Test: Generation, Conduction & Transmission of Nerve Impulse (NCERT) - NEET MCQ

The electrical potential difference across the resting plasma membrane is called as the resting potential. Its value is - 70 mV.

When a neuron is at resting potential i.e., not conducting any impulse; the axonal membrane is comparatively more permeable to K⁺ ions and nearly impermeable to Na⁺ ions. Consequently, the axoplasm inside the axon contains high concentration of K⁺ ions. In contrast, the fluid outside the axon has a high concentration of Na⁺ ions and thus forms a concentration gradient.

The chemicals releasing from a presynaptic neuron and interacting with specific receptors on postsynaptic neuron are called neurotransmitters. Cortisone is not a neurotransmitter.

At resting potential (polarized phase), the in side of the plasma membrane is negatively charged (-70 mV). As the stimulus reaches, it becomes positively charged (+45 mV, depolarized phase). As impulse passes away, it regains its original ionic distribution and again becomes negatively charged.

Action potential is a change in electrical potential that occurs across a plasma membrane during the passage of a nerve impulse. During this period, there is a localized and translent switch in electric potential across the membrane from -70 mV to +45 mV. It is due to the fact that the sodium channels open and the potassium channels remain closed. As a result, sodium channels permit the influx of Na⁺ by diffusion from extracellular fluid to intracellular fluid.

A nerve impulse is transmitted from one neuron to another with the help of chemicals called neurotransmitters that are released by the axon endings formed by the membrane of a pre-synaptic neuron which may or may not be separated by synaptic cleft.

The fatty myelin sheath of myelinated nerve fibres prevents the flow of ions between external fluid and fluid present within the axon. At the node of Ranvier, the insulating myelin sheath is absent and thus the ionic flow occurs at these points only. Therefore, the action potential jumps from node to node, due to which the transmission of impulse is more rapid myelinated fibres. This is called the saltatory conduction of nerve impulse.

Each Na⁺ -K⁺ pump expels three Na⁺ ions for every two K⁺ ions imported.

Due to a gap of 200Å in between two neurons, the electrical transmission of nerve impulse is not possible because the postsynaptic membrane cannot be depolarized without the aid of neurotransmitters (chemicals). Hence, in this way, the transmission of nerve impulse is an electrochemical incidence.

Synaptic vesicles of the synaptic knob secrete neurotransmitter (e.g., adrenaline). Spinal nerves and cranial nerves are myelinated nerves.

The electrical potential difference between outside and inside of a nerve fibre excitation (polarized nerve fibre) is known as resting potential whose value is -70mV.

Autonomic neural system controls and coordinates such organs which are under involuntary control and unstriated muscles of the body. Unmyelinated nerve fibres have Schwann cells which do not form myelin sheath.

The concentration gradients across the resting membrane are maintained by the active transport of ions by the sodium-potassium pump which transports 3 Na⁺ outward for 2K⁺ into the cell.

At electrical synapse, the transfer of impulse occurs by purely electrical means without involving any neurotransmitter.

In the resting state, the axonal membrane is polarised with more positively charged ions outside than inside, unequal distribution of ions is due to the selective permeability of the membrane, which forms impermeable barrier to sodium ion and the action of the sodium which pumps three sodium ions out of the neuron for every two potassium ions brought in.
Thus, the correct option is '(i) - polarised, (ii) - positively, (iii) - Na + , (iv) - sodium - potassium pump, (v) - three, (vi) - two.'