Nerve Impulse Transmission
Nerve impulses
➢ It is the sum total of various biochemical/electrical changes occurring in a
nerve fiber in response to a stimuli.
➢ Its propagation along the nerve fiber is called transmission.
Ions channel
Lipid bilayer of axolemma is a good electrical insulator so the main paths for
current to flow across the membrane are through the ion channels.
➢ When ion channels are open, they allow specific ions to move across the
plasma membrane, down their electrochemical gradient.
➢ As ions move, they create a flow of electrical current that can change the
membrane potential.
➢ Ion channels open and close due to the presence of “gates.”
➢ The gate is a part of the channel protein that can seal the channel pore shut
or move aside to open the pore.
Types of ion channels :
Leakage channel
➢ Gates of leakage channels randomly alternate between open and closed
positions.
➢ Axolemma has many more potassium ion (K+
) leakage channels than sodium ion
(Na+
) leakage channels.
➢ The potassium ion leakage channels are leakier than the sodium ion leakage
channels.
➢ Thus, the membrane’s permeability to K+
is much higher than its permeability to
Na+
.
Ligan gated channel
➢ Ligand-gated channel opens and closes in response to a specific chemical
stimulus.
➢ A wide variety of chemical ligands— including neurotransmitters, hormones,
and particular ions—can open or close ligand-gated channels.
Mechanical gated channel
➢ These channels open or close in response to mechanical stimulation in the
form of
○ Vibration and touch.
○ Pressure and tissue stretching
➢ Examples of mechanically gated channels are
○ Auditory receptors in the ears
○ Receptors that monitor stretching of internal organs
○ Touch receptors and pressure receptors in the skin.
Voltage gated channel
A voltage-gated channel opens in response to a change in membrane
potential (voltage).
➢ These participate in the generation and conduction of action potentials.
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