Life Sciences · Human Body · Homeostasis / Principles and Exploration
Nerve signals and response pathways — principles and investigation
The time it takes to react after receiving a stimulus includes the time it travels along the nerve and the delay it passes through the synapse. Compare by changing the stimulation location, conduction speed, number of synapses, and response path. Differences in the length of the spinal path and the path through the cerebrum are linked to the temporal history.
How does it work?
Fast conduction reduces movement delay, and long paths and many synapses increase delay.
Total delay = Σ(length / speed) + number of synapses × 0.5 ms
Try this investigation
- Pulses travel along the orange sensory pathways and blue motor pathways of the human silhouette. Screen playback is very slow.
- The spinal cord and brain pathways of knee stimulation are recorded at the same speed.
- Compare the delay by changing the conduction speed, stimulation location, and number of synapses one by one. Add 1.6 m and 2 synapses to the brain pathway.
Interpreting your results
What is the total delay of 1.6 m·50 m/s·2 synapses×0.5 ms?
1.6/50=0.032 s=32 ms. Add 2×0.5=1 ms to get 33 ms.
Assumptions and limitations
Use a virtual length, constant conduction velocity, and 0.5 ms per synapse. The circuit and number of synapses of the actual knee reflex have been simplified. Ankle pick is a comparative model of spinal reflexes. Sensory reception, muscle contraction time, and brain judgment time are omitted. Silhouettes are not to anatomical scale and do not predict individual reaction speed.