MCQs

Withdrawal from painful stimuli is a spinal reflex that produces a rapid response before the brain becomes consciously aware of the stimulus. The cerebrum interprets pain after the reflex has occurred.

The medulla oblongata forms the lowest part of the brain stem and is directly connected to the spinal cord, serving as a pathway for ascending and descending nerve impulses.

The cerebellum compares intended movement with actual movement and makes continuous corrections to maintain posture and balance. This function is essential during walking on uneven ground.

The cerebrum is the largest part of the brain and controls intelligence, memory, learning, reasoning, speech, emotions, and voluntary activities. The remaining options are functions of lower brain centers.

The hypothalamus acts as the body's thermostat. It detects changes in temperature and initiates sweating and vasodilation to lower body temperature.

The thalamus receives and relays almost all sensory information to the cerebral cortex. The hypothalamus regulates homeostasis, while the pons and medulla mainly conduct impulses and control autonomic functions.

The cerebellum coordinates voluntary muscle movements and maintains posture and balance. Damage produces ataxia, characterized by uncoordinated movements without causing paralysis.

The medulla oblongata contains vital autonomic centers controlling respiration, cardiac activity, and vasomotor functions. The cerebrum is involved in higher mental functions, the cerebellum coordinates movement, and the hypothalamus regulates homeostasis but does not directly control these vital reflexes.

Group A fibers (like somatic motor fibers and large sensory fibers for touch and position) are the thickest, most heavily myelinated fibers in the body, providing the fastest nerve conduction velocities.

Ependymal cells are ciliated, cuboidal-to-columnar glial cells that line the fluid-filled cavities of the CNS (ventricles and central canal) and help secrete and circulate cerebrospinal fluid.

Irritability (excitability) is the physiological ability of a neuron or muscle cell to respond to a stimulus by generating an electrical signal. Conductivity refers to its ability to transmit that signal.

Hyperkalemia reduces the concentration gradient for K⁺. As a result, less K⁺ leaves the cell through leak channels, leaving more positive charge inside and shifting the resting membrane potential toward depolarization.

In the PNS, a bundle of axons is called a nerve. In contrast, a bundle of axons in the CNS is called a tract. A ganglion is a cluster of cell bodies in the PNS.

Endorphins and enkephalins are endogenous opioids that bind to opioid receptors in the brain and spinal cord, powerfully blocking the transmission and perception of pain signals.

Axoaxonic synapses occur when one axon terminal synapses onto another axon terminal. They regulate (facilitate or inhibit) the amount of calcium that enters the second terminal, modulating neurotransmitter release.

Microglia act as the resident macrophages of the central nervous system, migrating to sites of injury or infection to clear away dead tissue, plaques, and pathogens.

The autonomic (visceral) nervous system controls involuntary physiological functions by regulating the activity of smooth muscles, cardiac muscles, and secretory glands.

Unlike acetylcholine which is destroyed by enzymes, monoamine neurotransmitters (like serotonin, dopamine, and norepinephrine) are primarily cleared by active reuptake transporters bringing them back into the presynaptic knob.

Drugs like local anesthetics (e.g., lidocaine) or neurotoxins (e.g., tetrodotoxin) block voltage-gated Na⁺ channels, preventing the massive sodium influx required to generate and propagate an action potential.