Ch. 1/11 Flashcards
Anatomy of skeletal muscles
Muscle fibers
Myofibrils
3 types of muscle tissues
Skeletal muscle: voluntary, skeleton
Smooth muscle: involuntary, hollow organs
Cardiac muscle: involuntary, heart
Review: which muscle tissue is voluntary?
Skeletal
TF: Skeletal muscle is entirely surrounded by endomysium
False
Epimysium
TF: The fascicles within skeletal muscle is surrounded by perimysium
True
SM: Consists of individual muscle cells (muscle fibers)
Fascicles
SM: Muscle fiber is surrounded by …
-consists of myofibrils divided into…
Endomysium
Sarcomeres
MF: Plasmalemma
Fuses with …
Conducts … …
Maintains … . … …
Tendon
Action potential
PH, transports nutrients
MF: Sarcoplasm: … Of muscle cell
Cytoplasm
MF: Unique features within sarcoplasm
Glycogen storage
Myoglobin
MF: Transverse tubules
Extension of …
Carries .. deep into …
Plasmalemma
Action potential ➡️ muscle fiber
MF: Stores Calcium
Sarcoplasmic reticulum (SR)
How many myofibrils per muscle fiber?
Hundreds to thousands
MS: Basic contractile element of skeletal muscle
Sarcomere
Sarcomere: Striped appearance/striations (4)
– A-bands: dark/blue stripes
– I-bands: light/pink stripes
– H-zone: middle of A-band
– M-line: middle of H-zone
Sarcomere: common boundary structure
A-disk
Sarcomere: Thin protein filament that shows up lighter under 🔬 (red)
Actin
Sarcomere: 3 proteins within Actin and their functions
– Actin: contains myosin-binding site
– Tropomyosin: covers active site at rest
– Troponin: anchored to actin, moves tropomyosin
TF: A-band contains only actin filaments
False
I-band
Actin filaments are anchored at …
Z-disk
Sarcomere: Thick filaments that show up darker under 🔬 (blue)
Myosin
TF: H-zone contains only myosin filaments
True
What band contains both protein filaments
A-band
Myosin’s globular heads protrude … from thick filaments and will interact w/… for contraction
360°
Actin filaments
Function of Titian
Stabilizes sarcomere
Centers myosin
Prevents stretching
Titin extends from … to …
Z-disk to M-band
Muscle fiber contraction starts with …
Nervous system
MFC: innervates muscle fibers and is the motor unit
α-Motor neurons
MFC: More operating motor units =
More contractile force
Events of Excitation-Contraction Coupling (6) ⭐️
- Action potential (AP) starts in brain
- AP arrives at axon terminal, releases acetylcholine (ACh)
- ACh crosses synapse, binds to ACh receptors on plasmalemma
- AP travels down plasmalemma, T-tubules
- Triggers Ca2+ release from sarcoplasmic reticulum (SR)
- Ca2+ enables actin-myosin contraction
Action potential arrives at ST from . … & causes mass release of Ca into sarcoplasm
T Tubule
TF: SR sensitive to chemical charge
False
Electrical
Ca2+ binds to … on thin filament to move …
Troponin
Tropomyosin
Cross-bridge
Myosin binds to actin,
allowing a contraction to occur
Sliding Filament theory
Myosin and actin filaments sliding past each other
SFT: When relaxed, myofilaments are stable
False
They overlap a little
SLT: Action where myosin head pulls actin towards Sarcomere center
Power stroke
TF: In actin myosin contraction, Sarcomeres, myofibrils, muscle fiber all lengthen
False
Shorten
SFT: After power stroke ends
– Myosin .. from active site
– Myosin head rotates … original position
– Myosin attaches to another active site farther .
Detaches
Back to
Down
SLT: Power stroke continues until:
Z-disk reaches … filaments
Or
AP stops, Ca get … … SR
Myosin
Pumped back into
What band does not change?
A-band
What important molecule/energy is involved in muscle contractions?
ATP
Function of ATP (2)
Binds to myosin head
Allows to release from actin filaments
What causes Rigor Mortis?
Lack of ATP production.
