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Pathophysiology 1 > Muscle Contraction > Flashcards

Muscle Contraction Flashcards

1
Q

What are 5 groups we can break skeletal muscle down into?

A 
Skeletal muscle 
Muscle fascicles 
Muscle fibre 
Myofibrils 
Sarcomeres
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2
Q

Skeletal muscle layer

A

Surrounded by epimysium

Separates the muscle from other muscles, bones and soft tissues

It contains fascicles of muscle fibres

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3
Q

Muscle fascicles

A

Contains muscle fibres

Surrounded by perimysium

Perimysium has blood vessels and nerves to supply muscle fibres

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4
Q

Muscle fibre

A

Surrounded by endomysium

Contains capillaries and nerve fibres for muscle cells. Also contains satellite cells in this layer to repair damaged tissue.

Contains myofibrils composed of actin and myosin

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5
Q

Myofibril

A

Surrounded by sarcoplasmic reticulum, T tubules and their terminal cisternae (for calcium release)

Triad = 2 terminal cisternae and a T tubule

Consists of sarcomeres

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6
Q

Sarcomeres

A

Thousands within a myofibril

Features:
Z lines at each end 
M line in middle 
I bands of actin 
A bands of actin and myosin 
H zone around M line (only myosin)

Also contains proteins
Titin within the I band
Z disc connects thin filaments to next sarcomere

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7
Q

3 categories of proteins in muscle

A

(Can’t resist science acronym)

CONTRACTILE PROTEINS = myosin and actin. Myosin binds to actin and pulls them along in contraction

REGULATORY PROTEINS= Switch on and off contractions. Eg, troponin and tropomyosin
In relaxed muscle, these two proteins block binding site on actin so myosin cannot bind and there is no contraction

STRUCTURAL PROTEINS- Provide alignment, elasticity and extensibility eg, titin, myomesin, nebulin and dystrophin

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8
Q

Myosin structure

A

Makes up thick filaments

Has 2 globular heads, a hinge and a tail

Myosin heads rotate and bind to actin binding sites to make cross bridges. Each myosin head has binding site for actin and binding site for ATP. Heads reach the nearest thin filaments.

Myosin tail extends to the M line and binds to other myosin tails

Hinge enables them to rotate and move

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9
Q

Actin structure

A

Thin filaments made of = Actin + troponin + tropomyosin

Relaxed muscle = actin-myosin binding site covered by troponin and tropomyosin

In contraction , calcium ions bind troponin so troponin and tropomyosin move away from binding site to expose them

Thin filaments held in place by Z lines

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10
Q

TITIN STRUCTURE

A

Titin protein anchors thick filament to M line and Z disc

End of myosin filaments to the Z discs can stretch up to 4 times resting length and spring back unharmed.

Plays role in eccentric contractions as it recovers muscle from being stretched.

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11
Q

Describe the other structural proteins

A

Myomesin makes the M line of sarcomeres. It connects to titin and adjacent thick filaments.

Nebulin is inelastic protein, connects to actin filaments and aligns actin filaments

Dystrophin links thin filaments to sarcolemma to transmit tension generated to the tendon

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12
Q

Sliding filament theory

A

H zone gets smaller in contraction

I band also gets smaller in contraction

A band stays same length in relax or contraction

Sarcomeres shorten in contraction

Myosin cross bridges pull on actin filaments and thin filaments slide inwards towards M line

Z discs move closer together as sarcomeres shorten

Sarcomere shortens, muscle fibre shortens and muscle therefore shortens,

HOWEVER myosin and actin remain same length (this is why A band same length)

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13
Q

Skeletal muscle pre-contraction

A

Nerve impulse reaches axon terminal at neuromuscular junction

Acetylcholine is released by synaptic vesicles and released into synaptic cleft between axon terminal and muscle cell.

Ach diffuses to bind to receptors on sarcolemma + sodium ion channels open.

Sarcolemma depolarised

Sodium ions rush into muscle cell

An actin potential spreads over sarcolemma and down T tubules to reach a triad (2 terminal cisternae and T tubule)

Terminal cisternae release calcium ions into sarcoplasm

Calcium binds to troponin so the troponin-tropomyosin complex moves away to reveal myosin binding site on actin.

