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Neuronal Pools

Transmission of signals. Spatial summationincreasing signal strength transmitted by progressively greater

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Neuronal Pools

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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

    • despite differences in function, pools share many similar principles

Transmission of signals

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 pools1

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 pools2

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 pools3

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 pools4

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

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

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