Skeletal muscle Flashcards
What is skeletal muscle
Voluntary - we can control them, regulate body temperature and control posture etc
Converts chemical energy (ATP) into mechanical energy
What does the perimysium do?
Coating.
Allows the muscles to slide over each other so less friction when more muscles are being activated
What is the muscle fasciculus
A bundle of muscle fibres
What is a muscle fibre (myocyte)?
Cylindrical, multinucleated cells composed of many myofibrils
What is a myofibril?
The basic rod-like unit of a muscle cell
What are myofilaments?
The myofibril’s thick, thin and elastic filaments.
What are myosin filaments?
The thick filaments
What is the functional unit of contraction called?
Sarcomere
what are F-actin filaments
The thin filaments
What are Titin filaments
Elastic filaments that run through the core of each myosin filament and anchor it to the Z-line (so myosin filaments don’t move)
Light microscope originally revealed ____ bands and ____ bands.
Fine dark lies called _____ bisect the _____ bands
- light (i bands)
- dark (A bands, A in dArk)
- Z-lines
- light
What is the sliding filament theory in terms of muscle contraction?
Describes the mechanism of muscle contraction
The thick and thin filaments slide over one another
Hence neither of the thick or thin filaments shorten
During contraction, the H-zone becomes narrower
The elastic titin filaments keep the thick filament in a central position
What function do myosin head groups have?
They bind to the actin (there’s an actin binding site on the head group)
Myosin headgroup has an ATPase site so ATP will be hydrolysed. The energy from hydrolysis of ATP will be used in the contraction process
What does Tropomyosin do in the thin filaments?
A protein that binds to and stabilizes actin filaments in cells.
What does Tropomyosin do in skeletal and cardiac muscle cells?
It’s released after interacting with troponin and calcium
Facilitates the binding of actin to myosin that causes muscle contraction
How do the myosin head group and actin interact if the actin’s myosin binding site is blocked by the tropomyosin?
In the presence of calcium ions
- Calcium ions bind to troponin which troponin will go through a conformational change.
- Then tropomyosin will go through a conformational change
- which will result in exposure of myosin binding sites on the actin molecules.
Where does the calcium come from that enables the binding between myosin head group and actin?
(HARD)
skeletal muscle is voluntary muscle therefore contraction requires nervous impulse
- impulse is transferred from a neuron to the sarcolemma of a muscle cell
- Impulse travels along sarcolemma and down the T-Tubules. Then, passes to the sarcoplasmic reticulum (SR)
- As impulse travels down SR the calcium gates in membrane of SR open.
As a result, calcium ions diffuse out of SR and among the myofilaments. - Calcium fills the binding sites in the troponin molecules which alters shape and position of the troponin to then cause movement of the attached tropomyosin molecule.
- movement of tropomyosin permits the myosin head to bind to the actin
When does a sarcomere shorten?
When myosin heads and thick myofilaments form crossbridges with actin molecules and thin myofilaments
How does the myosin head become activated before the cross bridge cycle can begin?
When ATP binds to the myosin head and is hydrolysed to ADP and inorganic phosphate.
The energy released from the hydrolysis of ATP activates the myosin head, forcing it into the “cocked” position
What is the cross bridge cycle? (HARD)
- CROSS BRIDGE FORMATION
The activated myosin head binds to actin and forms a cross bridge. Inorganic phosphate is released. The bond between myosin and actin become stronger
- THE POWER STROKE
ADP is released. The activated myosin head pivots, sliding the thin myofilaments toward the centre of the sarcomere
- CROSS BRIDGE DETACHMENT
When another ATP binds to the myosin head, the link between myosin and actin weakens. Myosin head detaches.
- REACTIVATION OF MYOSIN HEAD
ATP is hydrolysed to ADP and inorganic phosphate. The energy released during hydrolysis reactivates the head, returning it to the cocked position
When does cross bridge cycling end?
When calcium ions are actively transporter back into the sarcoplasmic reticulum.
How much does a single power stroke shorten the muscle?
By approximately 1% of the entire muscle. Therefore, to achieve an overall shortening of up to 35%, the whole process must be repeated many times
3 gradations of skeletal muscle contractions. And give their definitions
Twitch = single contraction and relaxation cycle produced by an action potential within the muscle fibre itself
Summation = if a twitch happens and then another twitch happens before the first one relaxes then the power can be added as a summation onto the previous twitch
Tetanus = if summation is done frequently enough then they will all contract to a maximum level
What happens when a motor neuron(unit) is stimulated? What’s the all-or-none principle?
Consists of a neuron and all the muscle fibres connected to it
When a neuron is stimulated, all of its fibres will contract completely
This is called the all or none principle
The more motor units stimulated, the stronger the muscle contraction
What’s the size principle (motor units)?
A motor neuron with a small number of fibers will have a certain amount of tension.
If want to increase this tension then need to recruit the motor neurons that have larger and more fibers to achieve the desired strength of contraction
