Nervous system MCQ Quiz - Objective Question with Answer for Nervous system - Download Free PDF

The correct answer is A and C

Explanation:

• The nerve action potential is a rapid electrical signal that travels along the axon of a neuron. It consists of different phases: depolarization, repolarization (descending phase), and hyperpolarization.
• The descending phase of the action potential, also known as repolarization, is critical for restoring the resting membrane potential after the neuron has been depolarized.
• Repolarization is driven by changes in the activity of voltage-gated ion channels, specifically potassium (K⁺) and sodium (Na⁺) channels.

Delayed opening of voltage-gated K⁺ ion channels (Option A):

• During the descending phase of the action potential, voltage-gated K⁺ channels open with a delay following depolarization.
• These channels allow K⁺ ions to move out of the neuron, making the inside of the cell more negative and contributing to the repolarization of the membrane.
• This is a key mechanism responsible for the descending phase.

Closing of voltage-gated Na⁺ ion channels (Option C):

• During the descending phase, voltage-gated Na⁺ channels, which were previously open during depolarization, close (inactivate).
• This prevents further influx of Na⁺ ions, halting the depolarization process and allowing repolarization to occur.
• The inactivation of Na⁺ channels is essential for the descending phase of the action potential.

Incorrect Options:

Rapid opening of voltage-gated Na⁺ ion channels (Option B):

• This is associated with the depolarization phase of the action potential, not the descending phase.
• During depolarization, the rapid opening of these channels allows Na⁺ ions to enter the neuron, making the inside of the cell more positive.

Leaky K⁺ ion channels (Option D):

• Leaky K⁺ channels contribute to maintaining the resting membrane potential, not the action potential phases.
• These channels are always open and allow a small amount of K⁺ to move across the membrane, maintaining the resting potential.

The correct order is: (C) → (A) → (B) → (D) → (E)

Explanation:

• Opening of voltage-gated Ca²⁺ channels (C)

  • An action potential reaches the synaptic terminal, leading to depolarization and opening of voltage-gated calcium channels.

• Exocytosis of synaptic vesicles (A)

  • The influx of Ca²⁺ triggers synaptic vesicles to fuse with the presynaptic membrane, releasing neurotransmitters into the synaptic cleft.

• Binding of neurotransmitter molecules to its receptors (B)

  • Released neurotransmitters bind to specific receptors on the postsynaptic membrane.

• Opening of Na⁺ channels and influx of sodium ions (D)

  • Binding of neurotransmitters leads to the opening of ligand-gated sodium channels, allowing Na⁺ influx.

• Generation of postsynaptic potential (E)

  • The influx of Na⁺ changes the membrane potential, generating an excitatory or inhibitory postsynaptic potential.

The correct answer is a-i, b-ii, c-iii, d-iv

Explanation:

a. C fibers are Non-myelinated, which means conduction is slower compared to myelinated fibers.

• Conduction velocity ranges from 0.5–2 m/s.
• Involved in transmitting dull, aching pain and temperature sensations.
• These fibers are responsible for the delayed pain after an injury.

b. Aγ fibers are Myelinated fibers.

• Conduction velocity ranges from 15–30 m/s.
• Found in the motor fibers of muscle spindles, responsible for regulating muscle tone and reflexes.
• Play a role in maintaining muscle sensitivity to stretch during movement.

c. Aα fibers are Myelinated fibers with the fastest conduction velocity, ranging from 80–120 m/s.

• Found in motor nerves controlling skeletal muscles.
• Also involved in transmitting proprioceptive information (e.g., position and movement sense).
• These fibers allow for rapid and precise control of muscle activity.

d. Aδ fibers are Myelinated fibers with a conduction velocity of 5–30 m/s.

• Transmit sharp, localized pain and temperature sensations.
• These fibers are responsible for the immediate sharp pain felt after an injury.

The correct answer is B and C.

