Question

Unidirectional transmission of a nerve impulse through nerve fibre is due to the fact that
a. Nerve fibre is insulated by a medullary sheath
b. Sodium pump starts operating only at the cyton and then continue into the nerve fibre
c. Neurotransmitters are released by dendrites and not by axon ending
d. Neurotransmitters are released by axon ending and not by dendrites

Answer 1

A nerve impulse is an electrical phenomenon, like a lightning strike. Due to a difference in electrical charges across the plasma membrane of a neuron, a nerve impulse occurs. How does this electrical charge discrepancy come about? The answer includes ions, which are atoms or molecules charged electrically.

Complete answer:
Nerve impulse in a resting state, ready to transmit a nerve impulse when a neuron is not actively transmitting a nerve impulse. The sodium-potassium pump maintains a difference in charge through the neuron's cell membrane during the resting state. The sodium-potassium pump is an active transport mechanism which moves sodium ions into cells from cells and potassium ions. The sodium-potassium pump transfers both ions from lower to higher concentration regions, using ATP and protein carrier energy in the cell membranes.

Neurotransmitters are also recognised as chemical messengers from the body. They are the molecules used to relay signals between neurons, or from neurons to muscles, by the nervous system. In the synaptic cleft, contact between two neurons occurs. Here, via the release of neurotransmitters, electrical signals that have travelled along the axon are momentarily transformed into chemical ones, triggering a particular reaction in the receiving neuron.

The nerve impulses are produced upon stimulus receipt. The impulses of the nerves are distributed in one direction. The release of neurotransmitters is the key cause for unidirectional transmission. The telodendrites, which are present at the ends of the axon, release neurotransmitters such as acetylcholine. The smaller extensions called the dendrites are not secreted by such transmitters. This allows the impulse to travel from the axon of one neuron to the dendron of the neuron in one direction.

Hence, the correct answer is option (D).

Note: An action potential, also referred to as a nerve impulse, is an electrical charge moving through a neuron's membrane. It can be produced when chemical signals from a neighbouring cell alter the membrane potential of a neuron. The cell membrane potential moves rapidly from negative to positive in an action potential as sodium ions move through ion channels into the cell, while potassium ions move out of the cell.