The General & Special Senses

1. The General & Special Senses Chapter 18

2. Introduction • Senses – our perception of what is “out there” • 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. General Senses • Includes senses that are associated with skin • Temperature, pressure, touch, pain, vibration, proprioception • Pass information along the spinal nerves and pathways to specific areas of the cerebral cortex

4. Special Senses • Olfaction, gustation, equilibrium, hearing, & vision • Found within complex sense organs • Pass information along the cranial nerves to specific areas of the cerebral cortex.

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

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

7. Central Processing and Adaptation • Sensory adaptation – the loss of sensitivity after continuous stimulation • Tonic receptors are always active • Phasic receptors only relay changes in the conditions they are monitoring • Role – prevents brain from being overloaded with unimportant information

8. Receptors of the General Senses

9. Nociceptors • Detect pain • Referred pain • Phantom pain

10. Mechanoreceptors • Respond to pressure & touch • Tactile receptors • Baroreceptors • Proprioreceptors • Thermoreceptors

11. Tactile Receptors • Found in the dermis

12. Baroreceptors • Monitor changes in pressure

13. Chemoreceptors • Detect chemicals in solution • Blood composition

14. The Special Senses

15. Olfaction (the nose) • Olfactory receptors • Can detect at least 50 different primary smells • Located in the epithelium of roof of nasal cavity

16. Olfactory Receptors • Molecules dissolve in the mucus of the epithelium • Olfactory neurons pass through the roof of the nasal cavity and synapse in the olfactory bulb • Olfactory tracts go directly to the cerebral cortex

17. Gustation (the tongue) • Taste receptors are in the taste buds • 6 primary tastes • Sweet, sour, salty, bitter, water, umami

18. Gustatory Receptors • Located in papillae on the surface of the tongue • Contain the gustatory receptors • Molecules dissolve in saliva

19. Gustatory Receptors

20. Pathway of Gustatory Sense • Cranial nerves relay sensory impulses to the cerebral cortex • All pass through the medulla & thalamus

21. Equilibrium & Hearing (the ear) • External ear • The auricle directs sound waves into the external auditory meatus to the tympanic membrane

22. The Middle Ear • Contains the auditory ossicles • Separated from the external ear by the tympanic membrane • Malleus • Incus • Stapes • Connected to the throat by the eustachian tube

23. The Inner Ear • Separated from the middle ear by the oval window

24. The Inner Ear • Consists of a series of canals filled with fluid

25. The Inner Ear • Consists of a series of canals filled with fluid • Vestibule • Semicircular canals • Cochlea contains • Organ of Corti

26. The Vestibule • Detects static position • Hair cells are embedded in a gelatinous material

27. Otoliths at Work • Otoliths are balanced on top of gelatinous material • Slide when head tips • Bend hairs • Generates nerve impulse

28. The Semicircular Canals • Detect dynamic balance • Arranged at right angles to each other • Hair cells are embedded in gelatinous material with fluid over it • Movement of head • Bends the hairs • Creates nerve impulses

29. Semicircular Canals at Work

30. The Cochlea • Divided into 3 tunnels by membranes • Tunnels connect with the oval window and round window • Organ of Corti

31. Cochlear Chambers

32. The Organ of Corti • Consists of hair cells on a basement membrane • Tips of hairs touch the tectorial membrane • Basement membrane vibrates • Hair cells bend • Sends a nerve impulse

33. Pathway of Auditory Sense

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

35. Vision (the eye) – Accessory Structures • Eyelids protect the eye • Conjunctiva lines the eyelid • Lacrimal apparatus • Lacrimal gland produces tears • Lacrimal canals drain tears into lacrimal sacs • Nasolacrimal duct drains into the nasal cavity • Extrinsic muscles move the eyeball

36. Structure of the Eye – 3 Tunics • Outer tunic • Includes cornea & sclera • Middle tunic • Includes choroid coat, ciliary body, lens, iris & pupil • Inner tunic (retina) • Contains photoreceptors • Rods & cones • Includes optic disc,macula lutea & fovea centralis

37. Photo of Posterior Eye

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

39. The 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 Retina • Cones allow for sharp color vision in bright light • Contain pigments • Macula lutea • Fovea centralis • Rods provide for vision in dim light • Contain the pigment rhodopsin • Most dense at periphery of retina

42. Photo of Posterior Eye

43. Pathway of Vision Sense

44. 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

45. Abnormal Vision • Myopia • Hyperopia • Presbyopia • Astigmatism