Axon reflex

The axon reflex (or the flare response) is the response stimulated by peripheral nerves of the body that travels away from the nerve cell body and branches to stimulate target organs. Reflex's are single reactions that respond to a stimulus making up the building blocks of the overall signaling in the body's nervous system. Neurons are the excitable cells that process and transmit these reflex signals through their axons, dendrites, and cell bodies. Axons directly facilitate intercellular communication projecting from the neuronal cell body to other neurons, local muscle tissue, glands and arterioles. In the axon reflex, signaling starts in the middle of the axon at the stimulation site and transmits signals directly to the effector organ skipping both an integration center and a chemical synapse present in the spinal cord reflex. The impulse is limited to a single bifurcated axon, or a neuron whose axon branches into two divisions and does not cause a general response to surrounding tissue.

The axon reflex arc is distinct from the spinal cord reflex arc. In the spinal cord reflex pathway the afferent neuron transmits information to spinal cord interneurons. These interneurons act collectively, process and make sense of inbound stimuli, and stimulate effector neurons acting as an integration center. The effector neurons leaving the integration center transmit a response to the original tissue the reflex arose resulting in a response. The axon reflex results in a localized response to only the locally innervated cells of the single neuron where the signal originated. The axon reflex pathway does not include an integration center or synapse that relays communication between neurons in the spinal cord reflex. The stimulus, therefore, is diverted to the effector organ without entering the neuronal cell body and therefore indicates that the axon reflex is not a true reflex where afferent impulses pass through the central nervous system before stimulating efferent neurons.

The axon reflex was discovered and was described as "a new type of peripheral reflex" that bypasses the integration center and synapse in the central nervous system. The discovery of the axonal reflex found that the axon reflex activates local arterioles causing vasodilation and muscle contraction. This muscle contraction was observed in people with asthma where the released neuropeptides caused the smooth muscle in the airway to contract. Similarly the release of cholinergic agents at sudomotor nerve terminals evokes an axon reflex that stimulates sweat glands inducing the body to sweat in response to heat. The axon reflex is possible through the transmission of signals from the cutaneous receptors on the skin.

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