Muscle structure and muscle contraction

Question 1

Process of myogenesis

Answer 1

-early in embryos development, some embryonic cells develop into embryonic muscle cells called myoblasts
-the myoblasts fuse together to from multi-nucleated fibres called myotubes
-the myotubes mature into microfibres

Question 2

skeletal muscle structure

Answer 2

-cardiac muscle and skeletal muscle are both striated
-a muscle is made up of long, strong fibres called myofibrils
-multiple myofibrils constitute a fibre and hundreds of fibres form a muscle
-fibres are made from several cells that fuse together

Question 3

Structure of muscle fibre

Answer 3

-fibres are surrounded by the sarcolemma
-around each myofibril is a network of tubes called the sarcoplasmic reticulum
-holes in the sarcolemma open into t-tubules which meet the sarcoplasmic reticulum
-in the space between the fibres and we find mitochondria in the sarcoplasm
-striations are altering bands of thick myosin and thin actin proteins

Question 4

Structure of the sarcomere

Answer 4

-each myofibril can be broken down into functionally repeating segments
-these are the smallest units that are able to contract
-they repeat over the entire length of the myofibril
-the length of one sarcomere is the distance from one z-line to the next one along the myofibril

Question 5

Muscle contraction steps

Answer 5

1. a nervous impulse arrives at the neuromuscular junction
   2.this causes acetylcholine to be released in the gap between the neuron and sarcolemma and the ‘signal’ travels down the t-tubules
   3.this in turn causes the sarcoplasmic reticulum to release calcium ions, Ca2+, over myofibrils
2. Ca2+ then binds to troponin, changing the shape of the tropomyosin, revealing binding sites on the actin filaments
   5.myosin heads are now free to attach to the actin forming a cross-bridge
   6.The heads then tilt towards the centre, pulling the actin filament inwards slightly and ADP is released.
   7.ATP is hydrolysed into ADP and P. This releases energy which causes the cross-bridge to break. The head moves back to it’s original conformation as the ATP has hydrolysed and the head is now free to attach to the actin again.