skeletal muscle function Flashcards
what are muscle fibres broken down into nd what do these do?
-are broken down into many myofibrils (causes muscle contraction)
-myofibrils are broken down into sarcomere
what is a fascicle?
group of muscle fibres (is surrounded by connective tissue which protects muscle fibres and gives it structure)
what does the sarcomere contain?
contain actin filaments and myosin filaments along z discs
what happens to sarcomere when muscle contracts?
- sarcomere shortens and myosin pull actin filaments together (z discs are pulled together
How are muscles activated (and sarcomeres shorten)?
-By motorneurons
-Brain sends electrical signals to muscles via motoneurons (originate from spinal cord) by creating an action potential (which is propagated along the motor neuron to the muscle)
-Happens at neuromuscular junction (where nerve ending meets muscle)
what is a motor unit?
composed of motor neurons and all the fibres it innervates
what is excitation-contraction coupling?
-the sequence of events by which an AP (an electrical event) in the sarcolemma of the muscle cell initiates the sliding of the myofilaments, resulting in contraction (a mechanical event).
Describe how calcium signals work?
1-calcium levels increase with the sarcoplasm
2-calcium binds to troponin
3- troponin and calcium complex pulls tropomyosin away from actin’s myosin binding site, allowing myosin to bind in presence of ATP
Describe the contraction relaxation cycle?
1-myosin heads hydrolyze ATP and become reorientated and energised results in ADP and one phosphate
2-myosin heads bind to actin, forming cross bridges
3-myosin heads rotate toward centre of sarcomere (power stroke)
4-More ATP is released and attaches to myosin head and cross bridge detaches
-contraction cycle continues if ATP is available and calcium level in sarcoplasm is high
how is neuromuscular activation measured?
-Using EMG electrodes: (non invasive)
surface electrodes measure electrical activity in muscle
Method:
-Measure grip strength of participant on a hand-grip dynamometer
-As force increases EMG activity increases (more muscle fibres must be activated in order to generate force- more action potentials within muscles)
what is the limitations of using EMG electrodes to measure neuromuscular activation?
-Tells us whether electrical muscle activity has increased or decreased but doesn’t tell us the increase/decrease
Alternative method to using EMG electrodes?
-Interpolated twitch technique- tells us how much of the muscle is able to be generated by the individual themselves voluntarily
-Electrical signal is sent from electrode across muscle to other electrode (electrodes are placed across quadriceps)
-Causes muscle to contract (is stimulated by electrical signals)- involuntary
-Then Compare increase in resting force and interpolated force (first electrical signal is sent at rest, then participant kicks and pushes force and electrical signal is sent- these 2 values are compared)
what can be used to determine muscle strength?
-size of muscle (Many sarcomeres arranged in parallel formation (cross sectional area) means more force is able to be generated)
-How quickly muscle can contract is determined by length of muscle fibres
what are the 3 types of muscle fibre?
Type1- smaller, produce less force, have more mitochondria (are more oxidative)-better for endurance
Type 2A and 2X- contract faster, larger, exert more power, (less oxidative)-will fatigue quicker
