06 - Skeletal Muscle Anatomy & Physiology Flashcards
What are the 3 types of muscles?
Smooth muscle
Cardiac muscle
Skeletal muscle
What jobs can muscle types perform?
Movement
Stabilization
Storing & moving substances
Generating heat
How do the types of muscles differ?
Morphology (how they look)
Body location
Funstion
Method of activation (contraction)
Put the different types of muscle cells in order from the smallest to the largest
Smooth muscle cell (smallest)
Cardiac muscle cell
Skeletal muscle cell (largest)
What are the key features of skeletal muscles?
- Massive
- Muscle fibre (one cell but very big)
- Has a lot of nuclei in one cell
- Voluntary
Where are skeletal muscle cells found?
MSK system
- Musculoskeletal system
Where are cardiac muscle cells found?
Heart
Where are smooth muscle cells found?
Hollow organs
Morphology of skeletal muscle cells
Striated, multinucleated
Morphology of cardiac muscle cells
Striated, 1-2 nuclei, branched
Morphology of smooth muscle cells
No striations, single nucleus, spindle shaped
Gap junctions in skeletal muscle cells?
No
Gap junctions in cardiac muscle cells?
Yes
- Intercalated disks
Gap junctions in smooth muscle cells?
Yes
Do cardiac muscle cells have autorhythmicity?
Yes
Do skeletal muscle cells have autorhythmicity?
No
Do smooth muscle cells have autorhythmicity?
Yes
What’s the speed of contraction of skeletal muscle cells (in comparison to the other 2 types of muscles)?
Fast
What’s the speed of contraction of cardiac muscle cells (in comparison to the other 2 types of muscles)?
Moderate
What’s the speed of contraction of smooth muscle cells (in comparison to the other 2 types of muscles)?
Slow
What is skeletal muscle regulated by?
Somatic nervous system
What is cardiac muscle regulated by?
Autonomic nervous system
Hormones
Pacemaker cells
What is smooth muscle regulated by?
ANS
Pacemaker cells
Hormones
Stretching
What nerve controls the contraction of skeletal muscles?
Peripheral nerves
- Peripheral nerve axons originate from motor neuron cell bodies in the spinal cord (somatic)
Which muscle type contraction accounts for all voluntary body movements?
Skeletal muscle
Layers of connective tissue that wrap around skeletal muscle
Endomysium
Perimysium
- Fascicle
Epimysium
What does endomysium surround?
Endomysium: surrounds each individual muscle fibre/cell
- endo - in, within
What does perimysium surround?
Perimysium: surrounds a bundle of muscle fibres
- peri - around
What does epimysium surround?
Epimysium: surrounds the entire muscle
- epi - on, upon
What are fascicles?
Fascicle: a bundle of fibres wrapped in perimysium
What are skeletal muscle cells also known as?
Skeletal muscle fibre
Myocyte
- myo - muscle
- cyte - cell
Around 50% of the cells in muscle is ______ that makes up the matrix?
Fibroblast
What does the 3 layers of connective tissues that wraps around skeletal muscle become?
Tendon
- All 3 layers contribute to the muscle sheath and become the tendon
What is the tendon continuous with?
The periosteum of bone
- pero - around
- osteum - bone
What is aponeurosis? Give an example
Broad flat tendon
eg. external obliques
What’s the order of the connective tissues (smallest to bigger) wrapping skeletal muscle?
Muscle fibre –> endomysium –> perimysium –> epimysium
- These forms a tendon
What are muscle cells filled with?
Myofibrils
What are myofibrils?
Sarcomeres in series
What are sarcomeres?
The basic contractile unit of muscle
- Responsible for muscle contraction
What is the smallest contractile unit in a skeletal muscle cell?
The sarcomere
What is the thick filament in a myocyte?
Myosin
What is the thin filament in a myocyte?
Actin
What has cross-bridges?
Myosin
- Thick filaments
What is from 1 z line to another z line?
Sacromere
What are the lines & bands & zones in a sacromere?
I band
A band
H zone
M line
Z line
What zone is shrinking during muscle contraction?
H zone
- Bring it closer to the center during muscle contraction
What are the lighter areas in a sarcomere?
I bands
- two 1/2 I bands
- B/c there are very little proteins therefore light can pass through easily
What are the darker zones in a sarcomere?
A bands
What are the lighter regions in a sarcomere called?
Isotropic regions
What are the darker regions in a sarcomere called?
Anisotropic regions
- an - without –> not letting light through
Largest protein in the body
Titin filament
What does the titin filament do (in a sarcomere)?
Attached to the M line
- Always ensure that the myosin filaments are always in the center of the sarcomere
- Keeping them there so they don’t go left or right
Titin filament properties
Elastic
- Got coils
- Can be stretched and it will recoil back to its original position
What is the M line in a sacromere?
A protein that bundles together the myosin filament
What are the 2 ways to get bigger muscles?
