Question

An inhibitory post synaptic potential is a membrane potential that:

A. Is slightly depolarized from resting membrane potential .

B. Is slightly hyperpolarized from resting membrane potential

C. Is a graded potential

D. Both B and C

Answer 1

Answer : D

IPSP is both hyperpolarized potential and a graded potential

• IPSP

A depolarized presynaptic membrane releases an inhibitory neurotransmitter like GABA; is released at the synaptic cleft.GABA attaches to the receptors on the postsynaptic membrane and open chloride ion channels( A type of ligand gated channel).Because the potential in the postsynaptic membrane is -70 mV and the chloride equilibrium potential is -90 mV, we get a net force on chloride directed inward.Since Cl- is a negatively charged ion, it hyperpolarizes the postsynaptic cell towards its equilibrium potential. e.g.. -70 mV to -85 mV.This 15 mV of hyperpolarization is referred to as the Inhibitory Post Synaptic Potential(IPSP).

IPSP make the membrane potential away from the threashold.Thus it inhibits the excitability of postsynaptic neuron further from firing an action potential.

• Graded potential

A graded potential is the initial potential gradient that is created in a resting nerve dendrite terminal to make the depolarization (in case of excitatory) OR hyperpolarization (in case of inhibitory) of the membrane for the first time.The Neurotransmitter binds to the receptor of Na+ and Ca2+ and cause the opening of these channels.The Na+ and Ca2+ influx occurs to create an increased potential gradient inside the cell to make an action potential .This occurs by opening of numerous channels at a time, making a summation of all to create the action potential.Hence it is a small movement of ions into the cell.