1. Chapter 16
The Special Senses

2. The Special Senses Chemical senses Vision The ear Taste (gustation)
Smell (olfaction)
Vision
The ear
Hearing
Equilibrium

3. Touch
The sense of touch is part of the General somatic senses____
This chapter deals with the Special category of the two left sensory boxes

4. TASTE Taste buds: mostly on tongue Two types
Fungiform papillae (small, on entire surface of tongue)
Circumvallate papillae (inverted “V” near back of tongue)

5. Taste buds of 50-100 epithelial cells each
Taste receptor cells (gustatory cells)
Microvilli through pore, bathed in saliva
Dissolved molecules bind & induce receptor cells to generate impulses in sensory nerve fibers

6. Types of taste
Sweet
Sour
Salty
Bitter
Umami “beef taste”- elicited by Glutamine
Gustatory (taste) pathway to brainstem & cerebral cortex via two cranial nerves:
VII (Facial n.) – anterior 2/3 of tongue
IX (Glossopharyngeal n.) – posterior 1/3 tongue and pharynx

7. Smell (olfaction) Olfactory epithelium in roof of nasal cavity
Has millions of bipolar neurons = olfactory receptor cells
Only neurons undergoing replacement throughout adult life
Olfactory hair (cilia) bind odor molecules
Mucus captures & dissolves odor molecules
Each receptor cell has an axon - are bundled into “filaments” of olfactory nerve
Penetrate cribriform plate of ethmoid bone & enter olfactory bulb
Smell
(olfaction)

8. * Olfactory bulb is in forebrain
In bulb nerve axons branch and synapse with mitral cells (neurons in clusters of “glomeruli”)
Mitral cells send signals via olfactory tract
Filaments of Olfactory nerve (CN I) *
Olfactory bulb__
_______Olfactory tract *

10. Anosmia: absence of the sense of smell
Trauma
Colds or allergies producing excessive mucus
Polyps causing blockage
1/3 are from zinc deficiency
Head injury
Aging

11. The Eye and Vision Vision is the dominant sense in humans
70% of sensory receptors in humans are in the eyes
40% of the cerebral cortex is involved in processing visual information
The eye (or eyeball) is the visual organ
Diameter 2.5 cm (1 inch)
Only anterior 1/6 visible
Lies in bony orbit
Surrounded by a protective cushion of fat

12. Accessory structures of the eye
Eyebrows
Eyelids or palpebrae
Upper & lower separated by palpebral fissure
Corners: medial & lateral canthi
Eyelashes

13. Eyelid tarsal plates give structure
Where orbicularis oculi muscles attach (close eyes)
Levator palpebrae superioris muscle
Lifts upper lid voluntarily (inserts on tarsal plate)

14. Tarsal glands – modified sebaceous (oil) glands in tarsal plates
Conjunctiva - transparent mucus membrane of stratified columnar epithelium
Palpebral conjunctiva
Bulbar conjunctiva
Covers white of eye but not the cornea (transparent tissue over the iris and pupil)

15. Lacrimal apparatus Responsible for tears
The fluid has mucus, antibodies and lysozyme
Lacrimal gland in orbit superolateral to eye
Tears pass out through puncta into canaliculi into sac into nasolacrimal duct
Empty into nasal cavity (sniffles)

16. Extraocular (extrinsic) eye muscles: 6 in #
Four are rectus muscles (straight)
Lateral rectus, medial rectus, superior rectus, and inferior rectus.
Two are oblique: superior and inferior

17. When Extrinsic Eye Muscles Contract
Superior oblique- eyes look out and down
Superior rectus- eyes looks up
Lateral rectus- eyes look outward
Medial rectus- eyes look inward
Inferior rectus- eyes looks down
Inferior oblique- eyes look in and up

19. Extraocular (extrinsic) eye muscles
Cranial nerve innervations:
Lateral rectus: VI (Abducens nerve)
Medial, superior, inferior rectus & inferior oblique:
III (Oculomotor nerve.)
Superior oblique: IV (Trochlear n.)

