
Explain other ways that humans sense their
environment and their spatial orientation in it
› olfactory receptors, proprioceptors, taste receptors,
receptors in the skin

Describe the structure and function of the parts of
the human eye
› cornea, lens, sclera, choroid, retina, rods and cones,
fovea centralis, pupil, iris, and optic nerve

Describe the structure and function of the parts of
the human ear
› pinna, auditory canal, tympanum, ossicles, cochlea,
organ of Corti, auditory nerve, semicircular canals, and
Eustachian tube

Table 1 pg 446

Figure 2 pg 447

Taste receptors are concentrated in
taste buds on our tongues

Specific chemicals stimulate receptors
› 5 types: sour, salty, sweet, bitter and savoury

each cell (each taste bud)can detect
all tastes, but is particularly responsive to
a certain type/chemical
This diagram isn’t actually
true, but people used to
think it was.

Has 3 separate layers
› Sclera
› Choroid Layer
› Retina
This is the white of your eye
 It is the outermost layer and its function is
to protect and maintain the shape of the
eye
 It includes the cornea and aqueous
humour

 Front
portion of sclera
 Clear
 Strongly
curved
 Starts to focus light
Clear
 Supplies nutrients to cornea
 Fills front (anterior) eye cavity

This is the middle layer of your eye
 It contains the blood vessels for the
retina
 It includes the iris, pupil, lens, vitreous
humour, and ciliary muscles

Iris is the coloured part that makes up the
front of choroid layer
 It contains muscles to change pupil
diameter

› Circular muscles close pupil
› Radial muscles open pupil

The pupil is just a hole in the iris that light
comes through
Smooth muscle that changes lens shape
 Attaches to ligaments which are
connected to lens
 Muscle contraction changes shape of
lens
 Secretes aqueous humour

Focuses light on retina
 Controlled by muscles of ciliary body
 Lens flattens for distant objects

› Image is inverted when light passes through
 Image is projected on retina upside-down.

The changing shape of the lens will focus
the image on the retina
Cloudy, jelly-like material
 Maintains the shape of the eyeball
 Helps focus light onto the retina

This is the innermost layer of your eye
 It contains photoreceptors and has 4
different layers of cells

› Pigmented epithelium
› Light-sensitive cells (sensory receptors)
› Bipolar cells
› Cell of the optic nerve

Light-sensitive cells (sensory receptors)
› Rods which are cells for low-intensity light
› Cones which are cells for high-intensity light
and identify colours
› Cones are concentrated in the fovea
centralis located at the back of the eye
› Rods are located around the periphery of
the fovea.
› There are no receptors (rods and cones)
where the optic nerve and retina join
 blind spot
Light enters the retina through the
pigmented epithelium, which helps focus
the light onto the rods and cones.
 The signal is then sent through the bipolar
cells to the cells of the optic nerve which
transmit the message to the brain.


Rods contain rhodopsin, a light senstive
pigment
› Light hits the rhodopsin and causes an
Action Potential in the rod.
› Neurotransmitters communicate this stimulus
(AP) to the bipolar cells and then to the
optic neurons
› Rhodopsin is sensitive to light and breaks
down in high light intensity, so it works best in
low light intensity situations
› Negatively affected by Vitamin A
deficiency.
Cones have a less sensitive pigment, so
they work better in high intensity
situations, allowing you to see colours.
 Each cone is sensitive to one of the three
primary colours of source light

› Red
› Blue
› Green

Combinations
of cones being
stimulated by
different
wavelengths
allows you to
perceive
different
colours
This happens when one
or more types of cones
are defective
 The most common type
is red-green
colourblindness where
the red sensitive cones
are defective


Positive = you can see the shape of a
camera’s flash after you close your eyes.
› Image has been “burned” onto your retina

Negative = color reversal
› caused by fatigue of cones responsible for
particular colors, while others continue to fire

Normal focusing of light
› Cornea bends light to pupil: light slows down
as it travels through the cornea (dense
material) = refraction of light inward toward
lens. Lens is thicker in middle than edges, so
light bends to a focal point (center of retina)

Viewing close up
› ciliary muscle contracts and lens becomes
thicker = additional bending of light. Pupil
constricts to focus the image (light is focused
more onto the fovea centralis)

Viewing farther away
› Relaxaion of ciliary muscle causes lens to thin
out. Pupil dilates to let in more light.

As you age: layers of protein cover the
lens, hardening it so it is less flexible; more
difficulty accommodating for close up
(reading).
Near-Sightedness (Myopia)
 Eyeball is TOO LONG
 Rays from distant objects focus in front of the
retina

Myopia can be corrected using a
concave lens.
Far-Sightedness-Hypermetropia
 Eyeball is TOO SHORT
 Rays from near objects focus behind the retina

Hypermetropia can be corrected with a
convex lens

Glaucoma
› Buildup of aqueous humour
› Increases pressure in the eye which causes
retinal ganglion cells (nerve cells) to die
› Results in loss of vision

Cataracts
› Lens becomes opaque
(can’t see through it)
› Light can’t pass through
› Can remove the lens
and wear strong
prescription glasses

Astigmatism
› Lens or
cornea is
irregularly
shaped
› Light doesn’t
focus on back
center of
retina (fovea
centralis)
Cool video on cow eye dissection

