BIOL 2457 1st Edition Lecture 35Outline of Last Lecture Sensory, motor, integrative systemsOutline of Current LectureThe special senses Olfaction Olfactory pathwaysNo synapse in the thalamus for arriving information Olfactory discriminationCan distinguish thousands of chemical stimuliCNS interprets smells by pattern of receptor activityOlfactory receptor population shows considerable turnoverNumber of receptors declines with age Anatomy of Taste Buds & 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. Gustatory discrimination  Primary taste sensationsSweet, sour, salty, bitterReceptors also exist for umami and water Taste sensitivity shows significant individual differences, some of which are inherited The number of taste buds declines with age  Vision or Sight Visible light: 400-700 nm. Accessory structures of the eye Eyelids (palpebrae) separated by the palpebral fissue Eyelashes Tarsal glands Lacrimal apparatus Accessory Structures of the Eye Eyelids or palpebrae- Eyelashes and eyebrows- Extrinsic eye muscles- 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 Responses of the Pupil to Light Pupil is an opening in the center of the iris.  Contraction of the circular muscles of the iris causes constriction of the pupil. Contraction of the radial muscles causes dilation of the pupil. Interior of the Eyeball Lens- lack blood vessels, consists of a capsule with proteins (crystallins) in layers; transparent. Lens 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. Refraction of Light Rays Refraction is the bending of light rays. The cornea and lens refract light rays. Accommodation & the Near Point of Vision Increase in the curvature of the lens for near vision is called accommodation. Near point of vision is the minimum distance from the eye that an object can be clearly focused. Refraction Abnormalities & their Correction Nearsightedness (myopia)- close objects seen clearly. Image is focused in front of the retina. Correction- use of concave lens. Farsightedness (hyperopia)- distant objects seen clearly. Image is focused behind the retina. Correction- use of convex lens. Rods and Cones Named after the shapes of their outer segments. Rod- Cones- three types: red, green and blue. Outer segment- contains photopigments. Transduction of light energy into receptor potential occurs here. Inner segment- contains the nucleus, Golgi complex and mitochondria. Photopigments Two parts: opsin (four types, three in the cones and one in the rod) and retinal (light absorbing part). Rhodopsin- photopigment in rods. Cone photopigments- three types.Absorption of light by a photopigment → structural changes. Bleaching & Regeneration of Photopigment1. Isomerization: In darkness, retinal has a bent shape called cis-retinal. Absorption of photon causes straightening of the retinal (t rans-retinal).2. Bleaching: trans-retinal separates from opsin.3. Regeneration: trans-retinal→ cis-retinal. Light and Dark Adaptation Light adaptation: Dark → light. Faster. Dark adaptation: Light →dark. Slow. Cones regenerate rapidly whereas rhodopsin regenerates more slowly. Color Blindness & Night Blindness Color blindness- inherited inability to distinguish between certain colors.Result from the absence of one of the three types of cones.Most common type: red-green color blindness. Night blindness or Nyctalopia- vitamin A deficiency. Processing of Visual Input Receptor potential in rods and cones→ graded potentials in bipolar neurons and horizontal cells→ nerve impulses in ganglion cells→ opticnerve→ optic chiasm→ optic tract→ thalamus→ primary visual area of cerebral cortex in occipital lobe.  Color sensitivity Integration of information from red, blue and green cones Colorblindness is the inability to detect certain colors Anatomy of the Ear Three main regions:External (outer) ear- auricle or pinna, external auditory canal, and tympanic membrane.Ceruminous glands- Middle ear- auditory ossicles: malleus, incus and stapes.Auditory (eustachian) tube. Internal (inner) ear- Labyrinth: bony and membranous. Bony labyrinth- perilymph and membranous labyrinth- endolymph. Oval window and round window- membranous regions. inner ear Components Vestibule contains the utricle and saccule Semicircular canals contain the semicircular ducts Cochlea contains the cochlear duct The Internal Ear Three parts: the semicircular canals, the vestibule (both contain receptors forequilibrium) and the cochlea (contains receptors for hearing). Semicircular canals: anterior, posterior and lateral. Ampulla- Vestibule consists of two sacs: utricle and saccule. Cochlea Snail-shaped. Section through the cochlea shows three channels: cochlear duct, scalavestibuli and scala tympani. Helicotrema Vestibular membrane Basilar membrane Spiral organ or Organ of Corti- hair cells. Physiology of Hearing Audible sound range: 20-20,000 Hz. Sound waves→ auricle→ external auditory canal→ tympanic membrane→ malleus→ incus→ stapes→ oval window→ perilymph of the scalavestibuli→ vestibular membrane→endolymph in the cochlear duct→ basilar membrane →hair cells against tectorial membrane → bending of hair cell