Explanation:

• Statement A: Correct. Warmth receptors are activated by a rise in temperature, leading to the opening of TRPV channels (a type of transient receptor potential channel). These channels allow the influx of Na⁺ and Ca²⁺, leading to depolarization and signal transmission for the perception of warmth.
• Statement B: Incorrect. Cold receptors are activated by a decrease in temperature, but they primarily involve the opening of TRPM channels (not K⁺ channels). TRPM8 is one of the key channels responsible for cold sensation, and these channels are activated by lower temperatures, not K⁺ channels.
• Statement C: Incorrect. Thermoreceptors do not primarily rely on G-protein-coupled receptors (GPCRs) for transducing temperature information. Instead, they mainly utilize ion channels, such as TRP channels (TRPV, TRPM, etc.), to directly detect temperature changes through changes in ion flux, without the involvement of GPCRs.
• Statement D: Correct. TRPM channels are specifically involved in detecting cold stimuli, particularly the TRPM8 channel, which is activated by cold temperatures and menthol.

Conclusion: The incorrect statements are B and C, so the correct answer is B and C.

The correct answer is C and D.

Explanation:

• Statement A: Correct. The depolarization of a neuron is caused by the influx of Na⁺ ions through voltage-gated sodium channels. This leads to the inside of the neuron becoming more positive, which initiates the action potential.
• Statement B: Correct. The repolarization phase involves the efflux of K⁺ ions through voltage-gated potassium channels, which helps return the membrane potential back toward the resting state after the depolarization.
• Statement C: Incorrect. The threshold potential is the membrane potential at which voltage-gated sodium channels open, not when potassium channels begin to open. Potassium channels start to open later in the action potential, typically during or after depolarization, contributing to repolarization. When the membrane potential reaches this threshold (typically around -55 mV), it triggers the opening of these sodium channels, leading to the rapid influx of Na⁺ ions and thus depolarization.
• Statement D: Incorrect. During the refractory period, a second action potential can only be triggered by a stronger-than-normal stimulus. This is due to the inactivation of sodium channels during the absolute refractory period and the need for the membrane potential to return to a more negative value for the relative refractory period. However, it does not account for the absolute refractory period, where a second action potential cannot be initiated regardless of stimulus strength. Therefore, this statement is incomplete as it does not fully capture the nature of the refractory periods.

Conclusion: The incorrect statements are C and D

The correct answer is a - iii, b - iv, c - i, d - ii

Explanation:

Types of Mammalian Nerve Fibers and Their Conduction Velocities:
1. Aa (Alpha) fibers:

• These are large-diameter, myelinated fibers. They are the fastest conducting fibers.
• Conduction Velocity: Typically in the range of 70-120 m/s.

2. B fibers:

• These are smaller diameter, myelinated fibers than Aa fibers. They belong primarily to the autonomic nervous system.
• Conduction Velocity: Generally in the range of 3-15 m/s.

3. Aδ (Delta) fibers:

• These medium-diameter, myelinated fibers are responsible for transmitting quick, sharp pain sensations.
• Conduction Velocity: Usually between 12-30 m/s.

4. Aβ (Beta) fibers:

•  These are medium to large-diameter, myelinated fibers involved in touch and pressure sensation.
• Conduction Velocity: Typically in the range of 30-70 m/s.

Therefore,

• Aa fibers should match with iii (70-120 m/s), as they are the fastest conducting fibers.
• B fibers should match with iv (3-15 m/s), which fits their slower conduction compared to other myelinated fibers.
• Aδ fibers should match with i (12-30 m/s), corresponding to their moderate conduction speed.
• Aβ fibers should match with ii (30-70 m/s), as they have a faster conduction velocity than Aδ fibers but slower than Aa fibers.

The correct answer is Norepinephrine

Explanation:

Norepinephrine (NE):

• Norepinephrine is synthesized in a unique pathway where its precursor, dopamine, is first synthesized in the cytoplasm.
• Dopamine is then transported into synaptic vesicles by the vesicular monoamine transporter (VMAT).
• Inside the vesicle, dopamine is converted to norepinephrine by the enzyme dopamine β-hydroxylase, which is present inside the synaptic vesicle. This makes norepinephrine the neurotransmitter synthesized within the synaptic vesicle.

TH: tyrosine hydroxylase; DD: DOPA decarboxylase; DA: dopamine; DBH: dopamine beta-hydroxylase; release of stored epinephrine (Epi) and norepinephrine (NE) (green arrows)

Epinephrine:

• Epinephrine is synthesized from norepinephrine, typically in the adrenal medulla, but in neurons, norepinephrine would first have to be synthesized in vesicles, and then epinephrine would need an additional synthetic process taking place in the cytoplasm if necessary, transported back into vesicles.

