MCQs

At the optic chiasm, fibers from the medial (nasal) half of each retina cross over (decussate) to the opposite side of the brain, while lateral (temporal) fibers stay on the same side.

Peripheral chemoreceptors located in the aortic arch and carotid bodies are highly sensitive to drops in arterial PO2​, triggering an increase in respiratory rate. Central chemoreceptors monitor CO2​ and pH, not O2​.

The sensory homunculus is a distorted topographical map of the body in the postcentral gyrus. Areas with high receptor density (lips, fingers) are represented by much larger areas of the cortex than regions with low density (back).

Visual information from the retinas travels via the optic nerve, optic chiasm, and optic tracts to the lateral geniculate nucleus of the thalamus, and finally projects to the primary visual cortex in the occipital lobe.

Calcium influx through voltage-gated calcium channels is absolutely essential for the exocytosis of neurotransmitter vesicles. Low extracellular calcium directly impairs this release mechanism.

The gate control theory suggests that non-painful tactile stimuli (rubbing) carried by fast, myelinated A-beta fibers activate inhibitory interneurons in the spinal cord, "closing the gate" to pain signals carried by slower C fibers.

The cerebellum receives continuous input from proprioceptors, the vestibular apparatus, and the eyes, integrating this information to coordinate smooth movements, posture, and equilibrium.

Sweet, bitter, and umami tastants bind to specific G-protein coupled receptors (GPCRs), activating secondary messenger cascades (like IP3/DAG) that eventually lead to cell depolarization. Salty and sour use direct ion channels.

Taste receptor cells are subjected to friction and heat, surviving only about 10-14 days. Basal cells at the periphery of the taste bud divide and differentiate to constantly replace them.

Unlike typical extracellular fluids, endolymph is rich in potassium and low in sodium. This high K+ concentration provides the electrochemical gradient that drives K+ into hair cells when mechanically gated channels open.

Sound waves vibrate the tympanic membrane, which moves the malleus, then the incus, and finally the stapes. The footplate of the stapes pushes directly into the oval window, transmitting pressure waves into the cochlear fluid.

Light activates phosphodiesterase, which aggressively breaks down cGMP. The drop in cGMP closes sodium channels, leading to the hyperpolarization of the rod cell.

Ruffini endings are deep, slowly adapting receptors that are highly sensitive to skin stretch, contributing significantly to kinesthetic sense and the control of finger position and grip.

In the dark, photoreceptors are depolarized and steadily release glutamate. This glutamate binds to inhibitory metabotropic receptors on ON-center bipolar cells, keeping them hyperpolarized (inactive) in the dark.

To focus on near objects (accommodation), the ciliary muscle contracts, acting like a sphincter. This releases tension on the suspensory ligaments, allowing the elastic lens to bulge and become more convex.

While the lens provides adjustable focus (accommodation), the cornea has a fixed curvature and the largest difference in optical density compared to air, providing about 70-80% of the eye's total refractive power.

The absolute threshold is the lowest level of stimulus energy that an organism can consciously detect consistently.

Unlike all other senses, the olfactory pathway routes directly from the olfactory bulb to the olfactory cortex (in the temporal lobe) without synapsing first in the thalamus.

Referred pain happens when sensory fibers from an organ (e.g., heart) and a somatic region (e.g., left arm) synapse on the same second-order neurons. The brain interprets the pain as coming from the more frequently stimulated somatic area.