Action Potentials and Muscle Physiology Exam 2, Exams of Biology

Download Action Potentials and Muscle Physiology Exam 2 and more Exams Biology in PDF only on Docsity! BME 365 Name: Exam 2 October 26, 2004 The exam consists of 10 questions. Show all work to receive credit. Clearly organize your work and draw a box around your final answers. NEATNESS COUNTS! Good Luck! Problem 1 (3): Problem 2 (4): Problem 3 (8): Problem 4 (10): Problem 5 (4): Problem 6 (7): Problem 7 (8): Problem 8 (4): Problem 9: (9): Problem 10 (8): Extra Credit (3) t-shirt (2) Total (100): Page 1 of 8 1. Draw a plot of membrane voltage versus time for a typical action potential, indicating resting, maximum, and minimum membrane voltage and approximate times that the minimum and maximum voltages occur. Answer: plot showing resting membrane voltage of ~-70 mV, rising rapidly to ~30 mV in about 0.5 ms and decreasing to ~-80 mV at about 1.5 ms, with a gradual return to the resting membrane potential Also indicate on this plot the approximate times at which the following events occur: i. Na+ activation gates open and close Answer: 0 ms and 1 ms ii. Na+ inactivation gates close and open Answer: 0.5 ms and 1 ms iii. K+ channels open and close Answer: 0-0.1 ms and 1 ms Which membrane mechanism is responsible for the absolute refractory period? Why? Why is the refractory period critical for AP propagation? Answer: Na+ activation and inactivation gates. Gates do not reset until membrane repolarizes, so additional APs have no effect. Without refractory period, APs would propagate bidirectionally, preventing specialization of neurons into afferent and efferent roles. 2. Name two types of synapses. Which is most common in the human body? Answer: Electrical and chemical. Chemical. What is an advantage of the less common type? Answer: Speed, because of the direct electrical connection. What is an advantage of the more common synapse type? Answer: Ability to produce different types and level of responses based on neurotransmitter amount and type. (more flexibility) List the steps from AP arrival at an axon terminal to the response of the post-synaptic neuron. Answer: Voltage gated calcium channels on axon terminal open Calcium enters terminal and binds to regulatory proteins Reg. proteins initiate exocytosis, which releases NT into synaptic cleft NT moves across cleft and binds to membrane receptor on post-synaptic neuron Response initiated in post-synaptic neuron Page 2 of 8 Copolymer 1 induces antigen specific suppressor T cells, which competitively bind to MHC molecules on surface of antigen presenting cells. It is injected; side effects include flushing, chest tightness, palpitations, anxiety. 7. Using the picture below, describe the atomic basis of selectivity of potassium ion channels. Answer: In the cytoplasm, water molecules surround potassium ions due to electrostatic forces. In the selectivity filter of the potassium ion channel, oxygen atoms line the channel at exactly the same spacing as found in solution. Thus, to the potassium ion, the electrostatic forces in the channel are the same as in solution and it can pass right through. Sodium ions are smaller, and the water molecules are closer in solution than in the channel, so they don’t pass through. 8. For parts (a) and (b) below, assume the duration of an action potential is 1 msec and the duration of a muscle twitch is 100 msec. a. You are performing an experiment on skeletal muscle in your lab (assume this muscle acts as it would intact in the body). You begin by initiating action potentials at a rate of 6 Hz. Sketch on the same graph both the applied stimuli and the resulting contractile activity of the muscle as functions of time for the first second of the experiment. Does the contractile activity as a function of time change if this stimulus frequency is continued ad nauseam? b. You now increase the action potential frequency to 20 Hz. Sketch the applied stimuli and the resulting contractile activity of the muscle for the first second of this experiment. Does the contractile activity as a function of time change if this stimulus frequency is continued ad nauseam? c. Now you inject an experimental drug designed to facilitate uptake of Ca2+ by the sarcoplasmic reticulum. You repeat the experiments described in parts (a) and (b). Page 5 of 8 What changes (if any) would you expect in the resulting contractile activity curves? Hint: what parameter(s) would be affected by quicker uptake of Ca2+ by the sarcoplasmic reticulum? Answer: a. Since the time between action potentials is greater than the twitch duration, each muscle twitch will be separate (i.e. there is no twitch summation). This contractile activity will remain the same until action potentials cease. b. Since the muscle twitch duration is longer than the time between stimuli, twitch summation will occur. This twitch summation will continue until the muscle reaches a state known as tetanus. At this point, the muscle produces a smooth, sustained contraction of maximal tension. If stimuli continue past this point, the muscle begins to fatigue and the strength of contraction decreases. c. Cross bridges will continue to cycle as long as sufficient Ca2+ is present to keep the troponin-tropomyosin complex away from the cross bridge binding sites on actin. Quicker uptake by the SR will result in lower Ca2+ concentration within the cell. Therefore, the duration of the muscle twitch will decrease. Since each twitch has a shorter duration, a higher action potential frequency will be needed to produce twitch summation and tetanic contraction. 9. Draw a diagram of a sarcomere in the resting state. Label all proteins. Label the disks, lines and bands. Draw the same sarcomere after contraction, showing which bands shorten and which remain the same length. Page 6 of 8 Explain how one could use diffraction to dynamically measure changes in sarcomere length. Muscle is essentially a living crystal. The repetitive structure of the sarcomere bands acts like a diffraction grating to produce a diffraction pattern. The angle of diffraction is related to the spacing of the light and dark bands. By monitoring changes in the diffraction angle, one can infer information about changes in the sarcomere length. Extra Credit: a. What was the last year in which the Boston Red Sox won the world series? 1918 b. How many Electoral College votes does Texas have? 32 c. What is Dr. RRK’s favorite book about baseball? Shoeless Joe by WP Kinsella Page 7 of 8