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Unformatted text preview: mical potential energy into an electrical
• amplitude and duration of signal are functions of transmitter
amount / duration of release.
• synaptic potential can be excitatory or inhibitory, depending
on receptor molecule;
– excitatory postsynaptic synaptic potential (EPSP)
– inhibitory postsynaptic synaptic potential (IPSP) – Lots of EPSPs increase the chance of the neuron to fire an AP 21 KNES 462 ©FK ‘08 1 KNES 462 NA in during AP Signal Integration I
• The current spreads ‘electrotonically’
(passively) from dendritic and somatic
synapses towards the axon hillock and the
initial segment of the axon.
• Integrative component sums all incoming
synaptic potentials. If the cell’s threshold for
excitability is exceeded by the net sum of
potentials, an action potential is generated.
– crucial role for voltage sensitive Na+ channels, located at
the axon hillock.
– if input signal > threshold of voltage-gated NA+ channels,
a sudden inrush of Na+ occurs, resulting in an action
potential. 22 KNES 462 ©FK ‘08 Signal Integration II • excitatory input causes inward current through Na+ and makes cell less negative
K+ channels depolarization.
• inhibitory input causes outward current through Clmakes more negative
23 KNES 462 ©FK ‘08 Signal Integration III
What determines a cell’s responsiveness? if the cells time constant is long enough to recieve two strimuli
would be summed and treted as 1 larger one • Temporal summation: depends
on time constant of cell.
– long time constant can
integrate longer intervals
between incoming stimuli. • Spatial summation: depends
on length constant of cell. these shape the respnsivenes and exitabiity of neurons – long length constant means
minimal signal decrement for
signal coming in at very
different sites of the neuron.
24 KNES 462 ©FK ‘08 2 KNES 462 Signal Integration IV
motor neiron recieved from 10000 pre syanptic endings • Neuronal integratio...
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