This part is excitation- contraction coupling

Contraction cycle begins

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14
Q

Skeletal muscle contraction cycle

A

Terminal cisternae of the SR release Ca++ ions that bind to troponin

Troponin and tropomyosin move away to expose binding sites on actin

Cross bridge formation: Myosin head rotates and binds to actin-myosin binding site to form actin-myosin cross bridge

Myosin head bends to pull actin along to the M line called POWER STROKE. ATP gets hydrolysed to ADP + Pi releasing energy and sarcomeres will shorten.

Cross bridge detachment: myosin head is bound to another ATP to release energy to detach myosin head from actin-myosin binding site

It will re attach to another site and happens in many sarcomeres at same item

Process occurs in plenty of ATP and Ca++

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15
Q

Define contraction cycle

A

The repeating sequence of events that causes thin filaments to slide between thick filaments

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16
Q

Describe muscle relaxation steps

A

Acetylcholinesterase breaks down acetylcholine in synaptic cleft

Ach can not bind to receptors on sarcolemma as it has been broken down = no action potentials in sarcolemma

Calcium ion release channels close

Calcium ions pumped back into terminal cisternae via active transport

Ca++ decreases in muscle cell

Calsequestrin (calcium binding protein) maintains calcium in terminal cisternae

Troponin and tropomyosin return to blocking binding sites

Muscle passively lengthens to rest

17
Q

Muscle fibre lengths

A

Optimal overlap of thick and thin filaments = max. Cross bridges can be formed and greatest tension produced

Muscle is stretched = fewer cross bridges and less force produced

Muscles shortened too much = fewer cross bridges, less forced and z lines crush thick filaments

Resting muscle length = 70-130% optimum muscle length

18
Q

Length tension curve

A

The curve would show that mid range of muscle work produces most tension in muscle

Too stretched or shortened too much= fewer cross bridges and less tension, so less force produced

19
Q

What is ATP used for?

A

To release energy for muscle contraction

To detach myosin heads from binding sites

For active transport of calcium ions back into terminal cisternae

Muscles use ATP quick and sarcoplasmic ATP only gives a few secs of energy

20
Q

What are 3 sources of atp production in muscle?

A

CREATINE PHOSPHATE

ANAEROBIC CELLULAR RESPIRATION

AEROBIC CELLULAR RESPIRATION

21
Q

What happens in creatine phosphate system?

A

Phosphate transferred from creatine phosphate to ADP to regenerate ATP

PHOSPHATE + ADP = ATP + CREATINE

3-6 more phosphocreatine in muscles than ATP

Regeneates ATP rapidly

Maximal contraction lasts for 15 secs , eg explosive sports

Another system used after 15 secs

Relaxing muscle = ATP breaks down into ADP and CREATINE phosphate and stores until needed

Contraction= phosphate transferred from CREATINE phosphate to ADP to form more ATP + (CREATINE)

22
Q

How do we obtain creatine?

A

Eating meat

Internal production in kidneys and liver

Creatin supplements

23
Q

Disadvantages to creatine supplements?

A

Body may stop producing own creatine

Waste product creatinine may increase and damage kidneys , creatinine levels in urine X90 more than normal

Side effects may be nausea, bad stomach and muscle cramps

Increased creatine not useful for events lasting longer than 15 seconds

24
Q

Anaerobic cellular respiration

A

Aka lactic acid system
Doesn’t need any oxygen

glycogen stored in muscle

Glucose phosphorylated to glucose phosphate and releases an ADP
ATP used to add another phosphate to form hexose bisphosphate
This slits into 2 TP
Triose phosphates oxidised to 2 pyruvates
Net gain of 2 ATP
Pyruvic acid converted to lactic acid and diffuses into blood.

Continues for 30-40 seconds like 200m run

25
Q

Aerobic cellular respiration;

A 
Cellular respiration can use:
Pyruvic acid from glycolysis 
amino acids
Fatty acid from adipose tissue 
Oxygen from blood or myoglobin

Produced ATP for activities over 30 secs. Eg, long distance run

Provides 90% ATP energy if activity lasts more than 10 mins

26
Q

Troponin

A

Made of 3 polypeptides and binds to :

Actin
Calcium
Tropomyosin

Pathophysiology 1 (22 decks)

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