MSK - muscle microstructure and contraction Flashcards
What muscles are under involuntary control?
and which system controls it?
Smooth muscles from autonomic nervous sysm
What is special about cardiac muscle?
can contract autonomously
but under influence of autonomic nervous system and chemicals
What muscles are under voluntary control?
What are there function?
skeletal muscles
attach bones to contract and bring about movement
Where are smooth muscles found?
A muscles eyes
B airways
C biceps
B
Which system control skeletal muscles
somatic nervous system
What are 3 connective tissue surronding each level of muscle tissue?
What do they surrond?
enodmysium - surrond a single muscle fibre
perimysium - surronds fascicles (multiple fibres of muscle)
epimysium - surronds entire muscle
Label diagram of muscle
What is muscle fibre compose of?
myofibrils
What is difference between myofibre and microfibril
myofibre - a muscle fibre, multinucleated muscle cell
myofibrils - Cylindrical organelles, found within muscle cells, that are the contractile unit of muscles.
What are 5 may components of skeletal muscle?
covered by plasma membrane - sarcolemma
T-tubules - tunnel into centre
sacroplasm - cytoplasm
network of fuild filled tubules - sacroplasmic reticulum
myofibrils
label this diagram of muscle fibre
Where are myoblobin and mitochondria found in muscle cell?
sacroplam
What is the ‘thin’ and ‘thick’ filament?
thin - actin
thick - myosin
Where are 2 types called and located on this diagram?
H disk and Z disk
do myofilaments extend along length of myofibres?
NO but they overlap arranged and in compartments (sarcomeres)
myfilaments are the protiens myosin and actin, they END
Do myofibrils extend along myofibres
YEs
composed of 2 main type of potiens - actin and myosin
is long line of repeating sacromeres
What seperates sacromeres
Z discs
What is A band
Where myosin is found
What is strucutre of myosin?
thickkk - golg clubs
2 globular heads
single tail formed from 2 alpha helices
tails of hundreds molecules form one filament
What strucutre of actin?
twisted into helix
each molecule has actin binding site
contains troponin and troponmysoin
Label this diagram of actin
What happens to A band, I band and H zone when contraction?
A same length - length of myosin
I band decreases
H zone narrows or disappears
Steps of intiation of muscle contraction?
phase 1: AP open voltage Ca2+ channels, Ca2+ enter pre-synpathic terminal, release of Acetylcholine binds to receptors + AP in muscle
Phase2:
- AP spread around surface membrance
Acetylcholine broken down by acetylcholine esterase, response stop
What is mechanism of actual muscle contractions
1) . action propagates into T-tubules
2) . DHP receptor in T sense chnage + change/opens ryanodine receptor in SR
3) . Ca2+ released from SR into space around filaments (actin and myosin)
4) . Binds to troponin and tropomypson moves
4) . Allows crossbridhes to attach to actin
5) . Ca2+ actively transported into continously while AP continue. uptake less than or equal to release rate
How exactly does myosin head couple to actin?
1) . Ca2+ causes troponin to move from tropomyosin chain
2) . exposes myosin binding sire on actin chain
3) . ‘charged’ myosin heads bind to exposed site on actin
4) . discharge of ADP causes ‘power stroke’ pulling actin towards centre of sarcromere
5) . ATP binding releases myson head from actin
6) . ATP hydrolysis energy ‘recharge’ myosin head
What nervous pathway for muscle contraction?
upper motor neurone in brain
to lower motor neurone brainstem/spinal cord
How does the nerves innervates muscles
single neurone innervates many muscles fibres however all in the same motor unit
What is a motor unit?
A single motor neuron all muscle fibres
when stimulated ALL muscle fibres in unit contract
Can other nerves inverve a muscle fibre that is already innverated by another nerves?
NOO
only one motor innverates those fibres in that motor unit
What controls the fine control?
each nerves innverates - less motor units and fibres
What are 3 types motor units?
Slow, fast (fatigue resistant), fast fatiguable
What are characteristics of slow motor units?
smallest diameter cell bodies
smalld endritic trees
thinnest axons
slowest speed
What are characteristics of fast, fatigue resistant motor units?
What are characteristics of Fast, fatiguable motor units?
larger diamter cell bodies
larger dentritic rrees
thicker axons
faster conducitivty
How does each type of motor neurone appear?
Properties of each of motor units?
What are 2 mechanisms that brain regulated force a muscle can produce?
recruitment and rate coding
How does recruitment work?
motors not randomly recruited
choosed based on size, small first (generally slow)
as more force more units
What does recruitment allow for?
fine control - under which low force levels are required
What is rate coding?
motor can fire at range of frequnecies
slow units at lower
as firing rate rate increase, force for each unit increasees
What happens when rate coding too fast?
Summation - unit fire at frequency too fast to allow muscle relax between AP
What is recruitment order of the type of muscles fibres?
slow then fast resistance then fast fatigue
So overall what happens when as force increase when carrying item?
Increases firing rate for each muscle unit
more fibred recruited
What are affects of neurotrophic factors?
prevent neuronal death and promote frowth after injury
changes characterisitic of muscle, effect on properties
What does the motor unit and fibre type depend on? Or is it indepedendent if so how
dependent on type of nerve innvating it
if slow, muscle beocmes slow
What are 3 types of muscle contraction?
isometric - no change in length of muscle
concentric- muscle shorterns as force/contraction
eccentric - muscle becomes longer, easily damaged, most force
How could injury to pathology affect muscle units?
leads to type 1 converted to 11
What affects microgravity have on fibres
slow to fast
What affects do aging have on muscle units?
loss of type 1 and 2, more 11
so more slower, type 1 fibres in ages muscles
