Approaches to Treatment and Therapy Chapter 16 Chapter 16 16 - 1.
Chapter 16
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Transcript of Chapter 16
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Chapter 16
The Special Senses
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The Special Senses
Chemical senses Taste (gustation) Smell (olfaction)
Vision The ear
Hearing Equilibrium
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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
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TASTE Taste buds: mostly on tongue Two types
Fungiform papillae (small, on entire surface of tongue) Circumvallate papillae (inverted “V” near back of tongue)
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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
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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
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Olfactory epithelium in roof of nasal cavity Has millions of bipolar neurons = olfactory receptor cells
Only neurons undergoing replacement throughout adult lifeOlfactory hair (cilia) bind odor molecules
Mucus captures & dissolves odor moleculesEach receptor cell has an axon - are bundled into “filaments” of olfactory nerve
Penetrate cribriform plate of ethmoid bone & enter olfactory bulb
Smell(olfaction)
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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__
_______Olfactory tract
Filaments of Olfactory nerve (CN I)
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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
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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
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Accessory structures of the eye
Eyebrows Eyelids or palpebrae
Upper & lower separated by palpebral fissure Corners: medial & lateral canthi Eyelashes
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Eyelid tarsal plates give structure Where orbicularis oculi muscles attach (close eyes)
Levator palpebrae superioris muscle Lifts upper lid voluntarily (inserts on tarsal plate)
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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)
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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)
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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
When Extrinsic Eye Muscles ContractWhen 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
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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.)
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3 Layers form the external wall of the eye
1. (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
2. (middle) Vascular: Choroid – blood rich, dark pigmented Ciliary body – attaches lens Iris (colored part: see next slide)
3. (inner) Sensory Retina and optic nerve
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1. (outer layer) Fibrous: dense connective tissue
Sclera – white of the eye Cornea
2. (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
3. (inner layer) Sensory Retina and optic nerve
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Layers of external wall of eye continued1. (outer) Fibrous: dense connective tissue
Sclera – white of the eye Cornea
2. (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
3. (inner) Sensory Retina
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Layers of external wall of eye continued
1. (outer) Fibrous: dense connective tissue Sclera – white of the eye Cornea
2. (middle) Vascular: uvea Choroid – posterior, pigmented Ciliary body Iris
3. (inner) Sensory Retina -------will cover after the chambers
and lens
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some pictures…
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Chambers and fluids
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
(see previous pics)
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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
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Cataract (opaque lens)
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(to a lesser degree, not shown here, the cornea also)
a. Resting eye set for distance vision: parallel light focused on retina
b. Resting eye doesn’t see near objects because divergent rays are focused behind retina
c. Lens accommodates (becomes rounder) so as to bend divergent rays more sharply, thereby allowing convergence on the retina
Note: images are upside down and reversed from left to right, like a camera
The eye is an optical device: predominantly the lens
Lens AccommodationLens 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
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Retina: develops as part of the brain
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:
1. (outer layer) Fibrous: dense connective tissueSclera – white of the eyeCornea
2. (middle layer) Vascular: uveaChoroid – posterior, pigmentedCiliary bodyIris
3. (inner layer) SensoryRetina and optic nerve
Remember the 3 layers of the external eye?
1. Photoreceptors2. Bipolor cells3. Ganglion cells
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Light passes through pupil in iris, through vitreous humor, through axons, ganglion cells and bipolar cells, to photoreceptors next to pigmented layer
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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
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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
http://www.yorku.ca/eye/rod-cone.gif http://www.secretbeyondmatter.com/ourbrains/theworldinourbrains_files/11-1.jpg
Cone SensitivityCone 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
COLORBLINDNESS
- 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
•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.
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One of the Ishihara charts for color blindness
Commonly X-linked recessive: 8% males and 0.4% females
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If you want more detail, it’s fascinating…
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Retina through ophthalmoscope
Macula: at posterior pole Fovea: maximal
visual acuity (most concentrated cones)
Optic disc: optic nerve exits
Vessels
Images Formed on the RetinaImages 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.
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Visual pathwaysGreen is area seen by both eyes, and is the area of stereoscopic vision
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.
