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