To begin the conditioned stimulus is sensed by the

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To begin, the conditioned stimulus is sensed by the brain, and the pons initiate an excitatory signal through its penduncle to the mossy fibers. Excitatory signals in the brain are defined as glutamatergic inputs, while inhibitory signals are GABAnergic inputs. The mossy fibers excite both the granule cells as well as the deep cerebellar nucleus. The granule cells have protrusions that extend as parallel fibers. The parallel fibers advance the excitatory signal to the mass of dendrites that protrude from the Purkinje cells. Purkinje cells, in turn, send an inhibitory signal to the deep cerebellar
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nucleus. Thus far, the deep cerebellar nucleus is receiving an excitatory signal from the mossy fibers as well as an inhibitory signal. The second pathway is from the unconditional stimulus. The signal is sent to the inferior olivary nucleus, which, through climbing fibers, sends an excitatory signal to the Purkinje cell. As a result, the signal decreases the efficiency of the Purkinje cell’s inhibitory signal to the deep cerebellar nucleus. As conditioning continues, long-term depression (LTD) occurs at the junctions of the Purkinje cell’s dendrites. LTD essentially causes the individual to form a new conditioned response to the conditioned stimuli. According to the Marr-Albus theory, the climbing fiber’s signal is essentially a teaching signal, and it is able to help form new reflexive conditional responses.
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  • Spring '12
  • EdwardHedgecock
  • cerebellar ataxia

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