1. Ch 9
The Senses

2. Sensory Receptors; specialized cells that monitor internal and external conditions.
Receptors CNS for interpretation
Adaptation is a decreased sensitivity to the presence of a constant stimulus.
I.e. not feeling your watch; jumping into cold lake (Work of RAS)

3. Your Senses can be divided into two categories
General Senses – receptors for temperature, pain, touch, pressure, vibration and body position
Scattered throughout the body
Special Senses – smell, taste, vision, balance and hearing
Concentrated with specific structures, called sense organs

4. General Senses Part of PNS Pain Receptors (Nociceptors)
Common in the superficial portions of the skin, joint capsules, along periosteum of bones,
Fast pain: carried by myelinated fibers
Slow pain: carried by unmyelinated fibers
Referred Pain: perception coming from other parts of body; parts of body are connected to by same spinal nerves. I.e. cardiac pain – originates in chest and left arm.

5. Temperature (thermoreceptors)
Nerve endings scattered beneath skin surface
Located in skeletal muscles, liver and hypothalamus as well. Why?
Receptors RAS system (Working right now in this room!!!)

6. Touch, Pressure and Position (Mechanoreceptors)
Respond to stretching, compression, twisting or other distortions of the cell membrane.
3 classes of Mechanoreceptors
Tactile (touch)
Baroreceptors (pressure)
Proprioceptors (position)
Contain mechanically regulated ion channels that open or close in response to stretching, compression, twisting or other distortions of the cell membrane

7. 6 Types of Touch Receptors
Free Nerve
endings
Hair Plexus
Merkel’s
Meissner’s
Pacinian
Ruffini’s

8. Baroreceptors: monitor changes in pressure
Surround the walls of hollow organs. I.e. blood vessels, lungs, stomach, bladder
Monitors BP – plays a role in regulating cardiac function and blood flow to tissues
Baroreceptors in lungs determine degree of lung expansion, which is relayed to pons and medulla
Controls urination and defecation in urinary and digestive systems

9. Examples of pressure receptors

10. Proprioceptors Monitors the position of joints,
tension in tendons and ligaments
State of muscle contraction
Lab Activity
Most information processed subconsciously

11. Smell and Taste
Chemoreceptors respond to chemical in a water solution.
Olfactory organs – provide a sense of smell
Consists of olfactory epithelium, receptors, supporting cells and basal (stem) cells
Olfactory glands produce a mucus that covers epithelium
Keeps area moist and free of dust/debris
Solvent that captures and dissolves air borne molecules
Constantly replaced; flushes away old odors
Nose diffuses chemicals thru mucus; mouth chemicals dissolve in saliva
Tissue is pseudostratified epithelium

12. Olfactory Receptors: modified neurons
An odor causes olfactory receptors to open Na+ channels and change membrane permeability.
Research in the 1990’s suggests we have 1000 smell genes
Genes only active in nose
Each gene codes for an odor binding protein; these receptor proteins only allow certain odors to bind to it.
Receptor cells replace themselves q 60 days. Function of basal or stem cells
10-20 million receptors are packed into a 5 cm2 area; animals have much larger numbers

13. Olfactory Receptors
10-20 million receptor cells are packed into a 5 cm2 area.

14. Olfactory Bulb: Cranial Nerve I
Axons leaving bulb travel to the olfactory cortex of cerebrum, hypothalamus and part of limbic system.
Elicits emotional responses to odors
Smells associated with danger (smoke, skunk)
Pleasant smells cause increased secretion of saliva and gastric juice
Unpleasant smells trigger protective reflexes (sneezing/coughing)
Lab Activity
Some of what we smell is really pain.
Nasal cavities contain receptors that respond to irritants such as ammonia, hot of peppers, chill of menthol. Reach the CNS via the trigeminal nerve, not the olfactory bulb

15. Taste
Tongue contains 3 types of cells: receptor, support and basal cells
Taste buds are the gustatory receptors distributed all over tongue.
Basal cells replace receptors q 7-10 days
Taste hairs extend from receptor cells and are bathed in saliva
Dissolved chemicals touch hair (microvilli), causing Na+ channels to open → A.P.

