Explain the following processes:

(a) Polarisation of the membrane of a nerve fibre

(b) Depolarisation of the membrane of a nerve fibre

(c) Conduction of a nerve impulse along a nerve fibre

(d) Transmission of a nerve impulse across a chemical synaps

Asked by Pragya Singh | 11 months ago |  62

1 Answer

Solution :-

(a) The membrane becomes polarized when its resting potential changes. The K+ and negatively charged proteins in the axoplasm are higher than the Na+ concentration  inside the axon when in resting condition. Thus, potassium ions move faster from the inside to the exterior than sodium ions. A positively charged membrane becomes negatively charged inside and a positively charged membrane becomes negative. An example of this would be polarized nerves or polarized membranes.

(b) An action potential occurs when a nerve fibre receives an electrical stimulus. As sodium ions pass through the membrane, potassium ions are less permeable. Consequently, the nerve fibre becomes positively charged inside, and negatively charged outside. This depolarization of the membrane is referred to as depolarization.

(c) Nerve fibres are divided into two types - myelinated and unmyelinated. Since Schwann cells surround the axon of a myelinated nerve fiber and form the myelin sheath, the impulse travels back and forth rapidly in myelinated nerve fibre. Ions cannot pass through the myelin sheath. The nerve fibres do not exchange ions and depolarise efficiently along their entire length as a result. Ranvier's nodes occur only at some points. A normal unmyelinated nerve fibre experiences ionic exchange along its full length, which then causes repolarization of depolarized areas and depolarization of other areas.

(d) On chemical synapses, there is a fluid-filled space between pre- and postsynaptic neurons, called a synaptic cleft. After receiving an impulse, synaptic vesicles move toward the plasma membrane and fuse with the plasma membrane in the synaptic cleft, where they release their neurotransmitters. A number of receptors are present on the postsynaptic membrane, which bind to released neurotransmitters. Postsynaptic neurons form new potentials in response to ion channels opened by this binding. An excitatory or inhibitory potential can be developed.

Answered by Abhisek | 11 months ago

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