Question

Directions: Use graph of change in membrane potential during a typical action potential in a nerve cell below to answer questions 30-32 +50 Action potential 0- potential (mv) Membran 50 - Threshold o 5 Resting potential -100 Time 32. On the graph, what is taking place at #2? A. Repolarization B. Hyperpolarization C. Depolarization D. None of the above 33. On the graph, what is taking place at #4? A. Repolarization B. Hyperpolarization C. Depolarization D. None of the above 34. On the graph, what is taking place at #5? A. Repolarization B. Hyperpolarization C. Depolarization D. None of the above F2 DH F9 F4 F5 FG F7

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Answer 1

Image 1:
Let us first understand the graph. The resting membrane potential (RMP) of a nerve cell is negative i.e around -70mV. This potential is caused by an unequal distribution of positive and negative ions and proteins inside and outside the cell. This is denoted by #1 in the graph. The membrane in this state is polarised.
When a stimulus greater than the threshold stimulus (about -55mV, #2) arrives, it changes the membrane permeability of ions by the opening of voltage-gated ion channels and causes their redistribution (Na+ influx). It results in change in membrane potential from negative to positive. This change is called depolarization of the membrane and is demonstrated in the graph by #3 by an upward spike.
After a small time interval, the voltage-gated ion channels begin to close and leaky channels allow passive efflux of K+ ions. This leads to re-polarisation. This is demonstrated by #4 in the graph.
Sometimes, excess efflux of K+ creates a greater potential gap than the RMP. This is called hyper-polarisation demonstrated by #5.

Ans. 32- Depolarization.
Both 2 and 3 constitute the process of depolarization.

Ans 33- Repolarization

Ans. 34- Hyperpolarization


Image 2:
In this midsagittal section of the brain, major structures are marked.
35- Cerebrum
It constitutes a major portion of the forebrain consisting of sulci and gyri.

36- Corpus Callosum
It is a band of white matter which separates the left and the right halves of the brain.

37- Medulla Oblongata
It is a stem like structure and part of the brainstem. It is a centre for control of autonomic activities.

38- Cerebellum
It is a part of the brainstem and centre for coordination of voluntary actions.