LSB231.5 Muscle Tissue Physiology Student Version Slides

8/8/2019 LSB231.5 Muscle Tissue Physiology Student Version Slides

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LSB231-Ph siolo


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Muscle Ph siolo

Muscle tissueMuscle tissuena omy o s e e a musc esna omy o s e e a musc es

The neuromuscular junctionThe neuromuscular junction

Huxleys sliding filament theoryHuxleys sliding filament theory

ContractionContraction

o or un so or un s

Types of skeletal muscle fibresTypes of skeletal muscle fibres

Other muscle typesOther muscle types


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Muscle Ph siolo

Learning objectivesLearning objectives n ers an e ana omy o s e e a musc e ce sn ers an e ana omy o s e e a musc e ce s

Understand the function of:Understand the function of:

The neuromuscular junctionThe neuromuscular junction

Excitation / Contraction CouplingExcitation / Contraction Coupling

o or un so or un s

Types of skeletal muscle fibresTypes of skeletal muscle fibres

Other muscle typesOther muscle types


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Muscle Tissue T es

Converts chemical energy into mechanical energy.Converts chemical energy into mechanical energy.

Three basic types of muscle:Three basic types of muscle:

SkeletalSkeletal striatedstriated voluntary controlvoluntary control

r ir i riri inv l n r n r linv l n r n r lSmoothSmooth nonnon--striatedstriated involuntary controlinvoluntary control


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Muscle Tissue T es

2. Skeletal

1. Cardiac

3. Smooth

voluntary involuntary

involuntary


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Muscle Tissue Functions

Muscle tissue facilitates;

Body posture

Stabilisation of joints Movement of substances internally

Regulation of organ volume


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Root words: refixes & suffixes

Root words:

Muscle from the Latin forlittle mouse mus

myo or mys gk = muscle sarco sarx k = flesh

plasm gk = form or mould

lemma = k sheath or husk(refers to plasma membrane)

mere = se ment


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Anatom of Skeletal Muscle

Levels of structure:Levels of structure:

Fascicle = (bundles)Fascicle = (bundles)

MyoMyo--fibril: linkedfibril: linked sarcomeressarcomeresThick and thin filamentsThick and thin filaments

Thick: myosinThick: myosin

Thin:Thin: actinactin and othersand othersSarcoplasmic reticulumSarcoplasmic reticulum

Stores and releases CaStores and releases Ca2+2+


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Skeletal Muscle Cross-Section

Endomysium = fine layer

of connective tissue

fibre (cell)

Perim sium = la er of

fibrous connective tissuewhich surrounds each

fascicle

Epimysium = layer of

tissue surrounds muscle

sometimes blends with

deep facia betweenneighbouring muscles


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Anatom of Skeletal Muscle


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Skeletal Muscle Fibres Stained

Alternating A (dark) and I (light) bands seen underthe microscope. Striated


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Muscle Fibres Cells

Muscle cells:

-,

Multinucleated formed from hundreds of embr onic cells

Nuclei are pressed against sarcolemma (plasma membrane)


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Muscle Fibres Cells

Muscle cells:

Myoglobin used to transport O (similar to haemoglobin)

Contain many glycosomes (granules of glycogen)


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M ofibrils

Myofibrils:

Run the whole length of

30cm long!)

Are 1-2m

Are composed of repeating

units called sarcomeres

Give the muscle cell its

stri ed striated

appearance


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Sarcomeres

Sarcomeres:

Are the individualcontractile units of muscle

fibres

Mainly consist of two

Thick filaments Myosin

Thin filaments - Actin


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Sarcomere:- Ma or Com onents


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Thin Filament

Thin filaments:

5-6nm in , 1 m long

G-actin proteins (g=globular)

Two chains of these molecules

are wound into an F-actinhelix (f=filamentous)

Each F-actin is attached to

the Z-line.


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Thin Filament

The actin filament has a

number of other proteins

F actin

tro om osin

troponins nebulin

Troponin (3 proteins)

TnC binds Ca2+

TnI binds Actin

Tropomyosin changes shapewhen troponin binds Ca2+


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Thin Filament

,

tropomyosin + actin prevents

m osin from bindin G actin activesite

Active site binds myosin during

contraction not at rest


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Thick Filament

The thick filaments are composed ofmyosin proteins and

arranged such that the tails are linked in the middle

A titin protein runs through the centre of each thick filament

and traverses the sarcomere


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Thick Filament

Thick Filament

-

1.6 microns long

~

thick filament

2 myosin polypeptide

chains wound around each other

ATP/ADP + Pi binding sites


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Thick Filament

Titin:

Very Large protein Largest po ypept e

discovered

attaches them to Z line

stabilises filaments

with nebulin

helps resist stretch a stretchy protein

allows muscle to spring

within core of thickmyosin filament


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Along the F-actin are attachment sites for the myosin heads.

