Transcript Grade12SenseOrgans_001

Grade 12: Sense Organs
Receptors
• Receptors detect a variety of
different stimuli such as light, sound,
touch, temperature, pressure, pain
and chemicals (taste and smell).
Receptor Types
Chemoreceptors
• respond to changes in chemical concentrations
Pain receptors
• respond to tissue damage
Thermoreceptors
• respond to changes in temperature
Mechanoreceptors
• respond to mechanical forces
Photoreceptors
• respond to light
Photoreceptors
• Rods for vision in dim light (120 million)
– Found more towards periphery
• Cones for color vision and visual
acuity (6 million)
– Only work in bright light
– Three types: red, green, and blue
• Overlap of three ranges gives us all the
colors
– Color blindness is sex-linked (males)
The Eye
The Eye - Protection
• Protected by bony cavity in the skull = Orbit
• Fat and connective tissue lies between eye
ball and skull
• Exposed part of the eye is protected by a
thin membrane = conjunctiva
• Eyelids
• Eyelashes prevent foreign particles
entering
• Tears secreted by lachrymal glands
keeping conjunctiva moist, anti-bacterial
The Eye: Structure Function
• Sclera
– Protects inner structures
– Maintains shape of eye
• Cornea
– Transparent, permits light to enter eye
– Refracts lights rays as to focus them on retina
• Choroid
– Pigmentation prevents reflection of light within the eye
• Suspensory ligaments
– Holds lens in position
• Ciliary muscles
– Alters shape of lens to “accommodate” for near or far objects
• Iris
– Contains radial and circular muscles which control amount of
light entering the eye (Pupillary Mechanism)
The Eye: Structure Function
• Retina
– Light sensitive layer(has photoreceptor rod/cone cells) so is
responsible for image formation
– Rod Cells responsible for images in dim light
– Cone Cells responsible for images in bright light and for colour
vision
• Lens
– Transparent therefore refracts light focusing it on retina
– Ability to change shape for near or distant vision (accomodation)
• Aqueous Humour
– Maintains shape of the cornea
– Supplies lens and cornea with food and oxygen
– Minor role in refraction
• Vitreous Humour
– Maintains shape of eyeball
– Minor role in refraction
Focusing On Retina
• as light enters eye, it is refracted by
• convex surface of cornea
• convex surface of lens
• image focused on retina is upside down and
reversed from left to right
Accommodation
changing of lens shape to view objects less than 6m away (near vision)
Accommodation
changing of lens shape to view objects less than 6m away (near vision)
Pupillary Mechanism
Adjustment of pupil size under varying light conditions
Pupillary Mechanism
Also known as pupil reflex!
• In dim light
– Radial muscles of iris
contract
– Circular muscles relax
– Pupil dilates
– Amount of light entering
eye increases
• In bright light
– Circular muscles of iris
contract
– Radial muscles relax
– Pupil constricts
– Amount of light entering
eye reduces
Diseases and Disorders of
the Eye
• Long-sightedness (Hypermetropia)
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Eyeball too rounded
Inability for lens to become more convex (especially the elderly)
Image of near object focuses beyond retina
They can see more than 6m away
• Short-sightedness (Myopia)
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Eyeball too long
Inability of lens to become flat enough (less convex)
Image of far objects focus in front of retina
They can see less than 6m away
• Astigmatism
– Unequal cornea or lens
– If degree of astigmatism is great enough to cause eyestrain,
headaches, distortion of vision, perscription lenses will be needed for
clear and comfortable vision.
Diseases and Disorders of the
Eye
Diseases and Disorders of
the Eye
• Cataracts
– The clear transparent lens of the eye becomes cloudy or opaque
– Synthetic lens (intraocular implant) can be surgically implanted if
necessary through using microscopic instruments
• Glaucoma
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Too much pressure in the eye
Leads to permanent damage of the optic nerve
Eventually leads to blindness (2nd leading cause)
Early detection is important
Treated with drops to reduce pressure or surgery
• Colour blindness
– Sex linked characteristic (affects mostly males)
– Difficulty in seeing red-green colour
– Complete colour-blindness individuals see everything in shades of
grey
Optical illusions
Eyes are playing tricks on
our brains
• The Dutch artist
M.C. Esher mixed
realistic detail
with strange
perspectives
that also provide
optical illusion's.
