Chapter 15: The Special Senses

Flashcards testing concepts of the special senses—olfaction, gustation, vision, hearing, and equilibrium—based on lecture notes.

Where is the olfactory epithelium located within the nasal cavity?

In the superior nasal cavity in the olfactory region.

Approximately how many olfactory neurons are located in the olfactory epithelium?

10 million olfactory neurons.

What are the enlarged ends of the dendrites of olfactory neurons called?

Olfactory vesicles.

What cellular signaling sequence occurs when an odorant binds to an odorant receptor on an olfactory hair?

The odorant activates a G protein, which activates adenylate cyclase to form cyclic AMP (cAMP) from ATP. cAMP then causes $\text{Na}^+$ and $\text{Ca}^{2+}$ channels to open, leading to influx of ions, depolarization, and action potentials.

How frequently are olfactory receptors replaced in the olfactory epithelium?

About every two months from basal cells.

Which major primary sense conveys sensory signals directly to the cerebral cortex without passing through the thalamus?

Olfaction (sense of smell).

What are the four main types of tongue papillae, and which type lacks taste buds?

Filiform, vallate, foliate, and fungiform papillae; filiform papillae do not contain taste buds.

How frequently are taste cells in a taste bud replaced?

Every 10 days.

Which primary taste sensation exhibits the highest sensitivity and lowest threshold?

Bitter (produced by toxic alkaloids).

Which cranial nerves carry taste sensations from different regions of the mouth and pharynx?

The chorda tympani (branch of facial nerve, VII) carries taste from the anterior two-thirds of the tongue; the glossopharyngeal nerve (IX) carries taste from the posterior one-third, vallate papillae, and superior pharynx; and the vagus nerve (X) carries taste from the tongue root and epiglottis.

Where are the primary cortical taste areas located in the cerebrum?

In the insula, deep within the lateral fissure between the temporal and parietal lobes.

What are the three structural layers or tunics that compose the wall of the eyeball?

The fibrous tunic (sclera and cornea), vascular tunic (choroid, ciliary body, iris), and nervous tunic (retina).

Which extrinsic eye muscle originates from the body of the sphenoid bone and passes its tendon through a trochlea?

The superior oblique muscle.

Which structure of the eye produces aqueous humor?

The ciliary processes of the ciliary body.

What are the functions and autonomic innervations of the sphincter pupillae and dilator pupillae muscles?

The sphincter pupillae is innervated by parasympathetic fibers (CN III) and contracts to decrease pupil size; the dilator pupillae is innervated by sympathetic fibers and contracts to increase pupil size.

What region of the retina provides the highest visual acuity?

The fovea centralis (located within the macula).

What range of electromagnetic radiation constitutes visible light detectable by the human eye?

$$380\text{ to }750\text{ nm}$$

What changes occur in the ciliary body and lens during accommodation for near vision?

Ciliary muscles contract, moving the ciliary body toward the lens and reducing tension on the suspensory ligaments, allowing the lens to become rounded/spherical.

How is myopia (nearsightedness) defined, and how is it optically corrected?

Myopia occurs when the focal point is in front of the retina because the refractive power is too strong or the eyeball is too long; it is corrected with a concave lens.

What visual pigment is present in rod photoreceptors, and what are its two constituent parts?

Rhodopsin, which consists of opsin bound to retinal.

How does exposure to light affect the membrane potential and neurotransmitter release of a rod cell?

Light activates transducin and cGMP phosphodiesterase, converting cGMP to GMP and closing $\text{Na}^+$ channels, causing hyperpolarization of the rod cell and a decrease in glutamate release.

What visual pigment is found in cone cells, and what are the three primary color sensitivities of cones?

Iodopsin; the three types of cones respond to blue, green, and red light.

Which ganglion cell axons cross to the opposite hemisphere of the brain at the optic chiasm?

Axons originating from the nasal retina (medial portion of the retina).

What structure connects the middle ear to the pharynx to equalize pressure?

The auditory (pharyngotympanic or eustachian) tube.

Which middle ear muscles attach to the malleus and stapes to dampen loud sounds?

The tensor tympani (attaches to the malleus) and the stapedius (attaches to the stapes).

How do endolymph and perilymph differ in their ion compositions?

Endolymph has high $\text{K}^+$ and low $\text{Na}^+$, while perilymph has low $\text{K}^+$ and high $\text{Na}^+$.

How does the width of the basilar membrane change along the cochlea, and how does this affect frequency detection?

The basilar membrane widens from $0.04\text{ mm}$ near the oval window (responds to high-frequency vibrations) to $0.5\text{ mm}$ near the helicotrema (responds to low-frequency vibrations).

What ion flow causes depolarization when stereocilia of hair cells bend toward the taller stereocilia?

Bending stretches tip links (gating springs), opening mechanically gated $\text{K}^+$ channels, allowing $\text{K}^+$ to flow into the hair cell from the endolymph.

Which inner ear structures evaluate static equilibrium versus dynamic equilibrium?

Static equilibrium is evaluated by the utricle and saccule (maculae) in the vestibule; dynamic equilibrium is evaluated by the crista ampullaris in the semicircular canals.

What is the medical term for age-related hearing loss?

Presbyacusis.