Skeletal muscles Flashcards
What is the purpose of skeletal muscles?
They move joints
How is skeletal muscle attached to bone?
Muscles are attached to bones via a Tendon
Which muscle is the strongest in the body?
Masseter
What are the 3 main types of muscles?
- Skeletal muscle
- Cardiac muscle
- Smooth muscle
Which of the 3 types of muscles are striated?
The striated and smooth muscles
What are the 3 layers of connective tissue called?
- Epimysium (outer muscle
- Perimysium (medium muscle)
- Endomysium (inside muscle)
Describe the Epimysium
Tendon is covered by a layer of connective tissue of epimysium (outer muscle)
Describe the Perimysium
Inside muscles are a numbers of muscle fibers arranged into muscle fascicles which are covered by another layer of connective tissue called the perimysium (medium muscle)
Describe the endomysium
Each individual muscle fibre is covered by connective tissue called endomysium (inside muscle)
Describe muscle fibres
They have a layer of endomysium around
The have capillaries in the connective tissue layer
They have a basal lamina
Are muscle fibres mono or multinucleated?
Multinucleated
Where are nuclei found in healthy muscle fibres?
At the end in healthy connective fibres
1 nucleus every 15 sarcomeres (35 microns)
Describe capillaries
They are elastic
How far apart are striation in muscle fibres?
1 striation is found ever 25 micrometers
How do multi-nucleated cells arise?
Because they are formed by proliferating myoblast that migrate to the developing limbs line up and then fuse to from muscle fibres (when muscles are being formed)
Where do the cells that don’t fuse together sit and what do they do?
The cells that dont fuse sit under the basal lamina as SATELLITE CELLS
They wait for stimulation and will either grow or form new myoblasts to repair damaged muscle
Where do muscle sarcomeres travel to and from?
Go from one end of the muscle fibre to another
Where is the Z disk found?
In the middle of the I band
What are the 3 types of banding in the muscle sarcomere called?
I Bands
A Bands
M Line
What is the M line?
The middle region of the sarcomere
What happen to the sarcomere during muscle contraction?
Sarcomere gets shorter
I band length decreases
A band stays the same
What are cross bridges and what do they do?
Projections that stick out from the thin filaments to the thick filaments
6 thin filament to 1 thick filament
Crossbridges can move out and attach to actin
What do thin filament contain?
Actin
What do thick filaments contain?
Myosin
How many thin and thick filaments make up one cross bridge?
6 thin
1 thick
What are the functions of satellite cells?
Growth and regeneration
What makes up 90% of muscle cells?
Myofibrils
What are myofibrils?
They are sarcomeres connected end to end for the length of the muscle
Name some some go the features observes in all myofibrils under a microscope
- A band
- I band
- M line
- Z line
- H zone
Describe A bands
They run the length of the thick Myosin filaments and appear dArker in colour under a microscope
Describe I bands
where there are only thin Actin Filaments found and appear lighter in colour under a microscope
Where is the M line and what does it do?
It is found in the A band
It is the point of attachment between Myosin filaments running in opposite directions.
What is the function go the Z line?
It is the point of attachment between Actin filaments running in opposing directions
Marks the end of a Sarcomere.
Where and what is the H zone found
H Zone lies inside the A Band
It s a stretch where Myosin exists but Actin does not.
Describe the shape of myosin molecules
They look fork shaped (trident with 2 prongs)
The head is 16 Nanometers long, the tail is 155 Nanometers long.
How many chains make up the myosin molecule
4 Light Chains are the pointy bits
The 2 Heavy Chains (which are Alpha Helical) coil around one another to form the ‘Tail’.
What is a crown in regard to myosin molecule?
A collection of 3 myosin molecules
OR
A collection of 6 myosin heads
What make up thick filaments in skeletal muscle?
Lots of myosin molecules
it is 1.6 micrometres long
In what direction does the tail of the myosin molecule point towards?
They point towards the M line
What is the ‘bare zone’ and why is it formed?
It is an area where there are no myosin heads
It is due to the myosin being in an Antiparallel arrangement
What are thin filaments also called?
F-Actin
What does F actin look like under a microscope?
They look like pieces of string with beads under the microscope
What are the sub units (beads) of F actin called?
G Actin
They repeat every 2.75nm
What does G actin form?
They form helices, which in turn repeat every 5.5 Nanometers & Pitch at 72 Nanometers
What does F actin end with?
They end with a blob subunit called Tropomodulin which occurs just before the Z-Line which marks the next Sarcomere
What is found between Tropomodulin and alpha actin
A capping protein
What is the alpha actin?
Alpha Actin forms the Z-line, it is a barbed shaped protein
What coils around the actin filament?
2 Nebulin molecules coil around the each Thin Actin Filament, spanning its whole length,
What are nebula molecules thought to do?
They thought to regulate the length of the Thin Filaments
Where to titins run?
