Download Signal summation occurs when impulses add together to

Signal summation occurs when impulses add together to reach the
threshold of excitation to fire a neuron.
LEARNING OBJECTIVE [ edit ]
Describe signal summation KEY POINTS [ edit ]
Simultaneous impulses may add together from different places on the neuron to reach the
threshold of excitation during spatial summation.
When individual impulses cannot reach the threshold of excitation on their own, they can can add
up at the same location on the neuron over a short time; this is known astemporal summation.
The action potential of a neuron is fired only when the net change of excitatory and inhibitory
impulses is non-zero.
TERMS [ edit ]
temporal summation
the effect when impulses received at the same place on the neuron add up
axon hillock
the specialized part of the soma of a neuron that is connected to the axon and where impulses are
added together
spatial summation
the effect when simultaneous impulses received at different places on the neuron add up to fire
the neuron
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Signal Summation
Each neuron connects with numerous other neurons, often receiving multiple impulses from
them. Sometimes, a single
excitatory postsynaptic potential (EPSP) is
strong enough to induce an action
potential in the postsynaptic neuron, but
often multiple presynaptic inputs must
create EPSPs around the same time for the
postsynaptic neuron to be sufficiently
depolarized to fire an action potential.
Summation, either spatial or temporal, is
the addition of these impulses at
the axon hillock . Together, synaptic
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summation and the threshold for excitation act as a filter so that random "noise" in the
system is not transmitted as important information.
Signal summation at the axon hillock
A single neuron can receive both excitatory and inhibitory inputs from multiple neurons. All these inputs
are added together at the axon hillock. If the EPSPs are strong enough to overcome the IPSPs and reach
the threshold of excitation, the neuron will fire.
One neuron often has input from many presynaptic neurons, whether excitatory or
inhibitory; therefore, inhibitory postsynaptic potentials (IPSPs) can cancel out EPSPs and
vice versa. The net change in postsynaptic membrane voltage determines whether the
postsynaptic cell has reached its threshold of excitation needed to fire an action potential. If
the neuron only receives excitatory impulses, it will also generate an action potential.
However, if the neuron receives as many inhibitory as excitatory impulses, the inhibition
cancels out the excitation and the nerve impulse will stop there. Spatial summation means
that the effects of impulses received at different places on the neuron add up so that the
neuron may fire when such impulses are received simultaneously, even if each impulse on its
own would not be sufficient to cause firing. Temporal summation means that the effects of
impulses received at the same place can add up if the impulses are received in close
temporal succession. Thus, the neuron may fire when multiple impulses are received, even if
each impulse on its own would not be sufficient to cause firing.