The ear is made up of three main
structures
› Outer Ear
 Gathers sound waves
 Transfers sound waves to middle ear
› Middle Ear
 Amplifies sound waves
 Transfers sound waves to inner ear
› Inner Ear
 Turns vibration signals (from sound waves) into
electrical impulses which are sent to the brain
through the auditory nerve
The outer ear consists of the pinna and
the auditory canal
 Pinna

› External ear flap
› Collects sound

Auditory Canal
› Carries sound to the eardrum
› Has sweat glands that produce ear wax

Tympanic membrane (Ear Drum)
› Thin tissue layer that receives sound
vibrations
› Sends the vibrations from the sound waves
into the middle ear
The middle ear consists of the ossicles
and eustachian canal
 Ossicles

› Consists of three small bones that amplify
and carry sound from tympanic membrane
to the oval window of the cochlea
 Malleus (hammer)
 Incus (anvil)
 Stapes (stirrup)
Sound vibrations transfer from the
tympanic membrane to the malleus,
which then hits the incus which hits the
stapes which vibrates against the
membrane covering the oval window of
the cochlea
 Sound is amplified by concentrating the
sound energy from the tympanic
membrane to the smaller oval window


Eustachian tube
› Does not help with hearing
› It is an air-filled tube that equalizes pressure
between the external and internal ear
› Where your ears “pop”
Inner Ear
The inner ear consists of the vestibule,
semicircular canals and the cochlea
 Vestibule (for balance)

› Involved in static equilibrium/head positiion

Semicircular canals (for balance)
› Involved in dynamic equilibrium/body
movement

Cochlea (hearing)
› Coiled structure that turns sound waves into
nerve impulses
› Contains the Organ of Corti
 Has sound receptors where waves become
impulses
 Hair cells attached to basilar membrane

Movement of fluid in the cochlea causes
the basilar membrane to vibrate
› Different pitches of notes make different
areas of membrane vibrate
Small hairs (cilia) are attached to the
basilar membrane
 The hairs rub and bend against the
tectorial membrane
 The bending generates a sensory nerve
impulse that is sent to the brain


http://www.nelson.com/ABbio2030/student/protect/animations/unit30Ac
h14.html#14.2
Hearing Summary So Far
Sound Waves
Sound Waves initiate a
series of movements
within the ear:
Tympanic
membrane
Hammer
Anvil
Stirrup
Oval window
Fluid inside a coiled tube (cochlea)
Round window
Sound waves push against tympanic
membrane; these vibrations are passed
onto the ossicles (malleus then incus and
finally stapes).
 The ossicles concentrate and amplify the
vibrations (exerting greater force by
concentrating the energy in a very small
area).

Oval window receives vibrations from stapes
which causes the oval window to move in and
out. This results in the round window (below it) to
also move in and out (in alternation with oval
window). The two windows moving in and out
cause fluid to move in the inner ear.
 The cochlea receives fluid waves and converts
them into electrical impulses.
 Fluid waves move the basilar membrane, the
hairs on the membrane brush against tectorial
membrane and bend. This stimulates sensory
nerves in the basilar membrane
impulses to
auditory nerve then to brain.

Small muscles in your ears help protect
your hearing
 When loud noises are around:

› Muscles attached to the malleus (hammer)
contract and restrict intense movements
› A second muscle contracts, pulling the
stapes (stirrup) away from the oval window,
limiting inner ear damage

This doesn’t work for sudden loud noises

Conductive Hearing Loss
› Sound waves can’t enter inner ear
› caused by wax buildup, middle ear infection, or
punctured eardrum
› Fixed by medical/surgical procedures

Sensorineural Hearing Loss
› Auditory nerve is severed or damaged or hair
cells of the cochlea are damaged or dead.
› caused by aging, loud noises, head trauma or
genetic conditions

Hearing Aids
› pick up sound (microphone), amplify it and
transmit it to eardrum
› won’t work for Sensorineural hearing loss
(vibrations can’t be transmitted to brain)

Cochlear Implants
› does not make sounds louder or clearer
› bypasses damaged parts and converts sounds into
electrical impulses that are sent to the brain.
› has a microphone (picks up sounds), a speech processor
(selects and arranges sounds), a transmitter and
receiver/stimulator receive signals from the speech
processor and convert into electrical impulses. Electrodes
send them to the auditory nerves.

* Doesn’t replicate exact sounds (like we hear them),
provides sounds that allow person to interpret their
environment. Over time, person learns to decipher
impulses and can understand speech.*

Static equilibrium (Am I upside down)
› Detected by the vestibule
Inner Ear

Static equilibrium (Am I upside down)
› Movement along one plane (vertical or
horizontal)
› Detected by the vestibule
› Involves two other structures
 Utricle
 Saccule
› Fluid filled
› Contains tiny hairs (cilia)
When the head is upright: calcium
carbonate crystals in the fluid (otoliths) don’t
move = fluid doesn’t move = cilia don’t move
 - When the head is bent forward: the otoliths
shift downward, pulling on the fluid.
 This causes the cilia to bend which stimulates
the nerve cell.
 Sends a nerve impulse to brain (cerebellum)
informing of head position relative to gravity

Inner Ear
Dynamic Equilibrium (Moving forwards or
backwards, spinning, flipping around)
 Detected by the semicircular canals

› Has 3 different fluid filled rings
 Vertical
 Horizontal
 Diagonal
Each canal has an ampulla (pocket)
that holds a cupula
 When you move, fluid in the semicircular
canals moves, bending cilia (that are on
hair cells found in the cupula).

› Results in nerve signals sent to brain.

Rapid, continuous movement of the
fluids causes motion sickness