Relaxation of muscles
The Stretch Reflex : (See Figure 13.15). The stretch reflex in its simplest form involves only 2 neurons, and is therefore sometimes called a 2-neuron reflex. The two neurons are a sensory and a motor neuron. The sensory neuron is stimulated by stretch (extension) of a muscle. Stretch of a muscle normally happens when its antagonist contracts, or artificially when its tendon is stretched, as in the knee jerk reflex. The cell bodies of the sensory neurons leading to the spinal cord are located in clusters, the dorsal root ganglia (DRG), next to the spinal cord. Their axon extends in both directions: a peripheral axon to receptors at the periphery and a central axon passing in The motor neuron diseases (MNDs) are a group of progressive neurological disorders that destroy motor neurons, the cells that control essential voluntary muscle activity such as speaking, walking, breathing, and swallowing. A motor neuron is a type of cell in the nervous system that directly or indirectly controls the contraction or relaxation of muscles, which in most cases leads to movement. Motor neurons are also called motoneurons or efferent neurons. As discussed earlier, a reflex involves at least 2 or 3 neurons. The typical components of a reflex are shown in Figure 13.12. The reflex shown in this figure is called a 3-neuron reflex because it requires three types of neurons: a sensory, an interneuron, and a motor neuron. A motor neuron (or motoneuron) is a nerve cell (neuron) whose cell body is located in the spinal cord and whose fiber (axon) projects outside the spinal cord to directly or indirectly control effector organs, mainly muscles and glands. 1 All of the motor neurons in a motor neuron pool innervate a single muscle (Figure 1.4), and all motor neurons that innervate a particular muscle are contained in the same motor neuron pool. 2  Thus, there is a one-to-one relationship between a muscle and a
http://www.unm.edu/~jimmy/reflexes_notes.htm http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/N/Neurons.html http://www.ninds.nih.gov/disorders/motor_neuron_diseases/detail_motor_neuron_diseases.htm http://www.wisegeek.com/what-is-a-motor-neuron.htm http://www.unm.edu/~jimmy/reflexes_notes.htm https://en.wikipedia.org/wiki/Motor_neuron http://neuroscience.uth.tmc.edu/s3/chapter01.html
motor neurons are an example of what type or class of neuron