Lecture 2 Flashcards
Muscle Function
what is torque
a measure of the force that can cause an object to rotate about an axis
what are the role of satellite cells
make more nuclei and help cell repair
explain the process of excitation contraction coupling = force generation
- nerve impulse travels down T tubules and causes release of Ca2+ from SR
- Ca2+ binds to troponin and causes position chnage in tropomyosin, exposing active sites on actin
- actin and myosin bind and contraction occurs
- ATP binding to myosin head, weakens its bind to actin so actin is released
what happens at the neuromuscular junction to cause a contraction
- action potentials arrive at each nerve at neuromuscular junction
- depolarisation of motor end plate (excitation) is required to initiate contraction
what happens to the muscle fibres is a motor neuron is stimulated
all fibres in that motor unit will contact synchronously
“all or none”
what is the size principle in terms of motor neurons and which is activated first
motor neurons are recruited progressively by axon size, small to large
smaller axons reach their threshold first and are therefore activated first
which type of muscle fibre is activated first and why is that
Slow twitch (Type I) muscle fibres are activated first
they have a lower threshold as they are smaller so are used first
what are the two major benefits to the size principle
- use fatigue resistant units longer
- finer regulation with low force
what does an increase stimuli (action potenital) initially do to muscle
increased frequency gives big increase force initially (summation)
what does further increase in frequency of stimuli (action potential) do to muscle after summation
further increase in frequency will have a diminishing effect until tetanus
what type of muscle fibre will always be used (low and also intense exercise
Type 1 = slow twitch
what type (s) of muscle fibre is mostly used during intense exercise
Type IIa and also Type IIx
more Type IIx
what is fatigue during exercise simply described as
reduction in strength
what are the peripheral fatigue mechanisms
force is inhibited before either ATP of glyocgen can become depleted
what is the optimal length tension relationship and why is it important
where the overlap between actin and myosin is best, allows for the most optimal force production
fibre length to muscle length is also important when generating force
give examples of the hamstrings and quads and how they differ
hamstrings :
- longer fibre/muscle, less cross sectional area
- gives rapid shortening
- more risk of tear
quads :
- shorter fibre / muscle, more cross sectional area
- gives greater force capacity
what is meant by “rate constraints” in terms of actin and myosin
cross bridges between actin and myosin attach / detach at certain rates
as velocity increases what happens to the number of cross bridges formed and force generated
as velocity increases the number of cross bridges decreases and less force is generated
muscles act around joints which means the force produced by a muscle is measure as …..
torque
- force at a particular distance from a joint axis, in Newton-meters, Nm
power athletes will generate more torque at all velocities compared to endurance athletes ….. TRUE / FALSE
also what will happen to force as it drops
TRUE
force will drop at similar rates (in relative terms)
if velocity is low what is an important force modulator
if velocity is low, length is an important force modulator
at eccentric velocities what is the determinant of force
muscle velocity dominates length as the determinant of force at eccentric velocities
what is the equation of power
work / time
what is the contraction time, motor neuron size, fatigue resistance, useful duration, force production and mitochondrial density of Type 1 fibres
contraction time = slow
motor neuron size = small
fatigue resistance = high
useful duration = hours
force production = low
mitochondrial density = high
what is the contraction time, motor neuron size, fatigue resistance, useful duration, force production and mitochondrial density of Type IIa fibres
contraction time = moderately fast
motor neuron size = medium
fatigue resistance = fairly high
useful duration = <30 mins
force production = medium
mitochondrial density = high
what is the contraction time, motor neuron size, fatigue resistance, useful duration, force production and mitochondrial density of Type IIx fibres
contraction time = fast
motor neuron size = large
fatigue resistance = intermediate
useful duration = <5 mins
force production = high
mitochondrial density = medium
what is the contraction time, motor neuron size, fatigue resistance, useful duration, force production and mitochondrial density of Type IIb fibres
contraction time = very fast
motor neuron size = vary large
fatigue resistance = low
useful duration = <1 min
force production = very high
mitochondrial density = low
what are the reasons that muscle loss occurs with aging
- loss of growth related hormones
- loss of IGF-1 (causes increased protein production and decreased breakdown)
- also sarcopenia (active loss of muscle)
- accumulate fate and denervated fibres in muscles
