The Muscular SystemThe Muscular System

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Muscle TissueMuscle Tissue

• Three typesThree types– Skeletal muscle-usually attached to Skeletal muscle-usually attached to

bonesbones– Smooth muscle-not under voluntary Smooth muscle-not under voluntary

controlcontrol– Cardiac muscle-found only in the heartCardiac muscle-found only in the heart

Skeletal muscleSkeletal muscle

• Responsible for voluntary movementsResponsible for voluntary movements• Have alternating light and dark bands Have alternating light and dark bands

called striations called striations • Consciously controlled by the CNSConsciously controlled by the CNS• Large cells with many nuclei, vary in Large cells with many nuclei, vary in

lengthlength• Complete muscles have muscle fibers, Complete muscles have muscle fibers,

connective tissues, blood vessels, connective tissues, blood vessels, nervesnerves

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A Muscle

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Sarcomere Muscle Diagram

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Sarcomere Muscle Diagram

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Skeletal Muscle Fiber

Smooth muscleSmooth muscle

• Cells are spindle-shaped, one nucleus, Cells are spindle-shaped, one nucleus, no striationsno striations

• Found in walls of hollow structures such Found in walls of hollow structures such as stomach, blood vessels, intestinesas stomach, blood vessels, intestines

• Can function without nervous Can function without nervous stimulationstimulation

• Connected to one another with gap Connected to one another with gap junctions that allow electrical signals to junctions that allow electrical signals to travel directly between muscle cellstravel directly between muscle cells

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Smooth Muscle Fibers

Cardiac muscleCardiac muscle

• Striated like skeletal muscleStriated like skeletal muscle• Smaller cells each with one nucleus Smaller cells each with one nucleus

(some may have 2 nuclei)(some may have 2 nuclei)• Not under direct control of CNSNot under direct control of CNS• Cardiac cells connected together by Cardiac cells connected together by

gap junctionsgap junctions

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Cardiac Muscle Fibers

Control of muscle Control of muscle contractioncontraction

• Begins at the neuromuscular junction Begins at the neuromuscular junction (point of contact between a motor neuron (point of contact between a motor neuron and a skeletal muscle cell)and a skeletal muscle cell)

• Vesicles in the axon of the neuron release Vesicles in the axon of the neuron release the neurotransmitter acetylcholine which the neurotransmitter acetylcholine which moves across the synapse to a receptor in moves across the synapse to a receptor in the muscle cellthe muscle cell

• Acetylcholine causes a release of CaAcetylcholine causes a release of Ca2+2+ ions that allow actin and myosin to ions that allow actin and myosin to interact producing a contractioninteract producing a contraction

Muscle contraction Muscle contraction

• Muscle cell remains contracted until Muscle cell remains contracted until release of acetylcholine stops and release of acetylcholine stops and enzymes destroy remaining enzymes destroy remaining neurotransmitterneurotransmitter

• CaCa2+2+ ion and pumped back into ion and pumped back into storagestorage

Interaction of muscles and Interaction of muscles and bonesbones

• Skeletal muscles attached to bones Skeletal muscles attached to bones with connective tissues called tendonswith connective tissues called tendons

• Pull on bones and make them work like Pull on bones and make them work like leverslevers

• Joints function as fulcrums (fixed point Joints function as fulcrums (fixed point around which levers move)around which levers move)

• Muscles provide force to move leversMuscles provide force to move levers• Skeletal muscles work in opposing Skeletal muscles work in opposing

pairs; when one contracts the other pairs; when one contracts the other relaxesrelaxes

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Bicep Contraction

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Bicep Muscles