Muscular System: Chapter 8 Click icon to add picture Chapter 8
Feb 24, 2016
Muscular
System:Chapter
8
Click icon to add picture
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 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
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
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
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
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
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
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
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
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
Sliding Filament ModelStructure ani
mationMuscle
shortens as filaments slide past each other
This means that the I-band will get smaller during a contraction
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
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
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
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
Quick ReviewWhich protein filaments are
involved in muscle contraction?◦A. Actin◦B. Myosin◦C. ATPase◦D. More than one answer is correct
Quick ReviewWhich muscle fiber structures are
involved in contraction?◦A. I-band◦B. Sarcomere◦C. Active site◦D. More than one answer is correct
Quick ReviewAcetycholine is a
neurotransmitter whose amount will increase during contraction (to a point); the amount then decreases to stimulate relaxation.◦True◦False
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
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
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
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
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
Quick ReviewMuscles could take hours to
recover from oxygen debt.◦True◦False
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
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
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
Muscle ToneA few motor units go through
sustained contractions Help keep posture and support
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
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
Cardiac MuscleCells form interconnecting
network Cells are connected at
intercalated disksImpulses can rapidly transmit
from cell to cellNetwork response is all-or-none
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
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
Animation and Quiz!Animation with Quiz:
http://bcs.whfreeman.com/thelifewire/content/chp47/4702001.html