Muscles Flashcards
(24 cards)
What are the 3 types of muscles?
- skeletal muscle
- cardiac muscle
- smooth muscle
Describe the features of skeletal muscles?
- tubular striated
- multiple nuclei per fibre
- regular parallel myofibril bundles
- voluntary
- neurogenic stimulation
- fast speed but short contraction duration
Describe the features of cardiac muscles?
- branched striated
- single nuclei per fibre
- branching myofibril network
- involuntary
- myogenic stimulation
- intermediate contraction speed and duration
Describe the features of smooth muscles?
- spindle non-striated
- single nuclei per fibre
- unorganised no myofibrils
- involuntary
- neurogenic
- slow contraction speed but long lasting
Describe the key components and functions of a muscle fibre?
Sarcolemma = cell-surface membrane
Sarcoplasm = muscle fibre cytoplasm
Transverse (T tubules) = sarcolemma extensions that transmit electrical signals ensuring entire muscle receives impulse simultaneously
Sarcoplasmic reticulum = specialised endoplasmic reticulum responsible for storing and releasing CA+ ions
Myofibrils = subcellular structures designed for contraction
Multiple nuclei = many nuclei as several cells merge to form muscle fibre
Mitochondria = release energy in the form of ATP for muscle contraction
What is a myofibril?
Core units of muscle fibres containing organised bundles of protein filaments
What are sarcomeres?
Repeating units that make up myofibrils
What are myosin filaments?
Thick filaments composed of long rod-shapes with bulbous heads that project to the side
What are actin filaments?
Thin filaments composed of two strands twisted around each other
What is the A band of a sarcomere?
Area with both myosin and overlapping actin filaments (darker in colour)
What is the I band of a sarcomere?
Area containing only light actin filaments (lighter in colour)
What is the Z line of a sarcomere?
Mark the boundaries of each sarcomere unit
What is the M line of a sarcomere?
The central line of a sarcomere
What is the H zone of a sarcomere?
Area with only myosin filaments (central lighter region in the A band)
What is the structure of myosin heads?
- hinge enabling movement
- 1 site for binding to actin
- another site for ATP binding
What is the structure of actin filaments?
- sites for myosin head attachment (actin-myosin binding sites)
- tropomyosin and troponin proteins attached
What happens when a muscle contracts?
Actin filaments are pulled closer towards each other and towards the M-line shortening the sarcomere
What are the key changes to the sarcomere during muscular contraction?
- I band and H-zone in sarcomeres shorten due to increased overlap of actin and myosin filaments
- A bands remain constant in length
What are the key stages in the sliding filament model?
1) Ca2+ ions bind to troponin altering its shape
2) change moves tropomyosin away from actin’s binding sites making them available for myosin
3) myosin heads attach to exposed actin filaments forming actin-myosin cross-bridges
4) myosin heads execute a power stroke pulling actin filament along and releasing ADP.
5) ATP molecule binds to myosin head leading to its detachment from actin
6) Ca2+ activates myosin’s ATPase activity breaking down ATP to ADP and Pi releasing energy
7) energy resets myosin head to its original position
8) myosin head reattaches to new actin site further along the filament
What are the ways ATP can be generated for muscular contraction?
- aerobic respiration
- anaerobic respiration
- ATP-PC system
What is a neuromuscular junction?
Where a motor neurone meets a skeletal muscle fibre
How does a motor unit determine contraction force?
To exert a strong force a large number of motor units are stimulated
What are the stages in neuromuscular transmission?
1) action potential arrives at end of neurone
2) triggers opening of Ca2+ ion channels and Ca2+ enters neurone
3) causes acetylcholine vesicles to release contents into synaptic cleft
4) acetylcholine diffuses across synaptic cleft
5) acetylcholine binds to receptors on sarcolemma leading to opening of sodium ion channels
5) results in the depolarisation of sarcolemma
What is the role of sarcoplasmic reticulum in muscle contraction?
When stimulated by arrival of an action potential Ca2+ channels open in the sarcoplasmic reticulum membrane releasing a flood of Ca2+ into sarcoplasm trigger for muscle contraction
