Download Slide 1

The Eye
Iris: the muscle that
adjusts the pupil to
regulate the amount of
light that enters the eye.


Pupil: the aperture in the middle of the iris of the eye.
The size of the aperture can be adjusted to control
the amount of light

Lens: a transparent, bi-convex body situated behind
the iris of the eye to focus an image on the retina

Retina: the innermost layer of the eye; contains rods
and cones, bipolar cells and ganglion cells
Sclera: the thick,
white outer layer that
gives the eye its
shape



Cornea: the clear part of the sclera at the front of
the eye
Choroid layer: the middle layer of the eye, which
absorbs light and prevents internal reflection.
This layer forms the iris at the front of the eye


Rods: photoreceptors in the eye; more sensitive to light
than cones, but unable to distinguish colour
Cones: colour receptors in the eye (red, green, blue)
Fovea centralis: concentration of
cones on the retina located directly
behind the centre of the lens.
Vision is the most acute here.


optic nerve: conducts information received from rods and
cones to the brain for interpretation.
Blind spot: an area on the retina where
there are no rods or cones present; locate
where blood vessels enter the eye



As light enters the eye, the pupil will dilate if
there isn’t enough light or it will constrict if
there’s too much.
As well, the shape of the lens changes
depending on how far away the object is.

Accommodation: in the eye, adjustment that
the ciliary body makes to the shape of the
lens to focus on objects at varying distances
When the object is far away, the lens is flattened
When the object is close, the lens is rounded


Light enters the eye through the pupil. As it does, light rays
become bent at the cornea and the lens in such a way that an
inverted and reversed image of the object focuses on the retina.
Information from this image is captured by rods and cones,
which transmit their info to bipolar cells and then ganglion cells
(optic nerve).
Cones transmit information to a single bipolar cell, but require more light
to become stimulated. As a result, cones see more detail and are best
suited for lighted situations (daytime).
◦ Rods, however, are very sensitive to light and cannot distinguish color. As
well, many rods connect to a single bipolar cell (up to 100 rods per bipolar
cell). This causes images to be blurry. As a result, rods are best suited to
situations where there isn’t much light and details are not important.
◦
Cataracts- cloudy or
opaque areas on the lens
of the eye that increases
in size over time and can
lead to blindness if not
medically treatment.

Glaucoma – build-up of
the aqueous humor in the
eye that irreversibly
damages the nerve fibres
responsible for peripheral
Vision.


Myopia – near-sightedness, or difficulty in
seeing things that are far away. The
condition is caused by too strong ciliary
muscles or a too-long eyeball
Hyperopia – far-sightedness, or difficulty in
seeing near objects. This condition is caused
by weak ciliary muscles or a too short eyeball
focus


Astigmatism – abnormality in the shape of
the cornea or lens that results in uneven
Corrective lenses – glasses, contact lenses
→ with near-sightedness, the image focuses in front of the
retina. This can be fixed using a concave lens
→ with far-sightedness, the image focuses behind the retina.
This can be fixed using convex lenses
→ astigmatisms are unique and may require combinations of
convex and/or concave lenses to bring images into focus on
the retina

Laser surgery – two types
→ Photorefractive keratectomy (PRK): noninvasive, simple procedure
→ LASIK surgery: more complex, some surgery
required (corneal)
→ Both surgeries may diminish eyesight

Corneal transplant
→ Corneas come from organ donors; no need
to match blood types
→ Recovery long; most patients do well though
→ Recurrence of disease unusual

Vitreous humor-the transparent
gelatinous substance filling the eyeball
behind the lens
Aqueous humor- watery fluid that fills
the space between the cornea and the
lens in the eye.



1. Outer ear
consists of the pinna (earlobe and ear) and
the auditory canal
auditory canal contain hairs and sweat
glands, some of which are modified to
secrete wax to trap foreign particles



Middle ear
tympanic membrane: the eardrum; a
membrane of thin skin and fibrous tissue that
vibrates in response to sound waves.
ossicles: the group of three small bones
between the eardrum and the oval window of
the middle ear; transmit sound waves from
the eardrum to the inner ear
 malleus - hammer
 incus – anvil
 stapes – stirrup

Eustachian tube: bony passage extending
from the middle ear to the nasopharynx that
plays a role in equalizing air pressure on both
sides of the eardrum.
 Yawning can cause
the air to move through
the tubes and the
ear will “pop”



3. Inner Ear
Vestibule: involved in balance and equilibrium
Semicircular canals: three tubes involved in
balance and equilibrium

Cochlea:
involved in hearing. A spiral-shaped
cavity of the inner ear that resembles a snail
shell and contains nerve endings essential for
hearing.
Vibrations from the stapes bone hits the oval window, which causes
it to vibrate.
 The oval window then pushes on the fluid within the vestibular canal
of the cochlea.
 The movement of the fluid within the cochlea places pressure on the
basilar membrane causing it to move. When it moves it causes the
hair cells attached to it to move.
 The hair cells stimulate the
tectorial membrane causing it to
generate an impulse.
 The impulse travels to the
auditory nerve where it is sent
to the brain.









