The reflex arc is the sequence of events since the body receives an external stimulus (seeing a mosquito landing on your hand) until it reacts (swapping at the mosquito). In the exposed example, the last components in the NS involved in the process are the Axons in motor neurons.
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The reflex arc refers to the sequence of events since the body receives an external stimulus until it reacts.
In general terms, a stimulus of varying nature reaches the body, the peripheric nervous system -PNS- receives the stimulus and sends this information to the central nervous system -CNS-. The CNS processes the information and sends another signal as a response to the stimulus.
Five elements compose the reflex arc, which are receptors, three types of neurons, and effectors.
The neurons involved in the mechanism are:
• Afferent or sensorial neurons
• Interneurons
• Efferent or motor neurons
Action:
• Ascending branch
The stimulus reaches the body and is received by the specialized sensory receptors. Afferent neurons, placed in the dermis and epidermis, receive this information from receptors, react and send it to the central nervous system as nerve impulses.
• Descending branch
Interneurons in the CNS, process the information and send a motor response. Efferent neurons carry the response from the CNS to the effector organs, which might be either a muscle or a gland.
Finally, the target tissue responds to the stimulus as a contraction -muscle-,or as hormones release -gland-.
A motor neuron is formed by a cellular body, dendrites (cytoplasmic extensions that receive stimuli from other cells), and a long axon that is capable of conducting the electrochemical signals. The axon brunches out into several extensions when it approaches the muscle. At the end of each brunch, the axon is inserted in the muscle fiber surface, composing neuromuscular join. This is the last part of the NS involved in the process before the muscle contracts.
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