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Up to 10000 different presynaptic endings on a

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Unformatted text preview: n depends on the summation of synaptic potentials which spread passively to the neuron’s trigger zone. – Up to 10,000 different presynaptic endings on a motoneuron • In order to analyze neuronal integration at the cell level, we need information about – passive properties of the postsynaptic cell (temporal / spatial constants?). – synaptic inputs (excitatory / inhibitory?) • highest excitatory postsynaptic potentials (EPSPs) are 0.2 - 0.4 mV in amplitude… • EPSPs are countered by inhibitory postsynaptic potentials (IPSPs) of other cells… – there is location, size, shape, proximity of synergistic and antagonistic synapses… 25 KNES 462 ©FK ‘08 all of that is leading up to the AP Signal Integration V receiving the input is graded but the action potetnial is all or nothing To fire or Not to fire id the stimuoi is too weak then there is no aciton potetnial at all. • this choice between competing alternatives also reflects a fundamental activity of the brain! simular to the computer precessses aslo based on a binary code. 26 KNES 462 ©FK ‘08 THE AO --leaded to release of nuerotransmitters Signal Conduction I • Action potentials (APs) are ‘all-or-none’ signals. – AP amplitude can be up to 110 mV. – Duration: ~ 1 ms. – Unlike input potentials, APs do not decay as they travel down the axon. – AP signaling very stereotyped all simular across neurons. – Frequency coding of information! 27 firing frequency KNES 462 ©FK ‘08 the myalin sheet is interupted byt hte nodes of ranier---the action potetnialhelps it jump the ap 3 KNES 462 Signal Conduction II • APs carried into the CNS by sensory neurons often indistinguishable from APs carried out by motoneuron! • Intensity of sensation or speed of movement are determined by frequency of APs; • Duration of sensation or movement determined by period over which APs are generated. • Meaning of signal is determined entirely by the neural pathway activated by that stimulus! 28 KNES 462 ©FK ‘08 Signal Output I • Output takes place via synapses: – electrical s.: also found in other body cells,...
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