4.4 Nerves and eyes

  • Created by: 14mut64
  • Created on: 12-05-19 10:57

Receptors and Stimuli

  • Organisms can respond to internal and external change in environment because they have receptors sensitive to stimuli
  • A co-ordinated response requires a stimulus, a receptor and an effector
  • Hormonal and Nervous communication
    • hormones are chemicals which are released; nerve signals are electrical impulses
    • hormones take longer to take action; nerve impulses are fast and take less time
    • hormones spread to a greater area of musles; nerve impulses are directed at one muscle
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Nervous Co-ordination

  • In humans a co-ordinated response follows the same pathway:
    • stimulus --> sense organ --> sensory neuron --> CNS (relay neuron) --> motor neuron --> effector (muscle or gland) --> response
  • Sensory neuron:
    • synapse connected to sense organ --> dendron --> cell body --> axon --> synapse connected to relay neuron
  • Relay neuron:
    • synapse connected to sensory neuron --> dendron --> cell body --> axon --> synapse with motor neuron
  • Motor neuron:
    • synapses connected to relay neuron --> cell body --> axon --> synapse connected with effector
  • Neurotransmitters are diffused across the synapse and bind to the membrane of the next neuron. They cause the impulse in the next neuron.
  • A reflec is a fast unconcious response to a stimulus, often to prevent harm. They are fast because the distance travelled by the nerve impulse is very short, and few synapses are involved.
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Eye diagram

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Eye components

  • Optic nerve - carries nerve impulses to the brain
  • Lens - changes shape to focus light on retina
  • Retina - light sensitive layer that an image is focused on; made of cones and rods
  • Iris - controls size of pupil; circular muscles contract to constrict pupil, and radial muscles contract to dialate pupil
  • Ciliary Muscles - relax and contract to change shape of lens; relax at long distance, contract at short distance (squeezing lens so that it can refract light better)
  • Suspensory Ligaments - contract and relax to change shape of lens; contract at long distance (to stretch lens because it doesn't need to refract light as much), relax at short distance
  • Sclera - white tough outer layer of eye
  • Pupil - the hole that lets light enter the eye
  • Cornea - the transparent layer that lets light in and helps focus light
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