text: how are involuntary and voluntary muscles different from each other? just three facts for each. thanx involuntary muscles are smooth, uninucleated, non-branching muscles that are not directly controllable at will. these include the radially arranged iris muscles, the digestive system, reproductive system, major blood vessels, the skin and internal organs, and are all controlled by the autonomic nervous systemthese muscles are not as free as the voluntary muscles such as your arms legs, fingers, etc..  the cardiac muscle in heart can be called an involuntary muscle, although it may be classified separately due to its structural differences. it is controlled by nerve impulses produced by a natural pacemaker called the sinoatrial node, the rate of which is controlled by the autonomic nervous system. smooth muscles are found in the digestive system, reproductive system, major blood vessels, the skin and internal organs, and is also controlled by the autonomic nervous system.  skeletal muscle is under conscious control and is, therefore, voluntary muscle.   voluntary muscles =somatic nervous system=the somatic nervous system is that part of the peripheral nervous system associated with the voluntary control of body movements through the action of skeletal muscles, and also reception of external stimuli. the somatic nervous system consists of afferent fibers that receive information from external sources, and efferent fibers that are responsible for muscle contraction.  the somatic system includes all the neurons connected with the muscles, sense organs and skin. it deals with sensory information and controls the movement of the body.  the basic route of the efferent somatic nervous system includes a two neuron sequence. the first is the upper motor neuron, whose cell body is located in the precentral gyrus (brodman area 4) of the brain. it receives stimuli from this area to control skeletal (voluntary) muscle. the upper motor neuron carries this stimulus down the corticospinal tract and synapses in the ventral horn of the spinal cord with the alpha motor neuron, a lower motor neuron. the upper motor neuron releases acetylcholine from its axon terminal knobs and these are received by nicotinic receptors on the alpha motor neuron. the alpha motor neurons cell body sends the stimulus down its axon via the ventral root of the spinal cord and proceeds to its neuromuscular junction of its skeletal muscle. there, it releases acetylcholine from its axon terminal knobs to the muscles nicotinic receptors, resulting in stimulus to contract the muscle.