Muscle Flashcards
What is the function of muscle?
To generate force and movement.
What can muscle function allow?
Expression and regulation- characterises people, regulates body functions, internal and external protection.
What are the 3 types of muscle?
Skeletal
Cardiac
Smooth
What does skeletal muscle allow?
Voluntary movement- controls body movement.
What does cardiac muscle allow?
Flow of blood through circulatory system.
What does smooth muscle allow?
Involuntary movement- influences movement of substances in body.
Is muscle excitable?
Yes- it can be electrically stimulated.
How is skeletal muscle characterised?
Large
Multinucleate
Striated
How is cardiac muscle characterised?
Smaller
Striated
Branched
Uninucleate
How is smooth muscle characterised?
Small
No striations
Uninucleate
What types of muscle are striated?
Skeletal
Cardiac
What type of muscle is not striated?
Smooth.
What type of muscle is multinucleate?
Skeletal.
How is skeletal muscle formed?
In utero by mononucleate myoblasts.
What are mononucleate myoblasts?
Precursor for in utero skeletal muscle development.
What happens to skeletal muscle fibres ing growth?
Skeletal muscle fibres can increase.
Can myoblasts replace skeletal muscle cells if damaged?
No- they cannot be replaced.
What are skeletal muscle fibres encased in?
Connective tissue sheath.
How is skeletal bone attached to bones?
Tendons.
How are skeletal muscle cells replaced after injury?
Satellite cells.
What do satellite cells do?
Replace skeletal muscle cells following injury- they differentiate to follow more muscle fibres.
Is the area between skeletal muscle and tendon clear?
No- there is no clear division but rather an area of hybrid cells.
Are satellite cells unlimited?
No- they are very limited which means that there is never full healing within skeletal muscle damage.
What happens to surrounding cells when skeletal muscle damage occurs?
Induced hypertrophy to try and compensate for the damaged muscle.
Is there ever complete recovery of skeletal muscle?
No- some cells will always form scar tissue.
Why is there large amounts of bleeding in skeletal muscle damage?
Very vascular structures with many blood vessels.
Why does skeletal muscle never fully recover from injury?
Myoblasts cannot replace cells and satellite cells are limited.
What are striations?
Stripes of protein bands- they start and finish at a molecular level.
What is the repeated unit between Z-lines in striations called?
Sacromere.
What is the sacromere?
Functional unit of muscle.
What is the functional unit of muscle?
Sacromere.
What are the 2 main proteins that give the sarcomere arrangement?
Actin and myosin.
How is myosin structured?
Thick filaments with myosin heads.
How is actin structured?
Thin filaments with binding sites for myosin head attachment.
What are actin and myosin major components of?
Sarcomere.
What does increased actin and myosin action lead to?
Increased generation of force.
What can actin and myosin action be altered by?
Chemical drugs / nutrients etc.
What cycle does actin and myosin act through?
Cross-bridge cycle.
How does the cross-bridge cycle work?
ADP + Pi are attached to myosin head.
Myosin head attaches to an exposed binding site on the actin filament.
The phosphate is released and the actin filament can slide along- the ADP is also released as it moves along.
The cross-bridge is broken again when ATP binds to the myosin head- it is broken back down to ADP + Pi and the structure is back at the beginning.
What are attached to the myosin head at the start of the cross-bridge cycle?
ADP + Pi.
What happens when a myosin head attaches to an exposed binding site on the actin filament?
Phosphate is released and actin filament can slide along- ADP is also released as it moves along.
How is the cross-bridge broken?
When ATP binds to the myosin head again.
What happens to ATP that breaks the cross-bridge cycle through binding to the myosin head?
Broken back down to ADP + Pi and the structure is back at the beginning again.
What 3 molecules regulate the cross-bridge cycle?
Calcium
Troponin
Tropomyosin
What does tropomyosin usually do?
Partially blocks myosin binding sites on actin filaments- it is held in position by troponin.
What does troponin do?
Holds the tropomyosin in place to block myosin binding sites on actin filaments.
What molecule partially blocks myosin binding sites on actin filaments?
Tropomyosin.
What molecule holds tropomyosin in place to block the myosin binding sites on actin filaments.
Troponin.
What is the function of calcium?
