Lecture 34 Flashcards
What is myofilament?
filamentous cytoplasmic organelle which gives the tissue its contractile property
3 types of striated muscle
skeletal, visceral, cardiac
Skeletal and visceral are voluntary, striated muscle. Where can they be found?
Skeletal : somatic/body wall
Visceral : soft tissue origin : tongue, pharynx, larynx, diaphragm, upper esophagus
What does syncytium mean?
multinucleated cell
Describe skeletal muscle development
- Mesenchymal cells differentiate into myoblsats which begin to form aggregates and line up into tube.
- Myotubes lengthen by incorporating additional myoblast by cell fusion
- Then, myofilaments appear, but nuclei are still centralized. As muscle fibers develop, cross-striated appearance is shown and nuclei are pushed peripherally.
- At last, muscle fibers are now thick and mature, consisting of alternate thick and thin myofilaments grouped into longitudinal bundles as myofibrils with nuclei located at periphery.
What is another name for skeletal muscle cell? (2)
myocyte or muscle fiber
What is satellite cells
formed from other myogenic stem cells, it is myoblast in connective tissue that can regenerate into myocyte.
3 organization of skeletal muscle
endomysium, perimysium, epimysium
what is endomysium?
a delicate layer of reticular fiber that surrounds individual muscle fiber
- contain small blood vessels and very fine neuronal branches
Perimysium
Groups of skeletal myocytes in fascicle or bundle. Each fascicle is surrounded by a layer of connective tissue
- Contain larger blood vessel and nerves
*
What is fascicles
functional unit of muscle fibers that work together
Epimysium
dense connective tissue sheath which encases multiple fascicles to form the total muscle
- contains major blood vessels and nerves
- essential for force transduction
- continues with tendon to attach muscle at the myotendinous junction
What is sarcolemma?
Plasma membrane of muscle fiber
Difference between type 1, type 2A, type 2B fibers
type 1 : slow oxidative fibers (marathoners)
- burn glucose and fatty acids
- small, red full of mitochondria, large amounts of myoglobin and cytochrome complexes.
- great resistance to fatigue
Type 2A : Fast twitch oxidative
Type 2B : Fast glycolytic (sprinter)
- burn glycogen and glucose
- large fibers, light pink
- contain less myoglobin, fewer mitochondria than type I and type IIA
- Fatigue prone
Difference between myofibrils and myofilaments
Myofibrils are specialized organelles composed of cytoskeletal elements (banded structure that extend length of the cell)
Myofibrils are made up of myofilaments, which are contractile elements.
- There are two types of myofilaments : Thick and thin with accessory proteins
Which structure is responsible for dark and light bands which accounts for cross striations of all striated muscle?
Thick and thin myofilaments
Define A, I bands, Z line, H band, M line
A : Dark I : Light Z : median dark of I H band : median lighter part of A M : middle line of H
What is sarcomere
functional unit of myofibril and basic unit of contraction, defined as segment of myofibril between two adjacent Z line
What is Thick filament made up of
MyosinII
What is thin filament made upof
actin
When stretched or contracted which part of myofilament change?
When stretched, Thin filament (I) would be stretched, moving away from A , so no overlapping, H increase
When contracted, I would move toward H band getting shorter , so more overlapping, and H decrease
*A never change
Structure of thin filament ( actin) (its synthesis)
- G-actin polymerize forming F-actin
- F-actin surrounded by tropomyosin which stabilize it.
- Troponin complex is attached to filament
- Troponin C : binds calcium
- Troponin T : binds to tropomyosin and anchors troponin complex
- Troponin I : Bind to actin, and inhibits actin-myosin interaction - Tropomodulin is attached and caps ‘-‘ end, regulating length of actin filament.
Structure of thick filaments
myosin II are aggregated tail tot ail to form thick filaments.
Cellular event leading to contraction
- Nerve impulse arrives at neuromuscular junction
- Release of acetylcholine into synaptic cleft, causing depolarization of sarcolemma
- Voltage-gated Na channels open and Na enters cell
- Depolarization of T-tubules
- Ca channel is activated, and Ca rapidly released from SR
- Ca binds to troponin C, causing contraction cycle to initate
- Ca returns to terminal cisternae