20. 3 Layers form the external wall of the eye
(outer) Fibrous: dense connective tissue
Sclera – white of the eye
Cornea
Clear because regular alignment
Role in light bending
Avascular but DOES have pain receptors
Regenerates
(middle) Vascular:
Choroid – blood rich, dark pigmented
Ciliary body – attaches lens
Iris (colored part: see next slide)
(inner) Sensory
Retina and optic nerve

21. (outer layer) Fibrous: dense connective tissue
Sclera – white of the eye
Cornea
(middle) Vascular: uvea
Choroid – blood rich, has dark pigmented that prevents light scattering
Ciliary body
Muscles – control lens shape
Processes – secrete aqueous humor
Zonule (attaches lens)
Iris
(inner layer) Sensory
Retina and optic nerve

22. Layers of external wall of eye continued
(outer) Fibrous: dense connective tissue
Sclera – white of the eye
Cornea
(middle) Vascular: uvea
Choroid – posterior, pigmented
Ciliary body
Iris
Opening is called PUPIL: lets in light
Acts like the diaphragm of a camera lens.
Regulates the amount of light that enters by contracting or dilating to see clearly.
Dark to dim light = dilation
Bright light and close vision = contraction
(inner) Sensory
Retina

23. Layers of external wall of eye continued
(outer) Fibrous: dense connective tissue
Sclera – white of the eye
Cornea
(middle) Vascular: uvea
Choroid – posterior, pigmented
Ciliary body
Iris
(inner) Sensory
Retina will cover after the chambers and lens

24. some pictures…

25. Chambers and fluids Vitreous humor in posterior segment
(see previous pics)
Vitreous humor in posterior segment
Jellylike
Forms in embryo and lasts life-time
Anterior segment filled with aqueous humor – liquid, replaced continuously
Anterior chamber between cornea and iris
Posterior chamber between iris and lens
Glaucoma when problem with drainage resulting in increased intraocular pressure

26. Lens: thick, transparent biconvex disc
Changes shape for precise focusing of light on retina
Onion-like avascular fibers, increase through life
Cataract if becomes clouded
Note lens below,
but in life it is clear
Cataract below: the lens is milky and opaque, not the cornea

27. Cataract (opaque lens)

28. The eye is an optical device: predominantly the lens
(to a lesser degree, not shown here, the cornea also)
Note: images are upside down and reversed from left to right, like a camera
Resting eye set for distance vision: parallel light focused on retina
Resting eye doesn’t see near objects because divergent rays are focused behind retina
Lens accommodates (becomes rounder) so as to bend divergent rays more sharply, thereby allowing convergence on the retina

29. Lens Accommodation
Light must be focused to a point on the retina for optimal vision
The eye is set for distance vision (over 20 ft away)
20/20 vision- at 20 feet, you see what a normal eye would see at 20 feet (20/100- at 20, normal person would see at 100)
The lens must change shape to focus for closer objects

30. Retina: develops as part of the brain
1. (outer layer) Fibrous: dense connective tissue
Sclera – white of the eye
Cornea
2. (middle layer) Vascular: uvea
Choroid – posterior, pigmented
Ciliary body
Iris
3. (inner layer) Sensory
Retina and optic nerve
Remember the 3 layers of the external eye?
Retina is 2 layers
Outer thin pigmented layer:
Melanocytes (prevent light scattering)
Inner thicker neural layer
Plays a direct role in vision
Three type of neurons:
Photoreceptors
Bipolor cells
Ganglion cells

31. Light passes through pupil in iris, through vitreous humor, through axons, ganglion cells and bipolar cells, to photoreceptors next to pigmented layer

32. Photoreceptor neurons signal bipolar cells, which signal ganglion cells to generate (or not) action potentials: axons run on internal surface to optic nerve which runs to brain
*Know that axons from the retina form the optic nerve, CN II

33. Photoreceptors: 2 types
Rod cells
More sensitive to light - vision permitted in dim light but only gray and fuzzy
Only black and white and not sharp
Cone cells
High acuity in bright light
Color vision
3 sub-types: blue, red and green light cones
*Know that rods are for B & W and cones are for color

35. Cone Sensitivity There are three types of cones
Different cones are sensitive to different wavelengths red- long green- medium blue- short
Color blindness is the result of lack of one or more cone type

