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The Special Senses
Chemical Senses
Chemical senses – gustation (taste) and olfaction (smell)
Their chemoreceptors respond to chemicals in aqueous solution
Taste – to substances dissolved in saliva
Smell – to substances dissolved in fluids of the nasal membranes
Taste Buds
Most of the 10,000 or so taste buds are found on the tongue
Taste buds are found in papillae of the tongue mucosa
Papillae come in three types: filiform, fungiform, and circumvallate
Fungiform and circumvallate papillae contain taste buds
Taste Buds
Figure 15.1
Anatomy of a Taste Bud
Each gourd-shaped taste bud consists of three major cell types
Supporting cells – insulate the receptor
Basal cells – dynamic stem cells
Gustatory cells – taste cells
Taste Sensations
There are five basic taste sensations Sweet – sugars,
saccharin, alcohol, and some amino acids
Salt – metal ions Sour – hydrogen ions Bitter – alkaloids such as
quinine and nicotine Umami – elicited by the
amino acid glutamate
Physiology of Taste
In order to be tasted, a chemical:
Must be dissolved in saliva
Must contact gustatory hairs
Binding of the food chemical:
Depolarizes the taste cell membrane, releasing neurotransmitter
Initiates a generator potential that elicits an action potential
Taste Transduction
The stimulus energy of taste is converted into a nerve impulse by:
Na+ influx in salty tastes
H+ in sour tastes (by directly entering the cell, by opening cation channels, or by blockade of K+ channels)
Gustducin in sweet and bitter tastes
Gustatory Pathway
Cranial Nerves VII and IX carry impulses from taste buds to the solitary nucleus of the medulla
These impulses then travel to the thalamus, and from there fibers branch to the:
Gustatory cortex (taste)
Hypothalamus and limbic system (appreciation of taste)
Gustatory Pathway
Influence of Other Sensations on Taste
Taste is 80% smell
Thermoreceptors, mechanoreceptors, nociceptors also influence tastes
Temperature and texture enhance or detract from taste
Sense of Smell
The organ of smell is the olfactory epithelium, which covers the superior nasal concha
Olfactory receptor cells are bipolar neurons with radiating olfactory cilia
Olfactory receptors are surrounded and cushioned by supporting cells
Basal cells lie at the base of the epithelium
Sense of Smell
Physiology of Smell
Olfactory receptors respond to several different odor-causing chemicals
When bound to ligand these proteins initiate a G protein mechanism, which uses cAMP as a second messenger
cAMP opens Na+ and Ca2+ channels, causing depolarization of the receptor membrane that then triggers an action potential
Olfactory receptor cells
Processing of scents in the olfactory bulb
Each of the glomeruli lining the olfactory bulb receives synaptic input from only one type of olfactory receptor responds to only one discrete component of an odorant.
The glomeruli sort and file the various components of an odoriferous molecule before relaying the smell signal to the mitral cells and higher brain levels for further processing
Signal transduction in an odorant receptor
Olfactory receptors are G protein–coupled receptors that dissociate on binding to the odorant. The α-subunit of G proteinsactivates adenylate cyclase to catalyze production of cAMP. cAMPacts as a second messenger to open cation channels. Inwarddiffusion of Na+ and Ca2+ produces depolarization
Olfactory Transduction ProcessOdorant binding protein
Odorant chemical
Na+
Cytoplasm
Inactive Active
Na+ influx causes depolarization
Adenylate cyclase
ATP
cAMP
Depolarization of olfactory receptor cell membrane triggers action potentials in axon of receptor
Olfactory pathway
Information is transmitted from the olfactory bulb by axons of mitral and tufted relay neurons in the lateral olfactory tract.
Mitral cells project to five regions of the olfactory cortex: anterior olfactory nucleus, olfactory tubercle, piriform cortex, and parts of the amygdala and entorhinal cortex.
Tufted cells project to anterior olfactory nucleus and olfactory tubercle; mitral cells in the accessory olfactory bulb project only to the amygdala.
Conscious discrimination of odor depends on the neocortex (orbitofrontal and frontal cortices).
Emotive aspects of olfaction derive from limbic projections (amygdala and hypothalamus).
