Know all about nerve impulse

This is in continuation to the last article focusing on neural system and mechanisms of neural coordination in a human body. Today, we will focus on the nerve impulse, its generation and conduction. Generation and conduction of nerve impulse • Neurons are excitable cells because their membranes are in a polarised state. • Different types […]

This is in continuation to the last article focusing on neural system and mechanisms of neural coordination in a human body. Today, we will focus on the nerve impulse, its generation and conduction.

Generation and conduction of nerve impulse

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• Neurons are excitable cells because their membranes are in a polarised state.
• Different types of ion channels are present on the neural membrane.
• These ion channels are selectively permeable to different ions.
• When a neuron is not conducting any impulse, i.e., resting, the axonal membrane is comparatively more permeable to potassium ions (K ) and nearly impermeable to sodium ions (Na ).
• Similarly, the membrane is impermeable to negatively charged proteins present in the axoplasm.
• Consequently, the axoplasm inside the axon contains high concentration of K and negatively charged proteins and low concentration of Na .
• In contrast, the fluid outside the axon contains a low concentration of K , a high concentration of Na and thus forms a concentration gradient.
• These ionic gradients across the resting membrane are maintained by the active transport of ions by the sodium-potassium pump which transports 3Na outwards for 2K into the cell.
• As a result, the outer surface of the axonal membrane possesses a positive charge while its inner surface becomes negatively charged and is, therefore, polarised.
• The electrical potential difference across the resting plasma membrane is called the resting potential.
• We might be curious to know about the mechanisms of generation of nerve impulse and its conduction along an axon.
• When a stimulus is applied at a site on the polarised membrane, the membrane at the site A becomes freely permeable to Na .
• This leads to a rapid influx of Na followed by the reversal of the polarity at that site, i.e., the outer surface of the membrane becomes negatively charged and the inner side becomes positively charged.
• The polarity of the membrane at the site A is thus reversed and hence depolarised.
• The electrical potential difference across the plasma membrane at the site A is called the action potential, which is, in fact, termed as a nerve impulse.

To be continued…
Dr. Modala Mallesh
Subject Expert
Palem, Nakrekal, Nalgonda
9989535675