The Muscular System

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Muscle Tissue Three typesThree types –Skeletal muscle-usually attached to bones –Smooth muscle-not under voluntary control –Cardiac muscle-found only in the heart

Skeletal muscle Responsible for voluntary movementsResponsible for voluntary movements Have alternating light and dark bands called striationsHave alternating light and dark bands called striations Consciously controlled by the CNSConsciously controlled by the CNS Large cells with many nuclei, vary in lengthLarge cells with many nuclei, vary in length Complete muscles have muscle fibers, connective tissues, blood vessels, nervesComplete muscles have muscle fibers, connective tissues, blood vessels, nerves

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To return to the chapter summary click escape or close this document. Sarcomere Muscle Diagram

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Smooth muscle Cells are spindle-shaped, one nucleus, no striationsCells are spindle-shaped, one nucleus, no striations Found in walls of hollow structures such as stomach, blood vessels, intestinesFound in walls of hollow structures such as stomach, blood vessels, intestines Can function without nervous stimulationCan function without nervous stimulation Connected to one another with gap junctions that allow electrical signals to travel directly between muscle cellsConnected to one another with gap junctions that allow electrical signals to travel directly between muscle cells

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Cardiac muscle Striated like skeletal muscleStriated like skeletal muscle Smaller cells each with one nucleus (some may have 2 nuclei)Smaller cells each with one nucleus (some may have 2 nuclei) Not under direct control of CNSNot under direct control of CNS Cardiac cells connected together by gap junctionsCardiac cells connected together by gap junctions

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Control of muscle contraction Begins at the neuromuscular junction (point of contact between a motor neuron and a skeletal muscle cell)Begins at the neuromuscular junction (point of contact between a motor neuron and a skeletal muscle cell) Vesicles in the axon of the neuron release the neurotransmitter acetylcholine which moves across the synapse to a receptor in the muscle cellVesicles in the axon of the neuron release the neurotransmitter acetylcholine which moves across the synapse to a receptor in the muscle cell Acetylcholine causes a release of Ca 2+ ions that allow actin and myosin to interact producing a contractionAcetylcholine causes a release of Ca 2+ ions that allow actin and myosin to interact producing a contraction

Muscle contraction Muscle cell remains contracted until release of acetylcholine stops and enzymes destroy remaining neurotransmitterMuscle cell remains contracted until release of acetylcholine stops and enzymes destroy remaining neurotransmitter Ca 2+ ion and pumped back into storageCa 2+ ion and pumped back into storage

Interaction of muscles and bones Skeletal muscles attached to bones with connective tissues called tendonsSkeletal muscles attached to bones with connective tissues called tendons Pull on bones and make them work like leversPull on bones and make them work like levers Joints function as fulcrums (fixed point around which levers move)Joints function as fulcrums (fixed point around which levers move) Muscles provide force to move leversMuscles provide force to move levers Skeletal muscles work in opposing pairs; when one contracts the other relaxesSkeletal muscles work in opposing pairs; when one contracts the other relaxes

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To return to the chapter summary click escape or close this document. Bicep Muscles