MCQs

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.

Bitter taste evolved as a protective mechanism against ingesting plant toxins, which are frequently alkaloids (like quinine, caffeine, and nicotine) or other nitrogenous compounds.

Otoliths (or otoconia) are heavy calcium carbonate crystals in the maculae of the utricle and saccule. Gravity pulls on them, shifting the gelatinous membrane and bending the underlying hair cells.

Many rod cells converge onto a single bipolar cell (and many bipolar cells onto a ganglion cell), increasing light sensitivity through spatial summation but sacrificing visual acuity. Cones have a 1:1 ratio in the fovea.

Lateral inhibition occurs when a strongly stimulated central neuron inhibits its less-stimulated neighbors via interneurons. This isolates the signal, improving stimulus localization and contrast.

The fingertips have extremely high densities of Meissner's corpuscles and Merkel discs with very small receptive fields, allowing for precise two-point discrimination and fine tactile resolution.

The axons of primary olfactory sensory neurons travel through the porous cribriform plate of the ethmoid bone to synapse with mitral and tufted cells in the olfactory bulb.

Pulmonary stretch receptors are a type of mechanoreceptor located in the smooth muscle of the airways. They detect mechanical deformation (stretching) during inspiration (Hering-Breuer reflex).