Acetylcholine (ACh):

• Acetylcholine is synthesized in the cytoplasm from choline and acetyl-CoA by the enzyme choline acetyltransferase. After its synthesis, acetylcholine is transported into synaptic vesicles by the vesicular acetylcholine transporter (VAChT).

Serotonin (5-HT):

• Serotonin is synthesized in the cytoplasm from the amino acid tryptophan by the enzyme tryptophan hydroxylase followed by aromatic L-amino acid decarboxylase. After its synthesis, serotonin is transported into synaptic vesicles by the vesicular monoamine transporter (VMAT).

The correct answer is B and C.

Explanation:

• Statement A: Correct. Warmth receptors are activated by a rise in temperature, leading to the opening of TRPV channels (a type of transient receptor potential channel). These channels allow the influx of Na⁺ and Ca²⁺, leading to depolarization and signal transmission for the perception of warmth.
• Statement B: Incorrect. Cold receptors are activated by a decrease in temperature, but they primarily involve the opening of TRPM channels (not K⁺ channels). TRPM8 is one of the key channels responsible for cold sensation, and these channels are activated by lower temperatures, not K⁺ channels.
• Statement C: Incorrect. Thermoreceptors do not primarily rely on G-protein-coupled receptors (GPCRs) for transducing temperature information. Instead, they mainly utilize ion channels, such as TRP channels (TRPV, TRPM, etc.), to directly detect temperature changes through changes in ion flux, without the involvement of GPCRs.
• Statement D: Correct. TRPM channels are specifically involved in detecting cold stimuli, particularly the TRPM8 channel, which is activated by cold temperatures and menthol.

Conclusion: The incorrect statements are B and C, so the correct answer is B and C.

The correct answer is the patient develops immunity against his own acetylcholine receptor

Explanation:

• Myasthenia gravis is an autoimmune disease where the body's immune system produces antibodies against its own acetylcholine receptors at the neuromuscular junction. This reduces the number of functional receptors available for acetylcholine to bind to, impairing muscle contraction and leading to muscle weakness and, in severe cases, paralysis
• It was noticed that immunization of experimental animals with purified acetylcholine receptors produced a condition of muscular weakness. This suggested a role for antibody to the acetylcholine receptor in the human disease. The antibodies reduce the availability of acetylcholine at motor end plates.

The autoimmune attack has several consequences:

• Reduction in Functional Receptors: The antibodies bind to and damage or destroy many of the receptors at the neuromuscular junction. With fewer functional receptors available to bind acetylcholine, the muscle fibers receive less stimulation, leading to impaired muscle contraction.
• Complement-Mediated Damage: The binding of antibodies to acetylcholine receptors also activates the complement system, a part of the immune system that helps clear pathogens. Activation of the complement system can lead to further damage to the neuromuscular junction.
• Endocytosis of Receptors: Antibody binding can promote endocytosis (internalization and removal) of acetylcholine receptors from the muscle cell surface, further reducing the number of receptors available for acetylcholine binding.

The correct answer is Option 3 i.e. B and C only

Explanation:

B. Delay and Unidirectional Signal Propagation: The process of signal transmission at a chemical synapse is indeed characterized by a slight delay, which occurs because the neurotransmitter must be released from the presynaptic neuron, diffuse across the synaptic cleft, and bind to receptors on the postsynaptic neuron. Additionally, this process is unidirectional; the signal moves from the presynaptic neuron to the postsynaptic neuron and not in the reverse direction. This ensures precise control of neural signaling.

C. Efflux of Ca⁺⁺ ions leading to release of neurotransmitter at the pre-synaptic terminal: When an action potential arrives at the presynaptic terminal, it triggers the opening of voltage-gated calcium channels, allowing an influx of Ca²⁺ ions into the presynaptic neuron. This influx of calcium ions prompts the synaptic vesicles containing neurotransmitters to fuse with the presynaptic membrane and release their contents into the synaptic cleft. Note that the terminology should actually state "influx" of Ca²⁺ ions, not "efflux." 

