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Special Senses. The Special Senses. Olfaction (smell) Gustatory (taste) Vision Hearing and Equilibrium. Olfaction. Olfactory receptors are in the roof of the nasal cavity Neurons with long cilia Chemicals must be dissolved in mucus for detection
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The Special Senses • Olfaction(smell) • Gustatory(taste) • Vision • Hearing and Equilibrium
Olfaction • Olfactory receptors are in the roof of the nasal cavity • Neurons with long cilia • Chemicals must be dissolved in mucus for detection • Impulses are transmitted via the olfactory nerve • Interpretation of smells is made in the cortex
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)
Gustation • Sweet (sugars) • Saccharine • Some amino acids • Sour • Acids • Bitter • Alkaloids • Salty receptors • Metal ions • Umami • Meaty/savory
Anatomy of Taste Buds and Papillae • The tongue is covered with projections called papillae • Filiform papillae—sharp with no taste buds • Fungiform papillae—rounded with taste buds • Circumvallate papillae—large papillae with taste buds • Taste buds are found on the sides of papillae
Physiology of Gustation • Gustatory cells are the receptors • Have gustatory hairs (long microvilli) • Hairs are stimulated by chemicals dissolved in saliva • Impulses are carried to the gustatory complex by several cranial nerves because taste buds are found in different areas • Facial nerve • Glossopharyngeal nerve • Vagus nerve • Impulse travels from receptors to medulla→ thalamus→ primary gustatory area of the cerebrum
Accessory Structures of Eye • Eyelids and eyelashes • Conjunctiva • Lacrimal apparatus • Extrinsic eye muscles
Accessory Structures of the Eye • Eyelids • Meet at the medial and lateral commissure (canthus) • Eyelashes • Tarsal glands produce an oily secretion that lubricates the eye • Ciliary glands are located between the eyelashes • Conjunctiva • Membrane that lines the eyelids • Connects to the outer surface of the eye • Secretes mucus to lubricate the eye and keep it moist
Accessory Structures of the Eye • Lacrimal apparatus = lacrimal gland + ducts • Lacrimal gland—produces lacrimal fluid; situated on lateral aspect of each eye • Lacrimal canaliculi—drain lacrimal fluid from eyes medially • Lacrimal sac—provides passage of lacrimal fluid towards nasal cavity • Nasolacrimal duct—empties lacrimal fluid into the nasal cavity
Accessory Structures of the Eye • Function of the lacrimal apparatus • Protects, moistens, and lubricates the eye • Empties into the nasal cavity • Lacrimal secretions (tears) contain: • Dilute salt solution • Mucus • Antibodies • Lysozyme (enzyme that destroys bacteria)
Accessory Structures of the Eye • Extrinsic eye muscles • Six muscles attach to the outer surface of the eye • Produce eye movements
Structure of the Eye • 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
Structure of the Eye: The Fibrous Layer • Sclera • White connective tissue layer • Seen anteriorly as the “white of the eye” • Cornea • Transparent, central anterior portion • Allows for light to pass through • The only human tissue that can be transplanted without fear of rejection
Structure of the Eye: The Vascular Layer • Choroid is a blood-rich nutritive layer in the posterior of the eye • Pigment prevents light from scattering • Modified anteriorly into two structures • Ciliary body—smooth muscle attached to lens • Iris—regulates amount of light entering eye • Pigmented layer that gives eye color • Pupil—rounded opening in the iris
Structure of the Eye: The Sensory Layer • Retina contains two layers • Outer pigmented layer • Inner neural layer • Contains receptor cells (photoreceptors) • Rods • Cones
Structure of the Eye: The Sensory Layer • Signals pass from photoreceptors via a two-neuron chain • Bipolar neurons • Ganglion cells • Signals leave the retina toward the brain through the optic nerve • Optic disc (blind spot) is where the optic nerve leaves the eyeball • Cannot see images focused on the optic disc
Retina View with Ophthalmoscope
Interior of the Eyeball • Lens • lack blood vessels, consists of a capsule with proteins (crystallins) in layers; transparent. • held in place by a suspensory ligament attached to the ciliary body • 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
Image Formation • 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
Vision • Emmetropia—eye focuses images correctly on the retina • Myopia (nearsighted) • Distant objects appear blurry • Light from those objects fails to reach the retina and are focused in front of it • Results from an eyeball that is too long • Hyperopia (farsighted) • Near objects are blurry while distant objects are clear • Distant objects are focused behind the retina • Results from an eyeball that is too short or from a “lazy lens”
