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

Muscle spindles are sensitive to changes in velocity and are innervated by type 1anerve fibers. These afferent nerve fibersconduct the impulse directly to the spinal cord, where they are immediately conducted via interneurons to alpha motor neurons, which stimulate musclecontraction.

Topic in NCERT: Transmission of Impulses

Line in NCERT: "The outer surface of the membrane becomes negatively charged and the inner side becomes positively charged."

Resting potential:

• Resting potential is the membrane potential of a neuron when it is not being stimulated.
• It is typically around -70mV in neurons.
• This resting potential is maintained by the sodium-potassium pump that actively transports ions across the neuron membrane.

Action potential:
Action potential is a brief reversal of the membrane potential that occurs when a neuron is stimulated.

• It is a rapid change in membrane potential that allows for the transmission of signals along the neuron.
• Action potential involves a depolarization phase followed by repolarization and hyperpolarization phases.

Repolarization:

• Repolarization is the phase of the action potential where the membrane potential returns to its resting state after depolarization.
• This process involves the closing of voltage-gated sodium channels and opening of voltage-gated potassium channels.
• Repolarization ensures that the neuron is ready to fire another action potential if it receives another stimulus.

Depolarization:

• Depolarization is the phase of the action potential where the membrane potential becomes less negative or even positive.
• It is caused by the influx of sodium ions into the neuron through voltage-gated sodium channels.
• Depolarization is essential for the propagation of the action potential along the neuron.

Topic in NCERT: RESTING POTENTIAL
Line in NCERT: "The electrical potential difference across the resting plasma membrane is called as the resting potential."

Action potentials are generated by special types of voltage-gated ion channels in a cell's plasma membrane. When the channels open (in response to depolarization in transmembrane voltage), they allow an inward flow of sodium ions, which changes the electrochemical gradient, which in turn produces a further rise in the membrane potential. This then causes more channels to open, producing a greater electric current across the cell membrane. The process proceeds until all of the available ion channels are open, resulting in a large upswing in the membrane potential. The rapid influx of sodium ions causes the polarity of the plasma membrane to reverse, and the ion channels then rapidly inactivate. As the sodium channels close, sodium ions can no longer enter the neuron, and then they are actively transported back out of the plasma membrane. Potassium channels are then activated, and there is an outward current of potassium ions, returning the electrochemical gradient to the resting state.

Topic in NCERT: Transmission of Impulses

Line in NCERT: "The rise in the stimulus-induced permeability to Na* is extremely short-lived."

• Activation of Sodium-Potassium Pump: When the sodium-potassium pump is activated, it exchanges sodium ions (Na⁺) for potassium ions (K⁺).
• Number of Ions Exchanged: The pump exchanges three sodium ions for every two potassium ions.
• Specifics: For every cycle of the pump, one ATP molecule is used to pump three sodium ions out of the cell and two potassium ions into the cell.
• Ratio: Therefore, the ratio of sodium ions to potassium ions exchanged is 3:2.

Topic in NCERT: Sodium-Potassium Pump
Line in NCERT: "The sodium-potassium pump which transports 3 Na outwards for 2 K into the cell."

Synapse, also called neuronal junction, the site of transmission of electric nerve impulses between two nerve cells (neurons) or between a neuron and a gland or muscle cell (effector). A synaptic connection between a neuron and a muscle cell is called a neuromuscular junction

Topic in NCERT: Transmission of Impulses

Line in NCERT: "A nerve impulse is transmitted from one neuron to another through junctions called synapses."

Neurotransmitters are the chemicals which help in the transmission of impulses from neuron to neuron and from to neuron the target tissue or cell. They are stored in the synaptic vesicles.

Topic in NCERT: NEURON AS STRUCTURAL AND FUNCTIONAL UNIT OF NEURAL SYSTEM

Line in NCERT: "Each branch terminates as a bulb-like structure called synaptic knob which possess synaptic vesicles containing chemicals called neurotransmitters."

The outer membrane has positive charge and inner membrane is negative. This is how the membranes of axon generally is. That is why the condition is known as resting potential. On stimulation by impulses, the membrane permeability changes resulting in negative outside and positive inside, that's action potential. 
Hence, the correct answer is Option B.

Topic in NCERT: RESTING POTENTIAL

Line in NCERT: "The electrical potential difference across the resting plasma membrane is called as the resting potential."

The correct answer is B: Post-synaptic membrane.
- Neurotransmitter receptor sites are typically located on the post-synaptic membrane.
- Post-synaptic membrane refers to the membrane on the receiving end of a synapse.
- When a neurotransmitter binds to its specific receptor on the post-synaptic membrane, it triggers a series of events that can lead to either excitation or inhibition of the receiving neuron.
- This process is fundamental to the transmission of signals between neurons in the nervous system.
Topic in NCERT: Transmission of Impulses
Line in NCERT: "The released neurotransmitters bind to their specific receptors, present on the post-synaptic membrane."