Cross bridges aren’t able to
detach and this causes
stiffness
When AP ends and electrical stimulation of SR stops
Muscle relaxation
TF: When muscle is relaxed, Ca is pumped out of SR
False
Pumped back into SR
Review: During muscle contraction, which one(s) shorten
H zone
I band
What prevents actin-myosin cross bridging?
Troponin and tropomyosin
Small (10-100 g) piece of muscle removed
Frozen, sliced, examined under microscope
Muscle biposy
Muscle Fiber Types:
-Slow form of myosin ATPase
-Peak tension in 110ms (slow twitch)
- ~50% of fibers in avg muscle
Type I
MF Type:
-Fast form of myosin ATPase
– Peak tension in 50 ms (fast twitch)
– Type IIa (~25% of fibers in an average muscle)
– Type IIx (~25% of fibers in an average muscle)
Type II
T1F: Efficiently produces ATP for … of fat & carbohydrates
Oxidation
T1F: Recruited most often during …
low-intensity
– aerobic exercise (e.g., marathon running)
– daily activities (walking)
– posture
T2F: Produces ATP through
Anaerobic pathways
Which muscle fiber has high aerobic endurance?
Type I Fibers
T2F: Type that involves more force and is more easily fatigued
*Used for short-high intensity events
Type IIa fiber
T2F: Type seldom used for everyday activities
*Short, explosive activites
Type IIx
Fast myosin ATPase =
Slower myosin ATPase =
Fast contraction cycling
Slower contraction cycling
Which type of fiber has a more developed SR?
Type II fibers
Motor units between Type I & Type II
Type I motor unit:
smaller neuron, <300 fibers
Type II motor unit:
larger neuron, >300 fibers
Peak power of fibers from greatest to smallest
Type IIx > type IIa > type I
Most influential in determining percentage
Genetic factors
TF: Arm and leg ratios are similar in one person
True
TF: Type I predominates in power athletes.
Type II predominates in endurance athletes
False
Switch athletes
TF: Soleus is type II in everyone
False
Type I
Other predictors of athletic success
– Cardiovascular function
– Motivation
– Training habits
– Muscle size
When a motor unit is recruited,
ALL of its fibers are activated
Motor unit recruitment
MFR: Method for altering force production
– Less force: fewer or smaller motor units (type I)
– More force: more or larger motor units (type II)
Recruitment Order of fibers (size principle)
– First: Smallest (type I) motor units
– Next: Midsized (type IIa) motor units
– Last: Largest (type IIx) motor units
order of recruitment
of motor units directly related to size of α-motor neuron
Principle of orderly recruitment
(size principle)
OR: Smaller motor u it’s are recruited first as … threshold
Low
OR: Higher threshold Motor units are recruited based on..
Increasing demand of activity
Types of dynamic muscle contraction
Concentric
Eccentric
MC:
• Muscle shortens while
producing force
• Sarcomere shortens,
filaments slide toward center
Concentric contraction
MC:
• Muscle lengthens while
producing force
• Cross-bridges form but
sarcomere lengthens
Eccentric contraction
MC: Muscle produces force but does not change length
Static (isometric) contraction
Factors for amount of force developed (NT,S,FS,MS,SC)
- Number and type of motor units activated
- Size of the muscle
- Frequency of stimulation of each motor unit
- Muscle fiber and sarcomere length
- Speed of contraction
NT:
• Type I motor units = .. fibers = .. cross-bridges =
.. force
• Type II motor units = .. fibers = .. cross-bridges =
.. force
Less
More
MS:
• Large muscles = more fibers = more cross-bridges =
more force
• Smaller muscles = less fibers = less cross-bridges = less
force
FS: Contractile response to SINGLE electrical stimulus
Twitch
FS: CONSECUTIVE STIMULI for greater force
Summation
FS: CONTINUED stimulation resulting in peak force
Tetanus
LT: Fibers have … length for force production
Optimal
LT: Optimal sarcomere length =
– Maximizes cross-bridge interaction
Optimal overlap of actin/myosin
Optimal sarcomere length =
– Maximizes cross-bridge interaction
Optimal overlap of actin/myosin
LT: Too short or too stretched =
Little or no force develops
Ability to develop force
also depends on speed
of contraction
Speed-Force relationship
SF: maximal force
development decreases at
higher speeds
Concentric
SF: maximal force
development increases at
higher speeds
Eccentric
