The General & Special Senses

1. The General & Special Senses Chapter 17

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

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 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. Gustation (the tongue) • Taste receptors are in the taste buds • 4 primary tastes • Sweet, sour, salty, bitter • Located in papillae on the surface of the tongue • Contain the gustatory receptors • Molecules dissolve in saliva

18. Pathway of Gustatory Sense • 3 cranial nerves relay sensory impulses to the cerebral cortex • Facial, glossopharyngeal, vagus • All pass through the medulla & thalamus

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

20. The Middle Ear • Located in the temporal bone • Contains the auditory ossicles • Malleus • Incus • stapes • Connected to throat by the eustachian tube

21. The Inner Ear • Located in the temporal bone • Separated from the middle ear by the oval window

22. The Inner Ear • 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

24. The Inner Ear • The bony labyrinth is divided into 3 areas • Vestibule contains • Saccule & utricle • Semicircular canals • Each has an ampulla • Cochlea contains • Organ of Corti

25. The Utricle & Saccule • Detects static position • Hair cells are embedded in a gelatinous material

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

27. The Semicircular Canals • Detect 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 head • Bends the hairs • Creates nerve impulses

28. Semicircular Canals at Work

29. The Cochlea • Divided into 3 tunnels by the vestibular and basilar membranes • Scala vestibuli ends in the oval window • Cochlear duct contains the organ of Corti • Scala tympani ends in the round window

30. Cochlear Chambers

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

32. Pathway of Auditory Sense

33. 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

34. 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

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

36. Photo of Posterior Eye

37. 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

38. 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

39. 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

40. Pathway of Vision Sense

41. 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

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