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Amplitude and duration of signal are functions of

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Unformatted text preview: mical potential energy into an electrical signal. • 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 channels hyperpolarization 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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