#1 of 70
SZABMU 2024 Reconduct
Permalink
Nociceptors are concerned with sensation of:
View Answer & Propolis Autopsy
Correct Key: Option C
Diagnostic Explanation
Concept:The nervous system has dedicated pathways to warn the organism of tissue damage.
Solution:- Nociceptors (from Latin nocere, to harm or hurt) are specialized free nerve endings that respond strictly to potentially damaging chemical, mechanical, or thermal stimuli. The brain interprets these signals as pain.
Why other options are incorrect:- Touch, Pressure, Vibration: These are benign mechanical stimuli detected by mechanoreceptors (like Merkel discs, Ruffini endings, and Pacinian corpuscles).
#2 of 70
SZABMU 2024
Permalink
Which part of the brain is responsible for the sensation of pleasure, punishment, fear, rage and sexual arousal?
View Answer & Propolis Autopsy
Correct Key: Option D
Diagnostic Explanation
Concept:The limbic system is the emotional center of the brain, utilizing specific nuclei for survival-based emotional responses.
Solution:- The amygdala plays a crucial and classical role in processing deep emotional responses tied to survival, encompassing feelings of intense fear, rage, punishment, and aspects of pleasure and arousal.
Why other options are incorrect:- Hypothalamus: While heavily linked to the limbic system (directing physiological arousal and basic drives), the emotional sensations of fear and rage are classically mapped to the amygdala in textbook curricula.
- Hippocampus: Memory formation.
- Cerebellum: Motor coordination.
#3 of 70
NUMS 2024
Permalink
During complex activity of flight, birds required the coordination of many skeletal muscles which part of their brain has to be well developed?
View Answer & Propolis Autopsy
Correct Key: Option D
Diagnostic Explanation
Concept:High-speed, 3D spatial maneuvering requires immense motor processing power to coordinate thousands of muscle fibers simultaneously.
Solution:- The cerebellum is strictly responsible for the precision, timing, and coordination of complex muscular activity. Because avian flight demands near-perfect, real-time balance and motor adjustment, the cerebellum is highly enlarged and exceptionally well-developed in birds.
Why other options are incorrect:- Cerebrum: Initiates voluntary action, but does not handle the rapid subconscious coordination required to stay airborne.
- Thalamus / Amygdala: Relays sensory info and processes emotions, respectively.
#4 of 70
NUMS 2024
Permalink
Which part of the brain is actively used by mathematician trying to formulate a new equation?
View Answer & Propolis Autopsy
Correct Key: Option B
Diagnostic Explanation
Concept:Abstract thought, logic, and problem-solving are higher-order cognitive functions.
Solution:- The cerebrum (specifically the highly developed frontal lobes of the cerebral cortex) is exclusively responsible for complex problem solving, mathematical reasoning, intelligence, and conscious logical thought.
Why other options are incorrect:- Hippocampus: Used for recalling old memories, but the cerebrum does the actual active analytical formulation.
- Pons: Autonomic bridge regulating sleep and breathing.
- Amygdala: Emotional processing.
#5 of 70
SZABMU 2024 Reconduct
Permalink
Sleep wake cycle is controlled by which part of brain?
View Answer & Propolis Autopsy
Correct Key: Option C
Diagnostic Explanation
Concept:Biological rhythms must be synchronized with external light cues to maintain homeostasis.
Solution:- The hypothalamus contains a specialized cluster of neurons called the suprachiasmatic nucleus (SCN). The SCN acts as the body's master circadian clock, receiving light data from the eyes to heavily regulate the 24-hour sleep-wake cycle.
Why other options are incorrect:- Thalamus: Blocks sensory input during sleep, but the hypothalamus dictates the rhythmic cycle itself.
- Hippocampus / Amygdala: Involved in memory and emotions, completely separate from circadian rhythm control.
#6 of 70
UHS 2024
Permalink
Which of the following is NOT a feature of Autonomic Nervous System?
A
Regulate response of visceral organs
B
Regulate response of glands
C
Regulate response of skeletal muscles
D
Regulate response of smooth muscles
View Answer & Propolis Autopsy
Correct Key: Option C
Diagnostic Explanation
Concept:The peripheral nervous system is split into somatic (voluntary) and autonomic (involuntary) divisions based on the target effector.
Solution:- The Autonomic Nervous System (ANS) innervates involuntary effectors: cardiac muscle, smooth muscle, and glands.
- Skeletal muscles are strictly voluntary and are innervated entirely by the Somatic Nervous System. Therefore, regulating skeletal muscles is NOT a feature of the ANS.
Why other options are incorrect:- Options A, B, and D describe the primary, involuntary targets of the autonomic nerves.
#7 of 70
KMU 2024
Permalink
The following function/activity is NOT controlled by the autonomic nervous system:
B
Smooth muscles contraction
C
Cardiac muscles contraction
View Answer & Propolis Autopsy
Correct Key: Option A
Diagnostic Explanation
Concept:The autonomic nervous system handles background life-support processes, completely devoid of conscious effort.
Solution:- Thoughts and emotions are high-level cognitive and limbic functions that occur within the central nervous system (cerebral cortex and limbic system). They are not executed or controlled by the efferent peripheral pathways of the Autonomic Nervous System.
Why other options are incorrect:- Smooth muscle, Cardiac muscle, and Salivation (glands): These are all classic, involuntary target effectors managed directly by the sympathetic and parasympathetic branches of the ANS.
#8 of 70
UHS 2024
Permalink
In human myelinated fibers nerve impulse travels at ____ meters per second.
View Answer & Propolis Autopsy
Correct Key: Option C
Diagnostic Explanation
Concept:Myelination vastly accelerates the speed of electrical conduction via saltatory propagation.
Solution:- In human neurobiology, the thickest, heavily myelinated somatic motor and sensory fibers (Type A-alpha fibers) have a maximum conduction velocity generally ranging from 100 to 120 meters per second (approx. 220-270 mph).
Why other options are incorrect:- Options above 120 m/s exceed the known physiological limits of human neuronal conduction.
#9 of 70
UHS 2024
Permalink
During non-conducting state, the neuron membrane is permeable to efflux of:
View Answer & Propolis Autopsy
Correct Key: Option B
Diagnostic Explanation
Concept:The resting membrane potential (-70 mV) is primarily established by the membrane's selective permeability to certain ions while at rest.
Solution:- During the non-conducting (resting) state, voltage-gated channels are closed, but un-gated "leak" channels remain open. The membrane has significantly more Potassium (\(\text{K}^+\)) leak channels than sodium leak channels, allowing a continuous outward leakage (efflux) of \(\text{K}^+\) down its concentration gradient, keeping the inside of the cell negative.
