Pretest-posttest designs grew from the simpler posttest only designs, and address some of the issues arising with assignment bias and the allocation of participants to groups. One example is education, where researchers want to monitor the effect of a new teaching method upon groups of children.
A neuromuscular junction (sometimes called a myoneural junction) is a junction between nerve and muscle; it is a chemical synapse formed by the contact between the presynaptic terminal of a motor neuron and the postsynaptic membrane of a muscle fiber.he development of the neuromuscular junction requires signaling from both the motor neuron's terminal and the muscle cell's central region. During development, muscle cells produce acetylcholine receptors (AChRs) and express them in the central regions in a process called prepatterning.
In order for skeletal muscle cells (muscle fibers) to contract, it is imperative they have communication with a motor neuron. A motor neuron is a nerve cell whose cell body is located in the spinal cord or brain. The axon of the nerve cell meanders toward the muscle it supplies. As it reaches the muscle, it branches: each branch going to a muscle fiber. The motor neuron, its axon branches, and all the muscle fibers it supplies is known as a motor unit and each muscle consists of numerous motor units (See Figure 1).