Download File - Ms Curran`s Leaving Certificate Biology

The Senses
Name the 5 Senses?
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Touch
Sight
Taste
Smell
Hearing
 Each sense has receptor cells, these
maybe neuron endings or specialised cells
in close contact with neurons.
Receptors
 Are specialised to respond to various
stimuli such as heat, light, pressure and
chemicals
 All of the above are forms of energy &
receptors convert this energy into
electrical impulses that travel along
neurons.
Touch
 Skin contains receptors for touch &
temperature
 These are found in different concentrations in
skin at various locations around the body.
 E.g. very few in the heel of the foot compared
to the elbow which has several (this is why
parents use their elbow to test the temp of a
babies bath.
Taste
 Receptors are located in taste buds. Which
are found on the top and sides of the tongue
& in some parts of the throat.
 4 basic taste receptors
 Sweet, bitter, sour & salt. (See diagram)
 Flavour of food is combination of taste, smell,
texture & temp, hence when we have a cold
food looses its taste.
Taste
Smell
 The nasal cavity has 20 million neurons to
detect smell (olfactory neurons)
 These respond to over 50 different chemicals
in a gaseous state, which combine to
produce 10,000 different smells.
 These receptors also adjust to a smell very
quickly & stop responding. Hence a smell
disappears after awhile.
Sight
Part of Eye Function
Conjuctiva
Sclera
Thin memb, protests sclera
(inflammation=Conjunctivitis)
White of eye, lets no light in, is tough & holds
shape of eye
Cornea
Clear part of eye, allows light into eye & bends
toward retina
Choroid
Layer which provides blood to eye & Melanin to
absorb light
Retina
Contains light receptors (cones&rods), Pigment =
rhodopsin
Fovea
Only contains cones, region of sharpest vision
Blind Spot
No rods/cones located here, nerve fibres leave eye
here
Part of Eye
Function
Optic Nerve
126 million axons carry impulses from rods &
cones to brain
Lens
Changes shape to focus light on retina
Ciliary Muscle
Causes shape of lens to change
Iris
Coloured part of eye, Controls amount of light
entering eye
Pupil
Opening in iris, lets light into eye, large opening
=dilated
Aqueous
Humour
Vitreous
Humour
Salt solution which holds the shape of front of
the eye
Viscous fluid, supports eye by exerting pressure
outwards
External muscle Eye is moved by 6 external muscles
Hearing
Function of the Ear
 Hearing & balance
 3 sections of ear (outer, middle & inner ear)
 Outer & middle ear filled with air
 Inner ear filled with fluid called lymph.
The Ear & Hearing
 Sound caused by vibrations in the air.
 Vibrations collected by outer ear, passed
through the middle ear (vibrations amplified)
and transferred to fluid in the Cochlea on inner
ear.
 Cochlea contains receptors which are
stimulated by pressure waves in lymph. These
receptors cause electrical impulses to be sent
to the brain which interprets them as sound.
Hearing
Part of Ear Function
Pinna
Collects & channels vibrations into Auditory canal
Auditory
canal
Carries vibrations to eardrum, wax secreted outside
eardrum to trap dust & protect the ear
Eardrum
(tympanic membrane) vibrates due to air vibrations
Ossicles
3 tiny bones in middle ear that vibrate & amplify
vibrations (hammer, anvil & stirrup)
Eustachian
tube
Runs from middle ear to throat, It equalises
pressure on either side of eardrum (pops when we
yawn)
Cochlea
Spiral tube (resembles snails shell) converts
pressure waves caused by vibrations into electrical
impulses which travel to brain
Cochlea
 Vibrations arrive at cochlea from stirrup which is
attached to a membrane on the cochlea called
the oval window.
 Vibrations pass through OW & form pressure
waves in lymph in cochlea
 Pressure waves stimulate receptors which form
a structure called the organ of Corti
 Receptors send electrical impulses to brain
Impulsestravel along auditory/cochlear nerve.
 Round window allows pressure waves to
dissipate out of cochlea into air of middle ear.
The Ear & Balance
 Balance largely detected in Vestibular
Apparatus in inner ear.
 VA Consists of 3 semicircular canals
 Person who damages VA loses sense of
balance
 VA is filled with Lymph
 Receptors in VA detect whether head is vertical
or not & other detect movement.
 Receptors send impulses to cerebellum of brain
through vestibular nerve.
Corrective measures for
hearing disorder
Disorder
 Glue ear = surplus sticky fluid in middle ear
which blocks the Eustachian tube & prevents
movement of eardrum & small bones in middle
ear
Correction
 Mild cases= nose drops to unblock ET
 Severe cases=small tubes called grommets
inserted which allow air into the middle ear &
forces fluid down ET. Grommets eventually fall
out themselves.