Physiology, drugs and Physiology, drugs and diseasedisease

Muscle Structure and Muscle Structure and FunctionFunctionFdSc FISMFdSc FISM

Year 2Year 2Janis LeachJanis Leach15/01/1015/01/10

ObjectivesObjectives Define 3 types of muscle tissueDefine 3 types of muscle tissue Describe the functions of muscleDescribe the functions of muscle Outline the structure of muscleOutline the structure of muscle Explain the sliding filament theoryExplain the sliding filament theory

Types of muscle tissueTypes of muscle tissue Skeletal muscleSkeletal muscle

Voluntary muscles – attachments to bonesVoluntary muscles – attachments to bones

Cardiac muscleCardiac muscle Involuntary muscle only present in the heartInvoluntary muscle only present in the heart

Smooth muscleSmooth muscle Involuntary muscle found in walls of hollow organsInvoluntary muscle found in walls of hollow organs

FunctionsFunctions MovementMovement Skeletal muscle contracts and exerts Skeletal muscle contracts and exerts

force on the skeletal systemforce on the skeletal system Cardiac muscle allows the pressure Cardiac muscle allows the pressure

to pump blood around the body to pump blood around the body Smooth muscle in the walls of blood Smooth muscle in the walls of blood

vessels maintains BPvessels maintains BP

FunctionsFunctions Postural maintenancePostural maintenance

Skeletal muscles maintain postureSkeletal muscles maintain posture Joint StabilityJoint Stability

Skeletal muscles contribute to joint Skeletal muscles contribute to joint stabilitystability

Heat GenerationHeat Generation Muscles produce heat during contractionMuscles produce heat during contraction Critical in maintaining normal body Critical in maintaining normal body

temperaturetemperature

Structure of muscleStructure of muscle

StructureStructure EpimysiumEpimysium

Whole muscle wrapped in connective tissueWhole muscle wrapped in connective tissue FasciclesFascicles

Bundles of muscle cellsBundles of muscle cells PerimysiumPerimysium

Surrounds the bundlesSurrounds the bundles Endomysium Endomysium

Each muscle fibre surrounded by sheath of tissue Each muscle fibre surrounded by sheath of tissue – gives strength and elasticity– gives strength and elasticity

Muscle cellMuscle cell Skeletal muscle cells are very large Skeletal muscle cells are very large

compared to other cellscompared to other cells Muscle cells or fibersMuscle cells or fibers are long are long

cylindrical cells with multiple oval cylindrical cells with multiple oval nucleui arranged just below the nucleui arranged just below the sarcolemmasarcolemma or plasma membrane. or plasma membrane.

Myofibrils (contractile elements of Myofibrils (contractile elements of the muscle cell)the muscle cell)

Muscle cellMuscle cell Note the alternating Note the alternating darkdark and and lightlight

bands in the muscle fiber that bands in the muscle fiber that consist of even smaller contractile consist of even smaller contractile units called units called sarcomeres sarcomeres ((muscle muscle segemen). The sarcomere is the segemen). The sarcomere is the smallest contractile unit of a muscle smallest contractile unit of a muscle fiberfiber

MyofibrilsMyofibrils thick filament thick filament myosin myosin thin filament thin filament actin actin

MyosinMyosin - Each filament within a scaromere - Each filament within a scaromere contains contains 200 myosin molecules. 200 myosin molecules.

Actin - Actin - Also has several regulatory Also has several regulatory proteinsproteins

Sliding filament theorySliding filament theoryHuxley’s sliding filament theory of Huxley’s sliding filament theory of

muscle contractionmuscle contraction Muscle cells shorten because their Muscle cells shorten because their

sarcomeres shorten. As the length of the sarcomeres shorten. As the length of the sarcomeres shortens, the myofibrils sarcomeres shortens, the myofibrils shorten resulting in a shortening of the cell shorten resulting in a shortening of the cell as a whole.as a whole.

The thick or thick filaments do not change The thick or thick filaments do not change length during shortening.length during shortening.

Sliding filament theorySliding filament theory As name of the theory suggests the As name of the theory suggests the

change in the length of the change in the length of the sarcomere is due to the sarcomere is due to the slidingsliding of the of the filaments.filaments.

The overlap of the thick and thin The overlap of the thick and thin filaments changes during shortening filaments changes during shortening with the with the thin filaments sliding toward thin filaments sliding toward the centre of the sarcomere.the centre of the sarcomere.

http://en.wikipedia.org/wiki/File:Sarcomere.gif

•During contraction the cross-bridges between the myosin and actin filaments pull them towards one another this increases the overlap and pulls the Z lines towards one another.

Contraction of skeletal muscle

Motor unitMotor unit Consists of motor neuron and all the Consists of motor neuron and all the

muscle fibres that it suppliesmuscle fibres that it supplies It is the functional unit of skeletal muscleIt is the functional unit of skeletal muscle 1 motor unit can supply 2000 muscle fibres1 motor unit can supply 2000 muscle fibres Precise movements – 1 unit will supply 2 or Precise movements – 1 unit will supply 2 or

3 fibres3 fibres Non precise – 1 will supply hundredsNon precise – 1 will supply hundreds A single motor unit will cause weak A single motor unit will cause weak

contraction of the entire muscle.contraction of the entire muscle.

TaskTask Describe the sliding filament theory Describe the sliding filament theory

in your own wordsin your own words

Explain what a motor unit isExplain what a motor unit is