initiation of muscle contraction

Question 1

what is the motor unit

Answer 1

• motor neurone and muscle fibres
• all muscle fibres within a motor unit contract and relax simultaneously
• precise movement = less fibres per motor neurone
• less precise movement = more fibres per motor neurone

Question 2

neuromuscular junction

Answer 2

connection between motor neurone and muscle fibre
- as nerve cell activated, action potential travels down axon
- when meet presynaptic terminal, Ca terminals opening = influx into the end of the nerve cell
- acetylcholine (ACh) released and transmitted across synapse + bind to receptor (AChE) on muscle and allow influx of sodium into fibre
- causes action potential to continue down the membrane of muscle

Question 3

excitation contraction coupling

Answer 3

• t tubules allow for action potential to pass through the cell to the centre to make sure everything contract at same time
• around each bundle of filaments
• highly associated with sarcoplasmic reticulum which stores calcium
• action potential releases calcium
• calcium acts on actin (associated with tropomyosin and troponin) and causes movement of troponin to uncover the binding sites for the myosin
• myosin can now bind to actin filament which trigger movement of muscle

Question 4

structure of sarcomere

Answer 4

• when relaxed, the filaments are slightly overlapping (apart)
• when contracted, the filaments greatly overlap and its much denser image

Question 5

mechanism of muscle contraction

Answer 5

1. calcium binding = causes troponin to move, uncovering binding sites, myosin cross bridge attaches to the actin myofilament
2. power stroke = myosin head pivots and bends as it pulls on the actin filament sliding it towards the m-line
3. as new ATP attaches to the myosin head, the cross bridge detaches
4. as ATP is split into ADP and P, cocking of myosin head occurs

Question 6

rigour mortis

Answer 6

• after death, cellular membranes become leaky
• Ca 2+ leak out of sarcoplasmic reticulum
• allow myosin head to bind to actin
• ATP synthesis stops- cross bridges can not be broken
• muscle in state of rigidity

Question 7

what is additional ATP supplied by

Answer 7

• phosphocreatine
• glycolysis
• cellular respiration

Question 8

phosphocreatine

Answer 8

• very high energy molecule found in muscle fibres, in conc > than ATP
• breaks down to form creatine and phosphate
• releases large amount of energy
• energy used to convert ADP into ATP
• provide enough energy for contraction for about 15 secs

Question 9

glycolysis

Answer 9

• creates 2 molecules of ATP from glucose (end product is pyruvate or lactate)
• breakdown of glycogen
• glycogen is stored in form of glucose
• stored in muscle and liver
• once enough ATP, muscle can contract for several mins

Question 10

cellular respiration

Answer 10

• aerobic
• pyruvate from glycosis used in krebs cycle in mitochondria
• produces 30 ATP molecules
• fatty acids can be used as an alternative fuel