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. Na+ K+ PUMP moves 3 Na outside the cell and 2 K outside the cell. Thus when the pump works once there is a net loss of one positively charged ion from the cell. Thus continuous working of this pump causes a reduction in the number of positively charged ions inside the cell. This leads to the development of negative potential inside the cell membrane and that is why it is called the electrogenic pump.

Active transport requires energy from the cell in the form of ATP. It occurs when substances move from areas of lower to higher concentration or when very large molecules are transported. This helps cells maintain homeostasis by keeping conditions within normal ranges inside all of an organism's cell

2. During resting conditions, the membrane is permeable to potassium ions and impermeable to sodium ions. This creates a positively charged extracellular space Electrostatic force pushes K+ inside the cell. The resting membrane potential is thus -70mv.

Derivation of Nernst equation-

Δ G =  Δ G ⁰ + RT ln Q

-nF E⁰_cell  + RT ln Q

E cell = E⁰_cell - RT / nF lnQ

E_{cell =} E⁰_cell - 0.0592V /n log Q.

Nernst potential for Na+ = +55mV, Nernst potential for Cl- = -65mV, Nernst potential for K+ = -90mV.

In response to a signal from another neuron, sodium- (Na⁺) and potassium- (K⁺) gated ion channels open and close as the membrane reaches its threshold potential causing an action potential.