• Option A (bidirectional signal propagation) is not characteristic of chemical synapses as they are inherently unidirectional.
• Option D is incorrect because it is the presynaptic neuron that experiences a significant influx of calcium ions leading to neurotransmitter release.
• The postsynaptic neuron receives the neurotransmitter, which may lead to changes in its membrane potential and possibly the generation of an action potential, but this does not involve the release of neurotransmitter by the postsynaptic neuron in response to calcium influx as part of the typical synaptic transmission process.

Conclusion:

Therefore, the answer that includes both B (delay and unidirectional signal propagation) and C (influx of Ca++ ions leading to neurotransmitter release at the presynaptic terminal) is the correct response, despite the minor miswording in C.

The correct answer is not show peak D and may not show C, but would show A and B.

Concept:

• Electrical stimulation of a region of the nervous system generates nerve impulses in centers receiving input from the site of stimulation.
• This method, using microelectrodes, has been widely used in animal studies; however, the precise path followed by the artificially generated impulse may be difficult to establish.
• Electrical and optical measurements of the nerve impulse for different stimulation voltages.
• The optical measurements were done in the pulsed mode using 1000 averages.
• The figures show the signals in time, the square-root of the power spectral density PSD and the 400 Hz frequency component.

​Fig 1: Optical measurement of nerve impulse

Fig 2: Action potential

• In addition to changes in the frequency of activity, nerve terminal impulse shape also changed with heating and cooling.
• At the same ambient temperature, nerve terminal impulses were larger in amplitude and faster in time course during heating than those recorded during cooling.
• Since the ion channels take time to open to allow the ions to travel across the membrane, cooling a neuron causes the ion channels to open more slowly, causing a reduction in the speed of the action potential as it travels down the axon.

Explanation:

• Lower temperatures generally slow down physiological processes, including the propagation of action potentials along nerve fibers.
• The peaks A, B, C, and D in the diagram likely represent action potentials or similar electrical activities arriving at the recording site at different times, which could be due to different conduction velocities in different fibers within the nerve bundle.
• At a lower temperature, the conduction velocity would decrease, particularly affecting the fibers that transmit signals for peaks C and D, which are later peaks and might represent fibers with inherently slower conduction velocities or longer pathways.
• Peaks A and B, arriving earlier, likely represent faster-conducting fibers that would still be able to transmit their signals at a reduced temperature, although possibly with some delay or reduction in amplitude.

​Hence the correct answer is Option 3

Concept:

• Electrical stimulation of a region of the nervous system generates nerve impulses in centres receiving input from the site of stimulation.
• This method, using microelectrodes, has been widely used in animal studies; however, the precise path followed by the artificially generated impulse may be difficult to establish.

​​​Explanation:

• Electrical and optical measurements of the nerve impulse for different stimulation voltages.
• The optical measurements are done in the pulsed mode using 1000 averages. The figures show the signals in time, the square-root of the power spectral density PSD and the 400 Hz frequency component.
• A cannula, often called a venflon™, is a small flexible plastic tube inserted into a vein.
• The cannula is to give you medication or fluids that you are unable to take by mouth or that need to enter your blood stream directly.
• There is a small coloured cap on the outside of the cannula.
• The term "chemical messengers of the body" is frequently used to describe neurotransmitters.
• The nervous system uses these molecules to send information between neurons or from neurons to muscles.
• The synaptic cleft is where two neurons communicate with one another (the small gap between the synapses of neurons)

​​Option1: animal variations only.

• Consider the explanation above thus this option is true
• As the experiment was done on different rats this option is possible as every individual has different responses to stimulus.

Option 2: stimulation of cell bodies or nerve fibers only. 

• Consider the explanation above thus this option is also true

​Option 3: difference in anatomical brain areas only. 

• Consider the explanation above thus this option is also true
• As different organisms have slight differences in the anatomy 

Option 4: variations in all the reasons mentioned in 1, 2 and 3.

• Consider the explanation above thus this option is  true

Hence the correct answer is option 4

The correct answer is Option 4 i.e.2‐3 days 

Key Points

• Peripheral nerves from the spinal cord extend their axons outwards and connect to different parts of the body like muscles.
• In adult humans, peripheral nerves can be of 1 meter long and upto 10,000 times in length to that of the cell body of the neuron. 
• Axonal transport is the mechanism by which nerve cells transport substances between the cell body and the axon tip, this transport is along the axon hence, the name axonal transport.
• Axonal transport is of two types: 
  • Anterograde transport (forward transport) - when the cargo is transported away from the cell body and towards the axon tip, it is called anterograde axonal transport.
  • Retrograde transport (backward transport) - when the cargo is transported towards the cell body then it is called retrograde transport. 
• Axonal transport occurs in both directions, motor proteins and microtubules are involved in the transport where the motor proteins connect the cargo to the microtubules and use energy to move the cargo\substances across the axon. 

