP’s that travel from the AV node down the bundle(s) of His, then to the Purkinje fibers, and finally to the contractile muscle of the ventricles.  [This triggers ventricular contraction.]  After about a second (at rest) the process repeats.

29. Describe the three general mechanisms involved in controlling arteriole diameter.

Local control – In active hyperemia, changes in the levels of molecules associated with metabolism influence vasoconstriction so that local conditions in tissues can influence blood flow as needed.  For example, CO₂, H⁺ and ¯O₂ all tend to cause arteriolar muscles to relax.

Neural control – Arteriolar muscle is innervated by the sympathetic nervous system.  Increased activity causes vasoconstriction, while decreased activity results in vasodilation.

Hormonal control – Epinephrine, for example, influences arteriolar muscles, causing relaxation in some (heart and muscles) and contraction in others.

30. Given what you know about pulmonary anatomy and ventilation, why does using a typical snorkel while skin diving require taking deeper breaths than normal?

A snorkel effectively adds to your anatomical dead space.  Normally, you might take a breath of 500 ml, of which 150 ml would be lost to the ADS.  This means 350 ml normally reaches the alveoli with each breath.  If a snorkel added (e.g.) 150 ml more to the “pipes” moving air between the atmosphere and your alveoli, your breaths would have to be
350 + 150 +150 = 650 ml to maintain your alveolar ventilation rate (assuming your ventilation rate did not change).

31. In what three forms is carbon dioxide transported in the blood?  Which of the three represents the largest amount of CO₂?

I should have added “and describe how they are formed” to this question, but since I didn’t a simple list will suffice:

Dissolved CO₂, carbamino compounds (mostly involving Hb) and bicarbonate ion.  Most CO₂ is carried as bicarb.

32. Describe the effects of an increase and decrease of arterial P_CO2 levels on ventilation rates.  How does this compare to the effects of similar changes in P_O2 levels?

Changes in arterial P_CO2 have a strong effect on ventilation.  A 10% increase in P_CO2 over normal levels (from 40 to 44 torr) causes a doubling of minute volume (from about 5 to 10 liters).  Further increases in P_CO2 cause further increases in ventilation.  In the other direction, a drop in P_CO2 results in a decrease in ventilation rate.  Responses to changes in P_O2 are much milder unless P_O2 drops below about 60 torr or so, at which point ventilation begins to increase rapidly [reaching levels of about 20 liters/min by the time P_O2 drops to 40 torr].  Increases in P_O2 do not have a significant effect on ventilation.