GCSE level School Biology revision notes: Sense organs - with particular reference to humans

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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


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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