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Biology 12
Unit 1:Maintaining Dynamic Equilibrium
Special Senses
 Input to the nervous system is in the form of our
senses: pain, vision, taste, smell, hearing, balance,
and others.
 Vision, taste, smell, and hearing input are the
special senses.
 Pain, temperature, and pressure are known as
somatic senses. Sensory input begins with sensors
that react to stimuli in the form of energy that is
transmitted into an action potential and sent to the
CNS.
Special Senses
Receptor
Taste
Smell
Pressure
Proprioreceptor
Ear
Ea r
Ear
Eye
Eye
Thermoreceptor
Other internal
receptors
Stimulus
(Energy)
Chemical
Chemical
Information Provided
Presence of chemicals in food.
Presence of chemicals in the air
(and in food)
Mechanical Movement of skin
Mechanical Movement of limbs
Sound
Direction and intensity of sound
waves
Mechanical Body movements and orientation
Light
Change in light intensity,
movement, colour
Heat
Flow of heat
(thermal)
various
Stretching of muscles and
arteries, concentration of blood
gasses, etc...
Taste & Smell
•Specialized receptors to detect presence of
chemicals in the external environment.
•Specific chemicals combine with receptors
causing an action potential.
•There are five types of specialized taste receptors
- salty, sweet, bitter, sour, savoury (glutamate).
•Taste and smell combine to give foods the
variety of flavours we associate with them.
The Eye - Structure
The Eye - Structure
 Anterior chamber- A cavity of the eye filled with
aqueous humour, a fluid that provides oxygen,
glucose, and proteins.
 Choroid Layer-rich in blood vessels that supply the
eye tissues with oxygen and nutrients.
 Ciliary body-Changes the shape of the lens, which
adjusts the eye's focus.
 Cornea and lens-Focuses light.
 Fovea-A depression in the retina where cones
(photoreceptor cells) are concentrated and vision is
most acute.
Iris-Colored part of the eye.
Optic disc-Round, flat structure where nerve fibres from
the retina converge, blind spot.
Optic nerve-Transmits information about images to the
brain.
Retina-Contains light-sensitive nerve cells.
Sclera-White, outer layer of the eyeball.
Vitreous-Transparent gel that fills the main cavity of the
eye.
The Eye - Photoreceptors
 The human eye can detect light in the 400-700
nanometre (nm) range, the visible light spectrum.
 Light with wavelengths shorter than 400 nm is termed
ultraviolet (UV) light.
 Light with wavelengths longer than 700 nm is termed
infrared (IR) light.
 In the eye, two types of photoreceptor cells
are clustered on the retina.
 Rods detect differences in light intensity.
 Cones detect colour.
 Rods are more common in a circular zone
near the edge of the eye.
 Cones occur in the centre (or fovea
centralis) of the retina.
 Light reaching a photoreceptor causes the
breakdown of the chemical rhodopsin,
which in turn causes a membrane potential
that is transmitted to an action potential.
The action potential transfers to synapsed
neurons that connect to the optic nerve.
The optic nerve connects to the occipital
lobe of the brain.
 Humans have three types of cones, each
sensitive to a different colour of light: red, blue
and green.
 Opsins are chemicals that bind to cone cells
and make those cells sensitive to light of a
particular wavelength (or colour).
 Humans have three different forms of opsins
coded for by two genes on the X chromosome
and one gene on chromosome 7.
 Defects in one or more of these opsin genes
can cause colour blindness, usually in males.
The Eye - Pathway
The Visual Pathway: from visual spectrum to the
brain.
From Nelson Biology
The Eye - Defects
 Astigmatism-is a hereditary impediment. It occurs when the
curvature of the cornea does not permit the image to project
itself correctly on the retina.
 Myopia-The person who suffers from myopia has shortsightedness. Myopia is a condition in which the image is
focused in front of the retina.
 Glaucoma-is a progressive blindness that causes severe
damage to the optic nerve. It is caused by an increased buildup of aqueous humour in the anterior chamber of the eye.
This disease can cause total blindness.
 Far-Sightedness (hyperopia)-The image is focussed behind
the retina. The person who suffers from farsightedness
cannot focus on near objects.
 Cataracts-A loss of transparency of the lens of the eye, or of
its capsule. Surgery, to remove the cataract, can restore the
sight.
The Eye - Technologies
 Corrective Lenses
 Glasses, contacts, surgical implants
 Radial Keratotomy
 Using a knife to reshape the cornea
 Laser Eye Surgery
 Using a laser to reshape the cornea
 Other Surgery
 Cornea transplants, cataract surgery
The Ear
The Ear - Structure
 External
 Pinna
 Auditory Canal
 Middle
 Ossicles (malius, incus, stapes)
 Tympanic membrane
 Eustachian tube
 Oval Window
 Round Window
 Inner
 Vestibule (utricle, saccule)
 Semicircular canals
 Cochlea
The Ear - Hearing
 Hearing involves the actions of the external ear,
eardrum, ossicles, and cochlea.
 In hearing, sound waves in air are passed from
vibrations of a gas (air outer ear) to a solid (ossicles
of middle ear) and then a liquid (fluid of the inner ear).
 Next these vibrations cause movement of hair cells in
the cochlea.
 Finally they are converted into action potentials in a
basilar membrane connected to the auditory nerve.
 Very loud sounds can cause violent vibrations in the
membrane under hair cells, causing a shearing or
permanent distortion to the cells, resulting in
permanent hearing loss.
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The Ear - Orientation and
Gravity
 Orientation and gravity are detected in the
vestibular apparatus made up of the utricle and
saccule.
 Calcium carbonate crystals shift in response to
gravity causing hair cells to bend thus providing
sensory information about gravity.
 Acceleration in three different planes of movement
is detected by the semicircular canals. Hair cells
respond to shifts of liquid within the canals,
providing a sense of acceleration.
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