Check out the high definition version of this video here : blip.tv 1- The body movements are controled by muscles. 2- while contracting, the muscle is reduced in length and join closer the 2 bones on which it is inserted. 3- However,it's the nervous system that controls the muscle contraction by the means of nerves. 4- Each nerve contains thousands of nerve fibers arranged in dendrites which carry out sensory information and axons that convey motor impulses. 5- Each motor neuron innervates several muscle fibers, 6- this association define what is called a motor unit. 7- In general, the fewer the muscle fibers are in a motor unit the more the movement is precise. 8- for example in the temporalis muscle there are 1000 muscle fibers per motor unit while in the external ocular muscles there are only 5, this reflects the accuracy of the eye movements. 9- The intensity of the muscle contraction is proportional to the number of motor units recruited. 10- A neuron gives several endings that sometimes scatter throughout the thickness of a muscle, 11- each terminal is intended to stimulate a single muscle fiber in a specific place: the neuromuscular junction. 12- Just before the axon terminal, the neuron loses its myelin sheath and forms a terminal button. 13- The terminal button contains many mitochondria that provides energy and several synaptic vesicles. 14- Each vesicle contains approximately 10000 of acetylcholine molecules, the unique neurotransmitter of the neuromuscular ...

• published: 10 Sep 2009
• views: 134772
• author: medbenmedben