Muscle Flashcards
Muscle makes up ______ of mass in humans
30-50%
What are the two types of striated muscle
Skeletal and cardiac
What is the non striated muscle type
Smooth
What is the only voluntary muscle type
Skeletal
Where is the site of most ANS innervation and function
Smooth muscle
What is the order of how a muscle is packed?
Muscle-fascicles-fibers(myocyte)-sarcomeres
Long, thin cell with multiple nuclei and many myofibrils
Muscle fiber (myocytes)
What is the muscle cytoplasm
Sarcoplasm, lots of mitochondria
What does each myofibril consist of
Many sarcomeres surrounded by the sarcoplasmic reticulum and T tubule system
Highly organized contractile and structural proteins
Sarcomeres
What muscle type does not have sarcomeres
Smooth
Thick and thin filaments
Contractile proteins
Thick filament
Myosin
What does myosin consist of
- intertwined heavy chains with globular heads
- heads bind actin and have ATPase activity
What is the makeup of actin
2 strands of F actin in a helix
What is F actin made of
Many G actin molecules
Where are hte myosin binding sites
Actin
Double stranded helix around actin. Covers the myosin binding site
Tropomyosin, regulatory
What is bound to tropomyosin
Troponin complex
Troponin T (TnT)
Binds the complex to tropomyosin
Troponin I (TnI)
- inhibitory
- holds tropomyosin in the myosin binding site
Troponin C (TnC0
Binds calcium, uncovers myosin binding site
Connect sarcomeres to sarcolemma and ECM
Dystrophin
What is the most common mutation that causes muscular dystrophy
Mutations in dystrophin
Holds thin filaments apart from one another
Nebulae
Holds thin filaments to z-disc
Alpha-actinin
Spring that runs though heavy chain and connects it to the z disc
Titan
Bisects the sarcomeres and bare zone, structural proteins that hold thick filaments in place
M line
Only heavy chains
Bare (H) zone
Thick and thin filaments, dark striations
A band
Only thin filaments, light striations
I band
Connects individual sarcomeres, bisects I band
Z-disc
Functional unit of muscle
Sarcomeres
Smallest part of muscle that can still perform its function, to contract and generate force
Sarcomeres
How does the sarcomeres shorten when stimulated
- actin is pulled towards M line
- bare zone gets smaller
- occurs along length of myofibril, fiber, fascicle, and muscle- causes movement
____ discs move closer together during sarcomeres contraction
Z disc
What happens to I band when sarcomeres contracts
Gets smaller
What happens to A band when sarcomere contracts
Stays the same
Where does the soarcolemma membrane cross myocyte
Between myofibrils
Myocytes are arranged to handle
Calcium to help depolarization of whole muscle as a unit
What is within the sarcolemma membrane
- T tubules
- dihydropyridine receptor (DHPR, voltage gated calcium channel)
____ stores calcium in the sarcolemma
Sarcoplamic reticulum
How does sarcoplasmic reticulum store calcium
- has SERCA (Ca2+-ATPase)
- most prevalent in the longitudinal SR
- pumps Ca2+ in, stores it to keep sarcoplasmic Ca2+ low
How does the SR run along the myofibrils
Parallel
What are the ends of the SR called
Terminal cisternae
What is special about the terminal cisternae?
- end of the SR
- has a ryanodine receptor (RyR, calcium release channel)
Where does the t tubule meet the SR?
In the triad
What is the triad
2 terminal cisternae, one t tubule
DHPR, RyR, and SR in relation to T tubule in skeletal muscle
All VERY close together along the T tubule system
ONLY IN SKELTAL MUSCLE,
Changes in the DHPR shape affect ____
RyR shape
What keeps free calcium low in the SR
Calcium binding proteins
Where does calcium reuptake occur
Longitudinal sections
Where does calcium release occur
Terminal areas
What are the steps of excitation in skeletal muscles
- AP in muscle membrane
2a. Depolarization of T tubules
2b. Opens SR Ca2+ release channels - Increased intracellular Ca2+ cxn
- Ca2+ binds troponin C
- Tropomyosin moves and allows interaction of actin and myosin
- Cross bridge cycling and force generation
- Ca2+ reaccumulated by SR—relaxation
Actions potential in the NMJ
Depolarizes down sarcolemma membrane and T tubules system
How does AP affect DPHR and RyR?
Causes confromational change in DPHR, whihc causes a change in RyR conformation and opens it
What does the opening of the RyR allow
Ca2+ from SR into cytosol
What does calcium bind once it is in the cytosol
TnC and causes contraction
How does calcium binding TnC cause contraction
- moves tropomyosin off binding pocket
- cross bridges cycling and force generation occurs
What sequesters Ca2+ in the SR
SERCA
When does relaxation occur
When tropomyosin moves back over binding site
Cross bridge cycling
Myosin binds actin and pulls it towards the M-line
Sliding filament theory
- actin and myosin slide past one another
- pulls z discs together, pulls sarcomeres together
- force is transferred to the connective tissue surrounded fiber
- eventually entire muscle shortens and moves bones
Myosin binding site at rest
Covered by tropomyosin
When myosin binds ATP
Myosin becomes cocked and has high affinity for actin
What causes tropomyosin to move off of binding site?
Calcium binding TnC
Once binding site is free and myosin binds ATP, what happens
Myosin finishes hydrolysis ATP and ADP and binds to actin
Once myosin is bound to actin
Myosin undergoes a conformation change, releases ADP and ‘ratchets”, this pulls the actin towards M-line
Power stroke
Myosin affinity for actin once it binds ATP
Lowered actin affinity
What happens once myosin binds ATP
Releases actin, partially hydroluyzes ATP and is recocked.
Cross bridging will repeat as long as what is available
Calcium and ATP
Relaxation
- Ca2+ resequesered into SR by SERCA
- TnC no longer bound to Ca2+
- tropomyosin covers actin binding site
- contraction stops and muscle can relax
Rigor Morris occurs shortly after death, what is the most direct cause
Lack of ATP, myosin cant break down without ATP
Malignant hyperthermia is potentially fatal genetic disorder characterized by hyper responsiveness to inhaled anesthetics. It results in elevated body temp, skeletal muscle rigidity, and lactic acidosis
Which of the following molecular changes could account for these clinical manifestations?
Prolonged opening of the RyR channel
Dumps Ca2+ and causes lots of contractions
What makes a motor unit
Neuron and all synapses myocytes
What leads to fine movements, such as EMO
Fewer cells per nerve
Each time a motor neuron fires, you get a _____
Muscle twitch
- a single AP
- a single generation of force
Single twitch in a single motor unit
Not sufficient for movement
Mechanism of tetanus
Increase twitches by recruiting more units (spatial) or stimulate the same unit numerous times (temporal)
-temporal works because there is a lag between excitation and force generation