• Waterfall
created in 1961.
Julian Beever
Julian Beever
External Ear
• Pinna (auricle)
• collects sounds waves
• auditory canal
• aka ear canal
• carries sound to
tympanic membrane
• eardrum
• aka ear tympanic
membrane
• vibrates in response to
sound waves
Middle Ear
• auditory ossicles
• vibrate in response to
tympanic membrane
• malleus (hammer), incus
(anvil), and stapes (stirrup)
• aka hammer, anvil & stirrup
• oval window
• stapes (stirrup) vibrates
against it to move fluids in
inner ear
Auditory Tube
• eustachian tube
• connects middle
ear to throat
• helps maintain
equal pressure on
both sides of
tympanic membrane
• usually closed by
valve-like flaps in
throat
Inner Ear
• System of labyrinths
•Bony labyrinth
• bony canal in temporal
bone
• filled with perilymph
• made up of semi-circular
canals, the vestibule
(saccule and utricle) and
the cochlea.
• Membranous labyrinth
• tube within bony labyrinth
• filled with endolymph
• contains the organ of corti
Inner Ear
Parts of Inner Ear
• cochlea
• functions in hearing
• snail-shaped
• Have hearing receptor
cells (hair cells) that bend
with different frequencies
to generate a nerve
impulse = Organ of Corti
• semicircular canals
• functions in equilibrium
and balance
• fluid-filled
Hearing Process
• Pinna trap and direct sound waves along
auditory canal
• Sound waves hit tympanic membrane causing it
to vibrate
• This causes ossicles to vibrate
• Stirrup causes membrane on oval window to
vibrate
• Sends waves in perilymph of vestibular canal
• Organ of Corti in the Cochlea is stimulated
• Stimulus is turned into nerve impulse
• Auditory Nerve sends signals to Cerebrum to be
interpreted
Balance and Equilibrium
• Sudden changes in speed and
direction causes endolymph in
semicircular canals to move
• These canals are in three
different planes, fluid in at least
one canal will move if ones
speed or direction changes
• Movement of flood stimulates
receptors called cristae within
the ampullae to move
• Ampullae are found at the
base of each semi circular
canal
• Cristae send impulses along
vestibular nerve branch to
cerebellum
Balance and Equilibrium
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In the sacculus and utriculus
When direction of head changes, gravitational pull stimulates different receptors
called maculae to move
Maculae send signal along vestibular branch of the auditory nerve to the cerebellum
Cerebellum sends impulses to muscles to restore balance and equibilbrium
Adaptations of the Ear
• Pinna is large and projected out of head to capture sound waves
• Cerumen (wax) and hairs in auditory canal trap small organisms
preventing entry
• Cerumen prevents drying out
• Hammer is attached to tympanic membrane so it can vibrate along with
the tympanic membrane
• Stirrup is attached to oval window
• Oval window also vibrates creating waves in the perilymph of the
vestibular canal
• Eustachian tube allows air to be released out of, or taken into, thus
equalizing pressure between middle and outer ear (prevents tympanic
membrane bursting.
• Round window acts as a cushion absorbing the pressure coming from
the waves
• Cochlea contains the organ of corti which is the receptor picking up the
stimulus of sound
• Auditory nerve arising from the cochlea transmits sound to the cerebrum
of the brain
Diseases and Disorders of
the Ear
• Middle Ear Infection
– Most common cause of earaches.
– Caused by viruses and bacteria
– Fluid build up results in increased pressure and inflammation
– Treated using medication or grommets, which are tiny plastic buttons
with a fine hole in the middle. These are inserted into eardrum
allowing air to enter giving time for the eustachian tube to recover
with all the fluid build up.
• Deafness
– Can be caused by: Fluid in the middle ear, damage to ear drum,
hardened wax in the ear, hardening of ear tissue, age, injuries to
parts of the ear, nerves or brain responsible for hearing.
– Treatment depends on the cause, not all cases are treatable.
Hearing aids make sound louder so that person can listen and
communicate. Cochlear Implants can also be used to treat
deafness. These don’t work by amplifying sounds but rather by
stimulating the auditory nerve in side the cochlear as the organ of
corti would normally do