Download 22 reflexes 1 - The reflex arc

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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.