The Special Senses
• Smell, taste, vision, hearing and equilibrium
• Housed in complex sensory organs
• Ophthalmology is science of the eye
• Otolaryngology is science of the ear
Physiology of Olfaction
Many different combinations of receptors produces the possibility for thousands of different odor sensations.
Low threshold, only few molecules needed.
Adaptation - rapid
Olfactory Pathway
Olfactory receptors
Olfactory (I) nerves
Olfactory tract
Temporal lobe (primary olfactory area)
Anatomy of Taste Buds and Papillae• Taste bud- made of three types of epithelial
cells: supporting cells, gustatory receptor cells and basal cells.
• About 50 gustatory cells per taste bud. Each one has a gustatory hair that projects through the taste pore.
• Taste buds are found in the papillae.
• Three types of papillae: vallate (circumvallate), fungiform and foliate.
Physiology of Gustation
• Five types of taste: sour, sweet, bitter, salty and umami.
• Tastant dissolves in saliva → plasma membrane of gustatory hair→ receptor potential→ nerve impulse via cranial nerves VII, IX and X→ medulla→ thalamus→ primary gustatory area of the cerebral cortex.
Wall of the Eyeball• Three layers:
– Fibrous tunic- outer layer• Sclera “white” of the eye
• Cornea-transparent coat
– Vascular tunic or uvea- middle layer• Choroid
• Ciliary body consists of ciliary processes and ciliary muscle
• Iris
– Retina- inner layer• Optic disc
• Macula lutea- fovea centralis
Interior of the Eyeball• Lens
– lack blood vessels, consists of a capsule with proteins (crystallins) in layers; transparent.
– divides the eyeball into two cavities: anterior and posterior.
- Anterior cavity- further divided into anterior and posterior chambers. Both are filled with aqueous humor.
- Posterior cavity (vitreous chamber)-filled with vitreous body.
Cavities of the Interior of Eyeball• Anterior cavity (anterior to lens)
– filled with aqueous humor• produced by ciliary body• continually drained• replaced every 90 minutes
– 2 chambers• anterior chamber between cornea and iris• posterior chamber between iris and lens
• Posterior cavity (posterior to lens)– filled with vitreous body (jellylike)– formed once during embryonic life– floaters are debris in vitreous
• Refraction: Bending of light as it passes from one substance (air) into a 2nd substance with a different density (cornea)
• In the eye, light is refracted by the anterior & posterior surfaces of the cornea and the lens
Image Formation