Striated Muscle Flashcards
What is the difference between isometric and isotonic contraction?
isometric –> same length
isotonic –> same force
What isa motor unit?
Single motor neuron and the muscle fibers it innervates
What are the 3 necessary components that cause muscles to contract?
- CALCIUM
- actin & myosin
- ATP
What 2 types of muscle are started muscle?
- Cardiac
2. Skeletal
What are the 2 components of smooth muscle that distinguish it from striated muscle?
composed of
1. Single Unit
(does not need nerve for each cell since impulses can be spread by way of gap junctions)
- Multi unit (NEED motor neuron innervation for all cells)
What type of muscle is found in stomach, bladder, uterus, and blood vessels?
Smooth muscle
What do both skeletal muscles & multi-unit smooth muscles have in common?
- Motor unit composition
2. Motor nerve REQUIRED
What do cardiac & single-unit smooth muscle cells have in common?
- Functional Syncytium (working together)
2. Automaticity
What are the 4 major characteristics of muscle?
- Contractility
- Excitability
- Extensibility
- Elasticity
What are the 3 main functions of muscles?
- Motion
- Maintenance of Posture
- Heat Production
Define the following:
- Fascicles
- Myofiber
- Myofibrils
- Myofilaments
- group of muscle fibers
- 1 muscle fiber/muscle cell
- made of sarcomeres
- Myosin & actin filaments
What makes up myofibrils and is termed the BASIC CONTRACTILE UNIT?
Repeating SARCOMERES
Name the term for the following definitions:
- surrounds individual fibers, contains capillaries
- Surrounds each fascicle, contains blood vessels and nerves
- surrounds entire muscle
- Endomysium
- Perimysium
- Epimysium
What are the 3 components of a tendon?
- Epimysium
- Perimysium
- Endomysium
–> at the end of muscles
What does each fasicle in muscle contain?
Bundle of muscle fibers
- cells
What is found in each muscle fiber? What 2 types of filaments is this composed of?
- Myofibrils
2. Thick & thin filaments
What gives muscle a striated appearance?
Arrangement of filaments
What is the basic contractile unit and what is it composed of?
SARCOMERE
(z-line to z-line)
- A band
- I band
- M line
- Z line
- H zone (in A band)
Name the components of the following:
- A band
- I band
- M line
- Z line
- dark - thick filament of myosin & some overlapping thin filaments of actin
- I = light = ACTIN ONLY!!
- Mline - proteins that anchor thick filaments
- Z - where actin filaments attach*
What is the I band composed of?
Actin only!
Where does calcium bind in the sarcomere? What moves out of the way to allow myosin head to bind to actin?
- Troponin - C
2. Tropomyosin
What is not found in smooth muscle that is in striated? What is common to both?
- Troponin
2. Tropomyosin
What is the only aspect of a sarcomere that does not move?
Z line
What binds actin and has ATPase activity: myosin or actin?
MYOSIN!!!
What is myosin composed of?
- 2 heavy, 4 light chains
2. tail & two GLOBULAR heads (cross-bridge)
What aspect of Myosin binds actin & contains ATPase activity?
GLOBULAR HEAD
- each head oriented 120 degrees from next pair, so myosin thick filaments interact w/ thin filaments
What are the 3 components of the THIN filament?
- ACTIN
- Troponin (I, T, C)
- Tropomyosin
How many tropomyosin and troponin complexes per 7 actin monomers?
1!
What type of actin is made of many double stranded helices? What type of monomers is it composed of?
- F-Actin (Filamentous)
- made of G actin monomers
(globular)
G actin has the binding site for what?
MYOSIN
What is the position of Actin at rest? When activated?
At rest:
binding site blocked by the troponin-tropomyosin complex (troponin anchored to tropomyosin)
Activated:
troponin-tropomyosin move into the “actin groove”,
Myosin binding site on actin is exposed (when calcium binds to tropomyosin)
What makes up more than 70% of all MYOFIBRILLAR protein?
Actin & Myosin
Define the following:
- Sarcolema
- Transverse Tubules (T-tubule)
- SR
- Muscle Triad
- Plasma membrane of muscle
- invaginations of sarcolemma into muscle fiber
- smooth ER of muscle
- 1 t-tubule w/ 2 lateral sacs of SR
Which part of the muscle conducts the AP & are closely apposed to SR?
T-Tubule
Where is calcium stored in a muscle?
Sarcoplasmic Reticulum
What is the function of Dihydropyridine Receptor (DHPR)? Where is it found?
- Voltage sensor
2. on T-tubule
What is the function of Ryanodine Receptor (RyR)? Where is it found?
- Calcium releasing channel
2. Found on the SR
What is the Calcium ATPase (calcium pump) in the SR membrane? Where and why does it pump calcium?
- SERA (sarcoplasmic & ER reticulum ATPase)
2. into the SR lumen to restore Calcium gradient
How does the Nervous System communicate with muscle?
NMJ
- neuromuscular junction
- similar to a synapse between neurons (
What NT does an NMJ use? What type of receptor is at the post-junctional membrane of NMJ?
- Acetylcholine
- AchR = NICOTINIC (enzymes break down acetylcholine)
- activated by ACh –> opens as a cationic channel
An action potential carried down the T-tubule causes the release of what? What occurs after this has been released?
Calcium
- Troponin binds Calcium
- tropomyosin moves
- myosin thick filament binds thin filament (actin)
- cross-bridge mechanically cocks and pushes the actin along w/ the use of ATP
What is the process whereby MEMBRANE depolarization (electrical) is transformed into a chemical signal to initiate muscle contraction?
