Muscle Flashcards
Outline the different features of an actin and myosin
Actin filaments- helical array of G-actin proteins- tropomyosin molecule covering actin-myosin binding sites held in place by troponin complex
Myosin molecules- tails form filament by wrapping around each other and hinged head with a binding site for actin and ATP
What happens during a muscle contraction?
During a muscle contraction- Ca2+ ions are released from the sarcoplasmic reticulum. These will bind to troponin molecule causing it to change shape, this pulls on the tropomyosin moving it away from the actin-myosin binding sites
Head of myosin will form an actin-myosin cross bridge with actin filament and a power stroke will occur. Ca2+ also activates ATPase activity of myosin- after power stroke myosin binds to ATP- causes breaking of bridge and energy used to reset myosin molecule back to original position
High intracellular Ca (10^05mM) is temporary (millisecond) before being actively transported back into sarcoplasmic reticulum.
Explain what the sarcomere is and how this changes in a muscle contraction
End of the sarcomere is marked by the Z-lines. These hold the actin filaments. In the middle of sarcomere there is the M- line- discs made of cross connecting elements of cytoskeleton holding myosin filaments
I- band- actin only
A- band- whole of myosin filament
H- zone- myosin only
During contraction- I band, H-zone and sarcomere gets smaller. A band stays same.
Structure of skeletal muscle
- Sarcomeres held in register by cross connections (intermediate filaments) between z- discs
- Gives striated appearance
- Linked to membrane and out to connective tissue
Relationship between myofibrils and fibres
- Myofibrils= many sarcomeres joined together
- fibres contain many myofibrils
Why is the nuclei seen to be on the side of the muscle fibre
Good for repair of muscle
What is a syncytium and why is this useful- give an e.g. of one
- Hundreds of muscle cells fuse to form syncytium- allows for multinucleated nature of skeletal muscle
- e.g. placenta
How wide / long is a muscle fibre
20-100 micrometres wide 1mm-8cm length
What is the length tension relationship in skeletal muscle?
- We see the most tension when there is some overlap between myosin and actin
- Muscles adapted to be within this maximal range
- Never no overlap and never full overlap (as lack of tension)
Explain membranes seen within skeletal muscle
- endomysium (loose connective tissue) around each muscle fibre- connects to basement membrane
- Perimysium- mixed connective tissue (dense and loose) forming fascicles
- Epimysium- loose connective tissue between fascia and muscle body
- Fascia- dense connective tissue covering muscle
Perimysium vs Perineurium
- perineurium= layer of endothelial like cells VS
- perimysium= connective tissue
Structure cardiac muscle
- NOT syncytial fibres
- mono/ di-nucleated cells with limb- like extensions
- Extensions connect to neighbouring cells via intercalated discs forming fibre- like 3D networks
- Produce force in direction of cells axis
Difference between myocardium and cardiomyocytes
Myocardium= cardiac muscle tissue Cardiomyocytes= individual muscle cells
What surround cardiomyocytes
- layer of close connective tissue
- layer of squamous endothelium
Why are the cells not all in 1 direction in cardiac muscle
- allow for wringing motion
- allows for effective emptying of blood from atria/ventricles