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Download 22 reflexes 1 - The reflex arc
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This document was created by Alex Yartsev ([email protected]); if I have used your data or images and forgot to reference you, please email me. Reflexes The reflex arc Sensory organ Afferent neuron Synapse The BELL-MAGENDIE law: In the spinal cord, the dorsal roots are sensory and the ventral roots are motor Efferent neuron Neuromuscular junction - Efferent axon At the sensory organ, the response is a NONPROPAGATED GRADED RESPONSE If it reaches threshold, it is interpreted into an ALL-OR-NONE ACTION POTENTIAL This travels along the afferent neuron The frequency of the action potentials is what determines the intensity of the stimulus At the synapse, the action potentials from the afferent neuron produce excitatory post synaptic potentials in the efferent neuron If these excitatory potentials summate enough to bring the efferent membrane to threshold, the efferent neuron fires The efferent axon also carries all-or-none action potentials The neuromuscular junction the response there is also the need for summation, but the excitatory post-synaptic potential is almost always large enough to produce a contraction The simplest reflex arc is one where there is just one synapse between the afferent and the efferent neurons This is what you call a MONOSYNAPTIC arc If there are any interneurons in the way between the afferent and the efferent neurons, this is called a POLYSYNAPTIC arc. There can be anywhere up to 200 synapses in a polysynaptic arc In the childish diagram above, some important elements have been omitted: depolarizing and hyperpolarizing influences descend from the CNS and affect the efferent neuron, or just about any other part of the arc. It is important to have some control over how sensitive the reflex is.