Titin runs parallel to the other fibers in the Sarcomere, with a single molecule going from Alpha Actin(to which it is attached) to the M-Line
What is the function of titins?
It helps organize the Z & M Lines during contraction, regulates Thick Filament Length and creates the resting Tension.
What causes muscle contraction?
The power stroke
What is the the powerstroke powered by?
Hydrolysis of ATP by Myosin which is classed an ATPase…
Talk through steps that form a power stoke?
- ATP binds to Myosin Head releasing it from Actin(by breaking cross bridge).
- ATP is Hydrolyzed, leaving Phosporyl and ADP bound to Myosin Head with Crossbridge to Actin
- Phosphoryl group is released from Myosin Head and energy released causes Powerstroke and ‘walking movement’
- ADP is released from Myosin Head
- Rigor ensues until new ATP molecule binds to Myosin Head, causing the Recovery Stroke…
What happens at each Z line
At each Z Line, the Myosin filaments are pointing in opposite directions, and this is known as Polarity Reversal.
What is polarity reversal?
At each Z Line, the Myosin filaments are pointing in opposite directions
What does the degree of overlap between Thick and Thin Filaments determine?
The force that can be produced
Describe the sarcomere during relaxation?
Not all the Mysosin Heads will be employed, but as the Actin is pulled across, the overlap increases to until maximum force is attained(at Saromere length of approx 2 Micrometers bear in mind they are normally 2.5 Micrometers)
How can you calculate the overall force of a given myofibril?
The overall force of a given Myofibril is the sum of all the individual Sarcomeres
How can you calculate the overall force of the muscle?
The overall force of the muscle is sum of all the Myofibrils
What can increase the force of contraction?
Calcium but its to a certain point
Name some regulatory proteins found in actin?
Troponin and Tropomyosin
With one molecule of Troponin every 7 G-Actins.
What does troponin consist of?
1, TnC
- TnL
- TnT
What does the TnC component of troponin do?
Binds to calcium
What does the TnL component of troponin do?
Is an inhibitor which binds to other sub units
What does the TnT component of troponin do?
Binds to tropomyosin
What is tropomyosin made up of?
2 coiled alpha helix chains that are 40Nm long
What do the Motor end plates from Motor Neurones deliver?
Acetocholine to muscle nerve receptors, producing an Action Potential
What produces an action potential?
The delivery of Acetocholine to muscle nerve receptors
How does an action potential spread from the sarcoplasm?§
Via T-Tubules to Dihydropyridine
What is dihydropyridine?
An L-Type Ca2+ receptor
What activates the Ryanodine receptor
dihydropyridine
Activation of the Ryanodine receptor leads to what?
Causes a release of Ca2+ Ions from the Sarcoplasmic Reticulum which binds to TnC of Troponin, which in turn binds to TnI.
Tropomyosin then moves to reveal Actin sites that allow crossbridges to form with Myosin Heads.
What happens when a cross bridge cycle is complete?
ATP driven pumps actively transport sCa2+ ions back into Sacroplasmic Reticulum, where it is bound by Calsequestrin Protein.
What is the concentration change of Ca2+ before and after Sarcoplasmic Reticulum release ?
Ca2+ con.c goes from less than 100 nanomoles before Sarcoplasmic Reticulum release to around 10 Micromoles.
What is a twitch?
A single stimulation
What is a summation
Multiple stimulations is a short time
What are incomplete Tetanus
faster successive stimulations
What are Complete Tetanus
‘fused’ stimulations
What determines the maximum tension?
The summation of action potentials
Along with the number of motor units that are recruited
What produces the greatest tension?
Larger Motor Neurons innervate the larget motor units, so producing the greatest tensions
How is ATP obtained and what is it needed for in muscle contraction?
ATP is needed to transport the Ca2+, and produce the Powerstroke.
It is obtained in the very short term by Creatine Phosphate, and in the longer run by Glycololysis (when Oxygen is scarce) or Oxidative Phosphorylation.
Where is short term ATP obtained from?
Creatine Phosphate,
Where is long term ATP obtained from?
Glycololysis or Oxidative Phosphorylation
What is a single stimulation called?
A twitch
What are Multiple stimulations is a short time called?
Summation
what are faster successive stimulations called?
incomplete Tetanus
what are ‘fused’ stimulations called?
Complete Tetanus
What do slow twitch fibres rely more on?
Oxidative Phosphorylation resisting fatigue
What do fast twitch fibres rely more on?
rely more on Glycolysis (and store more Glycogen for the job).
What come about when there is no more ATP?
Rigor Mortis
What does Rigor Mortis lead to
As there is no more ATP cross bridges can’t be broken
When does Rigor Mortis occur?
3 hours after death and continues until proteins breakdown
What allows muscles to be significantly greater in diameter than tendons?
muscle Tapers toward a thiner Tendon, which in turn attaches to bone.
This allows muscle to be significantly greater in diameter than tendon, allowing space for more Sarcomeres and thus more force..
What is Rigor Mortis ?
When there is no more ATP
