post synaptic potentials

Question 1

State the two fundamental properties of cells which give rise to the existence of a resting membrane potential

Answer 1

1. Unequal distribution of ions across membrane (maintained by Na+/K+ pump).
2. Selective permeability of the cell membrane.

Question 2

Define Concentration gradient

Answer 2

The difference in the concentration of a substance between two areas is called the concentration gradient .

The bigger the difference, the steeper the concentration gradient = faster diffuse.

Question 3

Define Electrical Potential

Answer 3

the difference in electric potential between the interior and the exterior of a biological cell

Question 4

define equilibrium potential

Answer 4

difference across the cell membrane that exactly balances the concentration gradient for an ion is known as the equilibrium potential. Because the system is in equilibrium, the membrane potential will tend to stay at the equilibrium potential.

Question 5

electrochemical gradient

Answer 5

The difference in charge and chemical concentration across a membrane.

Question 6

d. Calculate equilibrium potential using the Nernst equation

Answer 6

Ex= - (RT/(z x F)) ln ([X]i/[X]0)

Ex = Equilibrium potential for x
R = universal gas constant
T = temperature (K)
Z = ion charge
F = faraday’s constant
[X]0 = concentration of X outside the cell
[X]I = concentration of X inside the cell.
At body temperature: Ex = 60 log[X]0/[X]I millivolts

Question 7

e. Sketch a standard action potential

Question 8

f. Describe how action potentials propagate along the axon of non-myelinated neurones

Answer 8

Unmyelinated axons
local circuitcurrent passes from the active region to the neighbouring resting membrane. Current flow progresses smoothly along the axon membrane without discontinuous jumps
The facilitated diffusion of sodium ions into the cell means a current is produced as the open regions have a higher PD than the closed regions, this causes sodium ion channels to open up further down the membrane

Question 9

Describe how action potentials propagate along the axon myelinated neurones

Answer 9

Myelinated axons

The current can only cross the axon membrane at the nodes of Ranvier where there are breaks in the insulating layer of myelinAs a result the action potential is propagated in a series of jumps (salutatory conduction)Therefore diffusion only occurs in the nodes of ranvier

Question 10

Explain the functional significance of EPSPs and IPSPs

Answer 10

Excitatory Postsynaptic Potential (EPSP) = a temporary depolarisation of postsynaptic membrane potential caused by the flow of positively charged ions into the postsynaptic cell as a result of opening of ligand-gated ion channels.
Inhibitory Postsynaptic Potential (IPSP) = Kind of synaptic potential that makes a postsynaptic neuron less likely to generate an action potential

Question 11

i. Explain why the generation of postsynaptic potentials is an important factor in health and disease

Answer 11

Why is it important to know thisDue to drug pharmacology (to control pain)For muscle contractionsAnd learning and memory (lose memories when axons die)