The two main types of synapses that transmit nerve impulses between neurons are chemical synapses and electrical synapses. Chemical synapses involve the release of neurotransmitters across a synaptic cleft, while electrical synapses allow for direct flow of electrical current between neurons. While chemical synapses are more common, electrical synapses play a vital role in rapid signal transmission in certain neural circuits, ensuring swift communication between neurons.

Topic in NCERT: Transmission of Impulses

Line in NCERT: "A synapse is formed by the membranes of a pre-synaptic neuron and a post-synaptic neuron, which may or may not be separated by a gap called synaptic cleft. There are two types of synapses, namely, electrical synapses and chemical synapses."

The two main types of synapses that transmit nerve impulses between neurons are chemical synapses and electrical synapses. Chemical synapses involve the release of neurotransmitters across a synaptic cleft, while electrical synapses allow for direct flow of electrical current between neurons. While chemical synapses are more common, electrical synapses play a vital role in rapid signal transmission in certain neural circuits, ensuring swift communication between neurons.

Topic in NCERT: Transmission of Impulses

Line in NCERT: "A synapse is formed by the membranes of a pre-synaptic neuron and a post-synaptic neuron, which may or may not be separated by a gap called synaptic cleft. There are two types of synapses, namely, electrical synapses and chemical synapses."

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.

Topic in NCERT: Generation and Conduction of Nerve Impulse

Line in NCERT: "Consequently, the axoplasm inside the axon contains high concentration of K* and negatively charged proteins and low concentration of Na*. In contrast, the fluid outside the axon contains a low concentration of K*, a high concentration of Na* and thus form a concentration gradient."

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.

Topic in NCERT: Generation and Conduction of Nerve Impulse

Line in NCERT: "The rise in the stimulus-induced permeability to Na* is extremely short-lived. It is quickly followed by a rise in permeability to K*. Within a fraction of a second, K+ diffuses outside the membrane and restores the resting potential of the membrane at the site of excitation and the fibre becomes once more responsive to further stimulation."

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.
Topic in NCERT: Transmission of Nerve Impulse

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

Topic in NCERT: Sodium-Potassium Pump

Line in NCERT: "The sodium-potassium pump which transports 3 Na outwards for 2 K into the cell."

(i) Synaptic cleft of neurons secrete adrenaline: This statement is incorrect. The synaptic cleft does not secrete adrenaline; it is a gap between neurons where neurotransmitters are released by the synaptic vesicles of the neuron. Adrenaline, or epinephrine, is primarily secreted by the adrenal glands, not neurons.

(ii) Myelinated nerve fibres are enveloped with Schwann cells, which form a myelin sheath around the axon; This statement is correct. In the peripheral nervous system, myelinated nerve fibers are indeed covered by Schwann cells, which wrap around the axon multiple times forming the myelin sheath, which insulates the axon and facilitates faster transmission of electrical impulses.

(iii) Non-myelinated nerve fibre is enclosed by a Schwann cell that does not form a myelin sheath.: This statement is correct. Non-myelinated nerve fibers are also associated with Schwann cells in the peripheral nervous system, but these Schwann cells do not wrap around the axon in the same way and do not form a myelin sheath.

(iv) Spinal and cranial nerves are made of non-myelinated nerve fibres.: This statement is incorrect. Spinal and cranial nerves contain both myelinated and non-myelinated nerve fibers. They are not exclusively made of non-myelinated nerve fibers.
Based on the evaluation, the correct answer is: d) Statement (ii) and (iii) are correct but statements (i) and (iv) are incorrect.

Topic in NCERT: Myelination of Nerve Fibres

Line in NCERT: "Myelinated nerve fibres are enveloped with Schwann cells, which form a myelin sheath around the axon. Myelinated nerve fibres are found in spinal and cranial nerves. Unmyelinated nerve fibre is enclosed by a Schwann cell that does not form a myelin sheath."

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.

Topic in NCERT: Transmission of Impulses

Line in NCERT: "The axonal membrane is comparatively more permeable to potassium ions (K⁺) than to sodium ions (Na⁺). A synapse is formed by the membranes of a pre-synaptic neuron and a post-synaptic neuron."

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

Topic in NCERT: Transmission of Impulses

Line in NCERT: "At electrical synapses, the membranes of pre- and post-synaptic neurons are in very close proximity. Electrical current can flow directly from one neuron into the other across these synapses."

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.'
Topic in NCERT: NEURAL CONTROL AND COORDINATION
Line in NCERT: "the active transport of ions by the sodium-potassium pump which transports 3 Na outwards for 2 K* into the cell."