the role of the synapses
- Several presynaptic neurones might converge to one postsynaptic neurone. This would allow signals from different parts of the nervous system to create the same response. This could be useful where several different stimuli are warning us of the danger
- One presynaptic neurone might diverge to several postsynaptic neurones. This would allow one signal to be transmitted to several parts of the nervous system. This is useful in a reflex arc. One postsynaptic neurone elicits the response while another informs the brain
- Synapses ensure signals are transmitted in the correct direction- only the presynaptic knob contains vesicles of acetylcholine
- Synapses can filter out unwanted low level signals. If a low level stimulus creates an action potential in the presynaptic neurone it is unlikely to pass across a synapse to the next neurone because several vesicles of acetylcholine must be released to create an action potential in the postsynaptic neurone
what are all or nothing responses
An action potential is an all or nothing response. Once the action potential begins it does not vary in size or intensity. Once the action potential starts the neurone will conduct it along all of it’s length.
describe the frequency of transmission
When a stimulus is at higher intensity the sensory receptor will produce more generator potentials. This will cause more frequent action potentials in the sensory neurone. When these arrive at the synapse they will cause more vesicles to be released. In turn, this creates a higher frequency of action potentials in the postsynaptic neurone. Our brain can determine the intensity of the stimulus from the frequency of signals arriving. A higher frequency of signals means a more intense stimulus.
advantages of a myelinated neurone
- Increase the speed of transmission which means the signal reaches the end of the neurone much more quickly
- This enables a more rapid response to the stimulus
the role of the synapses 2
· Low level signals can be amplified by a process called summation. If a low level stimulus is persistent it will generate several successive action potentials in the presynaptic neurone. The release of many vesicles of acetylcholine over a short period of time will enable the postsynaptic generator potentials to combine together to produce an action potential. Summation can also occur when several presynaptic neurones each release small numbers of vesicles into one synapse.
· Acclimatisation- after repeated stimulation a synapse may run out of vesicles containing the transmitter substance. The synapse is said to be fatigued. This means the nervous system no longer responds to the stimulus. It explains why we soon get used to smell or background noise. It may also help to avoid overstimulation of an effector, which could damage it.
· The creation of specific pathways within the nervous system is thought to be the basis of conscious thought and memory