W8 | Special Senses

Olfaction

Special sense responsible for detecting smell/odor.

Olfactory Region

Region in the superior nasal cavity where smell detection occurs.

Olfactory Epithelium

Specialized epithelium containing about 10 million olfactory neurons involved in odor detection.

Olfactory Neurons

Sensory neurons that detect odor molecules.

Olfactory Hairs

Cilia extending from olfactory neurons that contain receptors for odorants.

Odorants

Airborne chemical molecules responsible for producing smells.

Olfactory Receptors

Receptors on olfactory hairs that bind odorants and initiate an olfactory response.

Olfactory Vesicles

Specialized structures at the ends of olfactory neuron dendrites from which olfactory hairs extend.

Olfactory Adaptation

Decreased sensitivity to an odor after continuous exposure.

Basal Cells

Cells that allow olfactory neurons to regenerate.

Cribriform Plate

Part of the ethmoid bone through which olfactory neuron axons pass toward the olfactory bulb.

Olfactory Bulb

Brain structure where olfactory neurons synapse with neurons that relay smell information.

Olfactory Tract

Pathway carrying olfactory information from the olfactory bulb toward the brain.

Piriform Cortex

Brain region involved in processing olfactory information.

Amygdala

Region involved in the emotional responses associated with smells.

Orbitofrontal Cortex

Brain region involved in higher processing of smell and odor perception.

Limbic System

Brain system associated with emotional and physiological responses to smells.

Olfactory neurons → Cribriform plate → Olfactory bulb → Olfactory tract → Olfactory cortex

Olfaction Pathway

Anosmia

Total or partial loss of the sense of smell

Gustation

Special sense responsible for taste.

Taste Bud

Sensory structure that detects taste stimuli.

Gustatory Cells / Taste Cells

Sensory cells within taste buds that detect tastants.

Basal Cells

Cells involved in regeneration of taste cells.

Supporting Cells

Cells that support the taste cells within a taste bud.

Taste Hairs / Microvilli

Projections from taste cells that extend through taste pores and interact with tastants.

Taste Pore

Opening through which dissolved tastants reach taste-cell microvilli.

Chemoreceptors

Taste receptors

Tastants

Chemical substances dissolved in saliva that stimulate taste cells.

Papillae

Structures on the tongue associated with taste buds.

Filiform Papillae

Most numerous papillae; do NOT contain taste buds.

Vallate Papillae

Largest papillae, arranged in a V-shape at the back of the tongue.

Foliate Papillae

Papillae especially sensitive to taste, particularly in children.

Fungiform Papillae

Papillae scattered across the surface of the tongue.

1. Salt

2. Sour

3. Sweet

4. Bitter

5. Umami

5 Tastants

Salt

Taste produced primarily when Na⁺ enters taste cells through ion channels.

Sour

Taste associated with H⁺ ions entering cells or blocking K⁺ channels.

Sweet

Taste that activates G-protein-coupled receptors.

Bitter

Taste that activates G-protein-coupled receptors; associated with detecting potentially toxic substances.

Umami

Savory taste stimulated by amino acids such as glutamate; uses G-protein mechanisms.

G Protein-Coupled Receptor (GPCR)

Receptor mechanism used especially for sweet, bitter, and umami taste detection.

Depolarization

Change in membrane potential produced when taste-cell stimulation causes the cell to become less negative.

CN VII — Facial Nerve

Carries taste from the anterior 2/3 of the tongue, excluding vallate papillae.

CN IX — Glossopharyngeal Nerve

Carries taste from the posterior 1/3 of the tongue AND vallate papillae

CN X — Vagus Nerve

Carries taste from the throat and epiglottis.

Tractus Solitarius

Brainstem pathway where taste signals travel after leaving the taste buds.

Medulla Oblongata

Brainstem region containing the tractus solitarius involved in taste processing.

Thalamus

Relay center receiving taste information before it reaches the cerebral cortex.

Insula

Cerebral region containing the taste areas where taste information is processed.

