Special Senses 2

Chemoreceptors on the tongue that detect dissolved molecules

Chemoreceptors

Capsaicin activates pain receptors → creates illusion of heat

Capsaicin

Cranial Nerve I (olfactory nerve)

Cranial Nerve I

Smell (olfaction)

Smell

Olfactory pathways connect to the hippocampus

Olfactory pathways

Clear, curved outer layer with many nerve endings

Cornea

Controls pupil size and eye color

Iris

Opening where light enters the eye

Pupil

What adjusts the lens for focusing?

Ciliary muscles

White outer layer of the eye

Sclera

Transparent membrane covering eye; inflamed in conjunctivitis

Conjunctivitis

Image focuses before the retina

Myopia

Image focuses behind the retina

Hyperopia

Blood in the anterior chamber of the eye

Hyphema

Extremely painful due to high nerve density in cornea

Corneal abrasions

Detects light and dark (black/white vision)

Rod cells

Detect color vision

Cone cells

High cone concentration; central vision

Macula

Part of macula responsible for sharpest vision

Fovea

Clumps in vitreous humor casting shadows on retina

Floaters

Uses rods only; rods can't detect color

Peripheral vision

Optic nerve exits retina; no photoreceptors

Blind spot

Human photoreceptors face backward; light passes through other cell layers first

Inverted retina

X chromosome

Color vision genes

One X chromosome only—no backup

Color blindness

What is the most common inherited color vision deficiency?

Red-green color blindness

Loss of all three cone types (rare total color blindness)

Trichromatopsia

Outer, middle, and inner ear

Ear parts

Malleus → Incus → Stapes

Ossicles

What connects the middle ear to the throat for pressure equalization?

Eustachian tube

Which cranial nerve carries hearing and balance information?

Vestibulocochlear nerve

Spiral-shaped hearing organ in the inner ear

Cochlea

Organ in the cochlea containing hair cells for sound detection

Organ of Corti

Base of cochlea (short, stiff hairs)

High-pitched sounds

Apex of cochlea (long, flexible hairs)

Low-pitched sounds

Sounds above 80 decibels

Hearing damage

Detect rotational (angular) movements

Semicircular canals

Detect gravity and linear acceleration

Utricle and saccule

Calcium carbonate 'ear rocks' in vestibular system

Otoliths

Sensory mismatch between visual and vestibular system

Motion sickness