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 Two general types
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