lab2 - Exercise 3.1 1. Dendrites and cell body 2. Resting...

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1. Dendrites and cell body 2. Resting membrane potential 3. a. Depolarization b. Sodium ions 4. Frequency; strength 5. The all-or-none law of nerve physiology states that a neuron either does not “fire” (to any subthreshold stimulus) or it “fires” maximally (to threshold stimulus). 6. When both recording electrodes are placed in the extracellular environment, the voltage between them is zero because there is no separation of charges between the two electrodes (no difference in potential). To record the resting membrane potential, one recording electrode should be placed inside the axon and the other should be placed outside. A membrane potential is recorded because the cell membrane maintains a separation of charges, or a potential difference, between the inside and outside of a cell. This membrane potential is the resting membrane potential of the axon. 7. At rest, the sodium-potassium active transport pump is dominant, pumping sodium ions out and potassium ions into the neuron cell cytoplasm – with ion gates closed. During rest some of the leaky channels are open in the axon membrane, allowing the K+ ions to move out of the membrane. A resting membrane potential of – 70 mV is maintained across the membrane. During the production of an action potential, the sodium channels open first allowing the initial entry of sodium ions into the neuron. This causes depolarization, which is the reversal of the membrane polarity from –ve to +ve). At the peak of the depolarization the sodium channels close. This is followed immediately by the opening of the potassium channels with potassium ions leaving the neuron cytoplasm (repolarization). The K+ channels remain open for expanded time, resulting in hyperpolarization. Both Na+ and K+ ion channels then close allowing the reestablishment of the original resting membrane potential. 8. The strength of a stimulus is coded in a single neuron axon by the frequency of generated action potentials. Stronger stimuli however, will excite a greater number of axons collected within a given nerve to produce a greater response. 9. As the strength of the stimulus was increased, more fibers within the nerve were stimulated to produce a greater number of individual neuron action potentials, resulting in an overall increase in the amplitude of the recorded sciatic nerve response. The whole nerve “action potential” observed in this exercise was therefore a composite of many individual neuron action potentials firing simultaneously. The whole nerve response, therefore could increase in size when a stronger stimulus was applied since a greater number of neurons responded with simultaneous action potentials. Exercise 3.2
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lab2 - Exercise 3.1 1. Dendrites and cell body 2. Resting...

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