Explanation: 

• The primary reason the movement of synaptic vesicles from the soma to the neuromuscular junction relies on fast axonal transport, rather than slow axonal transport, is due to the functional necessity and mechanisms involved:
  • Fast Demand: Synaptic vesicles contain neurotransmitters critical for neuronal communication. Efficient and timely delivery is essential for maintaining proper synaptic function and ensuring rapid and consistent signal transmission to muscles.

Mechanism of Transport:

• Fast Axonal Transport: This involves the use of motor proteins like kinesin and dynein, which transport cargo along microtubules at speeds of around 200-400 millimeters per day.
• Slow Axonal Transport: This primarily manages the transport of cytoskeletal elements and soluble proteins at a much slower rate, approximately 0.1-10 millimeters per day, which is not suitable for the transport needs of synaptic vesicles.
• Slow axonal transport is the mechanism that delivers the cytoskeletal components at the rate of less than 8mm per day. 
• Slow axonal transport mechanism is also called "stop and Go model" because during this transport myosin takes frequent stop which results in the slow transport of the substances.
• The crucial distinction between fast and slow axonal transport is that quick excursions in either the anterograde or retrograde direction are separated by protracted pauses for slow-moving cargo, such as neurofilaments.
• The numerous direction changes and the prolonged pauses both contribute to a net slow outward movement of slow axonal transport mechanism.
• So, it takes 2 to 3 days for the cargo to reach the neuromuscular junction at the person's foot.

Hence, the correct answer is Option 4.

The correct order is: (C) → (A) → (B) → (D) → (E)

Explanation:

• Opening of voltage-gated Ca²⁺ channels (C)

  • An action potential reaches the synaptic terminal, leading to depolarization and opening of voltage-gated calcium channels.

• Exocytosis of synaptic vesicles (A)

  • The influx of Ca²⁺ triggers synaptic vesicles to fuse with the presynaptic membrane, releasing neurotransmitters into the synaptic cleft.

• Binding of neurotransmitter molecules to its receptors (B)

  • Released neurotransmitters bind to specific receptors on the postsynaptic membrane.

• Opening of Na⁺ channels and influx of sodium ions (D)

  • Binding of neurotransmitters leads to the opening of ligand-gated sodium channels, allowing Na⁺ influx.

• Generation of postsynaptic potential (E)

  • The influx of Na⁺ changes the membrane potential, generating an excitatory or inhibitory postsynaptic potential.

The correct answer is a - iii, b - iv, c - i, d - ii

Explanation:

Types of Mammalian Nerve Fibers and Their Conduction Velocities:
1. Aa (Alpha) fibers:

• These are large-diameter, myelinated fibers. They are the fastest conducting fibers.
• Conduction Velocity: Typically in the range of 70-120 m/s.

2. B fibers:

• These are smaller diameter, myelinated fibers than Aa fibers. They belong primarily to the autonomic nervous system.
• Conduction Velocity: Generally in the range of 3-15 m/s.

3. Aδ (Delta) fibers:

• These medium-diameter, myelinated fibers are responsible for transmitting quick, sharp pain sensations.
• Conduction Velocity: Usually between 12-30 m/s.

4. Aβ (Beta) fibers:

•  These are medium to large-diameter, myelinated fibers involved in touch and pressure sensation.
• Conduction Velocity: Typically in the range of 30-70 m/s.

Therefore,

• Aa fibers should match with iii (70-120 m/s), as they are the fastest conducting fibers.
• B fibers should match with iv (3-15 m/s), which fits their slower conduction compared to other myelinated fibers.
• Aδ fibers should match with i (12-30 m/s), corresponding to their moderate conduction speed.
• Aβ fibers should match with ii (30-70 m/s), as they have a faster conduction velocity than Aδ fibers but slower than Aa fibers.