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Sense organs - with particular reference to humans
Doc Brown's biology exam revision study notes
See also detailed notes on the
nervous system and
brain
function
Introduction
What do we mean by a sensory
organ?
What are your five sense organs?
You have five different sense
organs, namely the ears, eyes, nose, skin and tongue which contain
receptors (groups of
specialised cells) that are sensitive to particular stimuli.
Sense organs as groups of receptor cells responding to
specific stimuli: light, sound, touch, temperature and chemicals.
detect signals, brain process - response
The ear sense organs detect sound
The human ear detects sound waves that enter the ear canal and cause
the eardrum to vibrate.
Three small bones transmit these vibrations to the cochlea which
generate nerve signals.
These nerve impulses (electrical signals) pass along the auditory
nerve to the brain, where they are interpreted as sound.
Your ear organ can detect and distinguish a wide range of frequencies
e.g. 20 to 20 000 kHz and a wide range of amplitude (loudness).
Sound waves properties,
uses of sound, ultrasound, infrasound
(GCSE physics notes, no ear diagram)
The eye sense organs detect visible light
The human eye detects visible light
frequencies/wavelengths - that's why these are referred to a s
'visible' light or the 'visible spectrum'. The eye and associated
optics are described in detail on the following two pages.
The eye - structure and function - correction of vision
defects (GCSE biology notes)
Optics - types of lens and uses,
experiments, ray
diagrams, correction of eye defects (GCSE physics notes)
The nose
sense organ detects chemical odours ('smells')
The inner roof of nose houses the olfactory system
whose receptor cells detect chemicals in the air - 'your sense of
smell'.
These olfactory cells respond to different chemicals
and you perceive the different generated nerve signals as a
different smells.
The odours may be aesthetically pleasing or
unpleasant to your sense of smell.
Animals can emit and detect very small quantities of
molecules called pheromones - often for sexual attraction
strategies.
The jury is out on whether this applies to human
beings other than specially designed perfumes, which perform the
same role sometimes!
A pheromone is defined as a secreted or excreted
chemical substance that triggers a social response in members of
the same species.
Pheromone molecules are capable of acting like
hormones outside the body of the secreting individual, to affect
the behaviour of the receiving individuals of the same species.
You skin
senses can detect
physical contact (touch), temperature ('hot and cold' surfaces) and
chemicals
Your skin has a variety of receptor cells that
respond to:
(i) A physical contact with the skin, from light
touching to detecting pressure.
(ii) A change in temperature on the skin surface
e.g. cold air or a hot surface.
(iii) The skin responds to irritating chemicals
that cause inflammation e.g. acids or alkalis.
The tongue -
detects the taste of different substances (different chemical)
Receptor cells on your tongue surface respond to
different chemical substances and the nerve signals generated are
perceived as 'taste', which may be pleasant or unpleasant.
See also detailed notes on the
nervous system
and
brain
function
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