Why other options are incorrect:- \(\text{Na}^+\) / \(\text{Ca}^{2+}\): Their permeability is exceedingly low at rest; allowing them to freely diffuse would instantly destroy the resting potential.
#10 of 70
SZABMU 2024
Permalink
In a resting membrane, the concentration of K+ ions on inside of the membrane is ____ times greater than outside the membranes.
View Answer & Propolis Autopsy
Correct Key: Option D
Diagnostic Explanation
Concept: Resting membrane ion concentration gradients.
Solution: Active transport by the Na⁺/K⁺ pump maintains an intracellular Potassium (\(K^+\)) concentration that is roughly 10 to 30 times greater inside the cell than in the extracellular fluid.
#11 of 70
NUMS 2024
Permalink
Which immediate change is brought about in the postsynaptic membrane on binding with excitatory neurotransmitter?
B
Sodium Potassium pump ceases to work
C
Sodium gets gates close
View Answer & Propolis Autopsy
Correct Key: Option D
Diagnostic Explanation
Concept:Excitatory neurotransmitters must encourage the postsynaptic cell to fire, which requires making the cell interior more positive.
Solution:- When an excitatory neurotransmitter (like glutamate or acetylcholine) binds to postsynaptic receptors, it triggers ligand-gated sodium gates to open. The resulting influx of positive \(\text{Na}^+\) ions initiates an Excitatory Postsynaptic Potential (EPSP), driving the cell toward threshold.
Why other options are incorrect:- Sodium gates close: This would prevent excitation entirely.
- Calcium gates open: This happens in the presynaptic terminal to release the neurotransmitter, not primarily in the postsynaptic membrane to generate the impulse.
- Pump ceases to work: The pump runs continuously in the background and is not immediately halted by synaptic binding.
#12 of 70
NUMS 2024
Permalink
During the conduction of nerve impulse, hyperpolarization would not occur if:
A
Sodium Potassium pump stopped working
B
Sodium gates did not close in time
C
Potassium gates were not so lousy
D
Calcium gets open instantly
View Answer & Propolis Autopsy
Correct Key: Option C
Diagnostic Explanation
Concept: Voltage-gated potassium channel kinetics.
Solution: Hyperpolarization occurs because voltage-gated \(K^+\) channels close slowly, allowing excess positive \(K^+\) to leak out. If \(K^+\) channels closed promptly upon reaching resting potential, hyperpolarization would not occur.
#13 of 70
NUMS 2024
Permalink
Which option given below characterizes refractory period?
A
Change in the type of ions across the membrane
B
Membrane potential +50mV
C
Reversal of charges across neural (neuronal) membrane
D
Next impulse can be conducted
View Answer & Propolis Autopsy
Correct Key: Option C
Diagnostic Explanation
Concept:Neurons require a brief recovery window before they can fire again to ensure impulses travel in only one direction.
Solution:- The absolute refractory period occurs directly during the action potential, heavily characterized by the active reversal of charges (depolarization and immediate repolarization). Because the sodium channels are already open or inactivated during this massive charge reversal, it is impossible for the membrane to respond to a new stimulus until resting states are restored.
Why other options are incorrect:- Next impulse can be conducted: This is the exact opposite of what "refractory" means.
- Membrane potential +50mV: This only describes the peak of the action potential, while the refractory period encompasses the falling phase as well.
#14 of 70
SZABMU 2024 Reconduct
Permalink
Nerve impulse conducted from one node of Ranvier to another skipping the myelinated regions moves up to ____ times faster than unmyelinated axons:
View Answer & Propolis Autopsy
Correct Key: Option D
Diagnostic Explanation
Concept:Saltatory conduction provides a massive evolutionary advantage in reaction speed.
Solution:- Because the myelin sheath insulates the axon and restricts ion exchange solely to the nodes of Ranvier, the action potential functionally "skips" down the axon. This mechanism is universally taught to allow impulses to travel up to 50 times faster than the continuous wave of depolarization seen in naked, unmyelinated axons of similar diameter.
Why other options are incorrect:- Options 30, 100, and 120 deviate from the standard textbook physiological metric established for this comparison.
#15 of 70
KMU 2024
Permalink
The neurotransmitter ____ is hydrolyzed by monoamine oxidase.
View Answer & Propolis Autopsy
Correct Key: Option A
Diagnostic Explanation
Concept:Enzymatic degradation is specific to the chemical structure of the neurotransmitter.
Solution:- Monoamine Oxidase (MAO) is an enzyme specifically designed to break down monoamine neurotransmitters (compounds featuring a single amine group connected to an aromatic ring). Adrenaline (epinephrine), along with dopamine and noradrenaline, falls directly into this structural category and is metabolized by MAO.
Why other options are incorrect:- Acetylcholine: Hydrolyzed strictly by Acetylcholinesterase, not MAO.
- Glutamate: An amino acid, cleared via reuptake transporters, not MAO.
- Note: While Serotonin is also a monoamine broken down by MAO, classical syllabus emphasis on catecholamine degradation pathways prioritizes Adrenaline/Noradrenaline as the primary textbook answer here.
#16 of 70
KMU 2024
Permalink
Diffusion of ____ across the post synaptic membrane causes it to depolarize.
View Answer & Propolis Autopsy
Correct Key: Option D
Diagnostic Explanation
Concept:Depolarization is defined as the interior of a cell becoming less negative, which requires the rapid entry of a positive ion.
Solution:- When an excitatory synapse is activated, ligand-gated channels open and allow an overwhelming influx (diffusion) of positively charged Sodium (\(\text{Na}^+\)) ions into the postsynaptic neuron. This neutralizes the resting negative charge, causing depolarization.
Why other options are incorrect:- Chloride ions (\(\text{Cl}^-\)): Entering the cell makes it more negative (hyperpolarization/inhibition).
- Potassium ions (\(\text{K}^+\)): Exiting the cell removes positive charge, leading to repolarization or hyperpolarization.
- Calcium: Works primarily in the presynaptic terminal, not for bulk postsynaptic depolarization.
#17 of 70
SZABMU 2024
Permalink
The neurotransmitters bind to the receptors on the postsynaptic membrane, triggering an action potential in the postsynaptic membrane by causing changes in:
A
Permeability of calcium ions
B
Concentration of certain ions
C
Permeability of certain ions
D
Concentration of calcium ions
View Answer & Propolis Autopsy
Correct Key: Option C
Diagnostic Explanation
Concept:Neurotransmitters act as keys that unlock highly specific gates on the receiving cell.
