muscular system: chapter 8
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Muscular System: Chapter 8. Chapter 8. Functions of Muscles . 1) Movement Move the skeleton Move food and body fluids Create heartbeat 2) Heat Production Used to regulate body temperature. Types of Muscle Tissue. 1) Skeletal Striated, Voluntary Multiple nuclei/cell - PowerPoint PPT PresentationTRANSCRIPT
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Muscular
System:Chapter
8
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Chapter 8
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Functions of Muscles 1) Movement
◦Move the skeleton◦Move food and body fluids◦Create heartbeat
2) Heat Production◦Used to regulate body temperature
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Types of Muscle Tissue1) Skeletal
◦Striated, Voluntary ◦Multiple nuclei/cell◦Ex: Quadriceps, triceps
2) Cardiac◦Striated, Involuntary◦1 nucleus/cell◦Ex: heart
3) Smooth◦Unstriated, Involuntary◦1 nucleus/cell◦Ex: stomach wall, espophagus
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Structure of a MuscleFascia
◦Outer layer of fibrous connective tissue
◦Continuous with tendon and/or boneEpimysium
◦Layer under the fasciaPerimysium
◦Layer under epimysium◦Wraps around bundles called
fascicles
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Structure of a Muscle (cont)Endomysium
◦Layer under perimysium ◦Wraps around muscle fiber
Sarcolemma◦Layer under endomysium◦Cell membrane of a muscle cell
(fiber)◦Surrounds bundles of myofibrils
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Structure of a Muscle FiberSarcolemma- cell membraneSarcoplasm- cytoplasmSarcoplasmic reticulum-
endoplasmic reticulumMultiple nuclei/cellMany mitochondriaTransverse tubules- membrane-
bound canals through the fiber; surrounded by cisternae of sarcoplasmic
reticulumFilled with bundles of myofibrils
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Structure of the MyofibrilComposed of myosin (thick) filaments and
actin (thin) filamentsFilaments overlap creating striationsZ-line- attachment for actin filamentsM-line- attachment for myosin filamentsI-band- zone containing only actin
filamentsA-band- zone containing myosin filamentsH-zone- zone containing only myosin
filamentsSarcomere- unit stretching from one Z-
line to the next
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Neuromuscular JunctionMotor neuron - nerve that connects to
muscle fiberNeuromuscular junction - connection
between nerve and muscle fiberMotor end plate - specialized area of
the sarcolemma modified to connect with the nerve
Neurotransmitters - messengers that are stored in synaptic vesicles in the neuron and released across synaptic cleft
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Motor UnitsA fiber usually has 1
neuromuscular junctionA motor neuron can be
connected to many fibersMotor unit - a motor neuron and
all of its connected fibers◦Fibers will contract as a unit
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Quick ReviewIf your muscle cells were not
producing enough ATP, which part of the cell is dysfunctional?◦A) Sarcoplasmic reticulum◦B) Sarcolemma◦C) Mitochondria ◦D) Nucleus
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Quick ReviewIf you were diagnosed with a
disease that affected your ability for your muscles to communicate (connect) to your nervous tissue, which part of your muscle would this affect?◦A) Motor unit◦B) Motor neuron◦C) Neuromuscular junction◦D) All of the above
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Sliding Filament ModelStructure ani
mationMuscle
shortens as filaments slide past each other
This means that the I-band will get smaller during a contraction
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Timeline of a ContractionStep 1- Release of Acetylcholine
◦Acetylcholine is a neurotransmitter made and stored in the neuron
◦Release with nerve impulse into synaptic cleft
◦Crosses cleft and binds with receptors on motor plate
Step 2- Muscle Impulse◦Binding of acetylcholine at motor plate
stimulates muscle impulse◦Impulse spreads across sarcolemma and
down into T-tubules
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Timeline of a Contraction (cont)Step 3- Movement of Calcium
◦Cisternae of sarcoplasmic reticulum become more permeable to Ca+ ions
◦Ca moves out of reticulum into sarcoplasm
Step 4- Exposing Binding Sites of Actin◦High Ca+ in sarcoplasm cause a change in
the actin filaments◦Troponin and tropomyosin
◦ Thin filaments attached to actin; act together to expose the binding site
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Timeline of a Contraction (cont)Step 5- Contraction
◦Readied myosin heads attach to exposed actin binding sites and pull
◦A new ATP must bind with the myosin ATPase before myosin will release binding site
◦Readied myosin head then binds with a new actin binding site
◦I-band gets smaller◦This will continue as long as acetylcholine is present
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Timeline of a Contraction (cont)
Step 6- Relaxation◦Two steps lead to relaxation:
1) Acetylcholinesterase breaks down acetylcholine
2) Once acetylcholine is low, Ca+ is actively pumped back into sarcoplasmic reticulum
◦Low Ca+ levels in sarcoplasm stop linkage of actin and myosin and muscle fiber relaxes to it normal length
Muscle Contraction Animation: Myofibril
Muscle Contraction Animation: Sarcomere
