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Flashcards in Muscle Power Deck (16):
1

Muscle basics?

Skeletal muscle - type of muscle moved - attached to bones by tendons
Ligaments attach bones to other bones
Skeletal muscles contract and relax to move bones at a joint
Bones of the skeleton are incompressible (rigid) - act as levers - giving muscles something to pull against
Muscles that work together to move a bone are called antagonistic pairs - contracting muscle is called the agonist and the relaxing muscle is called the antagonist

2

Structure of skeletal muscle?

Made up of large bundles of long cells - muscle fibres
Cell membrane of muscle fibres cells are called sarcolemma
Bits of the sarcolemma fold inwards across the muscle fibre and stick into the sarcoplasm (muscle cells cytoplasm) - folds called transverse (T) tubules - spread electrical impulses throughout the sarcoplasm so they reach all parts of the muscle fibre
A network of internal membranes called the sarcoplasmic reticulum runs through the sarcoplasm - stores and releases calcium ions - needed for muscle contraction
Muscle fibres have lots of mitochondria to provide the ATP thats needed fro muscle contraction
Muscle fibres are multinucleate (many nuclei)
Have lots of long, cylindrical organelles called myofibrils - made up of proteins and are highly specialised for contraction

3

Myofibril structure?

Thick myofilaments - made of myosin protein
Thin myofilaments - made of actin protein
Under microscope:
Dark bands - thick myosin filaments - some overlapping actin filaments - A-bands
Light bands - thin actin filaments only - I-bands
Myofibril made up of many short units - sarcomeres
Ends of each sarcomere are marked with a Z-line
Middle of each sarcomere is an M-line (Middle of Myosin filaments)
Around the M-line is the H-zone - only contains myosin filaments

4

Sarcomere structure?

Z-line - I-Band - A-band - H-zone - M-line

5

Sliding Filament Theory?

Myosin and actin filaments slide over eachother to make sarcomeres contract
Simultaneous contraction of sarcomeres means the myofibrils and muscle fibres contract
A-bands stay the same length
I-band gets shorter
H-zone gets shorter
Sarcomere get shorter

6

Myosin Filaments structure?

Have globular heads which are hinged - can move back and forth
Each myosin head has a binding site for actin and a binding site for ATP
Actin filaments have binding sites for myosin heads, called actin-myosin binding sites
Tropomyosin is found between actin filaments - helps myofilaments move past each other

7

Resting muscles binding?

Resting muscles the actin-myosin binding site is blocked by tropomyosin
Myofilaments can't slide past each other because the myosin heads can't bind to the actin-myosin binding site on the actin filaments

8

Muscle contraction process?

Action potentail from motor neurone stimulates a muscle cell - depolarises the sarcolemma - depolarisation spreads down the T-tubules to the sarcoplasmic reticulum
Causes the sarcoplasmic reticulum to release stored calcium ions (Ca2+) into the sarcoplasm
Ca2+ bind to a protein attached to tropomyosin - changes protein shape - pulls the attached tropomyosin out of the actin-myosin binding site on the actin filament
Exposes the binding site - allows the myosin head to bind
Bond formed when a myosin head binds to an actin filament = actin-myosin cross bridge
Ca2+ activate the enzyme ATP hydrolase which hydrolyses ATP into ADP + Pi to provide energy needed fro muscle contraction
Energy released causes the myosin head to ben, pulling the actin filament along in a 'power stroke'
Another ATP provides the energy to break the actin-myosin cross bridge, so the myosin head detaches from the actin filament after its moved
Myosin head reattaches to a different binding site further along the actin filament - new actin-myosin cross bridge is formed- cycle repeats
Many cross brides form and break rapidly - pulling the actin filament along - shorten the sarcomere - muscle contracts
Cycle continues as long as Ca2+ is present

9

End of muscle contraction?

Muscle stops being stimulated - Ca2+ leave their binding sites and are moved by active transport back into the sarcoplasmic reticulum
Causes tropomyosin molecules to move back, blocks the actin-myosin binding sites
Muscles aren't contracted because no myosin heads are attached to actin filaments
Actin filaments slide back to their relaxed position - lengthens the sarcomere

10

Ways in which ATP is generated for muscle contraction? Aerobic respiration.

Aerobic respiration:
- Most ATP is generated from oxidative phosphorylation in the cell's mitochondria
- Only works when there oxygen - long periods of low intensity exercise

11

Ways in which ATP is generated for muscle contraction? Anaerobic respiration.

Anaerobic respiration:
- ATP made rapidly by glycolysis
- End product of glycolysis is pyruvate - converted to lactate by lactate fermentation
- Lactate builds up in muscles and causes muscle fatigue
- Short periods of hard exercise

12

Ways in which ATP is generated for muscle contraction?
ATP-Phospocreatine (PCr) System?

ATP is made by phosphorylating ADP - adding phosphate group taken from PCr
ADP + PCr --> ATP + Cr (Creatine)
PCr is stored inside cells and the ATP-PCr system generates ATP very quickly
CPr runs out after a few seconds so its used during short bursts of vigorous exercise
Is anaerobic and alactic (doesn't form lactate)
Creatine is broken down to Creatinine which is removed by the kidneys - higher creatinine levels are higher in people who exercise regularly, with high muscle mass or have kidney damage

13

Types of muscle fibres in skeletal muscles?

Slow twitch and fast twitch

14

Slow twitch muscle properties?

Reddish is colour - rich in myoglobin - red coloured protein that stores oxygen
Lots of mitochondria
Mainly aerobic
Good blood supply
Produce weaker contractions
Produce slower contractions
Good for endurance activities
Do not fatigue quickly

15

Fast twitch muscle properties?

Contract very quickly
Few mitochondria
Mainly anaerobic
Fatigue quickly
Contract with greater force
Good for short bursts of activity
Poor blood supply (white fibres) - few myoglobin

16

How is ATP used in muscle contraction?

Attachment of corse bridges of actin and myosin
'Power stroke' - pulling of actin
Breaking of actin-myosin cross bridges - detachment of myosin heads
Myosin heads move back to original position