Question

BIO 474 Mid Term Review

1) Describe attributes of the active transport of ions and, specifically, characteristics of the electrogenic Na - K pump. How does active transport maintain homeostasis?

2) Describe the ionic basis of the resting potential and briefly outline the derivation of the Nernst potential. What are typical Nernst potentials for K+, Na+, Cl-, and Ca++? What influences might these potentials have on ionic currents in neurons?

3) Describe the voltage-clamp, how it is used to investigate voltage-dependent phenomena like the action potential. What are the membrane mechanisms (citing evidence) underlying the various "magical" properties fo the action potential?

4) Describe the unitary signal-channel events that can be recorded with patch-clamp electrodes. Name techniques for recording currents from single ion channels? How are those events related to membrane proteins (e.g. associated with the action potential) and to the large net currents recorded in standard voltage - clamp records?

5) Describe the evidence for quantal release of neurotransmitter at the neuromuscular junction, including those involving calculations of number molecules released.

6) Describe the following synaptic phenomena: adaptation, desensitization, facilitation, Post-tetanic potentiation, Neuromodulation. Describe the following modes of neural integration: spatial and temporal summation, convergence/divergence, feedback inhibition and excitation, reciprocal inhibition, and serial/parallel processing.

7) Draw and describe a cellular model for associative learning in some molecular detail. List 6 ways neurons can change PRE - synaptic and/or Post - synaptic actions/responses.

Answer 1

1) The transport that takes place with the expenditure of energy from low concentration of ions to the high concentration of ions against concentration gradient is called active transport.
An example of active transport is the sodium-potassium pump.
Cell transport helps cells maintain homeostasis by keeping conditions within normal ranges inside all of an organism's cells.
2) The resting potential is determined by concentration gradients of ions across the membrane and by membrane permeability to each type of ion.
Nernst equation relates the reduction potential of an electrochemical reaction (half-cell or full cell reaction) to the standard electrode potential, temperature, and activities (often approximated by concentrations) of the chemical species undergoing reduction and oxidation.
At physiological temperature, about 29.5 °C, and physiological concentrations (which vary for each ion), the calculated potentials are approximately 67 mV for Na+, −90 mV for K+, −86 mV for Cl− and 123 mV for Ca2+.

3) The voltage clamp is a technique used to control the voltage across the membrane of a small or isopotential area of a nerve cell by an electronic feedback circuit. Voltage clamp is fundamentally different from the current clamp since it enables control of the membrane voltage of the cell. Thus, the voltage clamp is an experimental method used by electrophysiologists to measure the ion currents through the membranes of excitable cells, such as neurons, while holding the membrane voltage at a set level.
rapid rise and subsequent fall in voltage or membrane potential across a cellular membrane with a characteristic pattern is called 'action potential'. To initiate a voltage response in a cell membrane sufficient current is required.
The membrane serves as both an insulator and a diffusion barrier to the movement of ions.
Stimulus starts the rapid change in voltage or action potential. In patch-clamp mode, sufficient current must be administered to the cell in order to raise the voltage above the threshold voltage to start membrane depolarization.
Depolarization is caused by a rapid rise in membrane potential opening of sodium channels in the cellular membrane, resulting in a large influx of sodium ions.
Membrane Repolarization results from rapid sodium channel inactivation as well as a large efflux of potassium ions resulting from activated potassium channels.
Hyperpolarization is a lowered membrane potential caused by the efflux of potassium ions and closing of the potassium channels.
Resting state is when membrane potential returns to the resting voltage that occurred before the stimulus occurred.