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Neuronal Pools. CNS composed of millions of neuronal pools number of neurons in these pools vary from a few to a vast number each pool has its own special characteristics of organization which affects the way it processes signals
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Neuronal Pools CNS composed of millions of neuronal pools number of neurons in these pools vary from a few to a vast number each pool has its own special characteristics of organization which affects the way it processes signals despite differences in function, pools share many similar principles Transmission of signals Spatial summation increasing signal strength transmitted by progressively greater # of fibers receptor field # of endings diminish as you move from center to periphery overlap between fibers Temporal summation increasing signal strength by frequency of IPS Neuronal Pools Input fibers divide hundreds to thousands of times to synapse with arborized dendrites stimulatory field Output fibers impacted by input fibers but not equally Excitation-supra-threshold stimulus Facilitation-sub-threshold stimulus Inhibition-release of inhibitory NT Neuronal Pools Divergence in the same tract into multiple tracts Convergence from a single source from multiple sources Neuronal circuit causing both excitation and inhibition (e.g. reciprocal inhibition) insertion of inhibitory neuron Neuronal Pools Prolongation of Signals Synaptic Afterdischarge postsynaptic potential lasts for msec can continue to excite neuron Reverberatory circuit positive feedback within circuit due to collateral fibers which restimulate itself or neighboring neuron in the same circuit subject to facilitation or inhibition Neuronal Pools Continuous signal output-self excitatory continuous intrinsic neuronal discharge less negative membrane potential leakly membrane to Na+/Ca++ continuous reverberatory signals IPS increased with excitation IPS decreased with inhibition carrier wave type of information transmission excitation and inhibition are not the cause of the output, they modify output up or down ANS works in this fashion to control HR, vascular tone, gut motility, etc. Rhythmical Signal Output Almost all result from reverberating circuits excitatory signals can increases amplitude & frequency of rhythmic output inhibitory signals can decrease amplitude & frequency of rhythmic output examples include the dorsal respiratory center in medulla and its effect on phrenic nerve activity to the diaphragm Stability of Neuronal Circuits Almost every part of the brain connects with every other part directly or indirectly Problem of over-excitation (epileptic seizure) Problem controlled by: inhibitory circuits fatigue of synapses decreasing resting membrane potential long-term changes by down regulation of receptors