L3 Striated Muscle Physio Flashcards
Layers in skeletal muscle
Epimysium (surrounds entire muscle)
Perimysium (surrounds each fascicle)
Fascicle (group of muscle fibers)
Endomysium/Sarcolemma (surrounds ind. fibers)
Myofiber/muscle cell
Myofibrils (repeating sarcomeres of thick and thin filaments)
Myofilaments (M-A filaments, 40 make up a myofibril)
*All connective tissue ends up in the tendon
Functional characteristics of skeletal muscle
Striated muscle, multi-unit
Physical characteristics of smooth muscle
2
Functional characteristics of smooth muscle
Single and multi-unit
Physical characteristics of cardiac muscle
2
Functional characteristics of cardiac muscle
Striated muscle, single-unit
Characteristics of myosin
Binds actin (at head)
Has ATPase activity (at head)
2 heavy chains make tail with 4 light chains at 2 heads (crossbridges)
What happens at the NMJ?
- AP impulse arrives
- Depolarization causes vesicles to fuse to end plate
- ACh release and diffuses across cleft
- ACh binds at post-synaptic receptor sites in the muscle
- Na channels open and Na influx occurs
- Depolarization of muscle cell
- If threshold reached, AP occurs, travels down sarcolemma and muscle contract
Chemical steps in crossbridge cycle
A + M, ADP, Pi (high actin affinity) Binding A-M, ADP, Pi Product release (-ADP, -Pi) A-M (cycle stops here if no ATP= rigor mortis) ATP binding (+ATP) A-M, ATP (low actin affinity) Dissociation p and partial p hydrolysis A + M, ADP, Pi (cycle stops here in relaxed living muscle)
Mechanical steps in crossbridge cycle
Ca binds to troponin-C
Myosin binds to actin
Powerstroke
Myosin hydrolyzes ATP and releases
How does crossbridge cycle result in shortening of muscle fiber?
Actin filaments are attached to Z line, bend in myosin pulls actin filaments towards H zone, sarcomere shortens and muscle contracts (sliding filament model)
What is the Length-Tension relationship?
If sarcomere is too short- there is steric hindrance between actin and myosin heads
If sarcomere is too long- there aren’t enough overlapping crossbridges, so there is less force
-There is an ideal length where there isn’t steric hindrance of A-M heads, but there is still crossbridge overlap to produce the optimal force
-Heart fxns at this optimal level- becomes stronger muscle as it is filling with blood
Explain curve shape of L-T diagram
As sarcomere length increases, stress on muscle cell increases until the length becomes too long and stress drops due to lack of available crossbridges
Force-Velocity relationship
Contracting a muscle without changing length, V=0
-Lifting a weight that = max. force of muscle
-Depends on # of A-M interactions
As weight drops, muscle can shorten with faster V
-No load= max V, depends on A-M ATPase activity
As weight increases, muscle lengthens with faster V
What is isometric muscle contraction?
Muscle is actively help at a fixed length
What is isotonic muscle contraction?
Muscle is actively contracting at constant force/load,
- No change in tension, muscle’s length changes
- Heart, lifting an object, walking, running
Explain differences in EC coupling in skeletal vs. cardiac muscle
Skeletal muscle: mechanical EC coupling
- DHPR is voltage sensor in T tubule, mechanically linked to RyR in SR, opens RyR when AP arrives and Ca released
- Every skeletal muscle cell has nerve connected to it- can control which fibers response to AP
Cardiac muscle: CICR
- DHPR is Ca channel that opens when AP arrives, Ca influx stimulates opening of RyR on SR and Ca release
- There isn’t a nerve for each muscle cell, controlling how much Ca goes through allows for regulation of force/which cells are activated
What is the sarcomere?
Contractile unit of the muscle cell
1 sarcomere= Z line to Z line
What makes up a sarcomere?
- A band= dark, thick myosin filaments with some overlapping thin actin filaments
- I band= light, thin actin filaments
- Z line= where actin filaments attach, connects to EC matrix and transmits force of contraction
- M line= proteins that anchor myosin filaments together
Characteristics of thin actin filament
F-actin make double strand helix
Made up of actin, tropomyosin and troponin- T, I, C
-T binds tropomyosin and actin
-I blocks myosin binding site, prevents muscle contraction
-C binds Ca: Ca binding makes A-M binding site free
What is the Transverse tubule?
T-tubules are dips in sarcolemma membrane that go deep into muscle, carry AP down into muscle to DHPR voltage sensor for Ca in SR
What is the sarcoplasmic reticulum?
SR is ER in the muscle that contains Ca stores, RyR mechanical Ca channel is connected to DHPR of T-tubules and is opened with AP arrives
What is the muscle triad?
1 T-tubule and 2 lateral SR sacs
What is SERCA?
Ca ATPase that pumps Ca back into SR to restore the Ca gradient
What is EC coupling?
Excitation-contraction coupling is where electrical membrane depolarization is transformed into chemical signals to initiate muscle contraction
-Ca is the link
Steps in EC coupling
- AP travels into T tubule
- Depolarization of DHPR
- Mechanical link to RyR causes conformational change
- RyR channel opens and Ca released from SR
- Ca initiates muscle contraction
- SERCA pumps Ca back into SR (muscle relaxes)
Steps in muscle contraction
- EC Coupling
- Ca binds troponin-C
- Troponin-I and tropomyosin move into actin groove
- Myosin binds to actin
- Crossbridge cycle/ powerstroke
- Ca sequestration= relaxation
When does myosin have the highest affinity for actin?
Right after the hydrolysis of ATP
When are ADP and Pi released during the cross-bridge cycle?
After myosin and actin bind
What things help to regulate strength of muscle contraction?
- Twitch summation
- Recruitment of additional motor units
- Muscle fiber thickness
- Length of fiber at onset of contraction (length-tension relationship)
What is twitch summation?
Length of twitch is longer than a single AP, so multiple APs can fire during a single muscle twitch= cumulative increase in Ca= more available actin filaments= more muscle contraction
What is recruitment of motor units?
Picking additional fibers to turn on and fuse their APs together to get a stronger contraction
How does muscle fiber thickness affect contraction?
More sarcomeres in parallel have a summative force
More sarcomeres perpendicular shorten more
Power-stress curve
Heart functions at the peak of the power-stress curve
What are the two types of isotonic contraction?
Concentric- muscle actively shortening, tension rises to meet resistance
Eccentric- muscle actively lengthening (damaging, muscle injury and soreness, increases muscle strength), lengthening due to resistance being greater than force muscle produces
What are 3 sources of muscle ATP?
- Creatine phosphate: Creat-P + ADP –> Creat + ATP
- first energy store used and depleated - Oxidative phosphorylation
- requires O2, muscles w/ high demand = red b/c of myoglobin - Glycolysis
- anaerobic, less efficient
What muscle fiber types are there?
Type 1- Slow fibers (endurance)
Type 2- Fast fibers
-2A= Red, fatigue resistant
-2B= White, fatiguing