36. COLORBLINDNESS
Comes from a lack of one or more types of color receptors.
Most are green or red or both and that is due to a lack of red receptors.
Another possibility is to have the color receptors missing entirely, which would result in black and white vision.
An inherited trait that is transferred on the sex chromosomes (23rd pair)- sex-linked trait
Occurs more often in males
Can not be cured or corrected

37. One of the Ishihara charts for color blindness
Commonly X-linked recessive: 8% males and 0.4% females

39. If you want more detail, it’s fascinating…

40. Retina through ophthalmoscope
Macula: at posterior pole
Fovea: maximal visual acuity (most concentrated cones)
Optic disc: optic nerve exits
Vessels
The Macula is a highly pigmented yellow spot at the center is the fovea. The macula contains the highest concentration of cone cells and high resolution vision. The yellow pigment absorbs blue and UV light which acts as a natural sunblock.

41. Images Formed on the Retina
If the image is focused at the spot where the optic disk is located, nothing will be seen. This is known as the blind spot. There are no photoreceptors there, as nerves and blood vessels pass through this point.

42. Green is area seen by both eyes, and is the area of stereoscopic vision
Visual pathways
At optic chiasm, medial fibers from each eye (which view lateral fields of vision) cross to opposite side of the brain. Optic tracts (of crossed and uncrossed fibers, sensing opposite side of visual field of both eyes) synapse with neurons in the thalamus. These axons form the optic radiation and terminate in the primary visual cortex in the occipital lobe. Left half of visual field perceived by right cerebral cortex, and vice versa.

43. Visual Pathway Photoreceptors of the retina Optic nerve
Optic nerve crosses at the optic chiasma
Optic tract
Thalamus
Visual Cortex of Occipital Lobe

44. Visual field defects print this out and follow from the fields to the visual cortex using 4 colors remember: fields are reversed and upside down
Visual fields
Location of lesion:
1. Optic nerve
ipsilateral (same side) blind eye
2. Chiasmatic (pituitary tumors classically)
lateral half of both eyes gone
3. Optic tract
opposite half of visual field gone
4. & 5. Distal to geniculate ganglion of thalamus:
homonymous superior field (4) or homonymous inferior field (5) defect 1. 2. 1. 3. 3. 2. 4. 5. 5. 4.
Visual cortex

45. Double vision: diplopia (what the patient experiences)
Eyes do not look at the same point in the visual field
Misalignment: strabismus (what is observed when shine a light: not reflected in the same place on both eyes) – can be a cause of diplopia
Cross eyed
Gaze & movements not conjugate (together)
Medial or lateral, fixed or not
Many causes
Weakness or paralysis of extrinsic muscle of eye
Surgical correction necessary
Oculomotor nerve problem, other problems
Lazy eye: amblyopia
Cover/uncover test at 5 yo
If don’t patch good eye by 6, brain ignores lazy eye and visual pathway degenerates: eye functionally blind
NOTE: some neurological development and connections have a window of time - need stimuli to develop, or ability lost

46. Illusions
Geometrical illusions

47. Illusions
Successive contrast : afterimages ...
fixate the black dot in the center for 60 seconds … and then look at a the black dot in the right panel !
afterimages are the consequence of encoding stimulus change in time:
intensity changes are encoded rather than intensity levels
adaptation leads to the loss of sensitivity to a particular feature
after disappearance of the stimulus the opposite feature is perceived due to opponent processing
                                            what do you see?

49. Auditory System

50. Terminology, remember…
Optic – refers to the eye
Otic – refers to the ear
Getting eyedrops and ear drops mixed up is probably not a good idea

51. Anatomy of the Ear The ear is divided into three areas
Outer (external) ear
Middle ear
Inner ear
(Add C. “INNER EAR” to notes)

52. The External Ear Involved in hearing only
Structures of the external ear
Pinna (auricle)- collects sound
External auditory canal- channels sound inward

53. The External Auditory Canal
Narrow chamber in the temporal bone- through the external auditory meatus
Lined with skin
Ceruminous (wax) glands are present
Ends at the tympanic membrane (eardrum)

