Download Topic A.3 notes

• Receptors in the nervous system the are sensitive to changes in
the environment around the cells.
• Humans have the 4 following types of specialized receptors
• Mechanoreceptors
• Respond to mechanical forces and movements
• Chemoreceptors
• Respond to chemical substances
• Thermoreceptors
• Respond to temperature changes
• Photoreceptors
• Respond to light
• Detection of chemicals in the air is carried
out by the Olfactory receptors.
• These cells have cilia that project into the
nasal cavity and their membrane contains
odorant receptor molecules which assist in
the sense of smell
• Different organisms have differing
amounts of odorant receptors
• Mice have over a thousand different receptors
which allows them to have a very keen sense
of smell
• Humans are severely lacking in odorant
receptors which provides an imprecise sense
of smell
• 1. sclera = opaque (usually white), fibrous, protective
layer of the eye containing collagen and elastic fibers
• 2. cornea = transparent front part of the eye that
covers the iris, pupil, and anterior chamber,providing
most of an eye's optical power
• 3. conjunctiva = membrane that covers the sclera
(white part of the eye) and lines the inside of the
eyelids
• 4. eyelid - outside flesh covering of the eye. Protects
from damage
• 5. choroid = vascular layer of the eye lying between the
retina and the sclera. The choroid provides oxygen and
nourishment to the outer layers of the retina
• 6. aqueous humor = thick, watery substance in the eye
• 7. pupil = variable-sized, black circular opening in the center of
the iris that regulates the amount of light that enters the eye
• 8. lens = transparent, biconvex structure in the eye
that,
along with the cornea, helps to refract light to focus on the
retina
• 9. iris = colored part of the eye
• 10. vitreous humour = the clear aqueous solution that fills the
space between the lens and the retina
• 11. fovea = responsible for sharp central vision
• 12. optic nerve = transmits visual information from the retina to
the brain
• 13. blind spot = the specific region of the retina where the optic
nerve and blood vessels pass through to connect to the back
of the eye
• 14. retina = thin layer of neural cells that lines the back of the
eyeball
• Light enters the eye through the cornea and the lens which
focuses it onto the retina.
• The retina is a thin layer of light-sensitive tissue at the back of
the eye.
• The retina involves two types of photoreceptors
• Rods and Cones
• Many nocturnal animals only have rods and cannot distinguish color
• Rods are very sensitive to light. But not color
• When exposed to bright light “bleaching” of rods can occur
• Cones are able to absorb different ranges of wavelengths of
light
• There are three types of cones in the human eye.
• Red, Green, Blue
• The relative stimulation of each of the three cone types allows
for interpretation of color
• Color vision is only in bright light and tends to fade in dim light
• Rods and cones synapse with neurons called bipolar cells
• Bipolar cells send the electrical impulses from the rods and
cones to the Ganglion cells
• If a rod or cone cell is not stimulated by light they will
depolarize and release an INHIBITORY Neurotransmitter onto a
bipolar cell.
• This causes that bipolar cell to become hyperpolarized and not transmit
impulses to its associated retinal ganglion cell.
• When light is absorbed by a rod or cone cell it becomes
hyperpolarized and stops sending that inhibitory
neurotransmitter to the bipolar cell
• This then allows the bipolar cell to depolarize, activating the adjacent
ganglion cell.
• Groups of rods send signals to the brain via a single bipolar
cell
• Grainy Picture
• Cones send signals to the brain via their own individual bipolar
cell
• High Definition vision!!
• Ganglion cells have cell bodies in the retina and synapse with
bipolar cells
• Ganglion cells pass across the front of the retina to form the
“blind spot”
• The “Blind spot” is actually where the ganglion cells combine to
form the Optic Nerve
• Transmit pressure waves into auditory sounds
• Brain interprets the information from the receptors
Structure
Function
Pinna
Collects sound waves
Eardrum
(tympanic
membrane)
Transmits sound waves to the inner ear bones
Bones of the middle
ear
(hammer, anvil,
stirrup)
Transmit and amplify (by up to 20 times) the sound waves
received from the eardrum
Also known as the malleus, incus and stapes
Oval window
Receives pressure from middle ear bones (stirrup) and
transmits pressure waves into the middle ear
Round window
Absorbs pressure waves after they travel through the
cochlea, preventing the waves from moving backwards
Semicircular canals
Help maintain balance by sensing position; hair cells
Auditory nerve
Made up of neurons that are activated in the cochlea by
pressure waves bending hairs in the inner ear; sends
messages to brain
Cochlea
Part of ear that contains hairs that are attached to neurons
and activated by pressure waves; transforms the pressure
waves into neural impulses
• Pinna
• Eardrum
• 3 smallest bones in the body (malleus, Incus and Stapes)
• Does both auditory and balance
• Cochlea and Vestibula or semicircular canals
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Pinna collects sound waves and passes them to the eardrum
The eardrum vibrates
Vibration of the eardrum puts pressure on the ear bones
Ear bones absorb the vibrations and amplify them
Vibrations reach the stirrup and act like a piston to convert it to
mechanical energy
• Mechanical energy is passed on to the cochlea via the oval and
round windows
• As it moves through the cochlea it causes the hair cells to bend
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Hair cells are varying heights and are in a jelly-like substance
Larger sound waves vibrate more hair cells
The more hair cells activated (bent) the louder the sound
The more frequent the sound waves the higher the pitch
(frequency)