Solution:- Receptors on the postsynaptic membrane are actually ligand-gated ion channels. When a neurotransmitter binds, it physically alters the shape of the channel, changing the membrane's permeability to certain ions (like allowing \(\text{Na}^+\) to rush in). This change in permeability allows ions to flow, altering the electrical potential.
Why other options are incorrect:- Concentration: Neurotransmitters don't directly alter the overall concentration of ions; they just open the gates (change permeability) so ions can move down their pre-existing concentration gradients.
- Calcium ions: Postsynaptic excitation relies primarily on Sodium and Potassium permeability, not Calcium.
#18 of 70
NUMS 2024
Permalink
What is the fate of our neurotransmitter after the transmission of nerve impulse across synapse?
A
Remains bound to post synaptic membrane
B
It is taken into post synaptic neuron
D
Remains stray in the synaptic cleft
View Answer & Propolis Autopsy
Correct Key: Option C
Diagnostic Explanation
Concept:Synapses must be "reset" almost instantly to allow the processing of new, incoming signals.
Solution:- To terminate the signal and prevent continuous, paralyzing stimulation of the postsynaptic cell, the neurotransmitter is swiftly removed from the cleft. A primary biological mechanism for this (classically seen with Acetylcholine) is being broken down by specific enzymes (e.g., acetylcholinesterase) directly in the synaptic cleft.
Why other options are incorrect:- Remains bound / stray: This would cause permanent activation and muscle tetanus/spasms.
- Taken into post synaptic neuron: Reuptake mechanisms pull the transmitter back into the presynaptic neuron, never the postsynaptic one.
#19 of 70
SZABMU 2024 Reconduct
Permalink
Which sequence will be followed when impulse travel from receptor to effector?
A
Motor neuron -> Inter neuron -> Sesory neuron
B
Inter neuron -> Sesory neuron -> Motor neuron
C
Sesory neuron -> Motor neuron -> Inter neuron
D
Sesory neuron -> Inter neuron -> Motor neuron
View Answer & Propolis Autopsy
Correct Key: Option D
Diagnostic Explanation
Concept:The reflex arc follows a strict anatomical highway from sensory input to physical output.
Solution:- 1. Sensory neuron: Carries the detected stimulus from the receptor towards the Central Nervous System (CNS).
- 2. Inter neuron: Located entirely within the CNS (spinal cord), it bridges the incoming and outgoing signals.
- 3. Motor neuron: Carries the command away from the CNS to the effector (muscle or gland).
Why other options are incorrect:- Any sequence that does not place the Inter neuron exactly in the middle of Sensory and Motor pathways is anatomically impossible.
#20 of 70
KMU 2024
Permalink
A motor neuron:
A
Carries impulse from effectors to CNS
B
Carries impulse from receptors to CNS
C
Connects sensory nerves to ganglions.
D
Carries impulse from CNS to muscles
View Answer & Propolis Autopsy
Correct Key: Option D
Diagnostic Explanation
Concept:Efferent pathways carry "effects" outward.
Solution:- By anatomical definition, a motor neuron (efferent neuron) has its cell body in the Central Nervous System (CNS) and projects its long axon outward to transmit electrical impulses from the CNS to muscles or glands (effectors), commanding them to act.
Why other options are incorrect:- Receptors to CNS: This is the strict job of the sensory (afferent) neuron.
- Effectors to CNS: Signals do not travel backwards from effectors.
- Connects nerves to ganglions: Describes structural anatomy, not the functional directionality of a motor fiber.
#21 of 70
SZABMU 2024
Permalink
The groups of ribosomes associated with rough endoplasmic reticulum and Golgi apparatus in the cell body of neuron is called:
View Answer & Propolis Autopsy
Correct Key: Option D
Diagnostic Explanation
Concept:Neuroanatomists name specific cellular structures based on historical staining techniques.
Solution:- When stained with basic dyes, the neuronal cell body shows prominent basophilic clumps. These clumps, discovered by Franz Nissl, are known as Nissl's Granules. They are structurally comprised of densely packed rough endoplasmic reticulum and free ribosomes used for high-capacity protein production.
Why other options are incorrect:- Soma: The entire cell body itself, not the specific organelles inside it.
- Neuroglia: The entire class of supporting cells (like astrocytes), not an organelle.
- Axofibrils: Cytoskeletal structures (neurofibrils) in the axon for transport, not protein synthesis.
#22 of 70
NUMS 2023
Permalink
Endorphins are produced in:
View Answer & Propolis Autopsy
Correct Key: Option A
Diagnostic Explanation
Concept:Endogenous pain regulation originates centrally within the nervous system.
Solution:- Endorphins are naturally occurring opioid peptides synthesized primarily in the pituitary gland and the hypothalamus within the brain in response to pain or stress.
Why other options are incorrect:- Adrenal gland: Produces stress hormones like cortisol and adrenaline.
- Stomach / Thymus: Involved in digestion and immunity, respectively, not endogenous analgesia.
#23 of 70
ETEA 2023
Permalink
The activities like sleeping, walking and dreaming are controlled by which part of the brain:
View Answer & Propolis Autopsy
Correct Key: Option A
Diagnostic Explanation
Concept:The brainstem contains distinct centers that regulate fundamental rhythmic and states-of-consciousness behaviors.
Solution:- The pons (Latin for "bridge") connects different parts of the brain. It houses specialized nuclei that are heavily involved in the regulation of sleep-wake cycles, the generation of dreams (especially REM sleep), and bridging motor tracts required for movements like walking.
Why other options are incorrect:- Cerebellum: Fine-tunes movement but does not generate sleep or dreams.
- Hippocampus: Memory consolidation.
- Olfactory bulb: Smell processing.
#24 of 70
ETEA 2023 Retake
Permalink
The total number of cranial nerves in human body are:
View Answer & Propolis Autopsy
Correct Key: Option A
Diagnostic Explanation
Concept:Nerves are always organized bilaterally (in symmetrical left-right pairs) as they exit the central nervous system.
Solution:- There are exactly 12 pairs of cranial nerves emerging directly from the brain/brainstem to innervate primarily the head and neck.
Why other options are incorrect:- 31 pairs: Represents the number of spinal nerves exiting the spinal cord.
- 24 pairs / 62 pairs: Anatomically incorrect groupings.
#25 of 70
UHS 2023
Permalink
The value of active membrane potential of the neuron is:
View Answer & Propolis Autopsy
Correct Key: Option C
Diagnostic Explanation
Concept: Action potential peak voltage conversion.
Solution: During peak depolarization, the active membrane potential reaches approximately +50 millivolts. Converting millivolts to volts (\(50 \text{ mV} / 1000 = \mathbf{0.05 \text{ Volts}}\)).
