. Write a short note on Neuromuscular Junction
1. Each skeletal muscle fiber is connected to an extension of a motor neuron that passes outward from the brain or spinal cord. Usually a skeletal muscle fiber contracts only upon stimulation by a motor neuron.
2. The site where the nerve fiber and muscle fiber meet is called a neuromuscular junction (myoneural junction). There, the muscle fiber membrane is specialized to form a motor end plate where nuclei and mitochondria are abundant, and the sarcolemma is extensively folded.
3. The end of the motor nerve fiber branches, projecting into recesses of the muscle fiber membrane at the motor end plate. The membrane of the nerve fiber and the membrane of the muscle fiber are separated by a small gap called the synaptic cleft. The cytoplasm at the distal ends of the nerve fibers is rich in mitochondria and contains many tiny vesicles (synaptic vesicles) that store chemicals called neurotransmitters.
4. When a nerve impulse traveling from the brain or spinal cord reaches the end of a motor nerve fiber, some of the vesicles release a neurotransmitter into the synaptic cleft. This action stimulates the muscle fiber to contract.