16. Four Primary Tastes Sweet – tip of tongue Salt – lateral tip
Sour – sides of tongue
Bitter – back of tongue

17. Taste Receptors respond more to unpleasant stimuli
Taste buds are monitored by cranial nerve 7 (facial), 9 (glossopharyngeal), 10 (vagus).
Taste is 80 % smell.
Think of how food tastes when you have a cold.
Try This!
Cranial nerves send impulses to thalamus and then primary sensory cortex.
Olfactory receptors play huge role in taste perception
1000 X more sensitive to tastes when organs are functioning (Think cold)

18. Vision: Eye Anatomy Eyes are hollow organs divided into two cavities.
Aqueous humor – liquid inside eyeball gives the eye shape
Wall of the eye contains 3 layers
Fibrous tunic – outer layer
Vascular tunic – middle layer
Neural tunic – inner layer

19. Fibrous Tunic Contains Functions Sclera – white of eye
6 eye muscles attach
Posterior surface contains blood vessels and nerves
Cornea – transparent light passes thru.
Functions
Mechanical support and some protection
Attachment site for 6 extrinsic eye muscles
Assists in focusing
Fibrous Tunic
Sclera is a layer of dense fibrous tissue that contains collagen and elastic fibers
Blood vessels lie under the sclera; but are very small so you only see white fibers. Thus white eyeball
Collagen fibers in cornea are arranged to allow light to pass through; gets oxygen by diffusing from air.

20. Vascular Tunic Functions Provide route for blood and lymph tissue
Iris – contains blood vessels, pigment cells, smooth muscle
Controls the size of pupil (center of iris) in response to light
Ciliary body – Thickened ring of tissue surrounding lens; forms aqueous humor and muscles maintain lens shape
Glaucoma – increased pressure in eye due to imbalance of A. humor
Choroid – blood vessel-rich membrane; delivers oxygen and nutrients to retina
Functions
Provide route for blood and lymph tissue
Transmits and Regulates amount of light entering eye
Circulate aqueous humor within eye
Control shape of lens
Smooth muscle represents all intrinsic eye muscles; 2 layers of smooth muscle
Explain dilation and constriction of pupil; controlled by autonomic nervous system
Muscles are responding to changes in light intensity

21. Iris
Ciliary Body
Vascular Tunic
Choroid

22. Tunic Neural Tunic: Retina Contains Photoreceptors – respond to light
Rods – light sensitive
Cones – color vision
3 types of cones Red/Green/Blue
provides perception of color
Give more clarity than rods
Fovea – largest concentration of cones; sharpest vision
Volunteers??? Anyone, Anyone!!
Neural Tunic: Retina
Tunic
Rods allow us to see in dim light; night driving. Located along sides of eye
Cones are red, green, blue; each type is sensitive to different range of wavelengths

23. Eye Anatomy

24. Color Blindness Ishihara Test
Caused by absence of certain cones. Most common, absence of red cones. Person can’t distinguish between red and green colors

26. What number do you see? Red/Green Colorblind?
Person with normal vision should see a five, Person with Red/Green should see a 2.

27. Optic disc – where the axons from neurons converge, forms optic nerve
No photoreceptors are found here.
Blind Spot

29. Try this

30. How Do You See?
Lens
Primary function is to focus image on the retinal receptors in the back of eye.
Focusing requires two steps
Light is bent when it passes between mediums of varying densities
Greatest refraction occurs when light passes thru cornea.
Focal point – when light bends to form a point
Focal Distance – distance between center of lens and focal point.
Focusing is accomplished by changing the shape of the eyeball.
Light bends 3 times cornea (most diffraction), entering and leaving lens. Doesn’t refract going thru V. humor

31. Pathway to the brain eye Occipital Lobe Optic Nerve II
Superior Colliculi
Pathway to the brain
Occipital Lobe

32. Depth Perception
Two eyes are better than one, especially when it comes to depth perception. Depth perception is the ability to judge objects that are near or farther than others.
To demonstrate the difference of using one vs. two eyes to judge depth, hold the ends of two pencils, one in each hand. Hold them either vertically or horizontally facing each other at arms-length from your body. With one eye closed, try to touch the end of the pencils together. Now try with two eyes, it should be much easier. (Can use fingers if you don’t have 2 pencils.)

