Tag: impulse and its transmission

Increased axon diameter in axons leads to increase action potential velocity. As there is an increase in diameter of a fibre, its internal resistance decreases. The internal resistance decreases faster relative to the membrane resistance - therefore the distance the membrane potential can travel is increased by an increased diameter. So, the correct answer is option B.

Myelin is an insulating layer or sheath, that forms around nerves, including those in the brain and spinal cord. It is made up of protein and fatty substances. The purpose of the myelin sheath is to allow electrical impulses to transmit quickly and efficiently along the nerve cells. Nerve impulses cannot pass through the myelination, so they jump from one node of Ranvier to the next. If the whole nerve becomes myelinated then the conduction will be stopped.

The speed with which the nerve impulse is conducted by axon is known as nerve conduction velocity. The speed of nerve conduction does not depend on the diameter of axon only rather it depends on the diameter of the nerve fibre. The diameter of nerve fibre is axon, neurilemma, and myelin sheath in myelinated axons while axon and neurilemma in unmyelinated fibre. Conduction velocity is high in myelinated nerve fibre with the greater diameter. So, the given statement is false.

Neurons send messages through electrical impulses called as nerve impulses. The nerve impulse is due to the changes occurring across the cell membrane. Cell membranes contain a sodium-potassium pump. The concentration of sodium and potassium ions is different across the membrane. This difference causes a voltage difference between the inside of the neuron and its surroundings. This is called as the resting membrane potential. The membrane potential is always negative inside the cell. The sodium and potassium channels in the cells are voltage-gated, meaning they can open and close depending on the voltage across the membrane. During action potential, permeability of the nerve cell membrane changes for both sodium and potassium ions. During depolarization, there is influx of sodium ions which makes inside of the cell positive. Depolarization is followed by repolarization during which the outflux of potassium ions takes place which makes inside of the cell negative. The whole process results in the propagation of a nerve impulse.