The binding of the myosin head to its actin binding site forms a

crossbridge


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Muscle Contraction

Each sarcomere that makes u the m ofibril

shortens when the muscle cell (fibre) contracts


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Muscle Contraction

cell


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Neural Control

CNS activates muscle somatic motor division

motor neurons

long axons m elinated

> 1m

nerve cell bod inspinal cord or brain

alwa s excitator


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Neural Control

Control over skeletal muscle

(connections cross over)

Contralateral

Motor cortex divided intoareas of the body

o or omuncu us

Stimulate - movement

precision and complexityof motor skills

Many other areas of brainalso involved


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The Neuromuscular Junction


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The Neuromuscular Junction

The neurotransmitter

is degraded by

acetylcholinesterase.

action potential which then

spreads over the whole surface of

the muscle cell.

The muscle cell starts to contract.


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Neuromuscular Junction vs S na se

1. Both separated by a synaptic cleft.1. Both separated by a synaptic cleft.

2. Neurotransmitter is released when calcium gates open.2. Neurotransmitter is released when calcium gates open.

. .. .

4. Neurotransmitter opens gates in the postsynaptic membrane.4. Neurotransmitter opens gates in the postsynaptic membrane.

5. The membrane potential change which results is graded.5. The membrane potential change which results is graded.


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Neuromuscular Junction vs S na se

erences

1. A synapse is a junction between two neurons.1. A synapse is a junction between two neurons.

A Neuromuscular Junction (NMJ) is between a neuron and aA Neuromuscular Junction (NMJ) is between a neuron and a

skeletal muscle cell.skeletal muscle cell.

2. There is always an action potential in a postsynaptic membrane2. There is always an action potential in a postsynaptic membrane

when neurotransmitter is released in an NMJ.when neurotransmitter is released in an NMJ.

A synapse needs summation of Excitatory Post synaptic Potentials.A synapse needs summation of Excitatory Post synaptic Potentials.

3. A NMJ is always excitatory.3. A NMJ is always excitatory.

A synapse may be excitatory or inhibitoryA synapse may be excitatory or inhibitory


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An action potential spreads rapidly over the muscle cell from

t e NMJ ut t ere is a rie atent perio 5 to 10 msecs

before contraction occurs


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Excitation

e ore a musc e ce can contract ca c um must e re ease

into the cytoplasm


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Com onents Needed For Excitation

The sarcolemma is the muscle cell membrane


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T-tubules are extensions of the muscle cell membrane deep

into the cytoplasm of the muscle cell.

They are filled with extracellular fluid.


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e sarcop asm c ret cu um s a networ o mem ranous

channels throughout the cytoplasm of the muscle cell.


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the T-tubule to the sarcoplasmic reticulum


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erm na c sternae are part o t e

sarcoplasmic reticulum which stores calcium


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a c um c anne s ea rom t e sarcop asm c ret cu um nto

the cytoplasm. They are normally closed.


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Calcium is continually being pumped from the

cytoplasm back into the sarcoplasmic reticulum.

This is an active transport process.


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Excitation Process

The action potential

spreads from theNMJ all over the

sarcolemma.

It spreads down into- .

It spreads throughthe junctional feetinto the

sarcop asm c

reticulum

E i i P


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Excitation Process

The calcium

channels are voltagegated and open.

a c um usesinto the cytoplasm.

Calcium binds to

troponin whichleads to the

attachment of

myos n ea s.

E it ti P


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Excitation Process

Myofibrils start to

contract.

Calcium is pumpedou o e

cytoplasm.

Myosin binding sites

are covered and themyofibrils relax.

Bi h i


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Biomechanics

.

.

To lift an object (i.e. shorten the muscle).

Bi h i


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Biomechanics

load unchanged (isotonic)

Tension = Load length unchanged isometric

Tension < Load muscle stretches eccentric

-bridges provide brake.

C t i i t i t ti


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Concentric isotonic contraction

resistance and the muscle shortens


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Isometric contraction


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Isometric contraction

Crossbridges cycle but can not overcome the

resistance wei ht

The muscle does not shorten

Eccentric contraction


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the muscle gradually lengthens



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Stren th len th relationshi s


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Stren th len th relationshi s

Stretching a muscle too much results in a decreased force

generated

A Muscle Twitch


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A Muscle Twitch

A Muscle Twitch


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A Muscle Twitch

A single action potential will cause a muscle to contract

briefly then relax

Muscle Twitch


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Muscle Twitch

Muscle twitch has 3 phases

Latent Period ECC isoccuring and muscle tension

is building.

Period of Contraction X

bridges are active from onset

development, lasts 10-100ms.

10-100ms, initiated by re-

entry of Ca2+ to SR

Muscle Twitch


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Muscle Twitch

Muscle twitch is rapid in

some muscles and slower inothers.

