1. The Senses
Chapter 14

2. Sensory receptors are highly modified dendrites of sensory neurons
They convert one source of energy into another
Light receptors in the eye convert light energy into electrical energy

3. Sensory adaptation occurs once the receptor becomes accustomed to the stimulus
The neuron stops firing even though the stimulus is still present
The adaptation indicates the new environmental condition is not dangerous

4. Taste Receptors
Specific chemicals dissolve on the tongue and stimulate receptors in the taste buds
5 tastes sweet, sour, salt, bitter, savoury
Each taste is associated with molecular shapes or charges
Salty taste Na+ ion
Savoury glutamic acid

5. Taste
Taste Buds
1-200 cells
Each cell can respond to chemicals, but they are more sensitive to one particular chemical
Works in coordination with your sense of smell to create the perception of flavour

6. Structure of the Eye
3 Layers
1. Sclera
2. Choroid layer
3. Retina

7. 1. Sclera Protective, outermost layer
Fibrous sclera maintains eye shape
Cornea is the clear part of the sclera that acts as a window, bending light toward the pupil
Cornea is not supplied with blood vessels
Oxygen is supplied by the gases dissolved in tears while nutrients are supplied by the aqueous humor, a transparent fluid behind the cornea

9. 2. Choroid Layer
Iris
Location: disk of tissue surrounding the pupil
Structure: made of a thin circular muscle that controls the size of the pupil
Function: regulates amount of light entering the eye
Middle layer that contains blood vessles that nourish the retina

10. 2. Choroid Layer Lens Focuses the image on the retina
Located directly behind the iris
Ciliary muscles change the shape of the lens

11. 2.Choroid Layer Vitreous Humour Location: behind the lens
Function: Maintains shape of the eyeball and allows light transmission to retina

13. 3. Retina Innermost layer containing the photoreceptors
Contains 4 layers of cells
Pigmented epithelium
Light sensitive
Bipolar
Optic nerve

14. A. Pigmented Epithelium
Between choroid layer and light sensitive cells
Pigmented granules prevent light from scattering

15. B. Light Sensitive Cells
Rods
Operate in low intensity light
Detect black and white
Cones
Require bright high intensity light
Detect colour

16. C. Bipolar Cells Receive nerve message from the rods and cones
Bipolar cells relay the message to the cells of the optic nerve

17. D. Optic Nerve Receives message from the bipolar cells
Optic nerve carries the impulse to the CNS
No rods or cones where the optic nerve connects to the retina
Due to lack of photosensitive cells, it’s referred to as a blind spot

18. Rods and Cones unevenly distributed Fovea Centralis
Located in the centre of the retina
Most sensitive area of the eye
Many cones packed closely together
Surrounded by rods

19. Your Turn
Label the provided eye diagram, compare with a friend

20. Chemistry of Vision 160 million rods surround cones in the retina
Rods contain rhodopsin AKA visual purple, which is a light sensitive pigment
Rhodopsin made of a form of Vitamin A and a protein called opsin
When a photon strikes the rhodopsin molecule it splits it into retinene (pigment) and opsin (protein)
This creates an action potential on the membrane of the rods

21. Chemistry of Vision
Neurotransmitters are released from the end plates of the rods
Impulse is conducted to bipolar cells and to a neuron of the optic nerve
Rods require rhodopsin, long term Vitamin A deficiency can damage the rods

22. Colour Perception
Cones are sensitive to one of the primary colours of source light (red, blue, green)
Brain interprets different colours when combinations of cones are stimulated by light
Yellow is perceived when cones sensitive to red and green wavelengths are stimulated
The three types of cones firing in different combinations allows you to see millions of shades of colour

23. Colour Blindness Occurs when one or more types of cones are defective
Inherited trait, more common in males
Red-Green blindness most common
Cones containing red-sensitive pigment don’t work

24. Afterimages Positive afterimage Negative afterimage
Occurs after you look into a bright light and close your eyes
Image of light can still be seen though your eyes are closed
Negative afterimage
Occurs when eye is exposed to bright coloured light for an extended period of time

25. Focusing the Image
Cornea refracts the light into the lens, bending the light ray
Lens is thicker in the centre, light is bent to a focal point
An inverted image is projected onto the retina