#26 of 70
SZABMU 2023
Permalink
The junction between the axon ending of a neuron and the dendrites of another neuron is called:
View Answer & Propolis Autopsy
Correct Key: Option A
Diagnostic Explanation
Concept:Neurons form complex interconnected networks by linking their terminal ends to the receiving ends of neighbors.
Solution:- The functional and anatomical connection point where the axon terminal of one neuron meets the dendrite (or soma) of another is called a synapse.
Why other options are incorrect:- Nissl's body: Granules of rough endoplasmic reticulum located within the cell body.
- Neuroglia: Support cells of the nervous system.
- Myelin sheath: The insulating fat layer wrapping the axon.
#27 of 70
SZABMU 2023
Permalink
During non-conducting state, the neuron membrane is permeable to efflux of:
View Answer & Propolis Autopsy
Correct Key: Option A
Diagnostic Explanation
Concept:The resting membrane potential is largely dictated by "leak" channels that remain open when the neuron is idle.
Solution:- In a non-conducting (resting) state, the neuronal membrane contains significantly more open potassium leak channels than sodium leak channels. Therefore, it is highly permeable to the slow, continuous efflux of potassium ions (\(\text{K}^+\)) moving down their concentration gradient out of the cell.
Why other options are incorrect:- \(\text{Na}^+\) / \(\text{Ca}^{2+}\): Their voltage-gated channels are strictly closed during the resting state to maintain the electrochemical gradient.
#28 of 70
SZABMU 2023
Permalink
GABA is an example of:
B
Inhibitory neurotransmitter
C
Excitatory neurotransmitter
View Answer & Propolis Autopsy
Correct Key: Option B
Diagnostic Explanation
Concept:Neurotransmitters can either encourage a neuron to fire (excitatory) or prevent it from firing (inhibitory).
Solution:- GABA (Gamma-Aminobutyric Acid) is the primary inhibitory neurotransmitter in the human central nervous system. It works by opening chloride channels, causing hyperpolarization and making it harder for the postsynaptic neuron to reach action potential threshold.
Why other options are incorrect:- Excitatory: Glutamate is the main excitatory neurotransmitter, performing the opposite function of GABA.
- Enzyme / Hormone: GABA is an amino acid derivative acting as a local synaptic messenger, not a systemic hormone or catalyst.
#29 of 70
SZABMU 2023
Permalink
What is the fate of neurotransmitters after provoking impulse in postsynaptic membrane?
A
Stay in synaptic cleft indefinitely
B
Recycled in synaptic cleft
D
Taken up by postsynaptic membrane
View Answer & Propolis Autopsy
Correct Key: Option C
Diagnostic Explanation
Concept:For clear and precise neural signaling, the synaptic cleft must be rapidly cleared of neurotransmitters once the message is delivered.
Solution:- To prevent continuous, paralyzing over-stimulation, neurotransmitters are swiftly removed. While some undergo presynaptic reuptake, a primary and definitive fate (especially for Acetylcholine) is being rapidly degraded by specific enzymes (like acetylcholinesterase) directly in the cleft.
Why other options are incorrect:- Stay indefinitely: This would cause lethal tetanic spasms or complete desensitization.
- Taken up by postsynaptic: Reuptake strictly occurs into the presynaptic neuron, not postsynaptic.
#30 of 70
ETEA 2023
Permalink
The size of synaptic cleft in electrical synapse is:
View Answer & Propolis Autopsy
Correct Key: Option C
Diagnostic Explanation
1. Concept:Synapses transmit nerve impulses either electrically or chemically. In an electrical synapse, pre- and post-synaptic membranes are in extreme proximity and connected by gap junctions (connexons), enabling direct and rapid ionic current flow.
2. Textbook Specification (KPK Biology / ETEA):According to the KPK Textbook Board Biology syllabus (Chapter: Nervous Coordination), the synaptic cleft in an
electrical synapse is only
0.2 nm wide, whereas in a
chemical synapse, the cleft is significantly wider at approximately
20 nm (or 20-30 nm).
3. Solution:- Electrical synapse synaptic cleft: 0.2 nm (Option C).
- Chemical synapse synaptic cleft: Approximately 20 nm.
4. Why other options are incorrect:- Option A (20nm): Characteristic cleft width of a chemical synapse.
- Option B (2nm): While certain international physiology references quote the physical gap of connexons as ~2 nm (20 Å), the authoritative KPK textbook line tested in ETEA examinations explicitly establishes 0.2 nm.
- Option C (0.2nm): Correct. Verbatim textbook specification for the electrical synapse cleft in the KPK MDCAT/ETEA curriculum.
- Option D (200nm): Disproportionately large for any anatomical synaptic cleft.
#31 of 70
ETEA 2023
Permalink
Which type of nerve impulse occurs in non-myelinated neuron fibers?
View Answer & Propolis Autopsy
Correct Key: Option D
Diagnostic Explanation
Concept:The presence or absence of myelin radically alters how an action potential propagates along the axon membrane.
Solution:- In non-myelinated neurons, voltage-gated channels are distributed evenly along the entire length of the axon. The action potential must depolarize every single adjacent patch of the membrane consecutively, resulting in a continuous impulse.
Why other options are incorrect:- Saltatory / Jumping impulse: These describe the highly rapid propagation in myelinated fibers, where the signal "jumps" between the nodes of Ranvier.
- Rapid impulse: Continuous conduction is comparatively very slow, not rapid.
#32 of 70
ETEA 2023 Retake
Permalink
What brings membrane potential to threshold?
A
Outflow of odium ions across the post synaptic membrane
B
Influx of sodium ions across the post synaptic membrane
C
Outflow of calcium ions across the post synaptic membrane
D
Influx of potassium ions the post synaptic membrane
View Answer & Propolis Autopsy
Correct Key: Option B
Diagnostic Explanation
Concept:Excitation of a neuron requires shifting its resting negative voltage towards a more positive critical threshold (-55 mV) to fire an action potential.
Solution:- When excitatory neurotransmitters bind to receptors on the post-synaptic membrane, they trigger ligand-gated sodium channels to open. The subsequent influx of positively charged sodium (\(\text{Na}^+\)) ions reduces the negative charge inside the cell, driving the membrane potential up to the threshold.
Why other options are incorrect:- Outflow of sodium / Influx of potassium: These ion movements would generally hyperpolarize the cell (make it more negative), moving it away from the threshold.
- Calcium: Primarily involved in neurotransmitter exocytosis at the terminal, not the initial postsynaptic depolarization in typical neurons.
