and are also called motor neurons.
(c) Interneurons connect neurons within specific
regions of the central nervous system.
Afferent and efferent also refer generally to
neurons that, respectively, bring information
to or send information from the brain.
Conduction of nerve impulse Across Neuron
(a) Resting potential: The permeability of
plasma membrane to K+ ions is greater than
its permeability to Na+ ions. So the surface
of axon carries a positive charge relative to
its interior; this electrical potential difference
across the plasma membrane is called resting
potential and it ranges from – 40 to – 90 mV.
(b) Action potential: When a threshold stimulus is
applied on the axon membrane, depolarisation
is caused by a rapid change in membrane
permeability. The membrane becomes more
permeable to Na+ than to K+. The interior
becomes electropositive and the ECF
becomes electronegative. The depolarisation
spreads, producing a local current, which
induces the nearby passive Na+ channels to
open and to depolarise the nearby site.
(c) Repolarisation: After about 0.5 ms,
permeability to K+ ion increases because
the build-up of positive charge inside the
cell opens the voltage gated K+ channels.
Movement of K+ ions outward, down their
concentration gradient, then re-establishes
the charge differences that existed before the
stimulus occurred.
(d) Hyperpolarisation: However K+ ion channels
remain open for a bit longer period so that the
membrane potential becomes more negative
than -70 mv. It is called hyperpolarisation. It
takes about 1-5m sec for repolarisation.
The exodus of K+ ions lowers the number of
positive ions within the cell and the potential
falls back towards the resting potential.
Functions Of Neuron:
Neurons (nerve cells) have three parts that
carry out the functions of communication
and integration: dendrites, axons, and axon
terminals. They have a fourth part the cell
body or soma, which carries out the basic life
processes of neurons.