- Increase the # of muscle cells
- Make the muscle cells bigger
Can all muscles increase the number of cells?
No
Not possible with skeletal muscle (can not create new muscle cells)
Possible with smooth muscle - hyperplasia
Why can you not make new skeletal muscle cells?
B/c who would control them?
- Each muscle cell is controlled by a motor neuron that originates from your cerebral cortex
- In order to do useful work, you can’t interrupt that connection therefore can not make new skeletal muscle cells
How to make skeletal muscle bigger?
Make the muscle cell bigger
- Do so by putting stress on the cells
- Use those muscles –> it will grow
- Don’t use those muscles –> you will lose it
Why might you lose skeletal muscle cells if you don’t use them?
B/c skeletal muscle cells take a lot of energy to keep it going (even at rest)
- Consumes a lot of ATP and amino acids to make the proteins (the contractile filaments inside that muscle)
How do muscles enlarge with use?
By adding sarcomeres
- Exercise stimulates production of actin and myosin filaments
- Increased number of myofilaments expands the fiber causing muscle enlargement and definition
What is the process called when your muscles enlarge with use?
Hypertrophy
- hyper - increase
- trophy - food
A process where we get a lot of nutrients to the muscle and it’s getting bigger
What causes fibre atrophy?
- Decrease sarcomere
- Immobilization (eg. cast)
- Weightlessness (eg. space flight)
- Denervation (eg. spinal cord injury)
What causes fibre hypertrophy?
- Increase sarcomere
- Training (eg. resistance training)
Atrophy
Losing muscle (not actually losing the muscle fibre but it’s shrinking)
Atrophy
- a - without
- trophy - food (nutrition)
What is the term for growing muscle?
Hypertrophy
What is the term for losing (shrinking of the) muscle?
Atrophy
What is the sliding filament theory?
Filaments slide past one another = shortening
- Thin actin filaments slide over the thick myosin filaments
- Requires an increase in Ca2+
- Repeated binding cycles between actin and myosin
How do filaments shorten?
The Z lines gets closer (the sarcomere shortens)
In a contraction what is shortening? What has no change?
Shortening: sarcomere, H & I bands
No change: A band
Why does I band APPEAR to shorten?
The proteins in there (actin and myosin) are not actually shortening
- There’s just an increase in their overlap
Does the sliding filament theory happen in 2D or 3D?
3D
What is the interaction between myosin and actin in 3D?
1 thick filament pulls on 6 thin filaments
1 thin filament can connect to 3 thick filament
- Myosin has “little arms” (cross-bridges) that can reach out in many different directions
How does the ATPase activity of myotin work?
Myosin has ATPase (an enzyme that breaks down ATP) activity
- The enzyme transfers the energy from ATP into the myosin head to change its configuration and shape
- Thus the myosin head can pull actin toward the center of the sarcomere
- Transfering energy to movement
Which direction does the myosin head point to?
Towards the center (both sides)
- B/c both sides are pulling actin in towards the center of the sarcomere
Where is the binding cite in thick filament?
Myosin heads
What is the thick filament made of?
End to end myosin molecules
What does a myosin consist of?
Myosin head
- Actin binding sites
- Myosin ATPase
Tail
Hinge
What is the regulator of muscle contraction? Think in terms of the filaments
Thin filament
- Determines when the muscle contracts
- By Ca2+
What does a thin filament consist of?
2 coiled chains of actin molecules
Tropomyosin
Troponin
What does the tropomyosin molecule do?
Tropomyosin molecules run along actin, blocking cross bridge binding site
What does troponin molecule do?
Troponin holds tropomyosin in place
What binds to troponin?
Ca2+
What happens when Ca2+ binds to troponin?
Ca2+ binds troponin, changes its confirmation which pulls tropomyosin away from the cross bridge binding site
- This allows for actin-myosin interaction to occur
When Ca2+ is removed, tropomyosin moves back to block cross bridge binding site (no actin-myosin interaction).
Can sarcomere lengthen?
No, they can only shorten (can not lengthen)
- can only pull not push
Steps in the cross-bridge cycling
- Energizing myosin
- ATP already bound to myosin
- ATP breaks into ADP+Pi (energized myosin) - Actin-myosin binding
- Actin binds to myosin when Ca2+ is available - Cross-bridge movement: POWER STROKE
- Energy stored in myosin used
- Cross-bridge moved
- Sarcomere shortens- Thick pull thin filament
- ADP & Pi released
- Thick pull thin filament
- Breaking the cross-bridge
- ATP binds to myosin
- Breaks the actin-myosin bond
Cycle restarts
What is the regulator of cross bridge cycling?
Ca2+
What breaks the actin-myosin bond in the cross-bridge cycling?
ATP
- ATP present –> breaks the bond & release the thick from thin filament
- If you’re alive this will happen
- If you’re dead –> no ATP –> no release
What is excitation-contraction coupling?
