In: Anatomy and Physiology
.1. Where are most graded potentials produced in a neuron?
a. In dendrites only
b. In both the dendrites and cell body
c. In axon terminals only
d. In both dendrites and axon terminals
2. During an action potential in a neuron, all voltage-gated sodium ion channels close
a. At the end of phase 1.
b. At the end of phase 2.
c. At the end of phase 3.
d. In the middle of phase 3.
1. Graded potentials are changes in the membrane potential occuribg due to opening of ligand gated ion channels. These graded potentials usually occur in the dendrite and cell bodies of the neuron. Answer : b. In both the dendrites and cell body
2. An action potential is generated due to flow of ions into and
out of the cell through voltage gated ion channels.
Action potential generation consists of 5 phases:
phase 0 : depolarisation
During this phase the sodium rapidly enters the cell through
voltage gated sodium channels reversing the polarity of cell
membrane.
Phase 1 : during this phase rapid entry of sodium into the cell
causes more positive charge inside the cell resulting in reversal
of polarity. This causes sodium channels to shut
phase 3: plateau phase
during this phase the shuting down of sodium channel causes the
opening of potassium channels leading to potassium moving out of
the cell. Calcium moves into the cell.
phase 4 : resting potential.
So we have seen that sodium channel closes at the end of phase
1.
Answer : a. At the end of phase 1.