33. What happens to the lens at close distances?
Close Images – longer focal distance; lens is rounded because ciliary muscles contract.
The closer the source, the longer the focal distance

34. Distant Objects –Shorter focal distance and flattened lens.

35. Keeping Focused
The lens constantly changes shape to keep the focal distance constant. – Image stays focused on retina.
I.e. looking at the board and then your paper.
20/20 vision means a person can see details at a distance of 20 feet as clearly as the “normal population” would.

36. Normal Vision; what is happening in the eye.

37. Near sighted (myopia) 20/30 vision Images forms in front of retina
Vision at close range will be normal, because lens can adjust and round up to focus.
Eyeball is too deep
Objects in the distance will be blurry and out of focus
20/30 vision

38. Corrected by wearing a diverging lens!
Diverging lens increase focal distance

39. Far Sighted (Hyperopia) Eyeball is too shallow
Person can see distant objects; not near objects
At close range the lens cannot provide enough refraction; point doesn’t focus at end of retina.

40. Corrected by wearing converging lens!
Converging lens – bends rays more.

41. Astigmatism occurs when the cornea is more oval than spherical
Astigmatism occurs when the cornea is more oval than spherical. The result is an unequal bending of the light which results in multiple focal points.
                                                  

42. Test for Astigmatism
To test your vision, stand about 20 feet from the chart. Test one eye at a time. If you see lines grey and other black you have an astigmatism.

43. Ear Anatomy Ear is composed of 3 anatomical regions
External Ear: Pinna – Tympanic membrane
Middle Ear: Tympanum – Auditory ossicles
Inner ear: Bony Labryinth

44. 3 Sections of EAR

45. External Ear Organs Pinna (auricle) External Auditory Canal
Functions to collect, direct sound waves to ear drum.
External Ear
Hairs prevent foreign object and insects from entering canal
Cerumen (ear wax) slows growth of microbes and reduces chance of infection.
Ends at Tympanum

46. Middle Ear Tympanum – ear drum; Auditory Tube (Eustachian tube)
Cavity is filled with air
Auditory Tube – equalizes pressure on either side of eardrum
Tympanum – ear drum; Auditory Tube (Eustachian tube)
Auditory Ossicles –
1. Malleus (hammer) 2. Incus (anvil) 3. Stapes (stirrup)

47. Inner Ear Vestibule – provides sensations of gravity and acceleration
Semicircular Canals – detect movement of head
Cochlea – provide sense of hearing
Hair Cells – receptors of inner ear for sound

48. Bony Labyrinth

49. How do we hear?
Sound waves cause the tympanic membrane to vibrate which moves the ossicles. Sound energy are converted to mechanical energy.
Ossicles transmit the in/out vibrations from tympanic membrane to ear’s inner fluid-filled chamber.

50. How Do you Hear?

51. What about Hearing?
Sounds set up vibrations in air that beat against the tympanic membrane.
Vibrations push the ossicles that press fluid in the inner ear against membranes.
Fluid causes forces that pull on tiny hair cells and stimulate neurons.
Neurons send impulses to the brain, which interprets them.
Tympanic membrane = eardrum
Ossicles = 3 tiny bones

53. Tiny Hair cells are in the cochlea in an area called the Organ of Corti.
Organ of Corti – Hair cells that cause depolarization of nerve cells when they are moved by sound waves.

54. Larger view of Organ of Corti.

55. Maintaining Equilibrium: How does it work?
When the head is upright, otoliths pushes the sensory hairs downward rather than side to side.
By tilting the head, the otoliths move causing the sensory hairs to be distorted. This is sent to the CNS for interpretation.
Within the vestibule and semicircular canals, tiny hairs are found along the membrane of these structures. Inside the canals, jellylike substance contains tiny calcium carbonate crystals called ear stones or otoliths. (o’to-lith)

56. Equilibrium
Ear responds to various head movements.
Static Equilibrium is controlled by the vestibule.
Respond to straight-line changes in speed and direction, but not rotation.
Dynamic Equilibrium is controlled by the semicircular canals.
Respond to changes in head position; rotating the head to say no.