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Quick ReviewWhich protein filaments are
involved in muscle contraction?◦A. Actin◦B. Myosin◦C. ATPase◦D. More than one answer is correct
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Quick ReviewWhich muscle fiber structures are
involved in contraction?◦A. I-band◦B. Sarcomere◦C. Active site◦D. More than one answer is correct
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Quick ReviewAcetycholine is a
neurotransmitter whose amount will increase during contraction (to a point); the amount then decreases to stimulate relaxation.◦True◦False
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Energy Sources for Contraction
1st source- available ATP’s (very small amount)
2nd source- Creatine phosphate breaks down to produce more ATP
3rd source- Cellular respiration to create new ATP’s◦Extra oxygen stored in myoglobin in
muscles4th source- Anarobic respiration
◦Creates a build-up of lactic acid
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Oxygen DebtLactic Acid is moved to the liver
to be converted back to glucoseOxygen debt
◦Amount of oxygen needed for liver to convert the lactic acid
◦How much is needed by the muscle to reset the other sources
Debt may take hours to repay after strenuous activity
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Muscle FatigueOccurs because:
◦Blood supply interrupted◦Acetylcholine used up◦Build-up of lactic acid which lower pH
of muscle which lowers muscles response to stimulation
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Muscle Fiber ResponsesThreshold stimulus - intensity
of stimulation needed to make a contraction occur
All-or-none response - muscle fiber responds fully or not at all
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Recording Muscle Fiber ContractionsRecording is a myogramLatent period- period of time
between stimulus and responsePeriod of ContractionPeriod of RelaxationMaking a muscle fiber go through
a single contraction is called a twitch
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Quick ReviewMuscles could take hours to
recover from oxygen debt.◦True◦False
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Quick ReviewWhich of the following is a reason
why a muscle could become fatigued?◦A. Blood supply increases◦B. Acetylcholine is present◦C. Build-up of lactic acid which
lowers pH of muscle◦D. None of the above
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Summation and TetanySummation - strength of
muscle fiber response increases if another stimulus is applied before relaxation is finished
Tetany - a sustained maximum muscle fiber response produced by a high frequency of stimuli that don’t allow the muscle to relax
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Recruitment Muscles do NOT have all-or-none
contractionsMuscles are made of many motor
units◦Respond to a variety of stimulus
strengths◦Muscle used for strength normally
have more bigger motor units◦Muscles used for fine movements
have more smaller motor units
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Muscle ToneA few motor units go through
sustained contractions Help keep posture and support
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Skeletal Muscle ActionOrigin - muscle attachment on bone
that is immobile during movementInsertion- muscle attachment on
bone that will moveFor any body movement:
◦Prime mover (agonist)- major muscle creating movement
◦Synergist- help with movement◦Antagonist – create movement in the
opposite direction
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Smooth MuscleContains myosin and actin
filaments but more randomly arranged (no striations)
Multiunit- stimulus is through nerves or hormones (iris or walls of blood vessels)
Visceral- cells can stimulate each other (walls of intestine, uterus, urinary tract)◦Peristalsis- wave-like contraction
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Cardiac MuscleCells form interconnecting
network Cells are connected at
intercalated disksImpulses can rapidly transmit
from cell to cellNetwork response is all-or-none
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Inherited Diseases of MuscleDisease name Description
Muscular Dystrophy
Missing proteins (specifically dystrophin – which attaches skeletal muscles together), weakened muscles, degenerate over time, specific type: Duchenne’s – only affects boys, die by early adulthood
Charcot-Marie-Tooth
Disease
Caused by duplicate gene (impairs insulating sheath around nerve cells – so nerves can’t stimulate muscles), causes slowly progressing weakness in muscles of hand and feed, symptoms can resemble AIDS, diabetes, vitamin deficiency
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Inherited Diseases of Muscle
Disease name Description
Myotonic Dystrophy
Delays muscle relaxation following contraction, causes facial/limb weakness and irregular heartbeat, caused by “expanding gene” – gets worse with subsequent generations
Hereditary Idiopathic
Dilated Cardiomyopat
hy
Very rare, heart failure – doesn’t begin until person’s 40s, lethal in 50% of cases within 5 yrs of diagnosis, caused by tiny genetic error in form of protein actin –cannot anchor to Z lines in heart muscles, causes heart chambers to enlarge and not function
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Animation and Quiz!Animation with Quiz:
http://bcs.whfreeman.com/thelifewire/content/chp47/4702001.html