Generation of nerve impulse - class-XI

Synaptic knobs, or axon terminals, contain synaptic vesicles filled with neurotransmitters that fuse with the presynaptic membrane to release their contents into the synaptic cleft upon action potential arrival.

The vagus nerve (cranial nerve X) is the primary parasympathetic nerve that innervates visceral organs in the thoracic and abdominal cavities, stimulating gastric juice secretion and stomach wall contractions.

Synaptic fatigue occurs when the rate of neurotransmitter release exceeds the rate of synthesis and transport, leading to the depletion of neurotransmitters in the synaptic knob.

Membrane potential is established by the unequal distribution of ions across the membrane, maintained by active transport (like the Na+/K+ pump) and the movement of ions through channels.

A nerve impulse travels from the dendrites to the cyton (cell body), then down the axon to the terminal branches.

During an action potential, depolarization is caused by the influx of sodium ions through voltage-gated Na+ channels, whereas repolarization is achieved by the efflux of potassium ions through the opening of voltage-gated K+ channels.

Saltatory conduction occurs in myelinated nerve fibers, where the action potential jumps between the Nodes of Ranvier.

The refractory period is the time during which a neuron is incapable of generating another action potential, occurring after depolarization and during repolarization.

Afferent (sensory) nerve fibers carry impulses from sensory receptors toward the central nervous system (CNS).

The cell bodies of motor neurons (somatic efferent neurons) are located in the ventral (anterior) horn of the spinal cord gray matter.

The Na+/K+ pump maintains the resting potential by actively transporting 3 Na+ ions out of the cell and 2 K+ ions into the cell for every ATP molecule hydrolyzed.

In the ear, the cochlea contains the organ of Corti, which converts mechanical vibrations into nerve impulses that travel via the auditory nerve.

The resting potential is the electrical potential difference across the plasma membrane of a neuron when it is not being stimulated.

Axo-axonic synapses can modulate the release of neurotransmitters from the terminal of the postsynaptic axon, effectively reversing or inhibiting the signal transmission.

The vagus nerve is the tenth cranial nerve (CN X) and is the primary component of the parasympathetic nervous system for the thoracic and abdominal viscera.

In a neuron, the axon is the process responsible for transmitting impulses away from the cell body (cyton). Dendrites, by contrast, typically carry impulses toward the cell body.

Depolarization occurs when the resting membrane potential becomes less negative. This is primarily caused by the rapid opening of voltage-gated sodium channels, allowing Na+ to rush into the cell.

In the resting state, there is a high concentration of Na+ outside the cell and a low concentration inside. Due to the concentration gradient, Na+ ions have a natural tendency to diffuse into the cell, though the membrane is relatively impermeable to them at rest.

A nerve impulse is an electrochemical signal. It involves the movement of ions across the membrane, creating a wave of electrical potential change along the axon.

At resting stage, the Na-K pump maintains a high concentration of K+ inside the neuron and a high concentration of Na+ outside the neuron.

The primary function of the axon is to conduct nerve impulses away from the cell body toward the axon terminals.

A polarized neuron is one that is at its resting potential, meaning there is a stable difference in electrical charge across the membrane (negative inside, positive outside).

During the depolarization phase of a nerve impulse, voltage-gated sodium channels open, allowing Na+ to move down its concentration gradient into the axoplasm.

Nodes of Ranvier are the periodic gaps in the myelin sheath along the length of an axon where the axonal membrane is exposed to the extracellular fluid.

Synaptic delay is the time required for the release of neurotransmitters, their diffusion across the synaptic cleft, and the binding to receptors on the postsynaptic membrane, typically lasting about 0.5 ms.

Repolarization occurs when sodium channels close and potassium channels open, allowing K+ to flow out of the cell to restore the negative resting potential.

In the resting stage, the neuronal membrane is much more permeable to potassium ions (K+) than to sodium ions (Na+), which helps maintain the resting potential.

The myelin sheath acts as an electrical insulator, preventing ion leakage and allowing saltatory conduction, which significantly increases the speed of nerve impulse transmission.

Unlike action potentials, which are 'all-or-none', graded potentials vary in amplitude and duration depending on the strength of the stimulus.

Electrical synapses allow for direct ion flow between neurons via gap junctions, making transmission significantly faster than the chemical process of releasing and binding neurotransmitters.

The Na-K pump is an active transport mechanism that uses ATP to move 3 Na+ ions out and 2 K+ ions in, working against concentration gradients to maintain the resting membrane potential.

A polarized neuron has a positive charge on the outer surface and a negative charge on the inner surface. Option D incorrectly states the reverse.

Calcium ions (Ca2+) are essential for the release of neurotransmitters from the presynaptic terminal at the neuromuscular junction.

Depolarization is the process where the membrane potential becomes less negative, which is driven by the influx of sodium ions (Na+) into the cell.

The sodium-potassium pump actively transports 3 Na+ ions out of the neuron and 2 K+ ions into the neuron, maintaining the electrochemical gradient.

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

When an action potential reaches the axon terminal, voltage-gated calcium channels open. The influx of Ca++ ions triggers the fusion of synaptic vesicles with the presynaptic membrane, releasing neurotransmitters into the synaptic cleft.

A neurotransmitter is a chemical messenger that carries, boosts and modulates signals between neurons and other cells in the body. In most cases, a neurotransmitter is released from the axon terminal after an action potential has reached the synapse. The neurotransmitter then crosses the synaptic gap to reach the receptor site of the other cell or neuron. 

During depolarization, sodium ions rush into the cell, making the interior more positive. Consequently, relative to the interior, the outer surface of the membrane becomes negatively charged compared to its resting state.