Skeletal Muscle Flashcards
What are the 3 types of muscle and where are they found?
Skeletal- voluntary,
Smooth- involuntary bladder
Cardiac- heart
What is all chemical energy/ATP converted into?
Mechanical energy
Define muscle fasciculus
a bundle of muscle fibres
Define muscle fibre/myocyte
cylindrical,
multinucleated cells composed of many myofibrils
Define Myofibril
the basic rod-like unit of a muscle cell
Define myofilament
the myofibril’s thick, thin and
elastic filaments.
Define myosin filament
the thick filaments
Define F-actin filament
the thin filaments
Define titin filaments
the elastic filaments that run
through the core of each thick filament and
anchor it to the Z-line
What are these parts mean in a muscle
Td
M
SR
T tubule
Td – tubular triads containing a flattened tubule of the T system (T) and a pair of terminal cisternae (TC).
M – mitochondria mostly localised in the I bands close to the parts of the actin and myosin filaments that interact during contraction.
SR – sarcoplasmic reticulum
T tubule – transverse tubule
What are these parts in a muscle?
I band
A band
H zone
M- line
Light band = I band
Dark band= A band
M-line is in between Hzone
H zone is distance between actin filaments
Where does Z-line bisect?
Bisects the I bands
Define sarcomere
basic unit of striated muscle tissue. The repeating unit between the 2 Z-lines
Describe the filament theory.
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 keeps the thick filament in a central position
How is myosin arranged in thick filament?
2 Bulbous head with cross bridges and a long tail
How is the actin arranged in thin filaments ?
Bound with troponin and tropomyosin with Ca2+ binding sites
What is the role of tropomyosin?
A protein that binds to and stabilizes actin filaments in cells
In skeletal and cardiac muscle cells, tropomyosin is released after interacting with troponin and calcium,
facilitating the binding of actin to myosin that causes muscle contraction
Describe the steps that causes the actin active sites on the troponin
AP down sarcolemma to T tubule to Sarcoplasmic reticulum. This activates voltage-sensitive receptors which triggers Ca2+ released from the terminal cisternae of SR amongst the myofilaments.
Ca2+ binds to troponin which undergoes a conformational change, exposing the actin active sites and removing blocking tropomyosin.
Describe the cross bridge cycle
Myosin and actin unbind.
Myosin heads cock then rebind to actin,Pi is released.
Power stroke occurs when Actin gets pulled toward middle of sarcomere, ADP released
New ATP binds to myosin head.
Repeat
Describe the process of muscle contraction in 7 steps
A nervous impulse arrives at the neuromuscular junction, which causes a release of a chemical called acetylcholine (ACh).
The presence of ACh causes the depolarisation of the motor end plate which travels throughout the muscle by the transverse tubules, causing calcium ions (Ca2+ ) to be released from the sarcoplasmic reticulum.
In the presence of high concentrations of Ca2+, the Ca2+ binds to troponin, changing its shape and so moving tropomyosin, revealing the myosin binding site of actin.
The myosin filaments can now attach to the actin, forming a cross-bridge.
Inorganic phosphate is released increasing the affinity of the myosin head group for actin
ADP released enables the myosin to pull the actin filaments inwards and so shortening the muscle. This occurs along the entire length of every myofibril in the muscle cell.
The myosin detaches from the actin and the cross-bridge is broken when an ATP molecule binds to the myosin head.
What happens in the muscle after the impulse has stopped?
the Ca2+ is pumped back to the sarcoplasmic reticulum and the actin returns to its resting position causing the muscle to lengthen and relax
What are 3 components that make up the strength of skeletal muscle contractions?
Twitch
Summation
Tetanus
Define twitch
single contraction and relaxation cycle produced by an action potential within the muscle fibre itself.
Define summation
if another action potential is applied before complete relaxation of the twitch, then the next twitch will sum onto the previous twitch.
Define tetanus
when the frequency of muscle action potentials increases such that the muscle contraction reaches its peak force and plateaus. At this level, then the contraction is a tetanus.
What does the magnitude of the tension determined by?
Frequency of the stimulation and the
initial resting length of muscle fibres
What is a motor unit?
What does the unit consist of?
How neuromuscular junction per muscle fibre?
What is the principle?
Unit= neuron and all muscle fibre attached
one neuromuscular junction per muscle fibre
All or none principle
Small motor units means what?
Muscles control fine movement
Large motor unit means what?
Large weight bearing muscles
What is the size principle?
Greater force means more motor units and larger fibres
