A reflex arc: rapid automatic coordination
| English | 中文 | Pinyin |
|---|---|---|
| sensory neurone/ˈsensəri ˈnjuːrəʊn/ | 感觉神经元 | gǎn jué shén jīng yuán |
| synapse/ˈsɪnæps/ | 突触 | tū chù |
What would explain this observation?
- A hand can withdraw from a harmful stimulus before a person consciously decides to move it. The response follows a coordinated nerve pathway.
- Start with a prediction. State the quantities or features you would compare, then decide what evidence could distinguish two explanations.
Build the model
- The nervous system enables responses to surroundings and coordinates behaviour. Receptors detect a stimulus and information travels as electrical impulses along neurones to the central nervous system, the brain and spinal cord. A response passes to an effector such as a muscle, which contracts, or a gland, which secretes.
- sensory neurone 感觉神经元: A neurone carrying information from receptors towards the CNS; synapse 突触: The junction across which a signal passes between neurones.
Which sequence is correct for the simplified reflex pathway?
A reflex pathway includes a sensory neurone carrying information from a receptor, a relay neurone in the CNS and a motor neurone carrying information to an effector. At a synapse a chemical messenger crosses the small junction between neurones and triggers a new electrical impulse in the next cell. Reflexes are automatic and rapid and do not involve the conscious part of the brain, helping protect the body from harm.
Match each technical term to its precise meaning.
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- A reflex pathway includes a sensory neurone carrying information from a receptor, a relay neurone in the CNS and a motor neurone carrying information to an effector. At a synapse a chemical messenger crosses the small junction between neurones and triggers a new electrical impulse in the next cell. Reflexes are automatic and rapid and do not involve the conscious part of the brain, helping protect the body from harm.
- Arrange a labelled reflex-arc model in the correct order and explain the direction of information at each connection. Compare automatic reflexes with deliberate choices without testing pain or injury. Use supplied timing tables to interpret responses; do not claim that a stimulus physically travels as an object through the nerve.
Which two habits make the investigation or model in this case more defensible?
Arrange a labelled reflex-arc model in the correct order and explain the direction of information at each connection. Compare automatic reflexes with deliberate choices without testing pain or injury. Use supplied timing tables to interpret responses; do not claim that a stimulus physically travels as an object through the nerve.
Work from known quantities
- State the known values and their units. Choose the relation because its assumptions fit this case, then rearrange before substitution.
- Known: fictional pathway stages take 8, 3 and 11 ms in a supplied model. Total model time = 8+3+11 = 22 ms, or 0.022 s. This sums the stated delays only. It is not a universal human reflex time and does not include any omitted receptor or muscle delay.
Supplied model delays are 9, 4 and 13 ms. Calculate their total. Use the same sequence: known quantities → model → relation → substitution → unit and interpretation.
Supplied model delays are 9, 4 and 13 ms. Calculate their total.
The result is 26 ms. Known: fictional pathway stages take 8, 3 and 11 ms in a supplied model. Total model time = 8+3+11 = 22 ms, or 0.022 s. This sums the stated delays only. It is not a universal human reflex time and does not include any omitted receptor or muscle delay.
Check the conclusion and its limits
- A reflex does involve the nervous system even though it is not a conscious choice. The sensory neurone leads towards the CNS; the motor neurone leads towards an effector. A synapse is a junction, not a whole sensory cell or a blood vessel.
- Return to the original observation. Explain what the result supports, which conditions it assumes, and one way to test a competing explanation.
A reflex cannot involve the spinal cord because it is not conscious. This claim is false: A reflex does involve the nervous system even though it is not a conscious choice. The sensory neurone leads towards the CNS; the motor neurone leads towards an effector. A synapse is a junction, not a whole sensory cell or a blood vessel.
A reflex arc: rapid automatic coordination: A reflex pathway includes a sensory neurone carrying information from a receptor, a relay neurone in the CNS and a motor neurone carrying information to an effector. At a synapse a chemical messenger crosses the small junction between neurones and triggers a new electrical impulse in the next cell. Reflexes are automatic and rapid and do not involve the conscious part of the brain, helping protect the body from harm.
A reflex cannot involve the spinal cord because it is not conscious.
A reflex does involve the nervous system even though it is not a conscious choice. The sensory neurone leads towards the CNS; the motor neurone leads towards an effector. A synapse is a junction, not a whole sensory cell or a blood vessel.
A neurone carrying information from receptors towards the CNS: write the technical term.
sensory neurone means A neurone carrying information from receptors towards the CNS.