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REFLEX ARC
A Reflex arc is the neural pathway that mediates a reflex action. In higher animals, most sensory
neurons do not pass directly into the brain, but synapse in the spinal cord. This characteristic allows
reflex actions to occur relatively quickly by activating spinal motor neurons without the delay of routing
signals through the brain, although the brain will receive sensory input while the reflex action occurs.
There are two types of Reflex Arc - Autonomic reflex arc affecting inner organs and Somatic reflex arc
affecting muscles.
When a reflex arc consists of only two neurons in an animal -one sensory neuron, and one motor
neuron-, it is defined as Monosynaptic. Monosynaptic refers to the presence of a single chemical
synapse. In the case of peripheral muscle reflexes like Patellar reflex, Achilles reflex, brief stimulation to
the muscle spindle results in contraction of the agonist or Effector muscle.
By contrast, in Polysynaptic reflex pathways, one or more Interneurons connect afferent (sensory)
and efferent (motor) signals. All but the most simple reflexes are polysynaptic, allowing processing or
inhibition of polysynaptic reflexes within the spinal cord.