Microscopic StructureMicroscopic StructureSkeletal MuscleSkeletal Muscle

Cells: muscle fibersCells: muscle fibers

(what are bone cells called?)(what are bone cells called?)

Highly organized and grouped togetherHighly organized and grouped together

Each fiber contains protein filamentsEach fiber contains protein filaments

which are threadlike structureswhich are threadlike structures

Two types of proteins:Two types of proteins:

a) actin (thin myofilaments)a) actin (thin myofilaments)

b) myosin (thick myofilaments)b) myosin (thick myofilaments)

Microscopic (cont)Microscopic (cont)Sarcomere (basic functional unit)Sarcomere (basic functional unit)

(basic building block)(basic building block) (? What is the basic unit called in the (? What is the basic unit called in the

skeletal system)skeletal system)Sarcomere is the contractile unit of skeletal Sarcomere is the contractile unit of skeletal

musclesmusclesActin and myosin overlap each otherActin and myosin overlap each otherSarcomeres are distinct from each other at Z Sarcomeres are distinct from each other at Z

lineslinesRefer to the diagram on page 136 and draw Refer to the diagram on page 136 and draw

a replica in your notes (use diagram A)a replica in your notes (use diagram A)

Motor UnitMotor Unit

Combination of specialized nerve cell Combination of specialized nerve cell known as a motor neuron and a known as a motor neuron and a muscle fibermuscle fiber

Neuromuscular junction; space Neuromuscular junction; space between muscle and motor neuronbetween muscle and motor neuron

Chemicals known as Chemicals known as neurotransmitters assist the impulse neurotransmitters assist the impulse to transfer to the muscle to transfer to the muscle

Muscle Fiber ContractionMuscle Fiber Contraction(Sliding Filament Model)(Sliding Filament Model)

Nervous system stimulates a muscle fiberNervous system stimulates a muscle fiberCalcium is released into the fiber’s cytoplasmCalcium is released into the fiber’s cytoplasmATP must also be suppliedATP must also be suppliedActin and myosin myofilaments form bridges that Actin and myosin myofilaments form bridges that act as levers to pull the filaments past each otheract as levers to pull the filaments past each otherThis causes the fiber to shortenThis causes the fiber to shorten

(muscle contraction)(muscle contraction)Refer to page 136 and draw a diagram of a Refer to page 136 and draw a diagram of a relaxed and maximally contracted sarcomere relaxed and maximally contracted sarcomere

QuestionsQuestions

Critical ThinkingCritical Thinking

Page 158 #16Page 158 #16

Chapter Test #5,6,7 and 9Chapter Test #5,6,7 and 955

Muscle StimulusMuscle Stimulus

All or None RuleAll or None Rule

A muscle will contract only when an A muscle will contract only when an applied stimulus reaches a certain applied stimulus reaches a certain level known as the threshold.level known as the threshold.

A threshold stimulus is the minimal A threshold stimulus is the minimal level of stimulation required to cause level of stimulation required to cause a muscle fiber to contract.a muscle fiber to contract.

Muscle Stimulation (cont)Muscle Stimulation (cont)All or None REsponseAll or None REsponse

Once a muscle fiber is stimulated to Once a muscle fiber is stimulated to the threshold level, it will completely the threshold level, it will completely contractcontract

This is called the All or None This is called the All or None ResponseResponse

Muscle Stimulation (cont)Muscle Stimulation (cont)Graded ResponseGraded Response

Not all fibers within a muscle have the Not all fibers within a muscle have the same threshold levelsame threshold level

Some fibers may require more or less of a Some fibers may require more or less of a stimulus in order for the fiber tho contractstimulus in order for the fiber tho contract

This allows for a “graded response” by the This allows for a “graded response” by the entire muscleentire muscle

This way we are able to control such This way we are able to control such things as heavy vs.light lifting or walking things as heavy vs.light lifting or walking vs. running vs. running

FatigueFatigue

If muscle cells are repeatedly If muscle cells are repeatedly stimulated; without rest…the stimulated; without rest…the strentgth of the contraction will strentgth of the contraction will decreasedecrease

If continued; the muscle may lose its If continued; the muscle may lose its ability to contract ability to contract

Oxygen DebtOxygen Debt

Paying back decreased energy Paying back decreased energy reserves through labored breathing, reserves through labored breathing, after the activity has ceasedafter the activity has ceased

Homeostasis is maintainedHomeostasis is maintained

Gets rid of lactic acid that built up Gets rid of lactic acid that built up from exercising with less oxygenfrom exercising with less oxygen

Lactic acid can cause muscle Lactic acid can cause muscle sorenesssoreness

Skeletal muscle ContractionsSkeletal muscle Contractions

Flexion/extensionFlexion/extension

Abduction/adductionAbduction/adduction

RotationRotation

Supination /pronationSupination /pronation

Dorsiflexion/plantar flexionDorsiflexion/plantar flexion

Show your partner each of these Show your partner each of these movementsmovements