The General & Special Senses

1. The General & Special Senses Chapter 18

2. Introduction • Senses – our perception of what is “out there” • 2 groups • General senses • Special senses

3. General Senses • Includes senses that are skin or kinesthetic • Temperature, pressure, touch, pain, vibration, proprioception • Pass information along the spinal nerves and pathways to the somatosensory 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 • Two general types • Exteroceptors • Interoceptors

6. Interpretation of Sensory Information • Occurs in cerebral cortex • Depends on the area of the cerebral cortex that receives the information • Also depends on the sequence of neurons carrying the information

7. Central Processing and Adaptation • 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 • Nociceptors detect pain • Referred pain • Phantom pain • Thermoreceptors detect changes in temperature

9. Referred Pain

10. Receptors of the General Senses • Mechanoreceptors respond to pressure & touch • Tactile receptors are found in the dermis • Baroreceptors monitor changes in pressure • Proprioceptors monitor positions of joints & muscles

11. Tactile Receptors

12. Some Enteroreceptors

13. Receptors of the General Senses • Chemoreceptors detect chemicals in solution • Smell • Taste • Blood composition

14. Chemoreceptors

15. The Special Senses

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

17. Nasal Cavity

18. Olfactory Receptors

19. Gustation (the tongue) • Taste receptors are in the taste buds • Can detect 4 primary tastes • Sweet, sour, salty, bitter • Located in papillae or bumps on the surface of the tongue (also on the walls of the pharynx & larynx) • Taste buds contain the gustatory receptors • Molecules dissolve in saliva • 3 cranial nerves relay sensory impulses to the cerebral cortex • Facial, glossopharyngeal, vagus • All pass through the medulla & thalamus

20. Tastes on the Tongue

21. Taste Buds

22. A Taste Bud

23. Pathway of Gustatory Sense

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

25. The Ear

26. The Middle Ear

27. The Inner Ear • Separated from the middle ear by the oval window • Consists of a series of canals called the bony labyrinth • Lined by a membranous labyrinth filled with endolymph • Perilymph flows between the bony and membranous labyrinth

28. The Inner Ear • The bony labyrinth is divided into 3 areas • Vestibule • Contains the saccule & utricle • Involved in static equilibrium • Semicircular canals • Each has an ampulla which contains receptors for head position • Cochlea • Contains the organ of Corti, the organ of hearing

29. The Semicircular Canals

30. The Utricle & Saccule • Detects static position • Hair cells are embedded in a gelatinous material • Otoliths are balanced on top • Slide when the head is tipped • Bend hairs, generating a nerve impulse

31. The Utricle and Saccule

32. Otoliths

33. Otoliths at Work

34. The Semicircular Canals • Detects dynamic balance • Arranged at right angles to each other • In the ampula, hair cells are embedded in gelatinous material (cupula) with fluid over it • Movement of the head bends the hairs, creating nerve impulses

35. Ampulla

36. Hair Cell

37. Semicircular Canals at Work

38. The Cochlea • Divided into 3 tunnels by the vestibular and basilar membranes • Scala vestibuli (top), ends in the oval window • Cochlear duct (middle), contains the organ of Corti • Scala tympani (bottom), ends in the round window

39. The Cochlea

40. Cochlear Chambers

41. The Organ of Corti

42. The Organ of Corti • Consists of hair cells on the basilar membrane • Tips of hairs touch the tectorial membrane • When the basement membrane vibrates, the hair cells are bent, sending a nerve impulse

43. Summary of Hearing • Sound waves enter the external auditory meatus • Tympanic membrane vibrates • Auditory ossicles vibrate • Oval window vibrates • Perilymph in scala vestibuli & scala tympani moves • Basilar membrane moves • Hairs rub against the tectorial membrane • Nerve impulse is sent along the vestibulocochlear nerve to the brain

44. Pathway of Auditory Sense

45. 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

46. The Eye

47. Structure of the Eye • Consists of 3 tunics (layers) • Fibrous tunic – outermost layer • Includes the cornea & sclera • Vascular tunic – middle layer • Includes the choroid coat, ciliary body, and lens, iris & pupil • Neural tunic (retina) – inner layer • Contains the rods & cones (photoreceptors) • Includes the optic disc (blind spot),macula lutea & fovea centralis

48. The Retina

49. Sagittal Section of the Eye

50. Photo of Posterior Eye