Binds to troponin which allows release of tropomyosin and unblocks the myosin binding site on the actin filament.
Why is calcium required for muscular contraction?
Required to bind to troponin and unblock tropomyosin which uncovers the myosin binding sites on the actin filament.
What molecule binds to troponin?
Calcium- binds to troponin to move tropomyosin out of the way and unblock myosin binding sites on the actin filament.
What is the main function of the sarcoplasmic reticulum?
Storage of Ca2+ ions.
Where does the sarcoplasmic reticulum exist in muscle cells?
Extends all over the muscle cell for easy access during extensive contraction.
Where do mitochondria exist in muscle cells?
All over the muscle cell for easy access during extensive contraction.
Where is calcium stored in muscle cells?
Sarcoplasmic reticulum.
What does a motor unit consist of?
Motor neurones and muscle fibres it acts on.
Where can muscle fibres of a motor unit be scattered?
Throughout the muscle.
What is the force exerted by a muscle called?
Tension.
What is the force acting on a muscle called?
Load.
What is tension?
Force exerted by a muscle.
What is load?
Force acting on a muscle.
What is a contraction with a constant length called?
Isometric.
What is an isometric contraction?
A contraction with a constant length.
Give an example of an isometric contraction.
Weightlifting.
What is a contraction with shortened length called?
Isotonic.
What is an isotonic contraction?
Contraction with a shortened length.
Give an example of an isotonic contraction.
Running.
What is a contraction with an increasing length called?
Lengthening contraction.
What is a lengthening contraction?
A contraction with increasing length.
Give an example of a lengthening contraction.
Sitting down.
How does a twitch occur?
Action potential > Muscle fibre > Twitch
What is the latent period?
Latent period is the time before the excitation contraction starts.
When does contraction occur?
Between start of tension and peak tension.
Do muscle fibres all have the same contraction time?
No- muscle fibres all have different contraction times.
What molecule is muscular contraction time dependent on?
Ca2+ concentration.
How are isometric contractions characterised?
Shorter latent periods but extended contraction event.
What happens to muscle contraction as load increases?
Contraction velocity and distance shortened decrease.
How can action potentials add up to give increased contraction?
Summation.
Why is tetanic tension greater than twitch tension?
Calcium levels never get low enough to retain the tropomyosin covering of myosin binding sites on actin filaments.
What does less overlap of filaments result in?
Less tension.
What does too much overlap of filaments result in?
Filament interference with each other.
What is the optimal length of muscle contraction?
The muscle length at which the greatest isomeric tension is seen.
What systems are muscles arranged in?
Lever systems.
What type of action between flexors/extensors does limb action require?
Antagonistic action of flexors and extensors.
What do lever systems amplify?
Muscle shortening velocity which therefore increases manoeuvrability.
Do muscles exert more force than the load they bear?
Yes.
Where does the energy for muscular contraction come from?
ATP.
How doe ATP power the cross-bridge cycle?
Hydrolysis of ATP energises cross-bridges as ATP binds to myosin and dissociates.
How does ATP act with calcium?
Powers Calcium-ATPase in the sarcoplasmic reticulum which allows contraction to end.
How does contraction end?
Pumping of calcium back into the sarcoplasmic reticulum through Calcium-ATPase.
What leads to muscle fatigue?
Repeated muscle stimulation.
What does muscle fatigue depend on?
Fibre type
Length of contraction
Fitness of individual
What can enable fatigued muscle to contract again?
Rest periods.
What does fatigue prevent?
Prevents muscles from using up vast amounts of ATP and not being able to generate new cross-bridge cycles.
What factors could cause fatigue in high-intensity, short periods of exercise?
Conduction failure due to depolarisation issues
Lactic acid acidifying proteins
ADP/Pi inhibition of cross-bridge cycle
What factors could cause fatigue in long-term, low intensity periods of exercise?
Decreased blood sugar
Decreased muscle glycogen
Dehydration
What is central command fatigue?
Central command fatigue refers to a lack of ‘will to win’- the cerebral cortex cannot excite motor neurones.
What is fatigue called when the cerebral cortex cannot excite motor neurones?
Central command fatigue.
How are the types of skeletal muscle fibres classed?
