Muscle & muscle function 1 Flashcards
3 types of muscle?
- Skeletal
- Smooth
- Cardiac
(memorize the pictures page 30)
What is the origin vs insertion?
origin: site that is relatively fixed
Insertion: site that is usually displaced by contraction
What is the chemical composition of muscle?
- Water: 75%
- Protein: 20%
Structural proteins (myosin, actin, collagen)
Enzyme proteins ((an)aerobic metabolism)
Functional proteins (myoglobin) - Other components: 5%
Energy substrates and metabolites
ATP and minerals
which statement is true?’
A) A single muscle cell can have a length of 30 cm
B) A muscle cell Is also called a ‘myofibril’ -> No: it’s a myofiber!
C) A single muscle cell contains one nucleus
D) Connection between a neuron and a muscle cell is called a ‘triad’
A) A single muscle cell can have a length of 30 cm
Wrong:
B) A muscle cell Is also called a ‘myofibril’ -> No: it’s a myofiber!
C) A single muscle cell contains one nucleus
D) Connection between a neuron and a muscle cell is called a ‘triad’
Recall the skeletal muscle components
FFEPEN
Fibers (multinucleated muscle cells)
Fasciculus (bundle of up to 150 muscle fibers)
Epimysium (connective tissue surrounding muscle)
Perimysium (connective tissue surrounding fasciculus)
Endomysium (Connective tissue surrounding muscle fibers)
How is each muscle fiber connected with the body?
Network of arteries, veins and capillaries around endomysium (each muscle fiber is connected)
Sarcolemma is..
Membrane enclosing muscle fiber
Myofibril is..
Basic unit of muscle fiber (diameter: 1 μm)
Transverse tubule is..
Invagination of sarcolemma
Sarcoplasmic reticulum (SR): what is it and what does it do?
Muscular smooth endoplasmic reticulum
Regulation of intracellular calcium
Structural integrity
Terminal cisternae?
Enlargement of SR around t-tubule
What is a triad?
T-tubule + 2 terminal cisternae
see p.32
Skeletal muscle strength is determined by the circumference of the muscle, true?
True, but only to some extent
What is fusiform vs pennate?
Fusiform: fibres are positioned from origin to insertion in a straight line
Pennate: fibres are positioned in a pennate form (schuin)
Why would you increase the angle of pennation, as this decreases force on the muscle exerted by each fiber?
= you can pack much more fibers in the space you have this way. (think of it of the stokbrood that you can slice diagonal, in many pieces, or horizontal, in only some pieces)
- Each muscle fiber loses force, but you can pack much more muscle fibres into one muscle. Total sum is larger!
What is a better reflection of muscle force?
Anatomical cross-sectional area (ACSA) or
PCSA = muscle volume/muscle fibre length
Physiological cross-sectional area (PCSA)
Total cross-sectional area of all muscle fibers
What is up- and downside of short fiber length relative to muscle length?
- increases max force
- decreases muscle range of motion and contraction velocity (snelheid)
Why is contraction velocity (speed) lower with short fiber length relative to muscle length?
Contraction velocity (speed) is lower, because in long, vertical fibers, contraction is faster: all the contractions are directly transferred to the muscle itself.
So, in summary:
X degree of pennation
Leads to X force/myofiber
and X total force muscle
and X velocity of contraction
Increase/decrease
Increase
Decrease
Increase
Decrease
What is meant with “sliding filaments”?
Actin and myosin, vs
A) Myofibers sliding along each other during contraction
B) Sarcomeres
D) Tropomyosin and troponin
What is the sarcomere and what are the functional proteins?
Sarcomere
Functional unit of myofibril
Runs from Z line to Z line
Length: c.a. 2.5-3.6 microm
Functional proteins
Actin
Myosin
Tropomyosin
Troponin
What is the sliding-filament theory?
- actin + myosin fibers overlap
- possibility for cross bridge formation (bridge between myosin and actin)
- Muscle fiber shortens because the myosin and actin filaments slide past each other
When is maximal tension reached?
at optimal overlap actin and myosin filaments
What does the joint angle influence?
sarcomere length but also efficacy of muscle contraction to cause joint rotation.
This contributes to different angle-force curves for different muscles
Force generated at outer end of lever depending on muscle force, but also A and B.
A effort distance (i.e., between joint axis
and muscle attachment)
B resistance distance (i.e., between joint
axis and outer end of lever)
If you zoom in further on the thick and thin filaments, you get the protein structure.
What do thick and thin filaments mainly exist of?
- Thick filament = mainly myosin
- Thin filament = mainly composed of actin
When contracting, there is a change in length of filaments.
True/false
False
Which filament protein is responsible for force generation? Why?
Myosin, Thick filament
Only myosin has ATPase. Not actin.
ATP is needed for sarcomere
shortening
What is another key player in contraction and why?
Calcium. Binding of calcium to troponin is needed for conformational change and contraction. Binding of calcium to troponin, results in a shift of tropomysin, which exposes the myosin-binding site. See p.37 image
Q: Muscle contraction requires energy (ATP), for what step of the process is ATP needed?
A) Movement of tropomyosin to expose myosin binding sites
B) Sliding of the filaments
C) Formation of actin-myosin cross bridges
D) Detachment of those cross-bridges
D) Detachment of those cross-bridges
Describe the role of ATP in muscle contraction
- ATP detaches myosin from actin
- Energy stretches myosin head (high energy form)
- Resulting in a ‘power stroke’, filament sliding
