1. The General & Special Senses
Chapter 18

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. 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. Referred Pain

9. The Special Senses

10. 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

11. Olfactory Receptors

12. Olfactory Receptors

13. Taste receptors are in the taste buds
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

14. Taste Areas of the Tongue

15. Taste Buds

16. Taste Bud

17. 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

18. The Ear

19. The Middle Ear

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

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

22. The Inner Ear

23. 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

24. Hair Cells in the Semicircular Canals

25. Consists of hair cells on a basement membrane
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

26. Organ of Corti

27. Organ of Corti

28. 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

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

30. The Eye

31. Consists of 3 tunics (layers)
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),

32. The Eye

33. Tunics of the Eye

34. Inner Tunic

35. The lens separates the interior of the eye into 2 cavities
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

36. Cavities of the Eye

37. Contains many blood vessels & nerves
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

38. The Pupil

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

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

41. Visual Receptors

42. 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

43. Abnormal Vision
Myopia
Hyperopia
Presbyopia
Astigmatism