Signals and Messages

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Signals and messages
An action potential is an all or nothing response.
All or nothing response to the fact that the neurone either conducts an action potential
or it does not.
The roles of synapses in the nervous system
transmit a signal from one neurone to another
in some places, several presynaptic neurones converge to one postsynaptic neurone so
that signals from different parts of the central nervous system can trigger the same
in other places, one presynaptic neurone might diverge to multiple postsynaptic
neurones which allows a signal to be transmitted from one neurone to several areas of the
nervous system simultaneously, useful in a reflex arc as one neurone can evoke a response
whilst one informs the brain
ensures that the movement of signals is in the correct direction
low level signals can be amplified by the process of SUMMATION
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 ACh must be released to create an action potential in the postsynaptic
Acclimatisation describes how neurones can eventually run out of the vesicles containing
the transmitter substances, preventing further responses from a particular stimulus (the
neurone is said to be fatigued) ­ which explains why after some time you get used to a
background smell or noise, and it also prevents overstimulation
The frequency of transmission
the frequency of transmissions over a synapse also vary
depending primarily on the intensity of the stimulus detected by the receptor,
a more intense stimulus will produce a higher frequency of action potentials
Synaptic summation
Summation is a term that refers to the way several small potential changes can combine to
produce one larger change in potential difference across a membrane.
There are two types of summation: spatial and temporal
Spatial summation
multiple neurones can fire impulses to
one receiving neurone as one of those
action potentials is not sufficient to
produce an action potential on the other
if they all fire simultaneously, the
impulse will continue along the
postsynaptic membrane
Damilola Fasoyiro A2 Biology

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EPSPs to generate an impulse
some will send IPSPs which inhibit the production of an action potential
An IPSP can override incoming EPSP signals from adjacent neurones
Temporal summation
one neurone fires multiple impulses from the
same place
pauses in between will not be sufficient to
generate an impulse on the receiving neurone
when fired with rapid succession of each
other, it will be enough to produce an action
potential on the postsynaptic membrane
Myelinated and non-myelinated neurones
Myelinated Neurone Non-myelinated neurone
Found in the…read more


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