Olfactory pathway
Olfactory Pathway
Olfactory receptor cells synapse with mitral cells
Glomerular mitral cells process odor signals
Mitral cells send impulses to:
The olfactory cortex
The hypothalamus, amygdala, and limbic system
Eye and Associated Structures
70% of all sensory receptors are in the eye
Most of the eye is protected by a cushion of fat and the bony orbit
Accessory structures include eyebrows, eyelids, conjunctiva, lacrimal apparatus, and extrinsic eye muscles
Eyebrows
Coarse hairs that overlie the supraorbital margins
Functions include:
Shading the eye
Preventing perspiration from reaching the eye
Orbicularis muscle – depresses the eyebrows
Corrugator muscles – move the eyebrows medially
Palpebrae (Eyelids)
Protect the eye anteriorly
Palpebral fissure – separates eyelids
Canthi – medial and lateral angles (commissures)
Palpebrae (Eyelids)
Lacrimal caruncle – contains glands that secrete a whitish, oily secretion (Sandman’s eye sand)
Tarsal plates of connective tissue support the eyelids internally
Levator palpebrae superioris – gives the upper eyelid mobility
Palpebrae (Eyelids)
Eyelashes
Project from the free margin of each eyelid
Initiate reflex blinking
Lubricating glands associated with the eyelids
Meibomian glands and sebaceous glands
Ciliary glands lie between the hair follicles
Palpebrae (Eyelids)
Conjunctiva
Transparent membrane that:
Lines the eyelids as the palpebral conjunctiva
Covers the whites of the eyes as the ocular conjunctiva
Lubricates and protects the eye
Lacrimal Apparatus
Consists of the lacrimal gland and associated ducts
Lacrimal glands secrete tears
Tears
Contain mucus, antibodies, and lysozyme
Enter the eye via superolateral excretory ducts
Exit the eye medially via the lacrimal punctum
Drain into the nasolacrimal duct
Lacrimal Apparatus
Extrinsic Eye Muscles
Six straplike extrinsic eye muscles
Enable the eye to follow moving objects
Maintain the shape of the eyeball
Four rectus muscles originate from the annular ring
Two oblique muscles move the eye in the vertical plane
Extrinsic Eye Muscles
Figure 15.7a, b
Summary of Cranial Nerves and Muscle Actions
Names, actions, and cranial nerve innervation of the extrinsic eye muscles
Figure 15.7c
Structure of the Eyeball
A slightly irregular hollow sphere with anterior and posterior poles
The wall is composed of three tunics – fibrous, vascular, and sensory
The internal cavity is filled with fluids called humors
The lens separates the internal cavity into anterior and posterior segments
Structure of the Eyeball
Figure 15.8a
Fibrous Tunic
Forms the outermost coat of the eye and is composed of:
Opaque sclera (posteriorly)
Clear cornea (anteriorly)
The sclera protects the eye and anchors extrinsic muscles
The cornea lets light enter the eye
Vascular Tunic (Uvea): Choroid Region
Has three regions: choroid, ciliary body, and iris
Choroid region
A dark brown membrane that forms the posterior portion of the uvea
Supplies blood to all eye tunics
Vascular Tunic: Ciliary Body
A thickened ring of tissue surrounding the lens
Composed of smooth muscle bundles (ciliary muscles)
Anchors the suspensory ligament that holds the lens in place
Vascular Tunic: Iris
The colored part of the eye
Pupil – central opening of the iris
Regulates the amount of light entering the eye during:
Close vision and bright light – pupils constrict
Distant vision and dim light – pupils dilate
Changes in emotional state – pupils dilate when the subject matter is appealing or requires problem-solving skills
Pupil Dilation and Constriction
Figure 15.9
The amount of light entering the eye is controlled by the iris.
Not all the light passing through the cornea reaches the light sensitive photoreceptors, because of the presence of the iris, a thin, pigmented smooth muscle that forms a visible ringlike structure within the aqueous humor
Bright light Normal light Dark
Controlled amount of light entering the eye
The neural pathways of the pupillary reflexes
Sensory Tunic: Retina
A delicate two-layered membrane
Pigmented layer – the outer layer that absorbs light and prevents its scattering
Neural layer, which contains:
Photoreceptors that transduce light energy
Bipolar cells and ganglion cells
Amacrine and horizontal cells
Retinal layers
Retinal layers
The retinal visual pathway extends from the photoreceptor cells(rods and cones, whose light-sensitive ends face the choroid away from the incoming light) to the bipolar cells to the ganglion cells. The horizontal and amacrine cells act locally for retinal processingof visual input.
Retina layers
Sensory Tunic: Retina
Figure 15.10a
The Retina: Ganglion Cells and the Optic Disc
Ganglion cell axons:
Run along the inner surface of the retina
Leave the eye as the optic nerve
The optic disc:
Is the site where the optic nerve leaves the eye
Lacks photoreceptors (the blind spot)
Retina seen through the ophthalmoscope
(a) A photograph and (b) an illustration of the optic fundus (back of the eye). Optic nerve fibers leave the eyeball at the optic disc to form the optic nerve. The arteries, arterioles, and veins in the superficial layers of the retina near its vitreous surface can be seen through the ophthalmoscope.
