Skeletal Muscles (Part 1) Flashcards
what proportion of human body weight is made up by muscle
40%
state what it is meant by the key term - excitability
the ability of muscle tissue to be electrically stimulated
state what it is meant by the key term - extensibility
the ability of muscle to be stretched it’s resting length (passive)
state what it is meant by the key term - elasticity
the ability of a muscle to return to it’s resting length (passive)
state what it is meant by the key term - contractility
the ability of a muscle to actively generate tension
state 3 facts about cardiac muscle
- actin and myosin form cross bridges - sliding filament mechanism
- node cells (pacemaker cells) produce spontaneous AP’s - autorhythmicity
- electrical coupling between cells
what is the refractory period time in cardiac cells? and what is the reason for this?
refractory period of 250 ms to prevent tetanic contractions
state 4 facts about smooth muscle
- actin and myosin form cross bridges - sliding filament mechanism
- surrounds cell structures
- changes in lengths changes the shape of cells
- controlled by the amount of Ca2+ in the cells
- Ca2+ release controlled by the autonomic NS
- spontaneous AP’s or drifting of polarity in some smooth muscle cells
state 3 facts about skeletal muscle
- changes in skeletal muscle moves skeleton
- actin and myosin form cross bridges - sliding filament theory
- controlled by motor neurones (voluntary and reflex)
how does skeletal muscle create and control movement? (2 things)
- skeletal muscle generates force to act on the skeleton
2. skeletal muscle changes length whilst generating force to move and control the skeleton
state 3 characteristics of skeletal muscle fibres
- multinucleate
- contains many mitochondria
- has transverse tubules (t tubules)
- myofibrils and sarcomeres
- sarcolemma, sarcoplasm, sarcoplasmic reticulum (SR)
state what it is meant by the key term - myofibrils
myofibrils are the structures that give skeletal and cardiac muscle their characterised striated appearance
state the two types of myofibrils
- actin (thin filament)
2. myosin (thick filament)
state what it is meant by the key term - sliding filament theory
muscle force and length change is generated buy the overlapping and interaction of actin and myosin filaments
which two people came up with the sliding filament theory?
- Andrew Huxley
2. Hugh Huxley
state 3 facts about actin
- contractile protein
- structure is like a string of pearls on a string and then the strand of pearls are twisted together
- each actin has a binding site for myosin
state 2 facts about tropomyosin
- regulatory protein
2. overlaps binding sites for myosin and inhibits interaction when the muscle is in it’s relaxed sate
state 3 facts about troponin
- regulatory protein
- troponin binds to Ca2+ reversibly and once bound change the conformation to pull tropomyosin away from the myosin binding site
- Ca2+ binding to troponin regulates skeletal muscle contraction because it moves the tropomyosin away and allow myosin to interact with the actin
state 2 facts about the sarcoplasmic reticulum (SR)
- homologous to ER
- stores and releases Ca2+
- T tubules connected to SR via junctions
- T tubule protein is a modified voltage gated Ca2+ channel known as dihydropyridine
explain the 6 steps of the excitation-contraction coupling reaction
- muscle AP propagated into T tubules
- Ca2+ released from lateral sac of SR
- Ca2+ binding to troponin removes blocking action of tropomyosin
- actin-myosin cross bridges form
- AP ends, Ca2+ re-uptake by SR
- Ca2+ removal from troponin restores tropomyosin binding action
state 3 things that occur when actin-myosin cross bridges form (expanding upon step 4 in the excitation-contraction coupling reaction)
- cross bridges move through power stroke sliding actin past myosin
- ATP cause release of myosin head and return to original state
- if Ca2+ still present, myosin head will attach again to new binding site
state what it is meant by the key term - motor unit
a motor unit is a motor neurone plus all the muscle fibres it innervates
state 2 additional facts about motor units
- one motor unit can innervate many muscle fibres, but one muscle fibre can only be innervated by one motor unit
- within a whole muscle there are many motor units
state what it is meant by the key term - neuromuscular junction
the neuromuscular junction is where the axon terminals establish synaptic contact with the motor end plate
state what it is meant by the key term - motor end plate
the region of the muscle fibre plasma membrane that lies directly under the terminal portion of the axon is known as the motor end plate
state the 8 steps of a neuromuscular junction
- AP propagates down motor neurone to axon terminals
- causes voltage-gated Ca2+ ion channels to open
- inc^ fluidity of ACh containing vesicles + causes them to fuse with membrane + release ACh into synapse
- ACh diffuses across synapse + binds to muscarinic receptors receptors which open Na+ channels
- Na+ entry cross motor end plate - depolarisation
- current spreads down sarcolemma
- muscle fibre AP propagated
- AP propagates along sarcolemma
state 3 facts about neuromuscular junctions
- are all excitatory
- ‘all or nothing’ principle
- contain acetylcholinesterase
state what it is meant by the key term - twitch contraction
the mechanical response to a single action potential
state the 3 phases of a twitch contraction (in order)
- latent period
- contraction time
- relaxation phase
state what it is meant by the key term - latent period (of a twitch contraction)
the period of time from the action potential to the onset of contraction. the time delay is due to the excitation-contraction coupling reaction
state what it is meant by the key term - contraction phase (of a twitch contraction)
this is the time when tension is developing due to cross-bridge cycling
state what it is meant by the key term - relaxation phase (of a twitch contraction)
this is the time where tension is decreasing (i.e., relaxing) and is longer than the contraction phase. this is due to the time it takes to get all the Ca2+ sequestered
state 3 facts about tetanic contractions
- multiple AP’s result in summation of tension/force
- if frequency is high, tetanic contraction occur when force remains constant(ish) for the period of activation
- typically a muscle force in functional activities
state what it is meant by the key term - tetanic contraction
is a sustained muscle contraction evoked when the motor nerve that innervates a skeletal muscle emits action potentials at a very high rate
skeletal muscle fibres do not have the same mechanical and metabolic characteristics. state the two characteristics muscle fibres are determined by
- the maximum shortening velocities (fast or slow)
2. the major pathway they use to re-synthesise ATP
state what it is meant by the key term - slow oxidative (SO) fibres
SO fibres combine low myosin ATPase activity with high oxidative activity
state what it is meant by the key term - fast oxidative glycolytic (FOG) fibres
FOG fibres combine high myosin ATPase activity with high oxidative capacity and intermediate glycolytic capacity
state what it is meant by the key term - fast glycolytic (FG) fibres
FG fibres combine high myosin ATPase activity with a high glycolytic capacity
state what it is meant by the key term - myosin isoforms
Some isoforms have specialised functions in certain cell types (such as muscle), while other isoforms are ubiquitous
state the 3 types of myosin isoforms
- myosin heavy chain 1
- myosin heavy chain 2a
- myosin heavy chain 2x
what is the function of the myosin isoforms ?
the type of myosin isoform determines the maximal rate of cross-bridge cycling, and thus, the maximal shortening velocities
state what it is meant by the key term - electromyography
the recording of the electrical activity of muscle tissue, or its representation as a visual display or audible signal, using electrodes attached to the skin or inserted into the muscle
what do oxidative fibres depend on ?
blood flow - the delivery of oxygen and nutrients
