Practice Questions

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.