(a) (b)
The Retina: Ganglion Cells and the Optic Disc
Figure 15.10b
A. Fovea centralisB. Macula luteaC. Optic NerveD. Arteries
The fovea centralis highest concentration of cone photoreceptors high level of cones
Color vision diameter human fovea centralis is about 0.04 inches (1 mm) 1% of the total surface of retina
Contributes to about 50% of the nerve opticfibers and about 50% of the brain volume in the visual cortex
The Retina: Photoreceptors
Rods:
Respond to dim light
Are used for peripheral vision
Cones:
Respond to bright light
Have high-acuity color vision
Are found in the macula lutea
Are concentrated in the fovea centralis
Blood Supply to the Retina
The neural retina receives its blood supply from two sources
The outer third receives its blood from the choroid
The inner two-thirds is served by the central artery and vein
Small vessels radiate out from the optic disc and can be seen with an ophthalmoscope
Inner Chambers and Fluids
The lens separates the internal eye into anterior and posterior segments
The posterior segment is filled with a clear gel called vitreous humor that:
Transmits light
Supports the posterior surface of the lens
Holds the neural retina firmly against the pigmented layer
Contributes to intraocular pressure
Anterior Segment
Composed of two chambers
Anterior – between the cornea and the iris
Posterior – between the iris and the lens
Aqueous humor
A plasmalike fluid that fills the anterior segment
Drains via the canal of Schlemm
Supports, nourishes, and removes wastes
Anterior Segment
Figure 15.12
Formation and drainage of aqueous humor
Aqueous humor is formed by a capillary network in the ciliary body
Drains into the canal of Schlemm, and eventually enters the blood
Lens
A biconvex, transparent, flexible, avascular structure that:
Allows precise focusing of light onto the retina
Is composed of epithelium and lens fibers
Lens epithelium – anterior cells that differentiate into lens fibers
Lens fibers – cells filled with the transparent protein crystallin
With age, the lens becomes more compact and dense and loses its elasticity
Mechanism of accommodation
(a) Suspensory ligaments extend from the ciliary muscle to the outer edge of the lens
Mechanism of accommodation
(b) When the ciliary muscle is relaxed, the suspensoryligaments are taut, putting tension on the lens so that it is flat and weak. (c) When the ciliary muscle is contracted, the suspensory ligaments become slack, reducing the tension on the lens, allowing it to assume a stronger, rounder shape because of its elasticity.
Light
Electromagnetic radiation – all energy waves from short gamma rays to long radio waves
Our eyes respond to a small portion of this spectrum called the visible spectrum
Different cones in the retina respond to different wavelengths of the visible spectrum
Light
Figure 15.14
Refraction and Lenses
When light passes from one transparent medium to another its speed changes and it refracts (bends)
Light passing through a convex lens (as in the eye) is bent so that the rays converge to a focal point
When a convex lens forms an image, the image is upside down and reversed right to left
Refraction and Lenses
Figure 15.16
Focusing Light on the Retina
Pathway of light entering the eye: cornea, aqueous humor, lens, vitreous humor, and the neural layer of the retina to the photoreceptors
Light is refracted:
At the cornea
Entering the lens
Leaving the lens
The lens curvature and shape allow for fine focusing of an image
Focusing for Distant Vision
Light from a distance needs little adjustment for proper focusing
Far point of vision – the distance beyond which the lens does not need to change shape to focus (20 ft.)
Figure 15.17a
Focusing for Close Vision
Close vision requires:
Accommodation – changing the lens shape by ciliary muscles to increase refractory power
Constriction – the pupillary reflex constricts the pupils to prevent divergent light rays from entering the eye
Convergence – medial rotation of the eyeballs toward the object being viewed
Focusing for Close Vision
Figure 15.7b
Problems of Refraction
Emmetropic eye – normal eye with light focused properly
Myopic eye (nearsighted) – the focal point is in front of the retina
Corrected with a concave lens
Hyperopic eye (farsighted) – the focal point is behind the retina
Corrected with a convex lens
Problems of Refraction
Figure 15.18
The refractive power of a lens is measured in diopters. The dioptric power (D) of a lens is the reciprocal of the focal length measured in meters:
Lens refrractions
For diverging lenses, the dioptric power is negative, so that a diverging lens with a focal length of 10 cm has a dioptric power of-10 D.
A converging lens with a focal length of 1 m has a power of 1 diopter. A lens with a focal length of 10 cm will have a power of 10 D and one with a focal length of 17 mm (the approximate focal length of the lens system of the human eye) has a dioptric power of:
Lens
A patient with hypermetropia has an eye with a focal length of 59 D but the retina is only 16 mm behind the lens instead of the usual 17 mm. What power of spectacle lens is required for correction?
To bring parallel light into focus in 16 mm requires a power of approximately 62.5D. Thus, in this case, a converging lens of 62.5 - 58.8 = 3.7 D is needed. (i.e. a converging lens of 3.7 D).
