Muscular

System:Chapter

8

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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 Model

Structure animation

Muscle 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:

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