The right order is
1. A receptor detects a signal
The stimulus (ie the external signal), by its action on the sensitive area of the sensory receptor called transducer site, creates a variation of potential whose course and amplitude depend on the stimulus.
This variation of potential constitutes the receiver potential.
This conversion of the stimulus into a receptor potential, called transduction, is related to changes in the permeability of the receptor cell membrane.
2. The sensory nerves sends a signal to spinal cord
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Sensory information is detected by peripheral sensory receptors and then transmitted to the central nervous system via sensory neurons, otherwise known as afferent fibers. These sensory neurons have a particular morphology, they are called "T" neurons because the single dendrite and the axon that emerge are contiguous to the cell body, located in the ganglion, then separate to connect the sensory receptor d one side, and the nerve center of the other.
3. The relay neuron sends a signal to motor nerves
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The motor nerves carry motor control from the central nervous system to the effectors that are mainly the muscles. These efferent nerve fibers originate in the central nervous system: the spinal cord and the motor brain centers. Efferent fibers emerge from the spinal cord through the ventral root of the ventral horn. From the spinal cord are motor neurons γ, which contact the neuromuscular spindle.
4. A muscle receives a signal to contract
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The neuromuscular spindle is a mechanoreceptor composed of modified muscle fibers. Arranged parallel to the muscle fibers, it is sensitive to the lengthening of the muscle, and translates a mechanical stimulus into a nervous message.
These spindles are sensory receptors. They therefore play an important role in static proprioception, as well as in kinesthesia.
They are also involved in the myotatic reflex: their role is then to increase the level of contraction of the muscle in response to its own stretching. The muscle tends to return to its original length.
5. A bone moves.
Muscular movement is based on the ability of a living structure to exert a force by shortening itself. Which requires:
* a contractile structure: the muscle
* a support structure (to be able to exert a force): the skeleton (bones and joints) and the tendons by which the muscles are attached to it
* a control system (the nervous system) and a control system (the nervous system or the immune system that act by chemical mediators (hormones, neurotransmitters ...) and adaptation (response to environmental stimuli) essentially comprising receptors (organs of internal and external perception) connected to the control nerve centers (brain).
Man uses the muscular force developed by his muscles that rely on a skeleton to perform movements under the control and control of the nervous system and organs of perception. put apart the reflexes, he can also use the movements of his limbs resting on the ground or water to move his whole body (walking, running, swimming ....).