Based on them being fast/slow shortening, and the oxidative/glycolytic pathways to generate ATP used.
Do fast-twitch fibres have high ATPase activity?
Yes.
Do slow-twitch fibres have high ATPase activity?
No.
What characterises oxidative muscle fibres?
Increased mitochondria, increased oxidative phosphorylation, increased vascularisation to deliver more oxygen and nutrients.
Why do oxidative muscle fibres have increased vascularisation?
Delivery of more oxygen and nutrients.
What molecule do oxidative muscle fibres include?
Myoglobin- increased oxygen delivery.
What does myoglobin do in oxidative muscle fibres?
Increases delivery of oxygen for oxidative phosphorylation.
What colour are oxidative fibres?
Red.
What characterises glycolytic muscle fibres?
Decreased mitochondria, more glycogen and glycolytic enzymes, lower blood supply.
What colour are glycolytic muscle fibres?
White.
Why do glycolytic muscle fibres have reduced vascularisation?
Less oxygen needed as glycolytic processes occur rather than oxidative phosphorylation.
What are the 3 types of skeletal muscle fibres?
Slow oxidative- resist fatigue
Fast oxidative- intermediate resistance to fatigue
Fast glycolytic- fatigue quickly
How do slow oxidative muscle fibres respond to fatigue?
Resist it.
How do fast oxidative skeletal muscle fibres respond to fatigue?
Intermediate resistance.
How do fast glycolytic skeletal muscle fibres respond to fatigue?
Fatigue quickly.
What is recruitment?
When an increased number of motor units is triggered.
When are an increased number of motor units triggered?
When there is an increased load.
What might an increased load lead to?
Increased recruitment of motor units.
What types of skeletal muscle fibres are recruited first?
Slow oxidative, then fast oxidative then fast glycolytic.
What is atrophy?
Decline in effectiveness.
What is disuse atrophy?
Decline in effectiveness due to muscle not being used.
What is denervation atrophy?
Decline in effectiveness due to nerve/NMJ destruction.
What does atrophy cause?
Decreases in muscle mass.
What effect does exercise have on muscle mass?
Hypertrophy (increased mass).
How is smooth muscle described?
Small, mononucleate, no striation.
What is smooth muscle innervated by?
Autonomic nervous system.
What is different in smooth muscle?
Excitation-contraction coupling.
How are actin/myosin filaments arranged in smooth muscle?
Diagonally.
How does the cross-bridge cycle work in smooth muscle?
Calcium binds calmodulin.
Calcium-calmodulin complex binds to myosin light chain kinase.
Kinase phosphorylates myosin cross-bridges with ATP.
Phosphorylated cross-bridges bind to actin and contraction can occur.
What does calcium bind to in smooth muscle?
Calmodulin.
What does calcium form when it binds to calmodulin?
Calcium-Calmodulin complex.
What does the calcium-calmodulin complex bind to?
Myosin light chain kinase.
What does myosin light chain kinase do?
Phosphorylates myosin cross-bridges with ATP- these can bind to actin and contraction can occur.
What enables contraction in smooth muscle cells?
Binding of phosphorylated myosin cross-bridges to actin- they are phosphorylated by myosin light chain kinase which is activated by the calcium-calmodulin complex.
How does smooth muscle relax?
Action of myosin light chain phosphatase- dephosphorylates the cross-bridges.
What does myosin light chain phosphatase do?
Dephosphorylates the cross-bridges to end contraction.
Where is calcium sourced from?
Sarcoplasmic reticulum Extracellular calcium (VG-channels)
Is there the same amount of sarcoplasmic reticulum in smooth muscle as in skeletal muscle?
No- smooth muscle has less.
In skeletal muscle, does one AP release enough calcium to saturate all troponin sites?
Yes.
In smooth muscle, does one AP release enough calcium to stimulate contraction?
Not always- only some sites are activated and they are graded.
What is smooth muscle tone?
Tone is a basal level of calcium in cells which means there is a constant state of tension.
Is smooth muscle always single-unit?
No- it can be single-unit (GIT, BV), or multi-unit (Airways/large blood vessels etc).c
Can an organ have different properties of single/multi-unit smooth muscle cells?
Yes- most organs have bits of both to add variation and increase ability to perform function.
