Structural properties and activation of muscle Flashcards
muscle’s prime function
convert chemical energy stored in ATP bonds into mechanical work
functions of muscle
- movement
- maintain posture when sitting and standing
- breathe, talk, eat
- hold body structures together
- act as a brake to slow movements
- source of heat
- dynamic metabolic store
muscoskeletal system
muscle, bone and connective tissue
how much of human is muscoskeletal system
~75% lean body mass of health person
major component of muscle
water - 75%!
20% of muscle is
protein
5% of muscle is
inorganic salts and other substances
muscle is comprised of
water 75%
protein 20%
5% inorganic salts and other
types of protein in muscle
1000s of different proteins.
40% is myosin
20% is actin
rest is other proteins including tropomyosin
epimysium
connective tissue around the muscle that holds structure
connective tissue around the muscle that holds structure
epimysium
what are myofibrils made up of
triations of sarcomas
sarcomas are the basic contractile unit
what are sarcomas
basic contractile unit
what is the basic contractile unit
sarcomas
composition of sarcomere
limits - dark bands
thick filaments - myosin
thin filaments - actin
thin filaments
actin
thick filaments
myosin
myosin
thick filaments of sarcomere
actin
thin filaments of sarcomere
how do the actin and myosin interact (brief)
sliding of the myosin head
key feature of filaments
they are not fixed so sarcomeres can shorten and contract
name of muscle fibre response to one electrical pulse
twitch
what causes an isometric twitch
it is a mechanical response to a single electrical response
Pt
max force peak twitch
EMD
electrical mechanical delay
TPT
time to peak tension
1/2RT
1/2 relaxation time
how many phases of a twitch, and what’s the difference
2
1st phase is fast
2nd phase is slow
what differs the response of fibre to electrical pulse
fibre type; slow or fast
fatigue
events of propagation of an action potential
- AP travels down t-tubule
- AP activates the sarcoplasmic reticulum
- SPR is open to release ca2+
- ca2+ binds to thin filament/actin
- myosin then binds to action
knowing events of propagation helps with what
knowing where problem is for targeting drug treatment
when are events of propagation disturbed
fatigue and disease
response to many electrical pulses
tetanus
tetanus
response to many electrical pulses
difference between twitch and tetanus
twitch = one electrical pulse tetanus = many electrical pulses
what happens when there is little to no gap between stimuli of muscle fibres
there is no time for relaxation, causing pulses to become fused
when do pulses become fused
when there is not enough time between multiple stimuli for relaxation
how long does half removal of calcium take
~80ms = long time
what happens at 10Hz
concentration of calcium builds, leading to partially fused tetanus
at what stimuli frequency does tetanus begin to fuse and why
10Hz, because the concentration of calcium starts to build
what does high rate of impulses cause high levels of
calcium in the cytoplasms
this interrupts cross-bridge cycling
what effect does consistently high levels of calcium in cytoplasm do
permits cross bridge cycling
what interrupts cross-bridge cycling
high rate of impulses which causes consistently high levels of calcium in the cytoplasm
functions of sarcomeres in series
- sprinter
- high velocity
- low force
function of sarcomeres in parallel
- body builder
- low velocity
- high force
in what contraction does muscle fibre length not change
isometric
in what contraction does muscle fibre shorten
concentric
isometric contraction
- myosin bound to actin
- myosin try to push action
- overall length of muscle doesn’t change
e. g holding a heavy load
concentric contraction
- myosin bound to actin
- myosin successfully push actin
- sarcomere shorting occurs
- muscle length shortens
e. g lifting a heavy load
high force low velocity
isometric contraction
low force high velocity
concentric contraction
when is force maximum
when velocity is zero
what is force when velocity is zero
force is maximum
power equation
power = force x velocity
how do force, power and velocity link
power = force x velocity
why can force not be produced with great velocity
when going fast, only a small proportion of myosin heads can attach
during which contractions can power be measured
concentric, not isometric
?
what athlete would have muscles in parallel
body builder
what athlete would have muscles in series
sprinter
what produces more power; muscles in series or parallel
both produce equal power!
- parallel = low velocity, high force
- series = high velocity, low force
factors of parallel power
- force adds up
- each elements feels only part of whole force
- movements do not add up
- each element experiences whole movement
factors of series power
- forces do not add up
- each element feels whole force
- movements do add up
- movement is shared between elements
defining fibre type for slow and fast twitch fibres
composition of myosin heavy chain isoform
how many types of myosin heavy chain
3
Type 1, Type 2a, Type 2x
What are the types of myosin heavy chain
Type 1, slow
Type 2a, fast
Type 2x fast
myosin heavy chains for fast twitch
type 2a
type 2 x
myosin heavy chains for slow twitch
typa 1
what myosin heavy chain has peak isometric force at 110ms
type 1
what myosin heavy chain has peak isometric force at 50ms
type 2a
when is peak isometric force for type 1 myosin heavy chain
110ms (slow)
when is peak isometric force for type 2a myosin heavy chain
50ms (fast)
what athlete has more type 1 myosin heavy chain
endurance athelte
what athletes have more type 2 myosin heavy chain
sprinters
what comprises a motor unit
a single motor neurone and all the muscle fibres that it innervates
how many muscle fibres does one motor neurone innervate
varies! some less than 10, some over 2,000
example of muscle that has few motor units
gastrocnemius
big muscle that needs to be efficient and so has few neurons that innervate lots of fibres
example of muscle with lots of motor units
extraocular muscles need to react quickly with fine tuning. Lots of neurons in charge of few fibres each
neural mechanisms responsible for muscle fibre recruitment
- spatial recruitment
- temporal recruitment
another term for muscle fibre recruitment
motor unit recruitment
spatial recruitment
for big muscles, legs
- recruit the minimum number of motor units needed
- smallest type I recruited first
- mid sized type IIa recruited next
- largest type IIx recruits last
what is the principle of spacial recruitment
Size/ Henneman principle
temporal recruitment
for fine and fast adjustment; eyes
- rate coding refers to the motor unit firing rate
- frequency
- active motor units can discharge at higher frequencies to generate greater tensions
- smaller muscles rely more on rate coding
- larger muscles of mixed fibre rely more on recruitment
wha affects whole muscle activation
- muscle arcitecture
- antagonist co-contraction
- neural activation
- temperature
- fibre type
- hormones
muscle architecture that affects activation
physiological cross-sectional area = PSCA
anatomical cross-sectional area = ACSA
- angle of pennation
variables of neural activation for muscles
- recruitment
- firing rate
- motor unit synchronisation
angle of pinnation
ideally muscles would have nicely arranged fibres for maximum force output
in reality, most have pinnation angles
pinnation angles give different force direction causing complicated transmission of force
how to measure ACSA
accurate: magnetic resonance image less accurate: - computerised topography - ultra sound b-mode - tape measure & skin fold - tape measure
relating muscle force to tendon force
muscle force =
tendon force/cos(pennation angle)
antagonist co-contraction
when one muscle contracts, the other relaxes
- antagonist muscle acts as brake, producing small but sufficient force to brake as needed and reduce eternal force of agonist
net force equation
force of agonist - force of antagonist
is myosin activation muscle activation
yes, but not solely! lots of other factors involved and needed to understand exercise and disease
