Module 4 Flashcards
What happens after muscle injury
new fibres are formed from myoblasts. These myoblasts are from satellite cells and these satellite cells fill in the gap by fusing and differentiate to promote muscle repair
What are the tiers of muscles
Muscle -> fasicles -> muscle fibre -> myofibre
why do muscle fibres push the nuclei up
proteins in fibres take up a lot of space. If the nuclei was in the middle, it would get crunched
What is myosin anchored to? what is actin anchored to?
Myosin is anchored in place by titin fibres and actin is anchored by Z lines
how does titin fibres help with contraction?
Titin is a green spring line that reaches down to myosin with its little attachment points, attaches to myosin and springs it back to length after myosin finishes sliding
how does muscle contraction occur
It occurs in 4 steps. Binding, Power stroke, detachment, binding.
Myosin head binds with actin and then power strokes by having myosin head pull actin filament inward. After the myosin head detaches and it rebinds to an actin molecule that is farther away. Cycle repeats
what is the composition of a muscle
layers of connective tissue epimysium binds to the entire muscle, perimysium binds to groups of fibers/ cells or fascicles, endomysium binds individual cells
What is the difference between the A band and the I band
A band is a thick filament located in the wide dark band. It has a lot of myosin and a few actin
I band is a light band that is between the ends of the A bands when thin filaments do not overlap the thick ones. It has a lot of actin
What is the difference between myosin and actin
myosin are thick filaments that are not bound to walls, their structure consists of two globular heads and one long tail to help bind with actin
actin are thin filaments that are bound to walls, the structure consists of tropomyosin and troponin where it regulates contraction (binding of actin filaments)
what are the functions of troponin and tropomyosin
tropomyosin is put over troponin to prevent binding actin with myosin. Troponin can only bind if tropomyosin is rolled over by calcium to expose the myosin binding site
When does ATP come in after muscle contraction and what does it do?
When calcium binds with troponin C, it rolls over tropomyosin so binding between myosin and actin happens. ATP pumps calcium out of cytoplasm back to the sarcoplasmic reticulum through sarcoendoplasmic reticulum calcium ATPase
What happens during excitation contraction coupling
Because resting muscle has low calcium concentration, when calcium enters the cytoplasm, it starts cross bridge cycling. It requires the release of calcium to start a spark. The calcium goes down the T tubule which connects from surface of muscle cell membrane to the central portion of muscle fibre
What does action potential do in excitation coupling contraction
Action potential changes the DHPR (dihydropyridine receptor), aka voltage gated sensor, shape and calcium is released. This does not require ATP. It is done by passive diffusion
How is action potential delivered for calcium release
Action potential is delivered by T tubules to many myofibrils so that calcium is sprayed everywhere to get it on troponin
what happens in between calcium release and a contraction
Calcium binds to troponin C, Troponin 1 rolls tropomyosin away from myosin binding site on actin so myosin can bind with acing. Myosin head flexes (power stroke)
when is ATP needed in the cross bridge cycle
ATP is needed during the detachment phase after when the myosin head pulls the actin. ATP binds with myosin so it detaches from actin and the myosin head stretches
What are the 3 roles of ATP in the cross bridge cycle
- Detachment
- Energized - ATP is released
- Binding - myosin and actin binding breaks down ATP to ADP and Pi
what are the factors of latent period between excitation and development of tension in skeletal muscle
- Time needed to release calcium from SR
- Moving tropomyosin
- Cycling cross bridges
what consists of a motor unit
one motorneuron and all the myofibres it innervates
what is the difference between bigger muscles and smaller muscles in terms of number of fibres and motor neurons innvervated
bigger muscles have more fibres but less motor neurons innervated but smaller muscles have less fibres but more motor neurons, which means more fine movements
what is asynchronous movement
asynchronous movement is having multiple motor units so it can give some motor units a break and use others
what factors influence the extent that tension will be developed
- frequency of stimulation
- length of fibre at onset of contraction
- extent of fatigue
- thickness of fibre
what is the difference between a twitch, a twitch summation, and tetanus
A twitch is a single action potential that causes a single contraction of a fibre but it is not noticeable. It is not enough to generate a muscle contraction.
A twitch summation is a restimulation of a muscle fibre when an action potential is generated before hasn’t relaxed yet, which leads to summating the force
Tetanus is repeated stimulation without having time to relax
what is the duration of twitch summation
adding more action potential within the 100msec
what does tetanus depend on
high levels of Ca2+ and as long as Ca2+ is available
what happens if second action potential occurs while Ca2+ released by first action potential is still present
max tetanic contraction
ensures 100% cross bridges form
constant spikes in calcium release from SR sustains this cross bridge cycling
When does Rigor Mortis occurs
It occurs when calcium isn’t brought back in
This happens when the body is dead and atiff and doesn’t produce ATP anymore. As a result, myosin and actin stays attached
what is myasthenia gravis
body’s own immune system attacks acetylcholine receptors leading to degradation. this causes weakness in eye muscles, muscle weakness, difficulty swallowing. This is due to less receptors, meaning less action potential, meaning muscle weakness
what is lambert-eaton myasthenic syndrome
body’s own immune system targets voltage gated calcium channels on presynaptic axon terminal. this causses less calcium channels, which leads to less calcium influx into terminal, less calcium activation of synaptotagmin, less vesicle fusion. This results in less acetylcholine release in NMJ. Symptoms are weakness in the limbs and severe symptomes can lead to muscle weakness in eyes, throat and face, dry mouth due to loss of some autonomic function
what is the contraction difference between lifting heavier loads vs lighter loads
lifting heavier loads will not last long in contraction because of the delay of action potential and time of contraction
lifting lighter loads will have longer lasting contraction because once excitation happens, contraction happens
what are type 1 fibres
fibres with slow twithc and slow contractions
doesn’t have a strong contraction but can contract for a long time without fatigue because they are surrounded by capaillaries that supply fibre and myoglobin to store in oxygen and mitochondria
what are type 2A fibres
fast twitch contraction with a lot of tension
in between type 1 and type 2X
metabolisum is between oxidative and glycolytic
what are type 2 X fibres
large fibres that produce strong contractions for a short period of time. easy to fatigue
glyoclytic metabolism