#33 of 70
NUMS 2023
Permalink
Site of the production of neurotransmitter is:
View Answer & Propolis Autopsy
Correct Key: Option D
Diagnostic Explanation
Concept:Neurotransmission is a highly directional process requiring the sender cell to manufacture and store chemical messengers.
Solution:- Neurotransmitters are synthesized, packaged into synaptic vesicles, and stored within the terminal buttons of the presynaptic neuron. Upon receiving an action potential, this presynaptic neuron releases them into the cleft.
Why other options are incorrect:- Post synaptic neuron: The receiver of the neurotransmitters.
- Synaptic cleft: The empty physical gap between the cells; nothing is produced here.
- Dendrite: The primary receiving structure, not the production/release site.
#34 of 70
NUMS 2023
Permalink
The junction between two neurons is:
View Answer & Propolis Autopsy
Correct Key: Option C
Diagnostic Explanation
Concept:Neurons form complex communication networks by forming highly specialized junction points.
Solution:- The functional connection where a nerve impulse is transmitted from one neuron to another is biologically defined as a synapse. It encompasses the presynaptic terminal, the cleft, and the postsynaptic membrane.
Why other options are incorrect:- Cleft: Refers strictly to the empty space within the synapse, not the functional junction as a whole.
- Axon / Impulse: Parts of a single neuron's structure and electrical activity.
#35 of 70
UHS 2023
Permalink
The pressure receptors that receive deep pressure stimulus in human body are called:
View Answer & Propolis Autopsy
Correct Key: Option D
Diagnostic Explanation
Concept:Mechanoreceptors in the skin are layered based on their function; superficial receptors detect light touch, while deeper receptors detect heavy force.
Solution:- Pacinian corpuscles are large, onion-like encapsulated nerve endings located deep within the dermis and hypodermis. They are specifically tuned to detect deep pressure and high-frequency vibrations.
Why other options are incorrect:- Meissner Corpuscles: Located near the skin surface to detect light touch and texture.
- Red blood Corpuscles: Erythrocytes (carry oxygen), not nervous tissue.
- Cholesterol: A structural lipid molecule.
#36 of 70
NUMS 2022
Permalink
Touch receptors are:
View Answer & Propolis Autopsy
Correct Key: Option C
Diagnostic Explanation
Concept:Mechanoreceptors in the skin are specialized to detect different mechanical stimuli such as touch, pressure, and vibration.
Solution:- Meissner's corpuscles are encapsulated nerve endings located in the dermal papillae, primarily responsible for detecting light touch and low-frequency vibration.
Why other options are incorrect:- Pacinian's corpuscles: Specifically detect deep pressure and high-frequency vibration.
- Olfactory receptors: Chemoreceptors located in the nasal cavity for smell.
- Nociceptors: Specialized free nerve endings that detect pain.
#37 of 70
DUHS 2022
Permalink
They detect pain and tissue damage:
View Answer & Propolis Autopsy
Correct Key: Option C
Diagnostic Explanation
Concept:Different sensory receptors are tuned to specific modalities of stimuli to protect and inform the body.
Solution:- Nociceptors are specialized sensory receptors that respond to damaging or potentially damaging stimuli by sending "possible threat" signals to the spinal cord and brain, resulting in the perception of pain.
Why other options are incorrect:- Baroreceptors: Detect changes in blood pressure.
- Chemoreceptors: Detect chemical changes (e.g., blood pH, taste, smell).
- Mechanoreceptors: Detect physical deformation like touch or pressure, but not inherently pain.
#38 of 70
NUMS 2022
Permalink
A long extension of nerve cell is called:
View Answer & Propolis Autopsy
Correct Key: Option A
Diagnostic Explanation
Concept:Neurons require specific anatomical structures to project signals across the body.
Solution:- The axon is the singular, long cytoplasmic extension of a neuron dedicated to carrying action potentials away from the soma.
Why other options are incorrect:- Auxins: These are plant hormones, completely unrelated to human neurobiology.
- Schwann cells: Glial cells, not extensions of the neuron.
- Dendrites: Usually short, tapering, and highly branched structures.
#39 of 70
SZABMU 2022
Permalink
Which axon would transmit an action potential most rapidly?
A
1 mm diameter neuron lacking myelin
B
1 mm diameter neuron with myelin
C
2 mm diameter neuron lacking myelin
D
2 mm diameter neuron with myelin
View Answer & Propolis Autopsy
Correct Key: Option D
Diagnostic Explanation
Concept: Factors influencing nerve conduction velocity.
Solution: Conduction speed increases with larger axon diameter and myelination. Myelination enables rapid saltatory conduction across nodes of Ranvier.
#40 of 70
ETEA 2022
Permalink
The type of neuron that carries nerve impulse from tissue and organ to the spinal cord and brain is:
View Answer & Propolis Autopsy
Correct Key: Option A
Diagnostic Explanation
Concept:Neural pathways are directional. Afferent pathways bring signals IN, while efferent pathways send signals OUT.
Solution:- Sensory (afferent) neurons detect stimuli in peripheral tissues and organs and carry those electrical impulses towards the Central Nervous System (spinal cord and brain) for integration.
Why other options are incorrect:- Motor neuron: Carries signals away from the CNS to effectors.
- Intermediate / Associative neuron: Synonymous with interneurons; located entirely within the CNS to process information.
#41 of 70
NUMS 2022
Permalink
An automatic, involuntary response to any change external or internal is called:
View Answer & Propolis Autopsy
Correct Key: Option A
Diagnostic Explanation
Concept:Nervous systems provide rapid, hardwired responses to specific stimuli to maintain homeostasis and avoid danger.
Solution:- A reflex is strictly defined as an automatic, involuntary, and virtually instantaneous movement or internal physiological response to a stimulus.
Why other options are incorrect:- Instinct: A complex, inherited pattern of behavior, not a simple physiological response.
- Taxis / Tropism: Directional movements in simpler organisms or plants in response to light, gravity, or chemicals.
#42 of 70
BUMHS 2022
Permalink
During an involuntary action, nerve impulse is passed through a pathway called:
A
Reflex action of nerve impulse
B
Reflex action of glands
C
Reflex arc and reflex action
View Answer & Propolis Autopsy
Correct Key: Option D
Diagnostic Explanation
Concept:Anatomical structures create the specific "wiring" for physiological behaviors.
Solution:- The actual anatomical pathway that a nerve impulse travels along to produce a reflex is termed the reflex arc. It structurally consists of the receptor, sensory neuron, integration center, motor neuron, and effector.
Why other options are incorrect:- Reflex action is the functional behavior or result (e.g., pulling your hand away), whereas the reflex arc is the physical pathway itself.
