1. The General & Special Senses Chapter 8

2. Introduction Senses – our perception of what is “out there” 2 groups –General senses Includes senses that are not specific Pass information through spinal nerves –Special senses Found within complex sense organs to cerebral cortex Pass information through cranial nerves to cerebral cortex

3. Receptors Sensory receptors are transducers –Change stimuli into electro-chemical impulses –Specific receptors can transduce only certain types of stimuli

4. Receptors

5. Interpretation of Sensory Information Occurs in cerebral cortex Depends on the area of the cerebral cortex that receives the information

6. Central Processing and Sensory Adaptation Sensory adaptation – the loss of sensitivity after continuous stimulation –Occurs in some types of receptors Role – prevents brain from being overloaded with unimportant information

7. Receptors of the General Senses Pain –Referred pain –Phantom pain Thermoreceptors detect changes in temperature Mechanoreceptors respond to pressure & touch Chemoreceptors detect chemicals in solution –Blood composition –(Smell) –(Taste)

8. What’s a Dermatome? A localized area of skin that is has its sensation via a single nerve from a single nerve root of the spinal cord. Shingles (Herpes zoster virus infection) typically affects one or several isolated dermatomes.

9. What’s a Dermatome? From Medical school Halloween party From Textbook

10. Referred Pain

11. The Special Senses

12. Olfaction (the nose) Olfactory receptors –Can detect at least 50 different primary smell –Located in the roof of nasal cavity –Molecules dissolve in the mucus or lipids of the epithelium –Olfactory neurons pass through the roof of the nasal cavity and synapse in the olfactory nerve –Olfactory tracts go directly to the cerebral cortex

13. Olfactory Receptors

15. Taste (the tongue) Taste receptors are in the taste buds –Can detect 4 primary tastes Sweet, sour, salty, bitter –Located in papillae on the surface of the tongue –Taste buds contain the taste receptors –Molecules dissolve in saliva –Cranial nerves relay sensory impulses to the cerebral cortex

16. Taste Areas of the Tongue

17. Taste Buds

18. Taste Bud

19. Equilibrium & Hearing (the ear) External ear –The auricle directs sound waves into the external auditory meatus to the tympanic membrane Middle ear –Contains the auditory ossicles Malleus, incus, stapes –Connected to throat by the eustachian tube Inner ear

20. The Ear

21. The Middle Ear

22. The Inner Ear Separated from the middle ear by the oval window Consists of a series of canals filled with fluid

23. The Inner Ear –Semicircular canals Contains receptors for head position –Cochlea Contains the organ of Corti, the organ of hearing

24. The Inner Ear

25. The Semicircular Canals Detects balance Arranged at right angles to each other Contain hair cells are embedded in gelatinous material with fluid over it Detect movement of the head –Bends the hairs, creating nerve impulses

26. Hair Cells in the Semicircular Canals

27. The Organ of Corti Detects sound waves Consists of hair cells on a basement membrane Tips of hairs touch the tectorial membrane When the basement membrane vibrates, the hair cells are bent, sending a nerve impulse

28. Organ of Corti

30. Summary of Hearing Sound waves enter the external auditory meatus Tympanic membrane vibrates Auditory ossicles vibrate Oval window vibrates Fluid in inner ear vibrates Basement membrane moves Hairs rub against the tectorial membrane Nerve impulse is sent along the auditory nerve to the brain

31. Diseases of Hearing External Otitis, the most common disorder of the outer ear, also know as Swimmer’s ear. The process develops due to loss of the protective cerumen (wax) and excessive moisture in the ear canal. Otitis Media is one of the most common diseases of children, due to chronic middle ear infection. Treatments: antibiotics, otomyringotomy (surgical insertion of rigid “ear tubes”). Conductive Hearing Loss, usually due to otosclerosis, progressive fixation of the stapes due to aging or disease.

32. Vision (the eye) Accessory structures –Eyelids protect the eye Conjunctiva lines the eyelid Lacrimal gland produces tears –Extrinsic muscles move the eyeball

33. The Eye

34. Structure of the Eye Consists of 3 tunics (layers) –Outer tunic – outermost layer Includes the cornea & sclera –Middle tunic Includes the choroid coat, ciliary body, and lens, iris & pupil –Inner tunic (retina) – inner layer Contains the rods & cones (photoreceptors) Includes the optic disc (blind spot),

35. The Eye

36. Tunics of the Eye

37. Inner Tunic

38. The Cavities of the Eye The lens separates the interior of the eye into 2 cavities –Anterior cavity in front of the lens Contains aqueous humor –Glaucoma –Posterior cavity behind the lens Contains vitreous humor

39. Cavities of the Eye

40. The Vascular Tunic Contains many blood vessels & nerves The iris controls the size of the pupil Suspensory ligaments attach the lens to the ciliary body –Controls the shape of the lens Allows focusing on near & distant objects Cataract

41. The Pupil

42. The Retina Cones allow for sharp color vision in bright light –3 types, each with a different pigment

43. The Retina Rods provide for vision in dim light –Most dense at the periphery of the retina –Contain the pigment rhodopsin

44. Visual Receptors

45. Summary of Vision Light rays enters through the pupil Light rays cross in the lens Retina receives reversed & upside down image Rods & cones are stimulated Optic nerve carries impulse to the brain

46. Abnormal Vision Astigmatism Occurs when the transparent media of the eye (includes the cornea, crystalline lens) are inconsistently or irregularly shaped. Causes blurred vision at far and near distances.

47. Abnormal Vision Cataracts A clouding and hardening of all or part of the transparent lens located inside the eye, most often caused by the aging process, UV light exposure, etc.

48. Abnormal Vision Glaucoma A condition characterized either by increased intraocular pressure- "high blood pressure of the eye" -that can result in damage to the optic nerve and to retinal nerve fibers, or by significant decreased intraocular pressure.

49. Abnormal Vision Hyperopia Farsightedness. A condition in which rays of light are focused behind the retina, so distant objects appear clearer than near ones.

50. Abnormal Vision Presbyopia Caused by the loss of elasticity in the lens inside the eye as part of the aging process, resulting in a gradual decline in a person’s ability to focus on close objects or to see small print. Virtually everyone is affected after the age of 40.

51. Abnormal Vision Myopia Near sightedness. A condition in which light rays are focused in front of the retina instead of on it, so near objects appear more clear than far ones.

52. Abnormal Vision Macular degeration Common eye age-related disease that causes deterioration of the macula, the central area of the retina, the paper-thin tissue at the back of the eye where light-sensitive cells send visual signals to the brain. Sharp, clear, “straight ahead” vision is processed by the macula.

53. Abnormal Vision Retinoblastoma Malignant tumor of the retina. Inherited form is caused by a genetic abnormality in the Rb gene.