1. The Special Senses

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

3. re: 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
Disolved molecules bind & induce receptor cells to generate impulses in sensory nerve fibers

6. Types of taste
Sweet
Sour
Salty
Bitter
Glutamate (MSG)
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
Pseudostratified columnar epithelium
Has millions of bipolar neurons = olfactory receptor cells
Only neurons undergoing replacement throughout adult life
Olfactory 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
Olfactory bulb__ *
___Filaments of Olfactory nerve (CN I)
_______Olfactory tract *

10. 1000 types of smell receptors (approx.)
Convergence of many receptor cell signals onto one glomerulus registers a signature pattern
Brain recognizes the pattern: sent to unclus (olfactory center) and limbic area
Anosmia: absence of the sense of smell
Trauma
Colds or allergies producing excessive mucus
Polyps causing blockage
1/3 are from zinc deficiency

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 # “EOMs intact” means they all work right
Four are rectus muscles (straight)
Originate from common tendinous or anular ring, at posterior point of orbit
Two are oblique: superior and inferior

17. Extraocular (extrinsic) eye muscles
Cranial nerve innervations:
Lateral rectus: VI (Abducens n.) – abducts eye outward
Medial, superior, inferior rectus & inf oblique: III (Oculomotor n.) – able to look up and in if all work
Superior oblique: IV (Trochlear n.) – moves eye down and out

18. Innervation

19. 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

20. 3 Layers form the external wall of the eye
(outer) Fibrous: dense connective tissue
Sclera – white of the eye
Cornea
100s of sheets of collagen fibers between sheets of epithelium and endothelium
Clear because regular alignment
Role in light bending
Avascular but does have pain receptors
Regenerates
(middle) Vascular: uvea
Choroid – posterior, pigmented
Ciliary body
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 – posterior, pigmented
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
Pigmented put incomplete: pupil lets in light
Sphincter of pupil: circularly arranged smooth muscle - parasympathetic control
for bright light and/or close vision
Dilator of pupil: radiating smooth muscle – sympathetic control
for dim light and/or distance vision
(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. 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

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

31. 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

32. 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

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

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

36. Retina through ophthalmoscope
Macula: at posterior pole
Fovea: maximal visual acuity (most concentrated cones)
Optic disc: optic nerve exits
Vessels

37. 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. Optic tracts (of crossed and uncrossed, sensing opposite side of visual field of both eyes) synapse with neurons in lateral geniculate of 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.

38. 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

39. 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

40. The Ear Parts of the ear Outer (external) ear
Middle ear (ossicles) for hearing)
Inner ear (labyrinth) for hearing & equilibrium

41. Sound in external acoustic meatus hits tympanic membrane (eardrum) – it vibrates
Pressure is equalized by the pharyngotympanic tube (AKA eustachian or auditory tube)

42. TM causes ossicles in air filled middle ear to move:
Malleus (hammer)
Incus (anvil)
Stapes (stirrup)
These are 3 of the smallest bones of the body
Ossicles articulate to form a lever system that amplifies and transmits the vibratory motion of the TM to fluids of inner ear cochlea via oval window

43. Skeletal muscles of middle ear
When loud, muscles contract, limiting vibration and dampening the noise

44. Inner ear = bony “labyrinth” of 3 parts
Cochlea - hearing
Vestibule - equilibrium
Semicircular canals - equilibrium
In petrous part of the temporal bone
Semicircular canals____
Filled with perilymph and endolymph
fluids
Vestibule___________
Cochlea_______________________

45. Spiral organ of Corti in cochlea contains receptors for hearing (amplifies sound 100 times)
Vibration of stirrup at oval window starts traveling waves displacing basilar membrane
Sensory hair cells stimulated
Nerve ending of cochlear nerve division of VIII (Vestibulo-cochlear n.)

46. Auditory pathway

47. Equilibrium pathway
Via vestibular nerve branch of VIII (Vestibulocochlear n.) to the brain stem
Only special sense for which most of the information goes to lower brain centers

48. Vestibule contains utricle and saccule
Each contains a macula
Senses static equilibrium and linear acceleration of the head
(not rotational movements)
Tips of hairs imbedded in otolithic membrane (calcium carbonate “stones”)
Vestibular nerve branches of VIII (Vestibulocochlear n.)

49. Semicircular canals Each of the 3 lies in one of the 3 planes of space
Sense rotational acceleration of the head
Duct with ampulla housing a small crest: crista ampulla
Hairs project into jellylike cupula & basilar cells synapse with fibers of vestibular nerve

50. VIII Vestibulocochlear nerve