MCQs

Synaptic fatigue occurs when the rate of neurotransmitter release exceeds the rate of its synthesis and recycling, causing a temporary failure of synaptic transmission despite incoming action potentials.

Conduction velocity is positively correlated with both axon diameter (reducing internal electrical resistance) and the presence of myelination (allowing fast saltatory conduction).

The Na⁺/K⁺ pump is an active transport ATPase that hydrolyzes ATP to move sodium and potassium against their concentration gradients, consuming a massive portion of the neuron's metabolic energy.

The patellar reflex is a monosynaptic spinal stretch reflex mediated specifically by the femoral nerve and the lumbar spinal cord segments L2, L3, and L4.

The efferent (motor) pathway carries signals away from the CNS to the target effectors (muscles or glands). The afferent (sensory) pathway carries signals toward the CNS.

Reciprocal inhibition ensures coordinated movement by using inhibitory interneurons to relax antagonistic muscles while excitatory pathways stimulate the agonist muscles.

Contralateral reflex arcs (e.g., the crossed extensor reflex) involve interneurons that cross the spinal cord midline to produce a motor response on the side of the body opposite to the stimulus.

GABA is the major inhibitory neurotransmitter in the brain, functioning primarily by opening chloride channels on postsynaptic neurons to induce hyperpolarization. Glutamate is the major excitatory neurotransmitter.

Temporal summation occurs when a single presynaptic neuron fires multiple times in rapid succession, allowing the resulting graded potentials to add together before the previous ones dissipate.

Multiple sclerosis is an autoimmune disorder characterized by the progressive demyelination of axons in the CNS, which disrupts saltatory conduction and leads to severe neurological deficits.

Because the membrane segment immediately behind the advancing action potential is in its refractory period (Na⁺ channels are inactivated), the impulse cannot spread backward, ensuring unidirectional propagation.

Nodes of Ranvier are the unmyelinated gaps between adjacent myelin segments (internodes) where action potentials are regenerated during saltatory conduction.

Parkinson's disease is characterized by the selective death of dopaminergic neurons in the substantia nigra of the midbrain, leading to tremors, rigidity, and loss of motor control.

Acetylcholinesterase (AChE) is the enzyme located in the synaptic cleft that rapidly hydrolyzes ACh into acetate and choline, terminating the synaptic signal to prevent continuous stimulation.

Spatial summation is the additive effect of graded potentials occurring at different physical locations (synapses) on the neuron at the same time. Temporal summation occurs at a single synapse over time.

Opening Cl⁻ channels (allowing Cl⁻ influx) or K⁺ channels (allowing K⁺ efflux) leads to hyperpolarization, moving the membrane potential further away from the threshold and inhibiting the neuron.

An EPSP involves the opening of cation channels (usually Na⁺), leading to a localized, graded depolarization that makes the postsynaptic neuron more likely to fire an action potential.

Neurotransmitters bind to specific ligand-gated receptors on the postsynaptic membrane, which undergo a conformational change to open ion channels and generate graded potentials.

Acetylcholine (ACh) is the primary neurotransmitter of the parasympathetic nervous system (both pre- and postganglionic), while the sympathetic system predominantly relies on norepinephrine for postganglionic signaling.