PHYSIOLOGY

1. Sensory Systems PHYSIOLOGY

3. Gustatory Receptors • Taste or Gustation • The sensation following the stimulation of oral chemoreceptors • Chemoreceptors are surrounded by supporting cells • Chemoreceptors are shed every 10-14 days and are renewed by division of the supporting cells.

4. Tastes • Four basic tastes • Sweet • Glucose, fructose, amino acids • Sour • H+ concentrations • Salty • Na+ concentration • Bitter • Quinine, caffeine, nicotine, strychinine, etc. • Umami • Produced by compounds like monosodium glutamate • Not a classic taste

5. Gustatory Transduction • Chemicals enter the pores of taste buds and react with the gustatory hairs • Chemicals may open sodium gates directly or may stimulate membrane receptors and G proteins and the second messenger system

9. Olfaction • Olfactory cells lie in a specialized region in the roof of the nasal cavity • The olfactory epithelium • Odors combine to produce depolarization and impulse activity • 80% of taste is smell • Olfactory neurons are bipolar neurons

10. Olfactory Receptors • Supporting cells secrete mucus • Continual degeneration and replacement of neurons • Every 60 days • Basal cells differentiate into olfactory neurons

11. Olfaction • Humans can detect about 104 different smells • Odiferous compounds are mainly organic • Containing 3-20 carbon atoms • Odiferous compounds reach the olfactory epithelium, aided by sniffing • The molecules must dissolve in the mucus layer (water soluble) to react with the receptors on the olfactory cilia

12. Odorant receptors • One receptor per olfactory neuron • 1000 different receptors • cAMP system is used for smells

13. Glomeruli • Olfactory neurons synapse with the olfactory bulb in regions called glomeruli • From the olfactory bulb to the temporal lobe • Each olfactory neuron synapses with only one glomerulus • Each glomerulus receives input from several thousand olfactory neurons in the epithelium • Each glomeruli receives input from neurons expressing the same receptor

17. Disorders of smell and taste • Anosmia • Inability to detect odors • Ageusia • Inability to detect tastes • Uncinate Fits • Hallucinations of smell

18. Vision

21. Functional Anatomy of the Eye • Three peripheral layers • Tough fibrous outer layer • Sclera and cornea • Middle layer • The choroid or pigmented layer • Absorbs light rays • Inner neural layer • The retina

23. Vitreous Humor • In the posterior chamber of the eye • Used to • Maintain the shape of the eye • Holds the retina in place • Produced in the fetal stage of development

25. Aqueous Humor • Produced by the ciliary muscles into the anterior chamber of the eye • Drains into the canal of Schlemm or Scleral Venous Sinus • ½ teaspoon is produced per day and this much drains per day • Clog of the canal may cause Glaucoma

27. Constriction of the Pupil • Miosis • Results in a better depth of focus • Light rays pass only through the central part of the lens • Sympathetic Nervous System • Dilator control • Mydriasis • Parasympathetic Nervous System • Constrictor control • Pupils are consensual

29. Lenses • Concave • Light bends outward • Convex • Light bends inward

30. Lens Focuses Light on the Retina • Light passes through the cornea and lens prior to striking the retina • Light must refract • Focal Point • The single point where the rays converge • Focal Length • Distance from the center of a lens to its focal point

32. Vision Problems • Hyperopia • Far-sightedness • The focal point falls behind the retina • Myopia • Near-sightedness • The focal point falls in front of the retina • Astigmatism • Caused by a cornea and/or lens that is not perfectly dome shaped

33. Convergence • The eye muscles pull eyes so that both eyes see one fused image

34. Accommodation • The process by which the eye adjusts the shape of the lens to keep objects in focus • Presbyopia • Hardening of the lens with age due to addition of layers to the lens • Focused at Infinity • The lens is pulled flat by tension in the ligaments • Close Up • The lens rounds up after the ciliary muscles contract and the suspensory ligaments relax

36. Eye • Optic Disc • Axons of the ganglion cells all form the optic nerve • The optic nerve leaves the eye at the optic disc • No rods or cones at the optic disc • Blind spot

38. Rods and Cones • Rods • More numerous than cones by a ratio of 20:1 • Function well in low light • Nighttime vision • Cones • High-acuity vision • Color vision during the daytime • High levels of light

39. Light • Each cone contains visual pigments that are excited by different wavelengths of light • Visual pigment • Bound to cell membranes of dendrites • The transducers that convert light energy into a change in membrane potential • Rods • Visual pigment is rhodopsin

40. Cones • Red, green, blue, yellow(?) cones • Each cone type is stimulated by a range of light wavelengths but is most sensitive to a particular wavelength • Colorblindness • Lack of cones • X-chromosome

43. Photoreceptors • Light passes the ganglion cells and does not stimulate them • Ganglion cells have action potentials • Light passes the bipolar cells and does not stimulate them • Bipolar cells only have graded response • Light is the ligand for either rods or cones • This depends on the kinetic energy of the light

44. Photoreceptors • Photoreceptors in the retina transduce light energy into electrical signals • The Fovea Centralis • The point on which light focuses

49. Phototransduction • Rhodopsin • Opsin plus 11cis retinal • Purple and “kinked” in shape • Visual pigment for rods • When activated by as little as one photon of light the 11cis retinal can be bleached • Bleaching • Light Changes 11 cis retinal to all trans retinal • All trans retinal is clear and a “straight” chain

50. Phototransduction • When a rod is in darkness • Rhodopsin is not active • cyclicGMP levels in the rod are high • Sodium channels are open • Depolarization of the rod