Ch8ppt special senses 1

PowerPoint® Lecture Slide Presentation by Patty Bostwick-Taylor, Florence-Darlington Technical College

Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings

PART A8

Special Senses


The Senses

Special senses

Smell

Taste

Sight

Hearing

Equilibrium


Structure of the Eye

Figure 8.4a


Structure of the Eye: The Fibrous Layer

Sclera

White connective tissue layer

Seen anteriorly as the “white of the eye”

Cornea

Transparent, central anterior portion

Allows for light to pass through

Repairs itself easily

The only human tissue that can be transplanted without fear of rejection


Structure of the Eye: Vascular Layer

Choroid is a blood-rich nutritive layer in the posterior of the eye

Pigment prevents light from scattering

Modified anteriorly into two structures

Ciliary body—smooth muscle attached to lens

Iris—regulates amount of light entering eye

Pigmented layer that gives eye color

Pupil—rounded opening in the iris


Structure of the Eye: Sensory Layer

Retina contains two layers

Outer pigmented layer

Inner neural layer

Contains receptor cells (photoreceptors)

Rods

Cones



Signals leave the retina toward the brain through the optic nerve

Optic disc (blind spot) is where the optic nerve leaves the eyeball

Cannot see images focused on the optic disc



Figure 8.5a



Neurons of the retina and vision

Rods

Most are found towards the edges of the retina

Allow dim light vision and peripheral vision

All perception is in gray tones



Neurons of the retina and vision

Cones

Allow for detailed color vision

Densest in the center of the retina

Fovea centralis—area of the retina with only cones

No photoreceptor cells are at the optic disc, or blind spot

The Eye: The RetinaPLAY



Cone sensitivity

Three types of cones

Different cones are sensitive to different wavelengths

Color blindness is the result of the lack of one cone type


Sensitivities of Cones to Different Wavelengths

Figure 8.6


The Eye: Lens and RetinaPLAY

Lens

Biconvex crystal-like structure

Held in place by a suspensory ligament attached to the ciliary body


Lens

Figure 8.4a


Lens

Cataracts result when the lens becomes hard and opaque with age

Vision becomes hazy and distorted

Eventually causes blindness in affected eye


Lens

Figure 8.7


Two Segments, or Chambers, of the Eye

Anterior (aqueous) segment

Anterior to the lens

Contains aqueous humor

Posterior (vitreous) segment

Posterior to the lens

Contains vitreous humor


Anterior Segment

Aqueous humor

Watery fluid found between lens and cornea

Similar to blood plasma

Helps maintain intraocular pressure

Provides nutrients for the lens and cornea

Reabsorbed into venous blood through the scleral venous sinus, or canal of Schlemm

The Eye: Interior Parts of the EyePLAY


Posterior Segment

Vitreous humor

Gel-like substance posterior to the lens

Prevents the eye from collapsing

Helps maintain intraocular pressure

The Eye: Posterior CavityPLAY


Pathway of Light Through the Eye

Light must be focused to a point on the retina for optimal vision

The eye is set for distance vision (over 20 feet away)

Accommodation—the lens must change shape to focus on closer objects (less than 20 feet away)



Figure 8.9



Image formed on the retina is a real image

Real images are

Reversed from left to right

Upside down

Smaller than the object


Images Formed on the Retina

Figure 8.10


A Closer Look

Emmetropia—eye focuses images correctly on the retina

Myopia (nearsighted)

Distant objects appear blurry

Light from those objects fails to reach the retina and are focused in front of it

Results from an eyeball that is too long


A Closer Look

Hyperopia (farsighted)

Near objects are blurry while distant objects are clear

Distant objects are focused behind the retina

Results from an eyeball that is too short or from a “lazy lens”


A Closer Look

Astigmatism

Images are blurry

Results from light focusing as lines, not points, on the retina due to unequal curvatures of the cornea or lens


Homeostatic Imbalances of the Eyes

Night blindness—inhibited rod function that hinders the ability to see at night

Color blindness—genetic conditions that result in the inability to see certain colors

Due to the lack of one type of cone (partial color blindness)

Cataracts—when lens becomes hard and opaque, our vision becomes hazy and distorted


Homeostatic Imbalances of the Eyes

Glaucoma—can cause blindness due to increasing pressure within the eye

Hemianopia—loss of the same side of the visual field of both eyes; results from damage to the visual cortex on one side only


The Ear

Houses two senses

Hearing

Equilibrium (balance)

Receptors are mechanoreceptors

Different organs house receptors for each sense


Anatomy of the Ear

The ear is divided into three areas

External (outer) ear

Middle ear (tympanic cavity)

Inner ear (bony labyrinth)


Anatomy of the Ear

Figure 8.12


The External Ear

Involved in hearing only

Structures of the external ear

Auricle (pinna)

External acoustic meatus (auditory canal)

Narrow chamber in the temporal bone

Lined with skin and ceruminous (wax) glands

Ends at the tympanic membrane


The Middle Ear (Tympanic Cavity)

Air-filled cavity within the temporal bone

Only involved in the sense of hearing


The Middle Ear (Tympanic Cavity)

Two tubes are associated with the inner ear

The opening from the auditory canal is covered by the tympanic membrane

The auditory tube connecting the middle ear with the throat

Allows for equalizing pressure during yawning or swallowing

This tube is otherwise collapsed


Bones of the Middle Ear (Tympanic Cavity)

Three bones (ossicles) span the cavity

Malleus (hammer)

Incus (anvil)

Stapes (stirrip)

Function

Vibrations from eardrum move the malleus anvil stirrup inner ear


Anatomy of the Ear

Figure 8.12


Inner Ear or Bony Labyrinth

Includes sense organs for hearing and balance

A maze of bony chambers within the temporal bone

Cochlea

Vestibule (static equilibrium – position of head)

Semicircular canals (dynamic equilibrium – movement of head)


Organs of Equilibrium

Figure 8.14a–b


Mechanism of Hearing

Figure 8.16a


Olfaction—The Sense of Smell

Olfactory receptors are in the roof of the nasal cavity

Neurons with long cilia

Chemicals must be dissolved in mucus for detection

Impulses are transmitted via the olfactory nerve

Interpretation of smells is made in the cortex


The Sense of Taste

Taste buds house the receptor organs

Location of taste buds

Most are on the tongue

Soft palate

Cheeks


Taste Buds

Figure 8.18


Taste Sensations

Sweet receptors (sugars)

Saccharine

Some amino acids

Sour receptors

Acids

Bitter receptors

Alkaloids

Salty receptors

Metal ions


Chemical Senses: Taste and Smell

Both senses use chemoreceptors

Stimulated by chemicals in solution

Taste has four types of receptors

Smell can differentiate a large range of chemicals

Both senses complement each other and respond to many of the same stimuli


Developmental Aspects of the Special Senses

Formed early in embryonic development

Eyes are outgrowths of the brain

All special senses are functional at birth

Ch8ppt special senses 1

Education

Transcript of Ch8ppt special senses 1