Download File - Mr Murphy`s Science Blog

Mr. E Murphy
Objectives
 Touch
 Taste
 Smell
 Sight
 Hearing
Introduction
 Balance may be a sixth sense
 Senses are based on receptor
cells forming a sense organ
 Specialised to respond to
various stimuli e.g. heat, light
etc.
 Receptors absorb these forms
of energy and convert into
electrical impulses that travel
along neurons
Touch
 Receptors found at different concentrations
around the body
 Many in the elbow, few in the heel
Taste
 Receptors for taste are in
taste buds
 Located on the top and side
of the tongue, also parts of
the lining of the throat
 Sweet, sour, bitter and salt
 Taste may stay longer if it
dissolves into the grooves of
the taste buds
Flavour is a combination of taste,
smell, texture and temperature
Smell
 Root of nasal cavity has
about 20 million neurons
to detect smell (olfactory
neurons)
 Respond to about 50
different gaseous
chemicals making up
10,000 smells
 Extremely sensitive,
adjust quickly to smells
Within a second of detecting a
new smell, 50 % of the sensation
will disappear
Sight
 Conjunctiva: Thin membrane protecting the sclera
 Sclera: White of the eye. Tough and opaque. Does
not allow light in.
 Cornea: Transparent part of the sclera. Allows light
into the eye and bends it towards the retina
 Choroid: Black pigment (melanin) to absorb light in
the eye
 Retina: Light receptors (rods and cones) are located
 Fovea: Area of retina only contains cones. Sharpest
vision
 Blind spot
 Optic nerve: Carry impulses to the brain
 Lens: Elastic transparent structure. Changes shape
to focus light on the retina
 Ciliary muscle: Surrounds the lens and causes the
shape of lens to change
 Iris: Controls amount of light entering the eye (eye
colour)
 Pupil: Opening in the iris
 Aqueous and vitreous humour
 External muscle
Hearing
Functions of hearing
 Hearing and balance
Structure of the ear
 Outer, middle and inner ear
 Outer and middle ear filled with
air
 Inner ear filled with fluid
(lymph)
http://mathsci.werribeesc.vic.edu.au/science7/multimedia/Ho
w%20the%20ear%20works.swf#
The ear and hearing
What causes sound?
Vibrations
 Vibrations in the air (or water etc.)
 Vibrations collected at the outer ear, passed
through the middle ear (amplifications)
 Transferred to the fluid in the inner ear
 Cochlea has receptors which are stimulated
by pressure waves in lymph
 Electrical impulse travels to the brain
(creates sound)
Parts of the ear
 Pinna: made of cartilage. Helps collect and channel
vibrations into the ear canal
 Auditory (ear) canal: Tube carries vibrations to the
eardrums. Wax traps dust (protection)
 Eardrum (tympanic membrane): Small, tightly
stretched membrane separates the outer ear from the
middle ear
- Vibrates due to air vibrations
Parts of the ear
 Ossicles: 3 tiny bones in the middle ear
Hammer, anvil and stirrup
 Stirrup is the smallest bone in the body
 These 3 bones transmit vibrations from the
outer to the inner ear and amplify
(increase) the vibrations
Parts of the ear
 Eustachian tube:
• Not really part of the ear
• Runs from the middle ear to
the pharynx (throat)
• Equalises pressure on either
side of the ear drum
• Prevents damage to the
eardrum caused by the
difference in pressure
Parts of the ear
Why would the eustachian tube
open?
 Yawn or swallow
 Up a mountain: external air
pressure increases
 Underwater: Air moves into middle
ear to equalise the increased
pressure from the water
 Common for infections to travel
between the throat and middle ear
Parts of the ear
Cochlea

Spiral tube, 3.5 cm long (snail’s shell)
Converts pressure waves from sound vibrations into
electrical impulses which travel to the brain
Parts of the ear
Cochlea

1.
How the cochlea works:
Vibrations arrive at the cochlea from the stirrup,
which is attached to the oval window
2. Vibrations pass through the oval window and
form pressure waves in the lymph
3. Pressure waves stimulate receptors (hairs) in the
cochlea (The organ of corti)
4. Receptors cause electrical impulses to travel to
the brain (auditory or cochlear nerve)
5. Round window allows the pressure waves to exit
The ear and balance
 Vestibular apparatus in the
inner ear detects balance
 Made up of 3 semi-circular
canals
 Balance also maintained due
to vision, receptors in
muscles, ligaments and
tendons and pressure
receptors in the soles of feet
 If the vestibular apparatus is
damaged, balance can be lost
Vestibular apparatus
Parts of the ear
What the vestibular apparatus
does?
Vestibular apparatus
 Its filled with lymph
 Receptors detect whether the
head is vertical or not
 Other receptors can detect
movement of the head
 All these receptors send
impulses to the cerebellum
through the vestibular nerve
http://www.bbc.com/news/health13358608
Hearing Defects
 Glue ear
• Common in children
• Surplus sticky fluid in the middle
ear
• Prevents free movement of the
eardrum and the small bones
• Results in some deafness
Correction
• Nose drops
• Grommets (small tubes allowing
air into the middle ear)
Summary
 The 5 senses
 Structure of the eye + roles of the different parts
 Structure of the ear + roles of the different parts
 6 revision classes before test
Exam Questions
 2011 Q15a
 2009 Q15b
 2007 Q15c
Solutions
2011 Q 15a
Solutions
2009 Q 15b
Solutions
2007 Q 15c