28. Viewing Close Objects Ciliary muscles contract, lens becomes thicker
Thicker lens further bends the light
Pupil constricts to bring the image into sharp focus

29. Viewing Distant Objects
Ciliary muscles relax causing the lens to become thinner
Pupil dilates to capture maximum light

30. Vision Defects Glaucoma Cataracts Buildup of aqueous humour
Drainage ducts become blocked
Fluid builds up in anterior chamber exerting pressure on the eye
Retinal ganglion cells die
Cataracts
Lens becomes cloudy

31. Astigmatism
Vision defect caused by abnormal curvature of the lens or cornea

32. Nearsightedness (Myopia)
Occurs when eyeball is too long
Lens can’t flatten enough to project image on the retina
CAN focus on close up objects
CANNOT focus on distant objects
Fix: Glasses with a concave lens

34. Farsightedness (Hyperopia)
Caused by eyeball that is too short
Images are brought into focus behind the retina
CAN focus on distant objects
CANNOT focus on close up objects
Fix: Glasses with convex lens

36. The Ear
3 Sections
1. Outer Ear
2. Middle Ear
3. Inner Ear

37. Outer Ear Pinna Auditory canal Ear flap that funnels sound into canal
Responsible for collecting the sound
Auditory canal
Carries sound to the eardrum
Lined with specialized sweat glands

38. Middle Ear Tympanic membrane (eardrum)
Thin layer of tissue that receives sound vibrations
3 ossicles
Malleus (hammer)
Incus (anvil)
Stapes (stirrup)

39. Middle Ear
Sound vibrations from tympanic membrane are concentrated in the malleus and transmitted successively to other ossicles
Stapes hits the membrane covering the oval window in the inner wall of the middle ear

40. Middle Ear
Eustachian tube extends from middle ear to the chambers of the mouth and nose
Allows equalization of air pressure on either side of the eardrum

41. Inner Ear Composed of 3 structures Vestibule Semicircular Canals (3)
Connected to middle ear by the oval window
Contains two small sacs; utricle and saccule
Establishes static equilibrium
Semicircular Canals (3)
Sit at different angles
Fluid inside provides information about dynamic equilibrium
Cochlea
Coiled structure containing rows of specialized hair cells
Hair cells respond to sound waves and convert them into nerve impulses

43. How We Hear Sound waves push against eardrum
Vibrations of eardrum are passed onto ossicles
Bones concentrate and amplify the vibrations by up to 3 times
Waves of fluid are created when the oval window gets pushed inward while the round window gets pushed outwards
Cochlea receives the fluid waves and converts them to electrical impulses-you hear them as sound

44. How We Hear
The main sound receptor in the cochlea is the organ of Corti
Houses a single inner row and three outer rows of specialized hair cells anchored to the basilar membrane
Vibrations in the fluid on either side of the basilar membrane cause the membrane to move, hairs on the cells bend as they rub against the tectorial membrane

45. How We Hear
Movement of hair cells triggers sensory nerves in the basilar membrane
Sound information is sent to the temporal lobe of the cerebrum via auditory nerves

46. When it`s noisy…
Muscles that connect the bones of the middle ear contract reducing the movement of the malleus
Second muscle contracts pulling the stapes away from the oval window, protecting the inner ear from powerful vibrations

47. Pitch Basilar membrane is narrow and stiff near the oval window
Narrow area is activated by high frequency waves which are turned into basilar membrane vibrations that cause hair cells to move
Hair cells trigger action potential, carried to the brain and registered as high pitch sounds

48. Pitch
Low frequency waves move deeper into the cochlea causing wider, more elastic area to vibrate
Stimulation of nerve cells in different parts of the cochlea lets you tell the difference between a high pitched whistle and a rumble of thunder

49. Static Equilibrium Movement along one plane
Saccule and utricle monitor head position
Cilia from the hair cells are suspended in a gelatinous material that contains otoliths
Normal head position otoliths are still
Head is forward
Gravity acts on otoliths, causing gelatinous material to shift and cilia to bend
Movement of cilia stimulates sensory nerve and information is relayed to cerebellum

50. Dynamic Equilibrium Provides information while moving
Balance is maintained by 3 semicircular canals
Each canal has a pocket called an ampulla
Inside the ampulla is a cupula containing cilia attached to hair cells
Hair cells bend causing an impulse that is carried to brain