Visual PathwayVisual Pathway Photoreceptors of
the retina
Optic nerve
Optic nerve crosses at the optic chiasma
Optic tract
Thalamus
Visual Cortex of Occipital Lobe
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Visual field defectsprint this out and follow from the fields to the visual cortex using 4 colors
remember: fields are reversed and upside down
1. Optic nerveipsilateral (same side) blind eye
2. Chiasmatic (pituitary tumors classically)lateral half of both eyes gone
3. Optic tractopposite half of visual field gone
4. & 5. Distal to geniculate ganglion of thalamus:homonymous superior field (4) or homonymous inferior field (5) defect
Visual cortex
Visual fields
1.
2.
3.
5.4.
Location of lesion:
1.
2.
3.
4.
5.
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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
Geometrical illusions
Successive contrast : afterimages ...
what do you see?
fixate the black dot in the center for 60 seconds ...
… and then look at a the black dot in the right panel !
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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
Anatomy of the EarAnatomy of the Ear
The ear is divided into three areas Outer
(external) ear
Middle ear
Inner ear
(Add C. “INNER EAR” to notes)
The External EarThe External Ear Involved in
hearing only
Structures of the external ear Pinna (auricle)-
collects sound
External auditory canal- channels sound inward
The External Auditory CanalThe 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)
The Middle Ear or Tympanic CavityThe Middle Ear or Tympanic Cavity
Air-filled cavity within the temporal bone
Only involved in the sense of hearing
The Middle Ear or Tympanic CavityThe 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
Bones of the Tympanic CavityBones of the Tympanic Cavity
Three bones span the cavity
Malleus (hammer)
Incus (anvil)
Stapes (stirrip)
http://www.ghorayeb.com/files/STAPES_on_a_Penny_375_SQ.jpg
http://medicine.wustl.edu/~oto/bbears/images/ossic.jpg
Bones of the Tympanic CavityBones of the Tympanic Cavity
Vibrations from eardrum move the malleus
These bones transfer sound to the inner ear
Inner Ear or Bony LabyrinthInner Ear or Bony Labyrinth
Also known as osseous labyrinth- twisted bony tubes
Includes sense organs for hearing and balance
Filled with perilymph
Inner Ear or Bony LabryinthInner Ear or Bony Labryinth 3 Subdivisions
Cochlea
Upper chamber is the scala vestibuli
Lower chamber is the scala tympani
Vestibule
Semicircular canals
ChochleaChochlea
Spiral organ of Corti
Receptors = hair cells on the basilar membrane
Scala tympani
Scala vestibuli
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)
Organ of CortiOrgan of Corti
Scala tympani
Scala vestibuli
Organs of HearingOrgans of Hearing Organ of Corti
Cochlear nerve attached to hair cells transmits nerve impulses to auditory cortex on temporal lobe
Scala tympani
Scala vestibuli
Mechanisms of HearingMechanisms 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
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Mechanisms of HearingMechanisms 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)
Continued stimulation can lead to adaptation (over stimulation to the brain makes it stop interpreting the sounds)
Mechanisms of HearingMechanisms of Hearing
Organs of EquilibriumOrgans of Equilibrium
Receptor cells are in two structures
Vestibule
Semicircular canals
Organs of EquilibriumOrgans of Equilibrium Equilibrium has two functional parts
Static equilibrium- in the vestibule
Dynamic equilibrium- in the semicircular canals
Static EquilibriumStatic Equilibrium Maculae –
receptors in the vestibule Report on
the position of the head
Send information via the vestibular nerve
Static EquilibriumStatic Equilibrium Anatomy of the
maculae Hair cells are
embedded in the otolithic membrane
Otoliths (tiny stones) float in a gel around the hair cells
Function of MaculaeFunction of MaculaeMovements cause otoliths to bend the hair cells (gravity moves the “rocks” over and pulls the hairs)
http://neuromedia.neurobio.ucla.edu/campbell/eyeandear/wp_images/177_macula_HP.gif
Dynamic EquilibriumDynamic Equilibrium Whole structure is the
ampulla
Crista ampullaris – receptors in the semicircular canals
Tuft of hair cells
Cupula (gelatinous cap) covers the hair cells
Dynamic EquilibriumDynamic 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
DYNAMIC EQUILIBRIUM STRUCTURES
http://www.faculty.une.edu/com/abell/histo/CristaAmp.jpg
http://neuromedia.neurobio.ucla.edu/campbell/eyeandear/wp_images/177_macula_crista.gif
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
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