Excitation - Contraction Coupling
- calcium is the link
- AP sent down, then calcium released
What are the 6 steps in EC?
- Action potential travels into T-tubule
- Depolarization activates DHPR
- DHPR conformational change activates RyR
- Ca2+ release from SR
- Ca2+ initiates muscle contraction
- SERCA pumps Ca2+ back into SR lumen (muscle relaxes)
What activates DHPR? What activates RyR?
- Depolarization
2. DHPR conformational change activates RyR
What are the 6 steps in muscle contraction?
- Excitation-Contraction Coupling
- Ca2+ binds troponin
- Troponin/tropomyosin move to actin groove
- myosin binds actin
- Crossbridge cycle/Powerstroke
- Calcium sequestration = relaxation
How does a muscle relax?
SERCA pumps Calcium back into SR
What is the universal trigger for muscle contraction?
CALCIUM RELEASE
What are 3 main events during muscle contraction?
- AP
- Myoplasmic Calcium release
- Twitch Force
What regulates striated muscle contraction?
Thin filament regulatory proteins
- troponin, tropomyosin
What are the 5 steps that occur during activation by Calcium release from SR? = CROSS - BRIDGE CYCLE
- Calcium binds Troponin C
- COnformational change in Tropomyosin, Troponin I has low affinity (inhibitory)
- Tropomyosin and troponins move into actin groove
- Myosin binding site on ACTIN exposed
- Mysin binds actin = CROSS BRIDGE CYCLE
What occurs in muscle in the absence of ATP?
Rigor Mortis
Because the basic cross-bridge mechanism is the same in all muscles, what is the only thing that differs?
HOW ACTIVATION OCCURS
Sarcomere filaments change lengths. True or False?
FALSE
- merely slide past one another
What are 4 ways to regulate the strength of muscle contraction?
- Twitch summation
- Recruitment of motor units
- Muscle fiber thickness
- Length of fiber at onset of contraction
What type of muscle is all or none?
SKELETAL
- in cardiac & smooth, stronger contraction is a result of increased calcium release = increase FORCE
How is the force exerted by the muscle controlled for skeletal muscle?
frequency of AP’s sent to fibers
- multiple AP’s can fire during a single muscle twitch
- each AP cause more Calcium release
- cumulative increase in Calcium = more thin filaments available = more cross bridges interact
What is tetanus?
Steady state force –> constantly keeping calcium release channel open (RyR)
= increased yet steady stimulation until stimulation ends or FATIGUE
How should a sarcomere be organized to increase force? To maintain force, but shorten muscle?
- Stack in PARALLEL (on top of one another)
2. Stack in SERIES (next to)
How much force does each muscle fiber produce?
0.3 N (pico-newtons)
What does the length tension graph look like? What happens if sarcomere is too short? Too long?
Hyperbola
- too short = too much steric hindrance
- too long - not enough cross-bridge overlap= LESS FORCE –> force decreases as pass intermediate length/tension
What prevents stretching a muscle apart completely?
TITIN
- source of passive force
What is the relationship between increasing velocity and force? Slow velocity?
INVERSE
- increase velocity, force decreases ( P= F *V)
P = W/T - decrease velocity when using LARGE force
What type of load does POWER peak?
INTERMEDIATE
- hyperbola (upside down U)
More or less force can be generated by what?
the load = stress
max stress = low velocity
What are 2 types of isotonic contractions? What remains unchanged in isotonic contraction?
- Eccentric
- Concentric
- TENSION is unchanged
- length changes***
What type of contraction involves muscle actively shortening? Lengthening?
- Concentric (tension same as muscle shortens)
2. Eccentric
What remains the same in isometric contraction?
Muscle LENGTH
What type of injury results from pedaling against a force? How can this be detected?
ECCENTRIC
- detect w/ serum CK levels
- Z disk misaligned***
What accounts for the main ATP consumption mechanism in Contracting Muscle?
Actomyosin ATPase
- others include:
SERCA, Na/K ATPase (10%)
What are 3 sources of ATP production?
- Creatine Phosphate - 1 ATP rapidly released
- Oxidative Phosphorylation - 30 ATP
- Glycolysis - 6 ATP
What is the first energy store used & depleted during muscle contraction?
Creatine Phosphate
- catalyzed by CK (Creatine Kinase)
What process produces lactate? Is this anaerobic or aerobic?
Glycolysis = anaerobic
- net 6 ATP
What make muscle red?
Myoglobin
- uses O2
- lots of mitochondria
What do source of ATP production do postural muscles use?
Oxidative Phosphorylation ( lots of ATP, but slowly produced)
What is muscle fatigue? Neuromuscular fatigue?
- lactate made from glycolsis when not enough O2
- Myasthenia Gravis
What are the main differences between Type 1 and Type 2 fibers?
Type 1 = slow, use oxidative phosphorylation (after creatine used up)
- not easily fatiguable
- POSTURAL muscles
- lots of mitochondria
Type 2:
fast twitch, GLYCOLYSIS
- produce lactate = easily fatiguable
- less mitochondria & myoglobin
If you were training for distance running, which type 2 fiber is best? For sprinting?
- Red Type 2A (fatigue resistance is higher)
2. White type 2B (low fatigue resistance, but for sustained phasic activity)
What is the main differencce in EC Coupling between skeletal and cardiac muscle?
DHPR
in Skeletal - voltage sensor (mechanical coupling)
in cardiac - calcium induced calcium release –> DHPR used as a channel
