Example 1
Order motor neuron, receptor, sensory neuron and muscle in a simple response.
Receptor → sensory neuron → CNS pathway → motor neuron → muscle. A withdrawal reflex commonly includes an interneuron in the CNS.
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Year 12 · SACE Stage 2
Nervous pathways and reflexes
Practise nervous-system organisation, neuron roles and synapse order.
Method and worked examples
The central nervous system consists of the brain and spinal cord. The peripheral nervous system connects the CNS with other parts of the body. Sensory neurons carry information from receptors toward the CNS; interneurons connect neurons within the CNS; motor neurons carry commands toward effectors such as muscles or glands. A nerve contains bundles of nerve fibres rather than being a single neuron.
At a typical chemical synapse, an arriving signal triggers neurotransmitter release from the presynaptic ending. The transmitter crosses the gap and binds receptors on the next cell. Its removal helps limit the signal. A withdrawal reflex can use a spinal pathway to produce a rapid protective response before conscious awareness. Not every reflex has the same number of neurons or identical pathway.
Example 1
Example 2
A nerve pathway is 0.6m long and conduction speed is 30m/s. Find travel time, ignoring synapses.
Time = distance/speed =300.6=0.02s. Synaptic delays would add to total response time.
Watch out: A spinal reflex can begin a response before awareness while information also travels to the brain.