Case 1
Case 2
The lens system would need to be 55.5 D to bring parallel light into focus on the retina. Thus a lens of 55.5 - 58.8 = -3.3 D would be needed for correction (i.e. a diverging lens of 3.3 D).
A patient with myopia has an eye with a focal length of 59 D, but the retina is 18 mm behind the lens instead of the usual 17 mm. What power of spectacle lens is required for correction?
D 55.5318X10
1
Photoreception – process by which the eye detects light energy
Rods and cones contain visual pigments (photopigments)
Arranged in a stack of disklike infoldings of the plasma membrane that change shape as they absorb light
Photoreception: Functional Anatomy of Photoreceptors
Figure 15.19
Photoreception: Functional Anatomy of Photoreceptors
Rods
Functional characteristics
Sensitive to dim light and best suited for night vision
Absorb all wavelengths of visible light
Perceived input is in gray tones only
Sum of visual input from many rods feeds into a single ganglion cell
Results in fuzzy and indistinct images
Cones
Functional characteristics
Need bright light for activation (have low sensitivity)
Have pigments that furnish a vividly colored view
Each cone synapses with a single ganglion cell
Vision is detailed and has high resolution
Cones and Rods
Figure 15.10a
Properties of Rod Vision and Cone Vision
Chemistry of Visual Pigments
Retinene or retinal is a light-absorbing molecule
Combines with opsins to form visual pigments
Similar to and is synthesized from vitamin A
Two isomers: 11-cis and all-trans
Isomerization of retinal initiates electrical impulses in the optic nerve
Structure of rhodopsin
Position of retinene1 (R) in the rod disk membrane
Chemistry of Visual Pigments
Figure 15.20
Ionic Basis of Photoreceptor Potentials
Na+ channels in the outer segments of the rods and cones are open in the dark current flows from the inner to the outer segment and synaptic ending of the photoreceptor.
The Na+–K+ pump in the inner segment maintains ionic equilibrium.
Release of synaptic transmitter is steady in the dark. When light strikes the outer segment initiate close the
Na+ channels hyperpolarizing receptor potential. The hyperpolarization reduces the release of synaptic
transmitter generates a signal in the bipolar cells leads to action potentials in ganglion cells The action potentials are transmitted to the brain.
Effect of light on current flow in visual receptors
In the dark, Na+ channels in the outer segment are held open by cGMP.
Light leads to increased conversion of cGMP to 5'-GMP, and some of the channels close hyperpolarization of the synaptic terminal of the photoreceptor.
Excitation of Rods
The visual pigment of rods is rhodopsin (opsin + 11-cis retinal)
Light phase
Rhodopsin breaks down into all-trans retinal + opsin (bleaching of the pigment)
Dark phase
All-trans retinal converts to 11-cis form
11-cis retinal is also formed from vitamin A
11-cis retinal + opsin regenerate rhodopsin
Excitation of rod
In the dark, rhodopsin retinene1 is in the 11-cis configuration.
Action of light change the shape of the retinene, converting it to the all-trans isomer alters the configuration of the opsin activates the associated heterotrimeric G protein (transducin or Gt1).
G protein exchanges GDP for GTP, and the subunit separates. This subunit remains active until its intrinsic GTPase activity hydrolyzes the GTP.
Termination of the activity of transducin is also accelerated by its binding of -arrestin.
Excitation of Rods
Figure 15.21
Excitation of Cones
Visual pigments in cones are similar to rods (retinal + opsins)
There are three types of cones: blue, green, and red
Intermediate colors are perceived by activation of more than one type of cone
Method of excitation is similar to rods
Phototransduction
Light energy splits rhodopsin into all-trans retinal, releasing activated opsin
The freed opsin activates the G protein transducin
Transducin catalyzes activation of phosphodiesterase (PDE)
PDE hydrolyzes cGMP to GMP and releases it from sodium channels
Without bound cGMP, sodium channels close, the membrane hyperpolarizes, and neurotransmitter cannot be released
Phototransduction
Figure 15.22
Light activates retinen1 activates Gt2
Gt2 in turn activates phosphodiesterase, catalyzing the conversion of cGMP to 5'-GMP.
This results in closure of Na+ channels between the extracellular fluid and the cone cytoplasm:
decrease in intracellular Na+ concentration
hyperpolarization of the cone synaptic terminals.
