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Neuronal Pools

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

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  1. 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

  2. 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

  3. 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

  4. 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

  5. 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

  6. 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.

  7. 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

  8. 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

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