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The Special Senses
Life Science
FLSS
All images used are taken from copyright-free sources e.g. Wikicommons Media or produced by UWS staff.
Special senses
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Sight
Hearing
Taste
Smell
Touch
Information about external environment  brain  response as necessary
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Senses interpret different forms of energy
Brain receives info from senses
Info/energy converted to electricity in a form brain can interpret
Sensory neurones
Specialised structures at dendrites
which respond to:
• Light
• Pressure
• Chemicals
Cell bodies often close to spinal cord
Sight
Iris
Eyelashes
Eyebrow
Upper eyelid
(palpebra)
Lacrimal
caruncle
Medial
commissure
Lateral
commissure
Palpebral
fissure
Pupil
Conjuctiva (over sclera)
Lower eyelid
(palpebra)
Sneakydaycrawler (2007)
http://commons.wikimedia.org/wiki/File:Hazel_eye_(1).jpg
Tear production
a. tear gland / lacrimal gland,
b. superior lacrimal punctum,
c. superior lacrimal canal,
d. tear sac / lacrimal sac,
e. inferior lacrimal punctum,
f. inferior lacrimal canal,
g. nasolacrimal canal
Erin_Silversmith (2006)
http://commons.wikimedia.org/wiki/File:Tear_system.svg
Holly Fischer (2013)
Http://commons.wikimedia.org/wiki/File:Three_Main_Layers_of_the_Eye.png?uselang=en-gb
Retina
• Image is focussed onto this inner
lining
• Retina has neurones which are
sensitive to light
• Light causes changes in
photosensitive pigments
• Changes are converted to nerve
impulses
• Impulses transmitted to brain via the
optic nerves
Retinal Cells
Two types of photoreceptors:
• Rods
– Dim light
– Black and white
• Cones
– Bright light
– Distinguish colour (red/green/blue)
OpenStax College (2013)
http://commons.wikimedia.org/wiki/File:1414_Rods_and_Cones.jpg?uselang=en-gb
Rods and cones
OpenStax College (2013)
http://commons.wikimedia.org/wiki/File:1414_Rods_and_Cones.jpg?uselang=en-gb
Pupil constriction/dilation
PUPIL
Bright Light
• Pupil constricts
• Circular muscles of iris contracts
• PARASYMPATHETIC CONTROL
Dim Light
• Pupil dilates
• Radial muscles of iris contract
• SYMPATHETIC CONTROL
UWS Staff (2015)
Hearing
Hearing
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Ears
Sound = sound waves / vibrations of air
Tympanic membrane (eardrum) vibrates
Ossicles vibrate
Via oval window, causes fluid in cochlear
duct to vibrate
• Hair cells stimulated
• Nerve impulses initiated in cochlear part
of vestibulocochlear nerve
brain
BruceBlaus. (2013)
http://commons.wikimedia.org/wiki/File:Bl
ausen_0328_EarAnatomy.png
BruceBlaus. (2013)
http://commons.wikimedia.org/wiki/File:Blausen_0330_EarAnatomy_MiddleEar.png
BruceBlaus. (2013)
http://commons.wikimedia
.org/wiki/File:Blausen_03
29_EarAnatomy_Internal
Ear.png
Balance
• 3 semicircular canals (one in each plane of space)
• Fluid-filled
• Movement of head  movement of fluid 
stimulation of hair cells  send impulses via vestibular
part of vestibulocochlear nerve  brain
Sense of balance involves brain integrating messages
from:
• Eyes
• Inner ear
• Proprioreceptors in muscles and joints
Taste
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10,000 taste buds in your mouth
Chemoreceptors
Sweet, sour, bitter, salt (and umami)
Sweet and salty are least sensitive
Bitter ones are most sensitive
Some researchers doubt the simplicity of this model
BITTER
Rainer Zenz (2007)
http://commons.wikimedia.org/wiki/Tongue
SALTY
SOUR
SWEET
Taste bud
Sunshineconnelly (2007)
http://commons.wikimedia.org/wiki/File:Anatomy_and_physiology_of_animals_Taste_buds_on_the_tongue.jpg?uselang=en-gb
Smell
• Also detected by chemoreceptors, in nasal cavity –
activated by volatile chemicals in the air
• Smell contributes to the fine perception of taste
BruceBlaus. (2013)
http://upload.wikimedia.org/wikipedia/commons/2/2e/Blausen_0872_UpperRespiratorySystem.png
Olfactory bulb
1: Olfactory bulb 2: Mitral cells 3: Bone 4: Nasal epithelium
5: Glomerulus 6: Olfactory receptor cells
Chabacano (2007)
https://commons.wikimedia.org/wiki/File:Olfactory_system.svg
Touch receptors
• Different receptors for hot, cold, pain,
pressure and light touch
• Unevenly distributed on skin and
mucous membranes
• Meissner’s corpuscles – detect light touch
• Pacinian corpuscles – detect pressure
• Free nerve endings – itch/tickle/temp/pain
(slowly and rapidly adapting)
US-Gov (2005)
https://commons.wikimedia.org/wiki/File:Skin.png