Sequence phototransduction in rods and cones
Adaptation
Adaptation to bright light (going from dark to light) involves:
Dramatic decreases in retinal sensitivity – rod function is lost
Switching from the rod to the cone system – visual acuity is gained
Adaptation to dark is the reverse
Cones stop functioning in low light
Rhodopsin accumulates in the dark and retinal sensitivity is restored
Visual Pathways
Axons of retinal ganglion cells form the optic nerve
Medial fibers of the optic nerve decussate at the optic chiasm
Most fibers of the optic tracts continue to the lateral geniculate body of the thalamus
Other optic tract fibers end in superior colliculi (initiating visual reflexes) and pretectal nuclei (involved with pupillary reflexes)
Optic radiations travel from the thalamus to the visual cortex
Pathways to the Cortex
Visual Pathways
Figure 15.23
Visual Pathways
Some nerve fibers send tracts to the midbrain ending in the superior colliculi
A small subset of visual fibers contain melanopsin (circadian pigment) which:
Mediates papillary light reflexes
Sets daily biorhythms
V1 Primary visual cortex
V2, V3, VP Continued processing, larger visual fields
V3A MotionV4v UnknownMT/V5 Motion; control of
movementLO Recognition of
large objectsV7 UnknownV8 Color vision
Functions of Visual Projection Areas in the Brain
A lesion that interrupts one optic nerve causes blindness in that eye (A).
Lesions affecting the optic chiasm destroy fibers from both nasal hemiretinas and produce a heteronymous (opposite sides of the visual fields) hemianopia (B).
A lesion in one optic tract causes blindness in half of the visual field (C) and is called homonymous (same side of both visual fields) hemianopia (half-blindness).
Occipital lesions may spare the fibers from the macula (as in D) because of the separation in the brain of these fibers from the others subserving vision
Transection of visual pathways
Transection of visual pathways
Blindness of the eye (A). Heteronymous
hemianopia (B) Homonymous hemianopia
(C) Occipital lession(D)
Depth Perception
Achieved by both eyes viewing the same image from slightly different angles
Three-dimensional vision results from cortical fusion of the slightly different images
If only one eye is used, depth perception is lost and the observer must rely on learned clues to determine depth
Depth Perception
Left: two eyes viewing an arrow lying in the frontal plane (no stereopsis)
Right: the arrow is inclined into the third dimension—it tends to point toward the observer.
Noncorresponding or disparate, points on the retinas can be projected to a single point, and it is essentially this fusion of disparate images by the brain that creates the impression of depth.
Represents the same object being viewed from different positions causing the image produced
within each eye to be different
On-center fields
Stimulated by light hitting the center of the field
Inhibited by light hitting the periphery of the field
Off-center fields have the opposite effects
These responses are due to receptor types in the “on” and “off” fields
Retinal Processing: Receptive Fields of Ganglion Cells
Figure 15.24
Retinal Processing: Receptive Fields of Ganglion Cells
Thalamic Processing
The lateral geniculate nuclei of the thalamus:
Relay information on movement
Segregate the retinal axons in preparation for depth perception
Emphasize visual inputs from regions of high cone density
Sharpen the contrast information received by the retina
Cortical Processing
Striate cortex processes
Basic dark/bright and contrast information
Prestriate cortices (association areas) processes
Form, color, and movement
Visual information then proceeds anteriorly to the:
Temporal lobe – processes identification of objects
Parietal cortex and postcentral gyrus – processes spatial location
Color Vision
Young & Helmholtz Trichromatic theory of color vision:
There is only one type of rod and this responds strongly to bluish-green light
Cones are divided into three categories, each of which has a different sensitivity to light
There are red light receptors, green light receptors and blue light receptors.
All colors of the visible spectrum can be seen by mixing the 3 primary colours (red, blue and green)
White objects reflect all colors to eye, black absorbs all colours so no light to the eye.
Color Vision
Young & Helmholtz Trichromatic theory of color vision:
There is only one type of rod and this responds strongly to bluish-green light
Cones are divided into three categories, each of which has a different sensitivity to light
"red" cones (64%) "green" cones (32%) "blue" cones (2%)
Trichromatic Theory
The photocells in our retina, called cones are responsible for our colour vision. There are 3 types of cones, each with a different iodopsin (a photosensitive pigment).
Each type of iodopsin can absorb and respond to a range of wavelengths:
erythrolabe: max. absorption at 565nm (red) chlorolabe : max. absorption at 535nm (green) cyanolabe : max. absorption at 440nm (blue)
Wavelengths of light absorbed by different cones
Color vision
Color vision is the capacity of an organism or machine to distinguish objects based on the wavelengths of the light they reflect, emit, or transmit.
Human's perception of colors is a subjective process
Brain responds to the stimuli that are produced when incoming light reacts with the several types of cone photoreceptors
Color vision
The resultant color depends on the differential stimulation of each, i.e. how many of each kind are stimulated.
The colour that our brain "sees" comes from the integration of impulses from the three types of cones.
Color mixing
Primary additive or substractive Additive mixing is most intuitiveAdd wavelengths: red+green = yellow red+blue = magenta blue+green = cyan red+green+blue=white Subtractive mixing is much less intuitive (but much
more common), subtractive mixing happens when pigments are mix together
Different pigments subtract different wavelengths
Additive primaries
Media that combine emitted lights to create the sensation of a range of colors are using the additive color system. Typically, the primary colors used are red, green, and blue.
