Chapter 13Chapter 13

Special Senses: The Eye and EarSpecial Senses: The Eye and Ear

The EyeThe Eye

Contains the sensory receptor cell for vision

The eyeball is the organ of sight that transmits an external image by the way of the nervous system- optic nerve-to the brain.

Other structures that play a role in vision:

eye muscles

eyelids

conjunctiva

lacrimal apparatus

The study of the eye is known as ophthalmology.

Contains the sensory receptor cell for vision

The eyeball is the organ of sight that transmits an external image by the way of the nervous system- optic nerve-to the brain.

Other structures that play a role in vision:

eye muscles

eyelids

conjunctiva

lacrimal apparatus

The study of the eye is known as ophthalmology.

Eye FigureEye FigureThe internal structures of the eye.The internal structures of the eye.

The EyeballThe Eyeball

The eyeball is composed of 3 layers:

sclera: Outer “white” layer; tough protective coating for the inner structures of the eye.

cornea: anterior, transparent portion of sclera which allows light to enter; bends/refracts light rays

choroid: Middle, opaque layer that provides the blood supply for the eye

iris: colored portion which contains smooth muscle; muscles change the size of pupil, thereby controlling how much light enters

pupil:opening in the center of the iris that allows light rays to enter the interior of the eyeball

ciliary body: intraocular eye muscles that change the shape of the lens

The eyeball is composed of 3 layers:

sclera: Outer “white” layer; tough protective coating for the inner structures of the eye.

cornea: anterior, transparent portion of sclera which allows light to enter; bends/refracts light rays

choroid: Middle, opaque layer that provides the blood supply for the eye

iris: colored portion which contains smooth muscle; muscles change the size of pupil, thereby controlling how much light enters

pupil:opening in the center of the iris that allows light rays to enter the interior of the eyeball

ciliary body: intraocular eye muscles that change the shape of the lens

The Eyeball (cont.)The Eyeball (cont.)

Retina:The 3rd and innermost layer of the eyeball.

Contains rods and cones

macula lutea (yellow spot)

fovea centralis: depression within macula lutea which is the point of clearest vision

optic disk: lacks sensory receptors and causes a blind spot in each eye’s field of vision

aqueous humor: watery-fluid space between cornea and lens

vitreous humor: semisolid gel large open area between the lens and the retina

Retina:The 3rd and innermost layer of the eyeball.

Contains rods and cones

macula lutea (yellow spot)

fovea centralis: depression within macula lutea which is the point of clearest vision

optic disk: lacks sensory receptors and causes a blind spot in each eye’s field of vision

aqueous humor: watery-fluid space between cornea and lens

vitreous humor: semisolid gel large open area between the lens and the retina

Eye MusclesEye Muscles6 muscles connect the eyeball to the skull

4 rectus-- pull the eye up, down, left and right;

2 oblique muscles--produce diagonal eye movement

6 muscles connect the eyeball to the skull

4 rectus-- pull the eye up, down, left and right;

2 oblique muscles--produce diagonal eye movement

The EyelidsThe Eyelids

A pair of eyelids over each eyeball provides protection from foreign particles, injury from intense light, and trauma.

Both upper and lower edges of the eyelids have eyelashes or cilia that protect the eye from foreign particles.

Sebaceous glands secrete lubricating oil onto the eyeball

A pair of eyelids over each eyeball provides protection from foreign particles, injury from intense light, and trauma.

Both upper and lower edges of the eyelids have eyelashes or cilia that protect the eye from foreign particles.

Sebaceous glands secrete lubricating oil onto the eyeball

ConjunctivaConjunctiva

The mucous membrane lining that forms a continuous covering on the underside of each eyelid and across the anterior surface of each eyeball.

Serves as protection for the eye by sealing of the eyeball in the socket.

The mucous membrane lining that forms a continuous covering on the underside of each eyelid and across the anterior surface of each eyeball.

Serves as protection for the eye by sealing of the eyeball in the socket.

Lacrimal ApparatusLacrimal ApparatusThe lacrimal gland is located under the outer upper corner of each eyelid.

Glands produce tears. Tears function of washing and lubricating the anterior surface of the eyeball.

Lacrimal ducts are located in the inner eye socket and collect tears and drain them into the nasolacrimal duct, which ultimately drains tears into the nasal cavity.

The lacrimal gland is located under the outer upper corner of each eyelid.

Glands produce tears. Tears function of washing and lubricating the anterior surface of the eyeball.

Lacrimal ducts are located in the inner eye socket and collect tears and drain them into the nasolacrimal duct, which ultimately drains tears into the nasal cavity.

The Path of VisionThe Path of Vision

When light rays strike the eye, the pass:

cornea--> pupil-->aqueous humor--> lens-->vitreous humor-->retina (rods and cones)

When light rays hit the retina, and upside-down image is sent nerve impulses to the optic nerve, which are sent to the brain, where the upside-down image is translated into the right-side up image we see.