#43 of 70
ETEA 2022
Permalink
The resting membrane potential of neuron is measured about:
View Answer & Propolis Autopsy
Correct Key: Option C
Diagnostic Explanation
Concept:When a neuron is not transmitting a signal, there is a stable, uneven distribution of ions across its membrane.
Solution:- The interior of a typical resting neuron is negatively charged relative to the exterior. This difference in electrical charge is the resting membrane potential, globally accepted to be approximately -70 millivolts (mV).
Why other options are incorrect:- -30 mV: Incorrect resting value.
- +50 mV: Represents the peak of an active action potential.
- 100 mV: Not a physiological resting state for human neurons.
#44 of 70
UHS 2022
Permalink
The neurotransmitter active outside CNS (Central Nervous System) is:
View Answer & Propolis Autopsy
Correct Key: Option A
Diagnostic Explanation
Concept:Neurotransmitters have specific functional domains within the body.
Solution:- Acetylcholine is the quintessential peripheral neurotransmitter. It is solely responsible for bridging the gap between motor neurons and skeletal muscle cells (neuromuscular junction) and is widely active in the autonomic nervous system outside the brain and spinal cord.
Why other options are incorrect:- Dopamine, Glutamate, Serotonin: While they may have some peripheral effects, they are overwhelmingly characterized as central nervous system (CNS) neurotransmitters responsible for mood, cognition, and motor regulation in the brain.
#45 of 70
NUMS 2022
Permalink
Molecules responsible for conveying message from one neuron to the next are called:
View Answer & Propolis Autopsy
Correct Key: Option C
Diagnostic Explanation
Concept:Action potentials cannot jump physical gaps; they require a chemical intermediary.
Solution:- Neurotransmitters are the packaged molecules stored in presynaptic vesicles that diffuse across the synaptic cleft to convey the neural message to the receptors of the adjacent post-synaptic neuron.
Why other options are incorrect:- Hormones: Transported via blood over long distances.
- Enzymes: Proteins that speed up reactions (e.g., Acetylcholinesterase breaks down the message, rather than conveying it).
#46 of 70
NUMS 2022
Permalink
The gap between neurons at a synapse is:
View Answer & Propolis Autopsy
Correct Key: Option B
Diagnostic Explanation
Concept:Neurons in a chemical synapse do not physically touch; they maintain a microscopic separation.
Solution:- The literal physical gap (approximately 20-30 nanometers wide) separating the presynaptic terminal from the postsynaptic membrane is anatomically termed the synaptic cleft.
Why other options are incorrect:- Synaptic knob: The swollen end of the presynaptic axon.
- Synaptic vesicle: The sacs inside the knob holding the neurotransmitters.
- Synaptic delay: The brief fraction of a millisecond it takes for the chemical process to occur, not a structural space.
#47 of 70
UHS 2022
Permalink
The part of brain which guides smooth and accurate motions and maintains body position is:
View Answer & Propolis Autopsy
Correct Key: Option B
Diagnostic Explanation
Concept:Motor commands originate in the cerebrum, but they must be refined and coordinated for fluid movement.
Solution:- The cerebellum (the "little brain" at the back of the skull) acts as a high-speed computer that calculates and refines muscular contractions, ensuring motions are smooth, accurate, and that posture and balance are seamlessly maintained.
Why other options are incorrect:- Cerebrum: Initiates voluntary movement but does not do the fine-tuning for balance.
- Medulla / Pons: Control vital autonomic functions like heart rate and breathing rhythms.
#48 of 70
SZABMU 2022
Permalink
The feelings and emotions of love and hate are controlled by:
View Answer & Propolis Autopsy
Correct Key: Option A
Diagnostic Explanation
Concept:The limbic system is the emotional brain, with specific sub-structures handling different emotional valences.
Solution:- The amygdala is an almond-shaped cluster of nuclei deep within the temporal lobe. It is fundamentally responsible for processing intense emotional responses, aggressive behaviors, fear, and strong feelings of love and hate.
Why other options are incorrect:- Hippocampus: Primarily involved in consolidating short-term memory into long-term memory.
- Thalamus: The sensory relay station.
- Hypothalamus: Homeostatic regulation (hunger, thirst, body temp).
#49 of 70
ETEA 2022
Permalink
The hind brain is comprised of all of the following except:
View Answer & Propolis Autopsy
Correct Key: Option C
Diagnostic Explanation
Concept:The brain is divided embryologically into the forebrain, midbrain, and hindbrain.
Solution:- The hindbrain (rhombencephalon) consists strictly of the pons, the medulla oblongata, and the cerebellum. The cerebrum, however, is the largest structure of the completely separate forebrain (prosencephalon).
Why other options are incorrect:- Options A, B, and D are all anatomically correct components of the hindbrain.
#50 of 70
DUHS 2022
Permalink
It is the site of all conscious activity:
View Answer & Propolis Autopsy
Correct Key: Option B
Diagnostic Explanation
Concept:Higher-order cognitive processing requires a massive network of unmyelinated neuronal cell bodies.
Solution:- The cerebral cortex (the highly convoluted outer layer of the cerebrum) is responsible for all conscious thought, sensory perception, voluntary movement initiation, language, and reasoning.
Why other options are incorrect:- Hind brain / Mid brain / Spinal cord: These regions deal with subconscious, involuntary, autonomic survival functions and reflex arcs.
#51 of 70
DUHS 2022
Permalink
Spinal cord comes out from the cranium though an opening known as:
View Answer & Propolis Autopsy
Correct Key: Option A
Diagnostic Explanation
Concept:The central nervous system is continuous, transitioning from the brain to the spinal cord as it exits the skull.
Solution:- The foramen magnum (Latin for "great hole") is the large opening at the base of the occipital bone through which the medulla oblongata extends downward to become the continuous spinal cord.
Why other options are incorrect:- Acetabulum: The hip socket where the femur attaches.
- Lumen: The hollow inside space of a tubular structure like a blood vessel.
- Ganglion: A cluster of nerve cell bodies in the peripheral nervous system.
#52 of 70
ETEA 2022
Permalink
Those nerves that originate from or lead to the brain are called cerebral nerves. These are ____ pairs of cerebral nerves in human.
View Answer & Propolis Autopsy
Correct Key: Option B
Diagnostic Explanation
Concept:The peripheral nervous system connects directly to the central nervous system via distinct sets of paired nerves.
Solution:- Cerebral nerves (commonly known as cranial nerves) emerge directly from the brain and brainstem. In humans, there are exactly 12 pairs of cranial nerves (e.g., Optic, Vagus, Olfactory).