When all pigments in conus are stimulated together, it is produced white color
Subtractive primaries
Media that use reflected light and colorants to produce colors are using the subtractive color method of color mixing.
Subtraction produce black color
Colorant is something added to something else to cause a change in color
Color blindness
Defect of vision affecting the ability to distinguish colors, caused by a defect in the retina or in other nerve portions of the eye.
Cause of color blindness: Genetic Aging Eye problems, such as glaucoma, macular degeneration,
cataracts, or diabetic retinopathy Injury to the eye Side effects of some medicines, overexposure to lead or
mercury Lesions of area V8 of the visual cortex
Distribution of cone cells in the fovea of a individual with normal color vision (left), and a color blind (protanopic) retina. Note that the center of the fovea holds very few blue-sensitive cones.
Genetic of CB
Non CB male: XY CB male: xY
Non CB female: XX CB female : xx
CB carrier female: xX
Type of color blindness
Monochromatism: Either no cones available or just one type of them.
Dichromatism: Only two different cone types, the third one is missing completely.
Anomalous trichromatism: All three types but with shifted peaks of sensitivity for one of them. This results in a smaller color spectrum.
Type of color blindness
Dichromats and anomalous trichromats exist again in three different types according to the missing cone or in the latter case of its malfunctioning.
Tritanopia/Tritanomaly: Missing/malfunctioning S-cone (blue).
Deuteranopia/Deuteranomaly: Missing/malfunctioning M-cone (green).
Protanopia/Protanomaly: Missing/malfunctioning L-cone (red).
Type DenominationPrevalence
Men Women
Monochromacy Achromatopsia 0.00003%
Dichromacy
Protanopia 1.01% 0.02%
Deuteranopia 1.27% 0.01%
Tritanopia 0.0001%
AnomalousTrichromacy
Protanomaly 1.08% 0.03%
Deuteranomaly 4.63% 0.36%
Tritanomaly 0.0002%
Different forms of color vision deficiency
NormalMonochromatism/
Achromatopsia
Complete green CB deutranopia
Complete Blue / yellow CB =Tritanopia
Normal Complete red CB Protanopia
Color blind diagnoses Holmgren threads Pseudo Isochromatic Plate Ishihara and American
Optical HRR Farnsworth test Anomaloscope Medmont C-100 color vision tester
Found by Dr. Shinobu Ishihara from Tokyo University in 1917
Most common and easy to used
Monochromatic dots of basic color that create number pattern
Tes Ishihara
Ishihara test from color blind person
American Optical HRR (Hardy-Rand-Rittler) Pseudoisochromatic Plates
5 6 7
1 2 3 4
Same condition as hair and skin, just lack of certain pigment in the eye cone.
Unique characteristic of an individu
Color blindness is not disease
The Ear: Hearing and Balance
The three parts of the ear are the inner, outer, and middle ear
The outer and middle ear are involved with hearing
The inner ear functions in both hearing and equilibrium
Receptors for hearing and balance:
Respond to separate stimuli
Are activated independently
The Ear: Hearing and Balance
Figure 15.25a
Outer Ear
The auricle (pinna) is composed of:
The helix (rim)
The lobule (earlobe)
External auditory canal
Short, curved tube filled with ceruminous glands
Outer Ear
Tympanic membrane (eardrum)
Thin connective tissue membrane that vibrates in response to sound
Transfers sound energy to the middle ear ossicles
Boundary between outer and middle ears
Middle Ear (Tympanic Cavity)
A small, air-filled, mucosa-lined cavity
Flanked laterally by the eardrum
Flanked medially by the oval and round windows
Epitympanic recess – superior portion of the middle ear
Pharyngotympanic tube – connects the middle ear to the nasopharynx
Equalizes pressure in the middle ear cavity with the external air pressure
Middle Ear (Tympanic Cavity)
Figure 15.25b
Ear Ossicles
The tympanic cavity contains three small bones: the malleus, incus, and stapes
Transmit vibratory motion of the eardrum to the oval window
Dampened by the tensor tympani and stapedius muscles
Ear Ossicles
Figure 15.26
Inner Ear
Bony labyrinth
Tortuous channels worming their way through the temporal bone
Contains the vestibule, the cochlea, and the semicircular canals
Filled with perilymph
Membranous labyrinth
Series of membranous sacs within the bony labyrinth
Filled with a potassium-rich fluid
Inner Ear
Figure 15.27
The Vestibule
The central egg-shaped cavity of the bony labyrinth
Suspended in its perilymph are two sacs: the saccule and utricle
The saccule extends into the cochlea
The utricle extends into the semicircular canals
These sacs:
House equilibrium receptors called maculae
Respond to gravity and changes in the position of the head
The Vestibule
Figure 15.27
The Semicircular Canals
Three canals that each define two-thirds of a circle and lie in the three planes of space
Membranous semicircular ducts line each canal and communicate with the utricle
The ampulla is the swollen end of each canal and it houses equilibrium receptors in a region called the crista ampullaris