Vision requires:

coordination of external eye muscles so that both eyes move together

correct amount of light admitted by the pupil

correct focus of light on the retina by the lens

optic nerve transmitting sensory images to the brain

When light rays strike the eye, the pass:

cornea--> pupil-->aqueous humor--> lens-->vitreous humor-->retina (rods and cones)

When light rays hit the retina, and upside-down image is sent nerve impulses to the optic nerve, which are sent to the brain, where the upside-down image is translated into the right-side up image we see.

Vision requires:

coordination of external eye muscles so that both eyes move together

correct amount of light admitted by the pupil

correct focus of light on the retina by the lens

optic nerve transmitting sensory images to the brain

The EarThe Ear

Contains the sensory receptors for hearing and equilibrium (balance)

Hearing and equilibrium sensory information is carried to the brain by the vestibulocochlear (cranial) nerve.

The ear is subdivided into 3 areas:

external ear

middle ear

inner ear

The study of the ear is referred to as otology, and the study of hearing disorders is called audiology.

Contains the sensory receptors for hearing and equilibrium (balance)

Hearing and equilibrium sensory information is carried to the brain by the vestibulocochlear (cranial) nerve.

The ear is subdivided into 3 areas:

external ear

middle ear

inner ear

The study of the ear is referred to as otology, and the study of hearing disorders is called audiology.

Ear FigureEar FigureThe internal structures of the ear.The internal structures of the ear.

External EarExternal Ear

Consist of 3 parts:

auricle: also known as the pinna; referred to as “the ear” because this is the only visible portion; earlobe functions like a funnel to capture sound waves as they pass the outer ear and channel through the external auditory meatus

auditory canal: canal that leads from exterior opening of the ear to the eardrum

ear wax or cerumen is produced within the auditory canal to help protect and lubricate the ear

tympanic membrane: eardrum; as sound moves along auditory canal, it strike the membrane causing it to vibrate; this conducts the sound into the middle ear

Consist of 3 parts:

auricle: also known as the pinna; referred to as “the ear” because this is the only visible portion; earlobe functions like a funnel to capture sound waves as they pass the outer ear and channel through the external auditory meatus

auditory canal: canal that leads from exterior opening of the ear to the eardrum

ear wax or cerumen is produced within the auditory canal to help protect and lubricate the ear

tympanic membrane: eardrum; as sound moves along auditory canal, it strike the membrane causing it to vibrate; this conducts the sound into the middle ear

Middle EarMiddle Ear

Located in a small cavity in the temporal bone of the skull

Air-filled cavity that contains 3 tiny bones called ossicles that are vital for the hearing process:

malleus:also known as the hammer

incus:also known as the anvil

stapes:also known as the stirrup; last of the ossicles that is attached to a very thin membrane that covers the opening to the inner ear called the oval window

The eustachian tube or auditory tube connects the nasopharynx with the middle ear. Each time one swallows the tube opens; this connection allows pressure to equalize between the middle ear cavity and atmospheric pressure.

Located in a small cavity in the temporal bone of the skull

Air-filled cavity that contains 3 tiny bones called ossicles that are vital for the hearing process:

malleus:also known as the hammer

incus:also known as the anvil

stapes:also known as the stirrup; last of the ossicles that is attached to a very thin membrane that covers the opening to the inner ear called the oval window

The eustachian tube or auditory tube connects the nasopharynx with the middle ear. Each time one swallows the tube opens; this connection allows pressure to equalize between the middle ear cavity and atmospheric pressure.

Inner EarInner Ear

Located in a cavity within the temporal bone

Fluid-filled cavity is referred to as the labyrinth

Contains the hearing and equilibrium sensory organs that contain hair cells (sensory receptors):

cochlea (hearing): hair cells referred to as organs of Corti

semicircular canals (equilibrium)

utricle (equilibrium)

saccule (equilibrium)

Located in a cavity within the temporal bone

Fluid-filled cavity is referred to as the labyrinth

Contains the hearing and equilibrium sensory organs that contain hair cells (sensory receptors):

cochlea (hearing): hair cells referred to as organs of Corti

semicircular canals (equilibrium)

utricle (equilibrium)

saccule (equilibrium)

The Path of SoundThe Path of Sound

Sound waves travel down the external auditory canal strike the eardrum, causing it to vibrate.

The ossicles conduct these vibrations across the middle ear from the eardrum to the oval window.

Oval window movements initiate vibrations in the fluid that fills the cochlea.

As fluid vibrations strike a hair cell, they bend the small hairs and stimulate the nerve ending, which then sends an electrical impulse to the brain on the cochlear portion of the vestibulocochlear nerve.

Sound waves travel down the external auditory canal strike the eardrum, causing it to vibrate.

The ossicles conduct these vibrations across the middle ear from the eardrum to the oval window.

Oval window movements initiate vibrations in the fluid that fills the cochlea.

As fluid vibrations strike a hair cell, they bend the small hairs and stimulate the nerve ending, which then sends an electrical impulse to the brain on the cochlear portion of the vestibulocochlear nerve.