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