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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
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
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