Coordination And Control: Mammalian Sense Organs
14.2 Mammalian Sense Organs
Sense Organs
- Groups of receptor cells responding to specific stimuli:
- Light → eyes
- Sound → ears
- Touch / Pressure → skin
- Temperature → skin
- Chemicals → nose (smell), tongue (taste)
Structure Of The Eye
| Part | Function |
|---|---|
| Cornea | Refracts light |
| Iris | Controls light entry by adjusting pupil size |
| Pupil | Hole allowing light to enter |
| Lens | Focuses light onto retina |
| Ciliary muscles & suspensory ligaments | Change lens shape for focusing |
| Retina | Contains light receptors (rods + cones) |
| Fovea | Area with highest receptor density (sharp vision) |
| Optic nerve | Carries impulses to brain |
| Blind spot | No receptors |
Written And Compiled By Sir Hunain Zia, World Record Holder With 154 Total A Grades, 7 Distinctions And 11 World Records For Educate A Change O Level And IGCSE Biology Full Scale Course
Pupil Reflex
- Bright light → circular muscles contract, radial relax → pupil smaller.
- Dim light → circular muscles relax, radial contract → pupil larger.
Accommodation
- Near objects → ciliary muscles contract, suspensory ligaments loosen, lens becomes fatter → more refraction.
- Distant objects → ciliary muscles relax, suspensory ligaments tighten, lens thinner → less refraction.
Rods vs Cones
| Feature | Rods | Cones |
|---|---|---|
| Sensitive to | Light intensity (black & white vision) | Colour (red, green, blue) |
| Location | Around retina edges | Concentrated at fovea |
| Low light? | Yes | No |
Written And Compiled By Sir Hunain Zia, World Record Holder With 154 Total A Grades, 7 Distinctions And 11 World Records For Educate A Change O Level And IGCSE Biology Full Scale Course