These receptors respond to angular movements of the head
The Semicircular Canals
Figure 15.27
The Cochlea
A spiral, conical, bony chamber that:
Extends from the anterior vestibule
Coils around a bony pillar called the modiolus
Contains the cochlear duct, which ends at the cochlear apex
Contains the organ of Corti (hearing receptor)
The Cochlea
The cochlea is divided into three chambers:
Scala vestibuli
Scala media
Scala tympani
The Cochlea
The scala tympani terminates at the round window
The scalas tympani and vestibuli:
Are filled with perilymph
Are continuous with each other via the helicotrema
The scala media is filled with endolymph
Fluid movement in cochlea
Fluid movement in cochlea
Fluid movement within the perilymph set up by vibration of the oval window follows two pathways:
Through the scala vestibuli, around the heliocotrema, and through the scala tympani, causing the round window to vibrate. This pathway just dissipates sound energy
A “shortcut” from the scala vestibuli through the basilar membrane to the scala tympani. This pathway triggers activation of the receptors for sound by bending the hairs of hair cells as the organ of Corti on top of the vibrating basilar membrane is displaced in relation to the overlying tectorial membrane
Basilar membrane (partly uncoiled)
Different regions of the basilar membrane vibrate maximallyat different frequencies.
The narrow, stiff end of the basilar membrane nearest the oval window vibrates best with high-frequency pitches.
The wide, flexible end of the basilar membrane near the helicotrema vibrates best with low-frequency pitches
Basilar membrane (completely uncoiled)
The Cochlea
The “floor” of the cochlear duct is composed of:
The bony spiral lamina
The basilar membrane, which supports the organ of Corti
The cochlear branch of nerve VIII runs from the organ of Corti to the brain
The Cochlea
Figure 15.28
Sound and Mechanisms of Hearing
Sound vibrations beat against the eardrum
The eardrum pushes against the ossicles, which presses fluid in the inner ear against the oval and round windows
This movement sets up shearing forces that pull on hair cells
Moving hair cells stimulates the cochlear nerve that sends impulses to the brain
Properties of Sound
Sound is:
A pressure disturbance (alternating areas of high and low pressure) originating from a vibrating object
Composed of areas of rarefaction and compression
Represented by a sine wave in wavelength, frequency, and amplitude
Properties of Sound
Frequency – the number of waves that pass a given point in a given time
Pitch – perception of different frequencies (we hear from 20–20,000 Hz)
Properties of Sound
Amplitude – intensity of a sound measured in decibels (dB)
Loudness – subjective interpretation of sound intensity
Figure 15.29
Transmission of Sound to the Inner Ear
The route of sound to the inner ear follows this pathway:
Outer ear – pinna, auditory canal, eardrum
Middle ear – malleus, incus, and stapes to the oval window
Inner ear – scalas vestibuli and tympani to the cochlear duct
Stimulation of the organ of Corti
Generation of impulses in the cochlear nerve
Transmission of Sound to the Inner Ear
Figure 15.31
Resonance of the Basilar Membrane
Sound waves of low frequency (inaudible):
Travel around the helicotrema
Do not excite hair cells
Audible sound waves:
Penetrate through the cochlear duct
Vibrate the basilar membrane
Excite specific hair cells according to frequency of the sound
Resonance of the Basilar Membrane
Figure 15.32
The Organ of Corti
Is composed of supporting cells and outer and inner hair cells
Afferent fibers of the cochlear nerve attach to the base of hair cells
The stereocilia (hairs):
Protrude into the endolymph
Touch the tectorial membrane
Excitation of Hair Cells in the Organ of Corti
Bending cilia:
Opens mechanically gated ion channels
Causes a graded potential and the release of a neurotransmitter (probably glutamate)
The neurotransmitter causes cochlear fibers to transmit impulses to the brain, where sound is perceived
Excitation of Hair Cells in the Organ of Corti
Figure 15.28c
Deflection of the basilar membrane
The stereocilia (hairs) from the hair cells of the basilar membrane contact the overlying tectorial membrane. These hairs are bent when the basilar membrane is deflected in relation to the stationary tectorial membrane.
This bending of the inner hair cells’ hairs opens mechanically gated channels, leading to ion movements that result in a receptor potential.
The role of stereocilia in sound transduction
The role of stereocilia in sound transduction
The role of tip links in the responses of hair cells
When a stereocilium is pushed toward a taller stereocilium, the tip link is stretched and opens an ion channel in its taller neighbor. The channel next is moved down the taller stereocilium by a molecular motor, so the tension on the tip link is released.
