PoH: Skeletal, Smooth and Cardiac Muscle Flashcards
Describe the 3 structural features of skeletal muscle
· Nuclei on peripheries
· Multinucleate
· Fibres are 10-100 micrometres diameter, up to 20cm long
Myoblasts in fetus, but not when born
Describe the 4 features of skeletal muscle’s ultrastructure
· Bundles of muscle fibre in connective tissue sheathes with other tissue and fat
· Attached to bone by tendons
· Satellite cells replace damaged cells by differentiating into fibres. Other fibres undergo hypertrophy to compensate
· Is red as contains blood vessels to allow good blood supply to get energy and offload CO2
Sketeletal muscle is made of bundles of what, which is made from what, which is made from what?
Muscle made of fascicles
Fascicles made of single muscle fibre (cells)
Fibres made of myofibrils
What happens if bodybuilders gain muscle too quickly?
Ischemia (interruption of blood supply)
What is the basic repeating unit that allows muscle to contract?
Sarcomere
What are thin filaments in muscle called?
Actin
What are thick muscle fibres called?
Myasin.
How do actin and myasin interact?
Actin filaments are interdigitating (sliding between) myosin filaments
Are cross-bridge heads found on actin or myosin?
Myosin
What is the x-bridge head made of?
Actin binding sites
ATP binding site
Light chains
Heavy chains
What shape do actin filaments form?
Hexagon
What shape do myosin filaments form?
Triangle
What is titin?
Makes sure myosin stays between actin filaments and doesn’t go too far from the Z lines. It acts like a guide spring or ropes
When a muscle is shortened, what happens to A bands, I bands and the H zone?
A band - unchanged
I band - reduced
H zone - reduced
What theory describes how muscle contract and relaxes?
Sliding-filament theory
When muscle is contracted what happens to myosin and actin?
Myosin stays the same
Actin slides between, shortening the muscle.
Name the 4 steps of the x-bridge cycle
- Detachment
- Hydrolysis
- Cross bridge
- Power stroke
The myosin heads latch onto the actin molecule binding sites, then flip and pull the sarcomere into a smaller contractive pattern
Which molecule starts to rise to form the x-bridge?
Ca2+
Contraction means the space between what gets smaller?
Z line and myosin
When does actin detach?
When new ATP binds to myosin head
What 3 molecules regulate the x-bridge cycle?
Troponin
Tropomyosin
Ca2+
How do troponin, tropomyosin and Ca2+ regulate the x-bridge cycle?
· Tropomyosin partially covers the myosin binding site
· Troponin holds tropomysin in position (cooperative block) to block the myosin binding site
· Ca2+ binds to troponin
· Troponin alters shape, pulling tropomysin away
Ca2+ is removed, blocking the site again
What can we measure to check for heart-attacks? It relates to x-bridge cycle
Cardiac troponin level
What graph describes the %of muscle length vs the % of max isometric tetanic tension?
The length-tension relationship
What’s the % of muscle length that generates the most amount of isometric tension?
Optimum length
If you stretch muscle, what does it do to compensate?
Try to contract back. The more force, the stronger the contraction
If muscle is overstretched, what’s happening to the muscle?
Actin and myosin no longer overlap, so x-bridge heads can’t bind to actin
it generates less tension
If muscle’s filaments are too close together, what’s happening to the muscle?
Actin and myosin inteferes with each other and some binding sites are not easy to access for actin
Describe agonist/antagonist and what makes it beneficial?
Another feature that makes muscles strong is their arrangement as a lever system – one muscle flexes and its antagonist extends. It amplifies muscle shortening velocity, producing increased manoeuvrability.
Define excitation-contraction coupling
converting a command from a nerve cell into mechanical force (contraction in the muscle)
How is calcium stored in muscle?
Sarcoplasmic reticulum
