Biology Paper 2


Components of a Reflex Arc

  • Stimulus
  • Receptor
  • Neurones
  • Effector
  • Response
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Gaps between neurones, and are found at each junction of a reflex arc. 

Nerve impulses need to travel across synapses

  • Arrival at the neurone
    • The electrical impulse reaches the end of the neurone before the synapse
    • This triggers the release of chemicals called neurotransmitters
  • Passing on the impulse
    • Neurotransmitters diffuse across the synapse
    • Neurotransmitters bind to receptors on the next neurone
    • The presence of neurotransmitters causes the production of an electrical impulse in the next neurone
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Parts of the Brain

  • Cerebral Cortex - responsible for conscious thought (e.g. memory, language and intelligence)
  • Cerebellum - responsible for muscle coordination. Important for muscle, posture, balance, and speech
  • Medulla - responsible for unconscious activities
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Control of Body Temperature

Thermoregulation - control of body temperature

  • Receptors detect temperature change and relay this information to the CNS
  • The CNS allows effects to respond

Receptors in the thermoregulatory centre of the brain (hypothalamus) monitor the internal body temperature as the blood flows through the brain

Receptors on the surface of the skin monitor the temperature at the surface of the body

If the body is too cold:

    • Muscle contractions increase - shivering
    • Hairs stand on end
    • Blood vessels vasoconstrict

If the body is too hot:

    • Sweat is released from sweat glands under the skin
    • Hairs lie flat
    • Blood vessels vasodilate
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Warming Up & Cooling Down


    • Sweat glands release water, which covers the skin
    • Heat energy from the body is transferred to this water, and when the water has enough energy, it evaporates
    • As the sweat evaporates, the heat energy is taken with it


    • Muscles start to contract automatically - this makes us shiver
    • Shivering requires energy - generated through respiration
    • Respiration produces heat - warms us up
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