Rapid, short duration

eyes

Slower lon er duration-Calf muscles

The effect of multi le stimulation


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called wave summation Due to additional stimulus before muscle has completelyrelaxed (repolarised)

Due to Ca2+ release from SR



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constant but is applied repeatedly Relaxation time between twitches becomes shorter [Ca2+] in sarcoplasm increases further

Degree of summation becomes greater



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muscle tension increases until maximum tension is reached Relaxation disappears & contractions are fused Result smooth, sustained contraction plateau

Skeletal muscle motor units


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The combination of the motor nerve cell (neuron) and all

the muscle cells it innervates is known as a motor unit



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Motor units are the functional divisions of a muscle.

Each muscle cell in a unit contracts at the same time.


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usc es conta n many motor un ts

Act as individual entities - contract as individual units.


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Motor unit recruitment


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Motor units are not allexcited simultaneously

nsion

stimulated to contractmotor unit 3

recruited

uscleT

While some motor unitsare contracting andmotor unit 21recruited

recruited

ole-M

shortening within the

muscle belly, others willmotor unit 1W

lengthening



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More force is generated in a muscle by recruiting more motor

units


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Stren th of motor units


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The more fibres in a motor unit the stronger the unit

Motor units motor control


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FINE MOTOR CONTROL The motor units have a small number of

musc e ce s.

e.g. in muscle moving the eyeball only

GROSS MOTOR CONTROL The motor units have a large number of

muscle cells

e.g. n t e erector sp nae musc es o t eback 1000 3000 muscle cells in each

Lets watch a movie of muscles in action


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then discuss muscle energy requirements

Muscle ener & metabolism


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Muscle cells have about 4-6 sec of ATP reserves

reat ne nase regenerates rom reat nephosphate (CP) almost immediately following hydrolysis of

Together ATP and CP stores fuel maximum power for 10-15 sec

Muscle ener & metabolism


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T es of muscle fibres


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Muscle fibres can be classified according to

ze: ys ca ame er

a e o con rac on: a e o ase ac v y

myosin and calcium/ATPase pump

Major pathway used to produce ATP

mitochondria.

l col tic: via l col sis lar e store of l co en .

T es of muscle fibres


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Muscle fibres can be classified according to

ype . ma , ow, x a ve res.ype . ma , ow, x a ve res.

ypeype aa.. --s ze, as , x a ve res.s ze, as , x a ve res.

ypeype . arge, as ,. arge, as , yco y cyco y c res.res.

,generated.

myofibrils.

Cross-section of skeletal muscle


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Stained to show the slow twitch (type I) fibres

(dark blue, mitochondria)

Slow and fast-twitch muscles


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A single skeletal muscle ismade up of both major fibre

types:-

i.e. slow twitch (ST) and

as w c

into motor units.

Motor units never have amixture of fibre types.

Slow and fast twitch muscles


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On average muscles contain:- 50% ST and 50% FT

but the percentages do change in individual muscles

Fast & slow-twitch fibre differences


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Speed at which the myosin head splits ATP

fibre

Fast twitch fibres have larger diameter axons

Slow twitch motor units have 10 - 200 fibres whereas fasttwitch typically have 300 - 800 fibres

Fast twitch motor units generate more force than slow twitch

Fast twitch motor units fatigue more quickly than slow twitch

Slow twitch fibres


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twitch motor unit

These take about 110milliseconds to reach

pea ens on w en

excited

Sometimes these arecalled type I or slow

oxidative (SO) fibres

ey ma e up a s ow

twitch motor unit

F i i i


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A slow twitch (SO) fibre is fatigue resistant

Fast twitch fibres


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They make up a fast twitchmotor unit

milliseconds to reach peak

They can be furthersubdivided into FTa, FTb,

and FTc fibres

Sometimes these are called

Glycolytic(FG) and Fast

Oxidative/glycolytic (FOG)

Fast twitch motor units


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In general there are 300to 800 muscle fibres in a

In eneral fast twitchmotor units are stronger

than slow twitch ones

Motor units are fast to

but fatigue easily

Fati ue due to lactic acid


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A fast twitch (FG) fibre fatigues quickly

It generates most of the lactic acid

Fati ue due to lactic acid


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.

It generates lots of lactic acid.



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In general small motor units are recruited before larger ones

-


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ar ac ssue

-


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ar ac ssue - sto ogy

joined together and function

as a s nc tium

The striated appearance isue to sarcomeres

fibres

-


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moot musc e

-


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moot musc e - structure

Spindle shaped

e ac n an myos n are no

arranged into sarcomeres

Roughly central nucleus

-


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moot musc e - sto ogy

-


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moot musc e - sto ogy

Artery wall

Smoothmusc e

Overwhelmed??...dont be!


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LSB231.5 Muscle Tissue Physiology Student Version Slides