When hairs return to their resting position, the motor moves back up the stereocilium.
Ionic composition (mmol/L) of perilymph
Auditory and vestibular pathways
Pathway for sound transduction
Auditory Pathway to the Brain
Impulses from the cochlea pass via the spiral ganglion to the cochlear nuclei
From there, impulses are sent to the:
Superior olivary nucleus
Inferior colliculus (auditory reflex center)
From there, impulses pass to the auditory cortex
Auditory pathways decussate so that both cortices receive input from both ears
Simplified Auditory Pathways
Figure 15.34
Auditory Processing
Pitch is perceived by:
The primary auditory cortex
Cochlear nuclei
Loudness is perceived by:
Varying thresholds of cochlear cells
The number of cells stimulated
Localization is perceived by superior olivary nuclei that determine sound
Deafness
Conduction deafness – something hampers sound conduction to the fluids of the inner ear (e.g., impacted earwax, perforated eardrum, osteosclerosis of the ossicles)
Sensorineural deafness – results from damage to the neural structures at any point from the cochlear hair cells to the auditory cortical cells
Tinnitus – ringing or clicking sound in the ears in the absence of auditory stimuli
Meniere’s syndrome – labyrinth disorder that affects the cochlea and the semicircular canals, causing vertigo, nausea, and vomiting
Mechanisms of Equilibrium and Orientation
Vestibular apparatus – equilibrium receptors in the semicircular canals and vestibule
Maintains our orientation and balance in space
Vestibular receptors monitor static equilibrium
Semicircular canal receptors monitor dynamic equilibrium
Anatomy of Maculae
Maculae are the sensory receptors for static equilibrium
Contain supporting cells and hair cells
Each hair cell has stereocilia and kinocilium embedded in the otolithic membrane
Otolithic membrane – jellylike mass studded with tiny CaCO3 stones called otoliths
Utricular hairs respond to horizontal movement
Saccular hairs respond to vertical movement
Anatomy of Maculae
Figure 15.35
Effect of Gravity on Utricular Receptor Cells
Otolithic movement in the direction of the kinocilia:
Depolarizes vestibular nerve fibers
Increases the number of action potentials generated
Movement in the opposite direction:
Hyperpolarizes vestibular nerve fibers
Reduces the rate of impulse propagation
From this information, the brain is informed of the changing position of the head
Effect of Gravity on Utricular Receptor Cells
Figure 15.36
Crista Ampullaris and Dynamic Equilibrium
The crista ampullaris (or crista):
Is the receptor for dynamic equilibrium
Is located in the ampulla of each semicircular canal
Responds to angular movements
Each crista has support cells and hair cells that extend into a gel-like mass called the cupula
Dendrites of vestibular nerve fibers encircle the base of the hair cells
Crista Ampullaris and Dynamic Equilibrium
Figure 15.37b
Activating Crista Ampullaris Receptors
Cristae respond to changes in velocity of rotatory movements of the head
Directional bending of hair cells in the cristae causes:
Depolarizations, and rapid impulses reach the brain at a faster rate
Hyperpolarizations, and fewer impulses reach the brain
The result is that the brain is informed of rotational movements of the head
Rotary Head Movement
Figure 15.37d
Role of the otolith organs
The hairs (kinocilium and stereocilia) of the receptor hair cells protrude into an overlying gelatinous sheet, whose movement displaces the hairs changes in hair cell potential.
The otoliths (“ear stones”): crystals of calcium carbonate suspended within the gelatinous layer, making it heavier giving more inertia than the surrounding fluid
otoliths
kinocilium
stereocilia
Tilt the head in any direction other than vertical (other than straight up and down) the hairs are bent in the direction of the tilt because of the gravitational force exerted on the top-heavy gelatinous layer produces depolarizing or hyperpolarizing receptor potentials depending on the tilt of the head.
The CNS thus receives different patterns of neural activity depending on head position with respect to gravity.
Role of the otolith organs – tilt the head
Role of the otolith organs - walking
As walk forward is started , the top-heavy otolith membrane at first lags behind the endolymph and hair cells because of its greater inertia. The hairs are thus bent to the rear, in the opposite direction of the forward movement of the head.
When walking pace is maintain, the gelatinous layer soon catches up and moves at the same rate as your head so that the hairs are no longer bent.
When walking is stopped, the otolith sheet continues to move forward briefly as the head slows and stops, bending the hairs toward the front.
Input and output of the vestibular nuclei
Balance and Orientation Pathways
There are three modes of input for balance and orientation
Vestibular receptors
Visual receptors
Somatic receptors
These receptors allow our body to respond reflexively
Figure 15.38