Why other options are incorrect:- 31 pairs: Refers to the number of spinal nerves.
- 6 and 14: Are incorrect anatomical counts.
#53 of 70
PMC 2020
Permalink
Which one of the following is common to all neurons?
A
A cell body which contains a nucleus
B
Presence of node of Ranvier
D
Presence of Schwann cells
View Answer & Propolis Autopsy
Correct Key: Option A
Diagnostic Explanation
Concept:Neurons come in many morphological classifications (unipolar, bipolar, multipolar), but they share fundamental cellular necessities.
Solution:- Regardless of type, every functional neuron must have a soma (cell body) containing a nucleus to direct protein synthesis and maintain cellular metabolism.
Why other options are incorrect:- Nodes of Ranvier, Myelin Sheath, Schwann Cells: These are characteristic of myelinated neurons only. Unmyelinated neurons lack these structures entirely.
#54 of 70
PMC 2020
Permalink
Neurons are cells adapted for the rapid transmission of electrical impulses. To do this, they have long thin processes called:
View Answer & Propolis Autopsy
Correct Key: Option A
Diagnostic Explanation
Concept:The morphology of a neuron is perfectly adapted for long-distance communication.
Solution:- Axons are the elongated, thin processes (fibers) that conduct electrical impulses (action potentials) away from the cell body over long distances (sometimes up to a meter in humans) to target effectors or other neurons.
Why other options are incorrect:- Dendrites: Typically short and highly branched; they receive signals rather than transmitting them over long distances.
- Myelin sheath / Schwann cell: These insulate the axon to speed up transmission, but they are not the "process" itself.
#55 of 70
PMC 2020
Permalink
Which of the following neurotransmitters function, both as neurotransmitter and hormones, decreasing our perception of pain?
View Answer & Propolis Autopsy
Correct Key: Option D
Diagnostic Explanation
Concept:The body has endogenous analgesic (pain-relieving) systems to cope with extreme stress or physical exertion.
Solution:- Endorphins (endogenous morphines) are neuropeptides produced by the central nervous system and pituitary gland. They bind to opiate receptors to significantly block pain signals and can induce feelings of euphoria.
Why other options are incorrect:- Epinephrine / Dopamine / Serotonin: While they affect mood and the "fight or flight" response, they are not primarily known as the body's natural painkillers.
#56 of 70
ETEA 2019
Permalink
____ is considered as chief structural and functional unit of nervous system.
View Answer & Propolis Autopsy
Correct Key: Option B
Diagnostic Explanation
Concept:Every organ system is built upon a foundational cellular unit that performs its primary functions.
Solution:- The neuron (or nerve cell) is the core component of the nervous system, uniquely specialized for generating, propagating, and transmitting electrochemical impulses.
Why other options are incorrect:- Nephron: The structural and functional unit of the kidney.
- Brain: The central processing organ, not the microscopic foundational unit.
- Cell: Too generic; many cells (like glia) support the nervous system but do not transmit primary impulses.
#57 of 70
MDCAT 2019
Permalink
The reflex action is the phenomena which only involves:
A
Brain, receptors, spinal cord
B
Receptors, neurons, brain
C
Receptors, effectors and spinal cord
D
Receptors and effectors
View Answer & Propolis Autopsy
Correct Key: Option C
Diagnostic Explanation
Concept:A spinal reflex arc is an involuntary, rapid response mechanism that bypasses conscious thought to protect the body.
Solution:- A standard spinal reflex relies purely on the peripheral and spinal pathways: it detects a stimulus (receptors), processes it at the level of the spinal cord via an interneuron, and immediately triggers a response via effectors. The brain is not actively involved in the reflex execution itself.
Why other options are incorrect:- Options involving the Brain represent conscious pathways or cranial reflexes, not the standard localized spinal reflex action meant by this specific curriculum question.
#58 of 70
MDCAT 2019
Permalink
In an action potential, the permeability of sodium ions in the neuron increases due to:
B
The action of the acetylcholinesterase enzyme
C
The opening of sodium channels/gates
D
Sodium ions forming an ionic bonding
View Answer & Propolis Autopsy
Correct Key: Option C
Diagnostic Explanation
Concept:Changes in membrane permeability are controlled by voltage-gated ion channels embedded in the lipid bilayer.
Solution:- When the membrane reaches threshold potential, voltage-gated sodium channels undergo a conformational change and open. This drastically increases the membrane's permeability to \(\text{Na}^+\), allowing a massive influx of sodium down its electrochemical gradient, triggering depolarization.
Why other options are incorrect:- Repolarization: Occurs due to the closing of sodium gates and the opening of potassium gates.
- Acetylcholinesterase: An enzyme that breaks down neurotransmitters in the synaptic cleft, unrelated to axonal sodium gates.
#59 of 70
MDCAT 2019
Permalink
If stimulation is above _, impulses travel to the brain along the sensory neuron.
View Answer & Propolis Autopsy
Correct Key: Option C
Diagnostic Explanation
Concept:Neurons obey the "all-or-none" principle. An action potential is only fired if a specific voltage criteria is met.
Solution:- The threshold potential (usually around -55 mV) is the critical level to which a membrane potential must be depolarized to initiate an action potential. If a stimulus brings the membrane above this threshold, a full impulse is generated and sent to the brain.
Why other options are incorrect:- Action Potential: This is the result, not the triggering requirement.
- Resting Potential: The baseline state. A stimulus must exceed resting potential significantly to reach threshold.
#60 of 70
AJK 2019
Permalink
Impulses jump across synapse in the form of chemical messenger such as:
View Answer & Propolis Autopsy
Correct Key: Option D
Diagnostic Explanation
Concept:Synaptic clefts are bridged by specialized neurochemical compounds.
Solution:- Dopamine is a major biogenic amine neurotransmitter in the central nervous system, heavily involved in motor control, reward pathways, and mood regulation. It carries the impulse chemically across the synapse.
Why other options are incorrect:- Glutamine, Arginine, Leucine: These are standard amino acids primarily used for protein synthesis or metabolic precursors, and are not classical neurotransmitters in this specific context (though Glutamine is a precursor to Glutamate, it is not the active messenger itself).
#61 of 70
MDCAT 2018
Permalink
Taste buds on the tongue are example of:
View Answer & Propolis Autopsy
Correct Key: Option D
Diagnostic Explanation
Concept:Gustation (taste) is fundamentally a chemical sense.
Solution:- Taste buds contain gustatory cells that bind to specific food molecules (tastants) dissolved in saliva. Because they detect chemical substances, they are classified as chemoreceptors.
