Involuntary muscle (or smooth muscle) is innervated by the autonomic nervous system and therefore is not under conscious control. It is not striated - rather, muscle cells contain small bundles of actin and myosin. It is found in the walls of the intestine, the iris, the walls of arteries and the walls of the uterus and cervix. Involuntary muscle contracts slowly but tires very slowly.
Cardiac muscle is found in the heart and can be divided into three sub-types of muscle: atrial muscle, ventricular muscle, and specialised excitatory and conductive muscle fibres. Cardiac muscle is myogenic meaning muscle fibres can stimulate contractions without needing input from a nerve impulse. Cardiac muscle is striated and contracts powerfully thoughout the life without tiring.
Voluntary muscle is responsible for causing movements of the skeleton at joints. It is innervated by the somatic nervous system. Voluntary muscle is striated and contracts quickly and powerfully but tires quickly.
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