Electrical signal (excitation) from brain along motor neuron tells a muscle to move (contraction)
- Anything that increases the amount of Ca2+ will cause a contraction
What determine if muscle contracts or not?
Motor neuron
Excitation
Action potential (AP) travels to the axon terminal (neuromuscular junction)
Where are APs propagated down to in muscle fibres?
T-tubules
- Muscle fibres are large, so to get deep into them, the AP is propagated down the T-tubules
Steps of excitation contraction coupling
Neurotransmission
Action potential
T-tubules
Sarcoplasmic reticulum (terminal cisternae)
Release of Ca2+
Contraction
What is the specialized area where Ca2+ are stored?
Terminal cisternae
What are T-tubules?
T-tubules are invaginations of the membrane (allow APs to go deep inside the cell to deliver the message)
What is a triad?
1 T-tubule & 2 terminal cisternae
What proteins link the T-tubules and the sarcoplasmic reticulum?
DHP receptor
Ryanodine receptor
When does relaxation occurs?
When Ca2+ is re-sequestered
Steps in the release of Ca2+ to muscle contraction
- Muscle AP propagated down the Transverse tubule (T-tubule)
- Ca2+ released from terminal cisternae
- The ryanodine receptor is like a plug to the terminal cisternae (where Ca2+ are stored)
- AP triggers the movement of the DHP receptor which moves the ryanodine receptor
- The “plug” is moved, thus Ca2+ are released - Ca2+ binding to troponin removes blocking action of tropomyosin
- Cross bridge moves
- Ca2+ taken up to the terminal cisternae
- Ca2+ removal from tropin restores tropomyosin blocking action
What is happening in the latent period in excitation-contraction coupling?
Sending AP to get Ca2+
- Very short
Factors regulating force production
- Muscle length
- Action potential frequency
- Number of fibres per motor unit and the cross-sectional area of those muscle fibres (how many fibres will active)
What is a motor unit?
One motor neuron and all the muscle fibres it innervates
How does muscle length regulate force production?
Too stretched or too compressed decreases force production
How does AP frequency regulate force production?
Summation of stimulation
- Of Ca2+
- Single twitch
- Wave summation
- Unfused tetanus
- Fused tetanus
What is tetanic force?
Multiple APs in a row
More Ca2+
Every cross bridge can be activated
Stronger contraction
How does # of fibres per motor unit regulate force production?
The size of the motor unit determines the amount of force produced
- 1 motor neuron branch to several muscle fibres
- When it send signal, all muscle fibres connected will contract
What are different types of motor units based on?
Muscle fibre types
- Muscle fibre differ in size and ease of activation
What are skeletal muscle fibre types based on?
Speed of contraction and/or metabolic profile
What are the skeletal muscle fibre types?
- Slow and fast fibres
- Oxidative and glycolytic fibres
Skeletal muscle fibre types:
Speed of contraction
Slow and fast fibres
- Dependent on the rate of myosin ATPase action
- Slow fibre types contract more slowly but are more fatigue resistant
- Fast fibres generate more power but fatigue more rapidly
Skeletal muscle fibre types:
Metabolic profile
Oxidative and glycolytic fibres
- Oxidative fibres
- Glycolytic fibres
What does oxidative fibres use?
Primarily use O2 for ATP production (aerobic)
What does glycolytic fibres use?
High capacity for ATP production without O2 (anaerobic)
What are the 3 skeletal muscle fibre types?
Slow oxidative
Fast oxidative glycolytic
Fast glycolytic
Order the skeletal muscle fibre types in order from the most fatigue resistant to the most easily fatigued
Slow oxidative (fatigue resistant)
Fast oxidative glycolytic (less fatigue resistant)
Fast glycolytic (quickly fatigued)
Order the skeletal muscle fibre types in order of the smallest diameter to the larger diameter
Slow oxidative (small diameter)
Order the skeletal muscle fibre types in order of blood supply
Slow oxidative
- Rich blood supply
Fast oxidative glycolytic
- Rich blood supply
Fast glycolytic
- Few capillaries
What respiration does each skeletal muscle fibre type use?
Slow oxidative
- Aerobic respiration
Fast oxidative glycolytic
- Aerobic & anaerobic respiration
Fast glycolytic
- Anaerobic respiration
What are each skeletal muscle fibre types most used for?
Slow oxidative
- Posture & endurance
Fast oxidative glycolytic
- Walking & sprinting
Fast glycolytic
- Power movements
Motor unit recruitment order
- Slow oxidative
- Fast oxidative glycolytic
- Fast glycolytic
- Motor units are recruited in this order during EVERY task
- Everytime start with the smallest one (slow-oxidative) then if need more then increase
What does the motor unit recruitment depend on?
SIZE principle - motor units are recruited (activated) according to size (first to be recruited are Slow Oxidative, then Fast Oxidative Glycolytic then Fast Glycolytic)
- In this way, fatigue resistant fibers are always first
- The number of motor units recruited depends on the force required to perform the task