Taste buds → Tractus solitarius → Thalamus → Insula

Taste Pathway

Fibrous Tunic

Outer layer of the eyeball consisting mainly of the sclera and cornea.

Sclera

White outer layer of the eye that provides protection and shape.

Cornea

Transparent, avascular structure that allows light to enter and provides major light refraction.

Vascular Tunic

Middle layer consisting of the choroid, ciliary body, and iris.

Choroid

Vascular layer supplying the eye and containing blood vessels.

Ciliary Body

Contains ciliary muscles that adjust lens shape and produces aqueous humor.

Iris

Colored part of the eye that controls pupil size.

Pupil

Opening in the iris through which light enters the eye.

Nervous Tunic

Inner layer of the eyeball; the retina.

Retina

Neural layer containing the photoreceptors—rods and cones.

Macula

Area of the retina associated with high visual acuity.

Optic Disc

Area where the optic nerve exits the eye; contains no photoreceptors, making it the blind spot.

Lens

Transparent, biconvex structure that focuses light onto the retina.

Suspensory Ligaments

Structures that suspend and attach the lens to the ciliary body.

1. Anterior Chamber

2. Posterior Chamber

3. Vitreous Chamber

Eye Chamber

Anterior Chamber

Space between the cornea and iris containing aqueous humor

Posterior Chamber

Space between the iris and lens containing aqueous humor.

Vitreous Chamber

Largest eye chamber; contains vitreous humor.

1. Aqueous Humor

2. Vitreous Humor

Eye Humors

Aqueous Humor

Fluid in the anterior and posterior chambers that helps maintain intraocular pressure.

Vitreous Humor

Gel-like substance in the vitreous chamber that helps maintain eye shape and supports the retina.

Photoreceptors

Specialized retinal cells that detect light; mainly rods and cones.

Rods

Photoreceptors responsible for night/non-color vision; highly sensitive to light.

Rhodopsin

Light-sensitive pigment found in rods that participates in phototransduction.

Cones

Photoreceptors responsible for color vision and high visual acuity in bright light.

Bipolar Cells

Retinal neurons that relay signals from photoreceptors toward ganglion cells.

Ganglion Cells

Retinal neurons whose axons form the optic nerve.

Phototransduction

Conversion of light stimulation into electrical signals.

Optic Nerve (CN II)

Carries action potentials from the retina toward the brain.

Optic Chiasm

Site where nasal retinal axons cross to the opposite side.

Optic Tract

Continuation of visual fibers after the optic chiasm.

Lateral Geniculate Nucleus (LGN)

Thalamic relay nucleus involved in visual processing.

Superior Colliculi

Structures involved in visual reflexes.

Optic Radiations

Fibers projecting from the LGN to the visual cortex.

Visual Cortex

Area in the occipital lobe responsible for processing visual information.

Retina → Optic nerve → Optic chiasm → Optic tract → LGN → Optic radiations → Visual cortex

Visual Pathway

Refraction

Bending of light as it passes from one medium to another.

Accommodation

Adjustment of lens shape to focus on near objects.

Emmetropia

Normal vision in which the eye focuses distant objects appropriately.

Convergence

Inward rotation of the eyes when focusing on a nearby object.

Near Point of Vision

Closest distance at which an object can remain clearly focused.

Myopia

Nearsightedness; distant objects appear blurry; corrected with concave lenses.

Hyperopia

Farsightedness; close objects appear blurry; corrected with convex lenses.

Presbyopia

Age-related loss of lens flexibility causing difficulty focusing on near objects.

Astigmatism

Irregular curvature of the cornea or lens causing blurred vision.

External Ear

Part of the ear that collects sound waves.

Auricle / Pinna

Cartilaginous external ear structure that directs sound into the ear.

External Acoustic Meatus

Canal leading toward the tympanic membrane; contains hairs and ceruminous glands.

Ceruminous Glands

Glands that produce earwax (cerumen).

Tympanic Membrane

Eardrum; vibrates in response to sound waves.

Middle Ear

Air-filled cavity containing the auditory ossicles that transmit sound vibrations.