10.1 Senses and sense organ

Sensitivity: ability to detect and respond to stimuli

Stimuli: changes in the environment that cause a response

  1. specialised sensory cells detect stimuli
  2. send signals to the brain through nerves
  3. produces sense
Sense organs Stimuli Sense
Eye Light Sight
Ear Sound Hearing
Nose Smells Smell
Tongue Flavours Taste
Skin Touch, pain, pressure, temperature Touch

10.2 Sight

Eyebrow • prevent sweat from getting into the eyes
Eyelash • prevent small particles from getting into the eyes
Eyelid • close to protect eyes from dirt and strong light
• blink to moisten the eyes surface
Cornea • focuses light
Iris • control size of pupil
Pupil • regulates amount of light entering
Focusing muscle • changes thickness of the lens
Lens • focuses light
Jelly-like fluid • maintains shape of eyeball
• focuses light
Retina • contains light-sensitive cells 
◦ detect light and *produce signals* |

| Optic nerve | • transmits signals to the brain | | Blind spot | • where optic nerves leaves the eyeball • no light-sensitive cells | | Sclera | • protects eyeball |

  1. Light from the object enters our eyes through the cornea
  2. Cornea, lens, and jelly-like fluid focuses light onto the retina
  3. A sharp and inverted image is formed on the retina
  4. The light-sensitive cells are stimulated by light to produce signals
  5. Signals are sent to the brain through optic nerve
  6. The brain interprets signal as upright image

Our lens is elastic

| Look at near object | • focusing muscle contract • thicker lens | | --- | --- | | Look at distant object | • focusing muscle relax • thinner lens |

| Cone cells | • detect color • works in bright light | | --- | --- | | Rod cells | • cannot detect color • works in dim light |