54. The Middle Ear or Tympanic Cavity
Air-filled cavity within the temporal bone
Only involved in the sense of hearing

55. The Middle Ear or Tympanic Cavity
Two tubes are associated with the inner ear
The opening from the auditory canal is covered by the tympanic membrane (eardrum)
The auditory tube connecting the middle ear with the throat (also know as the eustacian tube)
Allows for equalizing pressure during yawning or swallowing
This tube is otherwise collapsed

56. Bones of the Tympanic Cavity
Three bones span the cavity
Malleus (hammer)
Incus (anvil)
Stapes (stirrip)

58. Bones of the Tympanic Cavity
Vibrations from eardrum move the malleus
These bones transfer sound to the inner ear

59. Inner Ear or Bony Labyrinth
Also known as osseous labyrinth- twisted bony tubes
Includes sense organs for hearing and balance
Filled with perilymph

60. Inner Ear or Bony Labryinth
3 Subdivisions
Cochlea
Upper chamber is the scala vestibuli
Lower chamber is the scala tympani
Vestibule
Semicircular canals

61. Chochlea Spiral organ of Corti
Receptors = hair cells on the basilar membrane
Scala vestibuli
Scala tympani

62. Organ of Corti
Gel-like tectorial membrane is capable of bending hair cells (endolymph in the membranous labyrinth of the cochlear duct flows over it and pushes on the membrane)
Scala vestibuli
Scala tympani

63. Organs of Hearing Organ of Corti
Cochlear nerve attached to hair cells transmits nerve impulses to auditory cortex on temporal lobe
Scala vestibuli
Scala tympani

64. Mechanisms of Hearing
Vibrations from sound waves move tectorial membrane (pass through the endolymph fluid filling the membranous labyrinth in the cochlear duct)
Hair cells are bent by the membrane

66. Mechanisms of Hearing An action potential starts in the cochlear nerve
The signal is transmitted to the midbrain (for auditory reflexes and then directed to the auditory cortex of the temporal lobe)

67. Mechanisms of Hearing
Continued stimulation can lead to adaptation (over stimulation to the brain makes it stop interpreting the sounds)

68. Organs of Equilibrium Receptor cells are in two structures Vestibule
Semicircular canals

69. Organs of Equilibrium Equilibrium has two functional parts
Static equilibrium- in the vestibule
Dynamic equilibrium- in the semicircular canals

70. Static Equilibrium Maculae – receptors in the vestibule
Report on the position of the head
Send information via the vestibular nerve

71. Static Equilibrium Anatomy of the maculae
Hair cells are embedded in the otolithic membrane
Otoliths (tiny stones) float in a gel around the hair cells

72. Function of Maculae
Movements cause otoliths to bend the hair cells (gravity moves the “rocks” over and pulls the hairs)

73. http://neuromedia. neurobio. ucla

74. Dynamic Equilibrium Whole structure is the ampulla
Crista ampullaris – receptors in the semicircular canals
Tuft of hair cells
Cupula (gelatinous cap) covers the hair cells

75. Dynamic Equilibrium Action of angular head movements
The cupula stimulates the hair cells
Movement of endolymph pushes the cupula over and pulls the hairs
An impulse is sent via the vestibular nerve to the cerebellum

76. DYNAMIC EQUILIBRIUM STRUCTURES

77. http://neuromedia. neurobio. ucla

78. Deafness
Hearing loss- due to disease (ex. meningitus), damage, or age related
Conduction deafness- prevention or blocking sounds from entering inner ear.
Ex. ear wax, ruptured ear drum, middle ear inflammation (otis media), and otosclerosis (hardening of the ossicles of the ear)
Sensoneural deafness- damage to the neural structures from any point from the cochlear hair cells to and including the auditory cortical cells
Partial or complete deafness, or gradual loss over time

79. Deafness
Tinnitus- ringing or clicking sound in the absence of auditory stimuli; 1st symptom of cochlear nerve degeneration
may result from inflammation of the inner or middle ear
side effect from medicine such as aspirin
Symptoms- vertigo, nausea, hearing loss
Meniere's Syndrome- labyrinth disorder; effects both semicircular canals and cochlea