Skeletal Muscle Flashcards
What are the functions of muscles?
Movement (skeletal, intestinal, cardiac).
Static support.
Heat production.
What are the three layers of muscle?
Epimysium, perimysium and endomysium.
How are parallel muscles organised?
Fascicles all have a common point of attachment and are parallel to one another.
How are circular muscles organised?
A ring of muscle that surrounds a bodily opening. It constricts and relaxes to control blood flow.
How are pennate muscles organised?
Feather shaped. Fascicles attach at an angle to a central tendon. Can be unipennate, bipennate or multipennate.
What are the miscellaneous shapes of muscles?
Fusiform.
Quadrate.
Triangular.
Longitudinal.
Convergent.
Define tendon.
Connects muscles to bone.
Tough and round.
Some muscles share a common tendon.
Define aponeurosis.
Connects muscles to muscles.
Delicate and flat.
What do tendons and aponeuroses have in common?
Made of dense fibrous CT.
They don’t shorten.
They alter force direction.
What can myotomes and dermatomes test for?
Lesions of the spinal cord.
Motor or sensory loss can be checked by testing joint movement or an area of skin.
Describe skeletal muscle.
Bundles of fibres.
Attached to bones by tendons.
Muscles are arranged in lever systems - amplifies muscle shortening velocity and manoeuvrability.
Describe skeletal muscle cells.
Multinucleate (on the periphery).
Formed by mononucleate myoblasts (does not replace cells if damaged).
How are they replaced if damaged?
Satellite cells replace muscle cells by differentiation.
Other fibres undergo hypertrophy.
Muscles never fully recover.
Only myosin is?
Ends of sarcomere?
Myosin and actin in a sarcomere?
Middle of sarcomere?
H zone.
Z lines.
A band.
M line.
How are filaments organised in muscle, and how does this help function?
Myosin - triangles.
Actin - hexagons.
Striations and regular arrangements - very strong, can generate a lot of force.
What occurs during muscle shortening?
I band and H zone reduces.
Describe the cross-bridge cycle.
- An increase of [Ca2+] causes myosin to bind with actin.
- ADP and Pi detach, causing movement.
- ATP binds to myosin and causes myosin to detach from actin.
- ATP is hydrolysed and this energises the cross-bridge for the cycle.
Describe tropomyosin and troponin.
Tropomyosin - covers the binding site.
Troponin - holds tropomyosin in position.
Ca2+ binds to troponin and alters the shape, causing tropomyosin to pull away.
Describe excitation-contraction coupling.
- An AP in muscle occurs.
- Ca2+ is released from lateral sacs.
- Ca2+ binds to troponin and moves tropomyosin.
- Cross-bridge occurs.
- Ca2+ is taken up into the SR.
- Troponin restores tropomyosin position.
Where is Ca2+ stored?
Where does depolarisation spread down?
Sarcoplasmic reticulum.
T-tubules.