Why other options are incorrect:- Thermoreceptors / Pressure receptors: Present on the tongue for temperature and texture, but they are not the taste buds themselves.
- Photoreceptors: Found only in the retina of the eye.
#62 of 70
MDCAT 2018
Permalink
How many sodium ions are pumped out in response to two potassium ions transported into the membrane?
View Answer & Propolis Autopsy
Correct Key: Option D
Diagnostic Explanation
Concept:The resting membrane potential is actively maintained by an electrogenic pump powered by ATP.
Solution:- The Sodium-Potassium Pump (\(\text{Na}^+/\text{K}^+\) ATPase) utilizes one molecule of ATP to actively transport 3 \(\text{Na}^+\) ions out of the cell while simultaneously bringing 2 \(\text{K}^+\) ions into the cell. This 3:2 ratio maintains the negative charge inside the membrane.
Why other options are incorrect:- Options 1, 2, and 4 do not reflect the strict stoichiometric 3:2 ratio characteristic of this fundamental cellular pump.
#63 of 70
MDCAT 2018
Permalink
When a nerve impulse jumps from one node of Ranvier to the next in a myelinated neuron, it is called
View Answer & Propolis Autopsy
Correct Key: Option A
Diagnostic Explanation
Concept:Myelination alters how action potentials propagate, making the nervous system highly efficient.
Solution:- Because the myelin sheath prevents ion leakage, depolarization can only occur at the exposed gaps known as Nodes of Ranvier. The impulse appears to "leap" from node to node, a phenomenon strictly termed saltatory conduction.
Why other options are incorrect:- Resting / Membrane potential: Refer to voltage states, not the physical movement of the impulse.
- Synapses: The junction between two entirely separate cells.
#64 of 70
MDCAT 2018
Permalink
In nervous system, chemical messengers are called
View Answer & Propolis Autopsy
Correct Key: Option C
Diagnostic Explanation
Concept:Chemical signaling depends on the system utilized (Nervous vs. Endocrine).
Solution:- In the nervous system, the highly specific endogenous chemicals that transmit signals across a synaptic cleft from one neuron to another target cell are specifically called neurotransmitters.
Why other options are incorrect:- Hormones: Chemical messengers of the endocrine system that travel via the bloodstream.
- Enzymes: Biological catalysts, not signaling messengers.
- Chemoreceptors: The sensory structures that detect chemicals.
#65 of 70
MDCAT 2017
Permalink
Which of the following produce response?
View Answer & Propolis Autopsy
Correct Key: Option A
Diagnostic Explanation
Concept:In the nervous system, the complete pathway of a response involves a receptor, an integrating center, and an effector.
Solution:- Receptors detect the stimulus.
- Sensory neurons carry the signal to the CNS.
- Motor neurons carry the signal from the CNS to the effectors (muscles or glands), which execute the actual physical or chemical response.
Why other options are incorrect:- Nerve: Acts as a transmission cable but does not produce the final physiological response.
- Stimulators: Initiate the sensory process.
- Brain: Processes the information but relies entirely on effectors to execute the action.
#66 of 70
MDCAT 2017
Permalink
Pick out the pressure receptors.
View Answer & Propolis Autopsy
Correct Key: Option C
Diagnostic Explanation
Concept:Receptors are classified based on the type of stimulus energy they transduce into electrical signals.
Solution:- Pressure is a mechanical force. Mechanoreceptors (like Pacinian corpuscles) are specifically designed to detect mechanical deformation of the receptor membrane caused by pressure or stretch.
Why other options are incorrect:- Chemoreceptors: Respond to specific molecules/chemicals.
- Photoreceptors: Respond to photons (light).
- Thermoreceptors: Respond to changes in temperature.
#67 of 70
MDCAT 2015
Permalink
Conduction of action potentials from one node of Ranvier to another in myelinated neurons is through:
C
Resting Membrane Potential
View Answer & Propolis Autopsy
Correct Key: Option D
Diagnostic Explanation
Concept:Myelin acts as a high-resistance electrical insulator, forcing the action potential to "skip" down the axon.
Solution:- In myelinated axons, ion channels are concentrated at the nodes of Ranvier. The electrical impulse jumps from node to node, a highly efficient and rapid process known as saltatory conduction (from the Latin saltare, to jump).
Why other options are incorrect:- Depolarization / Hyperpolarization: These are phases of the action potential itself, not the mechanism of propagation along the axon length.
#68 of 70
MDCAT 2015
Permalink
In the following diagram of action potential in a neuron, '2' depicts:
View Answer & Propolis Autopsy
Correct Key: Option A
Diagnostic Explanation
Concept:An action potential graph tracks membrane voltage over time, featuring distinct phases dictated by specific ion channels opening and closing.
Solution:- Phase 1: Resting state.
- Phase 2: Depolarization. Voltage-gated \(\text{Na}^+\) channels open, allowing an influx of sodium ions, causing the membrane potential to rapidly become positive.
- Phase 3 & 4: Repolarization (falling phase).
- Phase 5: Hyperpolarization (undershoot).
Why other options are incorrect:- Repolarization: Occurs during the downward slope of the graph.
- Hyperpolarization: The dip below the baseline resting potential.
#69 of 70
MDCAT 2015
Permalink
Neurotransmitter secreted at synapse outside the central nervous system is:
View Answer & Propolis Autopsy
Correct Key: Option D
Diagnostic Explanation
Concept:Different neurotransmitters dominate different divisions of the nervous system.
Solution:- Outside the CNS, within the Peripheral Nervous System (specifically at the neuromuscular junction and in autonomic ganglia), Acetylcholine (ACh) is the primary active neurotransmitter responsible for stimulating skeletal muscles and parasympathetic responses.
Why other options are incorrect:- Dopamine: Primarily active within the brain (CNS).
- Androgen: A steroid hormone, not a neurotransmitter.
- Polypeptide: A broad category of molecules, not specific.
#70 of 70
LUMHS 2015
Permalink
For the impulse to transfer from presynaptic to post synaptic neuron, the substance required is: [LUMMHC-2015]
View Answer & Propolis Autopsy
Correct Key: Option D
Diagnostic Explanation
Concept:Exocytosis of neurotransmitters is entirely dependent on a specific extracellular ion.
Solution:- When an action potential reaches the axon terminal, it opens voltage-gated Calcium (\(\text{Ca}^{2+}\)) channels. The influx of calcium ions forces synaptic vesicles to fuse with the presynaptic membrane, releasing the chemical messenger into the cleft. Without calcium, this transfer cannot occur.
Why other options are incorrect:- Sodium / Potassium: Required for the action potential along the axon, but they do not directly trigger vesicular exocytosis.
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