1. UNIT 5: Nervous System
Senses

2. Somatic Senses
Somatic senses are associated with receptors in the skin, muscles, joints, and viscera (organs of the body)
Include senses of touch, pressure, temperature, & pain

3. EXAMPLES ONLY: FYI Type of stimulus Name of the nerve receptor
Cold Krause’s end bulbs
Warmth Ruffini’s end organ
Touch Meissner’s corpuscle
Deep pressure Pacinian corpuscle
Pain (free nerve ending)(no special name)
Encapsulated receptors

6. Receptors may also exhibit a characteristic known as adaptation
Means that the frequency of the receptor potential decreases over time in response to a continuous stimulus
Axon sends fewer impulses, therefore the intensity of the sensation decreases
Ex. Feeling your clothes
on your skin

7. Olfaction (Smell) and Gustation (Taste)
Our senses of smell and taste are closely related
Both play a role in food selection because we smell food at the same time we taste it
Receptors for both smell and taste are chemoreceptors
Sense chemicals that dissolve in fluids

10. Sense of Taste (Gustation)
Taste buds are the sense organs that respond to gustatory stimuli
Taste buds are located on small elevated projections on the tongue called papillae
About 10,000 on your
tongue, 1,000 on the
roof of mouth

11. Each taste bud contains specialized gustatory cells
Tiny cilia-like gustatory hairs extend from each gustatory cell into an opening called a taste pore
Taste occurs when the gustatory hairs (chemoreceptors) are stimulated by chemicals in the saliva

14. Taste buds will respond to chemicals for sweet, sour, salty, bitter, and umami (MSG)
All taste buds will respond to each chemical to some degree, but respond most effectively to one of the four
The tastes we perceive are from a mixture of the four and our sense of smell
Our taste buds may also sense a 6th taste: metallic, alkaline

16. Sense of Smell (Olfaction)
Olfactory receptors are also chemoreceptors
Olfactory cells have cilia extending into nasal mucosa
Lines nasal cavity and septum
Smell occurs when enough odorant molecules stimulate a receptor and trigger an action potential

18. We have over 400 types of olfactory receptors which sense different odorant molecules
With a few hundred types of olfactory receptors we are also able to sense thousands of smells
Odorant molecules will bind in different patterns to receptors which the brain interprets as different smells

19. More Smell Info
The olfactory receptors are located high in the nasal cavity so a person may have to sniff forcefully to smell light odors
We also will “adapt” to smells
Smells may seem to become less intense
Video link: 3 min, is shows smell; 7.5 min. in shows taste

20. Sense of Hearing: The Ear
The ear has two sensory functions
Sense of Hearing and Balance
Structure of the Ear
The ear is divided into three parts: the external ear, the middle ear, and the inner ear

22. External Ear Consists of three parts
Auricle (pinna)- flap on the side of the head
External Auditory Meatus- ear canal, which leads from the auricle into the ear canal
Modified sweat glands secrete cerumen (ear wax)
Tympanic Membrane (eardrum)- stretches across the inner end of the auditory canal, separating it from the middle ear

24. Middle Ear (Tympanic Cavity)
Auditory Ossicles- Malleus, incus, stapes
3 very small bones named for their shape (hammer, anvil, stirrup); amplify sound
Several openings into the inner ear responsible for passing sound vibrations
Ex: Oval Window, opening into the auditory (Eustachian) tube

27. Auditory (Eustachian) Tube- composed partly of bone and partly of cartilage
Extends from the middle ear cavity into the throat
Helps to equalize pressure between the middle and outer ear and prevents membrane rupture; occurs when you yawn or swallow

29. Has structures that help to produce both hearing and balance
Inner Ear
Has structures that help to produce both hearing and balance
cochlea (hearing), vestibule (balance), semicircular canals (balance)

30. Sense of Hearing
Sound occurs from vibrations that travel through the ear and move fluid in the cochlea
cochlea means “snail”
Fluid then stimulates hair cells in the Organ of Corti
Organ of Corti- contains the hearing receptors attached to hair cells

35. Hearing Test
Hearing Test 2

36. Sound transduction animation
Pathway of Sound Waves
Sound waves enter outer ear & vibrate tympanic membrane this causes the malleus to move the incus  the incus moves the stapes  this bone sitting in the oval window causes fluid in the cochlea to move  the fluid moves the basilar membrane which stimulates the hair cells of the Organ of Corti
Sound transduction animation

37. Sense of Balance or Equilibrium
This sense is really two senses using two different sense organs within the ear
Vestibule (static) and Semicircular Canals (dynamic)

38. Vestibule: STATIC EQUILIBRIUM (FYI)

39. Semicircular Canals: DYNAMIC EQUILIBRIUM (FYI)

40. Vision:
The eye is the sense organ for vision and converts light into electrical impulses

41. Structure of the Eye
Approximately 5/6 of the eye lies within the bony protection of the orbit, leaving only the small anterior surface exposed
3 layers of tissues make up the eyeball: sclera, choroid, and the retina
Outermost layer: Sclera becomes
the cornea in front
Middle layer: Choroid becomes
the iris in front

43. Retina- incomplete innermost layer of the eyeball
Has no anterior portion
Optic disk: “blind spot”
Retina also contains photoreceptor
neurons: rods and cones
More rods than cones
Cones are densely packed in the fovea centralis
No rods in the fovea

46. The Process of Seeing
For vision to occur, an image is focused on the retina to stimulate rods and cones, and the resulting nerve impulses must be conducted to the visual areas in the cerebral cortex to be interpreted
Animation!

47. Light bends in eye fluid
Click picture for animation
Light bends in eye fluid
Lens actively bends light to focus an image on the retina

49. The Role of Photopigments
Both rods and cones contain photopigments, which are light-sensitive compounds
In the presence of lights, photopigments undergo structural changes which trigger an impulse (action potential) for the brain to interpret
Rods: much more sensitive to light  help you see when there is less light
Cones: detect color

50. ROD PHOTOPIGMENTS: RHODOPSIN retinol + opsin protein

51. Vitamin A is necessary to make photopigments in rod cells

53. GLASSES

54. Labels:
Sclera/cornea, choroid/iris, retina
Lens
Aqueous humor
Vitreous humor
Pupil
Blind spot
Optic nerve
Fovea

55. Other cool other things about the eye:
Pupil dilation/constriction
Function of aqueous humor
“floaters”
going into dark theatre eyes need to adjust (bleaching)