PINNA-Funnel-shaped flap that directs sound waves into the
auditory canal
AUDITORY CANAL-Canal that carries sound waves to the eardrum
TYPANIC MEMBRANE- A thin membrane that is vibrated by sound
waves
OSSICLES – Three bones () They are the smallest bones in the
human body. The eardrum vibrates, and this vibrates the
hammer, than the anvil and the stirrup one after another
The stirrup then vibrates the Oval Window
COCHLEA- This is a spirally coiled tube containing fluid and the
actual organ of hearing (the Organ of Corti). Each Organ of Corti
contains thousands of sensitive hairs that are vibrated by sound
waves. The hairs initiate nervous impulses in the
Auditory Nerve which carries messages to the brain

Nerve Deafness
◦ caused by damage to hair cells in the spiral organ
◦ typically found with aging and cannot be reversed
◦ hearing loss uneven, some frequencies more
affected than others

Conduction Deafness
◦ usually caused by damage to the outer or middle
ear that affects transmission to the inner ear
◦ not usually a total loss of hearing; can be helped
with hearing aids

Ear Infections
◦ caused by fluid build-up behind the eardrums,
common in children
◦ fluid builds up because of the shallow angle of the
auditory tube

Hearing Aids

Eustachian tube implants
◦ also called tympanostomy tube surgery; used to
treat infections
◦ tiny plastic tubes are placed in a slit in the eardrum,
relieving the pressure from the built-up fluid and
allowing in to drain
Cholinesterase- an enzyme,
found in the heart, brain, and
blood, that breaks down
acetylcholine to acetic acid
and choline. If the
acetylcholine did not break
down then it would remain
in the synapse.


Cochlea:
involved in hearing. A spiral-shaped
cavity of the inner ear that resembles a snail
shell and contains nerve endings essential for
hearing.
Vibrations from the stapes bone hits the oval window, which causes
it to vibrate.
 The oval window then pushes on the fluid within the vestibular canal
of the cochlea.
 The movement of the fluid within the cochlea places pressure on the
basilar membrane causing it to move. When it moves it causes the
hair cells attached to it to move.
 The hair cells stimulate the
tectorial membrane causing it to
generate an impulse.
 The impulse travels to the
auditory nerve where it is sent
to the brain.









PINNA-Funnel-shaped flap that directs sound waves into the
auditory canal
AUDITORY CANAL-Canal that carries sound waves to the eardrum
TYPANIC MEMBRANE- A thin membrane that is vibrated by sound
waves
OSSICLES – Three bones () They are the smallest bones in the
human body. The eardrum vibrates, and this vibrates the
hammer, than the anvil and the stirrup one after another
The stirrup then vibrates the Oval Window
COCHLEA- This is a spirally coiled tube containing fluid and the
actual organ of hearing (the Organ of Corti). Each Organ of Corti
contains thousands of sensitive hairs that are vibrated by sound
waves. The hairs initiate nervous impulses in the
Auditory Nerve which carries messages to the brain


ATP- adenosine triphosphate: serves as a
source of energy used to power the Na/K
pump.
Glucose and oxygen and required for cellular
respiration to obtain energy.
CNS cannot regenerate.
 Stroke- lack of oxygen to the brain.

May use blood clotting drugs, which need to be taken within at least 3 hrs.
 Asprin reduces the thickness of platelets, so it decreases clots form forming.
However if the blood is thinned and an aneurysm (broken blood vessel) occurs
then the bleeding can be worst.

Spinal cord injury- Damage is usually
permanent and can lead to paralysis(a loss or
impairment of voluntary movement in a body
part).
 Found a gene that inhibits spinal regeneration. A protein
that prevents tissue growth is now being researched.

PET scan
◦ Positron emission tomography
◦ uses short-lived radioactive substances to produce
three-dimensional colored images of those
substances functioning within the body.