{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

Exam_3_key - Name_KEY BIOLOGY 325H Genetics Spring 2010...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
Name _______KEY________ 1 BIOLOGY 325H Genetics Spring 2010 Exam 3 Before you do anything else , please: check to make certain that your copy of the exam is complete, i.e. 5 pages. print your name legibly in the space provided at the top of every page. _________________________________________________________________ 1. [15 pts] A. Action potentials are described as 'all-or-nothing' because they do not occur in any sort of partial or intermediate size. Explain this all-or-nothing behavior based on the physiology of the voltage-gated sodium channel. The voltage-gated Na channel displays positive feedback: i.e. membrane depolarization opens Na channels, which allows Na + ions to enter the cell, which depolarizes the membrane more, and thereby opens more Na channels. If an excitable cell membrane is depolarized to its threshold potential, this positive feedback becomes unstoppable and the cell opens essentially all of its Na channels to produce a full blown action potential. B. A neuron can use action potentials to communicate its level of excitation to the rest of the nervous system. What feature of the action potential does the neuron vary to convey information about levels of excitation? The level of a neuron's excitation is conveyed by the frequency of its action potentials. More frequent action potentials indicate a higher level of excitation. C. During an animal's lifetime, its motor neurons frequently conduct action potentials from the central nervous system to a muscle, but never from the muscle to the central nervous system. Explain in terms of anatomy and/or physiology why motor neurons only experience action potentials going one direction and not the other. Action potentials are initiated by and subsequently propagate away from a site of super- threshold depolarization. In the case of a motor neuron, this depolarization is provided in the CNS by EPSPs from other neurons. Because the motor neuron is presynaptic to the muscle cell, it does not receive any EPSPs from it, nor initiate any action potentials at the site where they touch.
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Name _______KEY________ 2 2. [10 pts] Yo-Yo Ma is a renowned cellist. When drawing his bow across the strings, Yo-Yo is able to vary the force of his hand and finger muscles with great precision. Describe the two different ways in which Yo-Yo's nervous system can control the amount of force being generated by one of his finger muscles. 1. By varying the number of motor neurons that send action potentials to the muscle, Yo-Yo can control the fraction of muscle fibers that contract. 2. By varying the frequency of action potentials in a given motor neuron, Yo-Yo can modulate the level of force generated by the muscle fiber postsynaptic to that neuron. 3. [15 pts] We have discussed several plasma membrane proteins that are only found on a restricted portion of the nerve cell. Correctly name (or accurately describe, for partial credit) membrane proteins that show each of the following patterns of distribution. One protein per part is sufficient; wrong guesses count against.
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

Page1 / 5

Exam_3_key - Name_KEY BIOLOGY 325H Genetics Spring 2010...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon bookmark
Ask a homework question - tutors are online