Muscle Tissue Flashcards
Muscle fibers of skeletal muscle characteristics and function?
- Function: force generation
- multinucleated
- nuclei at periphery
- rich capillary network to meet metabolic demands
- collagenous CT
Purpose of connective tissue in skeletal muscle?
- transfers force to bone
- contains high amounts collagenous
- fibers aligned parallel to greatest force
Where does skeletal muscle develop from?
Somites (dermomyotomes)
Process of skeletal muscle development?
- Dermomyotome splits off into dorsal and ventral muscle masses
- Myoblasts (single cells) migrate from somite
- Myoblasts fuse together and make multinucleated cells called Myotubes
- process called syncytium
Sarcoplasm?
muscle cell cytoplasm
Sarcolemma?
muscle cell membrane
Outer layer of muscle cell membrane?
- interacts with ECM and coatings
- transmits force
Inner layer of muscle cell membrane?
- true cell membrane
- lipid layer
Muscle cell contents?
- primarily myofibrils packed into tubes
- gives striated appearance
Cardiac Muscle characteristics?
- Net like organization
- striated
- complex junctions
- intercalated discs (transmits force)
- found only in heart - Fatigue Resistance
- one or two nuclei
- larger more numerous T tubules
- extensive Mitochondria (continuously functioning)
Skeletal muscle organization of Myofibril?
- A band: made of Myosin thick filaments
- I band: made of Actin, Troponin, Tropomyosin thin filaments, attached to Z line
- Z band: filament anchoring site
- H band: middle of A band
- M line: myosin anchoring site
Length of Sarcomere?
extends from one Z line to the next Z line
Sarcomere thick filaments?
Myosin (A band)
- Myosin contains enzyme ATPase which hydrolyzes ATP to ADP + P (cofactor: Actin)
- reaction binds Myosin heads to Actin
- two heavy chain- tail region
- four light chain- globular heads
- hinge region- aids in movement of head
Sarcomere thin filament?
Actin (I band):
- F and G actin
- Troponin (T, C, I)- bound to Tropomyosin, prevents Actin and Myosin binding
- Tropomyosin- binds to F actin
- Globular actin (G) binds Myosin
- moves in response to calcium
What does Myosin anchor to?
M line
What does Actin anchor to?
Z line
Steps of Muscle contraction in the myofiber?
- Influx of calcium
- Calcium binds Troponin
- Troponin moves to expose Actin binding site
- Myosin heads bind to Actin binding site
- Hinge region of Myosin deforms (as a result of ATP hydrolysis)
- Power stroke- Myosin moves against Actin
-result of hundreds of actin/myosin cross bridges happening
How long does a muscle contraction last?
continues until calcium is depleted
What happens to the size of I and H bands during muscle contraction?
- I band: decreases in size
- A band: decreases in size
- Z lines come closer together
Reason for Rigor Mortis?
- calcium leaks from SR
- binds to Troponin, exposing Actin
- Myosin bind Actin, tightening the muscle
- lack of ATP causes inability of Myosin to release Actin
Where does Calcium in muscle cell come from?
Sarcoplasmic Reticulum (ER)
Muscle cell Triad?
-formed by SR and T tubule
What are Transverse (T) tubules?
- invaginations of Sarcolemma
- transmit depolarization
- surround A and I bands
Depolarization of cell membrane?
- T tubules are connected to SR via gates
- Depolarization of T tubule physically stimulates SR
- causes mechanical deformation and triggers release of calcium from SR
- SR releases calcium into cytoplasm
Motor unit?
single motor neuron and the muscle fascicles it innervates
Myoneural junction?
- motor nerves branch out within perimysial layer
- motor unit
- end foot: nerve terminal
- motor end plate: end of motor neuron where it attaches to muscle cell
What determines the precision of movement in motor units?
- related to number of muscle fibers innervated by motor neuron
- single motor units for fine motor control in fingers
- motor unit where nerve innervates many muscle fibers for more gross movements (quads)
Steps of skeletal muscle contraction at motor end plate to inside cell?
- Action potential at nerve terminal
- Acetylcholine released at synaptic cleft
- ACh binds to receptors on Sarcolemma
- Sodium influx into myofiber
- Membrane depolarized
- T tubules depolarized
- SR mechanically deformed
- Calcium released from SR
- Contraction stimulated
- Excess ACh hydrolyzed by Acetylcholinesterase
- Muscle returns to resting state
Epimysium?
- external sheath of dense irregular connective tissue around entire muscle
- transmits the force
Permysium?
layer covering each bundle of muscle fibers (fascicles)
Endomysium?
layer covering each individual muscle fiber
Dystroglycan Complex parts?
- Dystrophin binds actin at end
- Dystroglycans (alpha-DG and beta GD) binds with Actin
- Sarcoglycans (alpha, beta, gamma, delta) attach with beta DG
- associated proteins (NOS)
Function of Dystroglycan Complex?
- connect Actin in cytoplasm to ECM
- transmit generated force from inside Sarcolemma to CT outside
Dystroglycan pathologies?
- Duchenne Muscular Dystrophy
- mutation in Dystrophin - Limb Girdle Muscular Dystrophy (LGMD)
- mutations in Dystroglycans, Sarcoglycans, or other associated proteins
Intercalated Discs 3 components?
- Fascia Adherens (hemi-Z bands)
- connects sarcomeres to membranes - Macula Adherens
- connects cells to cells - Gap junctions
- communications
- signal in one cell triggers contraction in next cell
2 Types of Smooth Muscle?
- Single Unit
- single neuron innervates many muscular cells
- walls of hollow viscera (esophagus)
- Function: propel luminal contents, regulate flow of contents (peristalsis) - Multiunit
- single neuron innervates one muscular cell
- found in trachea, iris of eye, hair of skin
- Function: piloerection, shape changes
Smooth Muscle contraction steps?
- Intracellular calcium increases from calcium channels and release from SR
- Calcium binds to Calmodulin (CaM)
- Calmodulin activates Myosin light chain Kinase (MLCK)- Myosin heads
- Phosphorylated Myosin light chain combines with Actin
- Contraction occurs
- ATP is broken down
Dense bodies function?
- Two types:
- membrane
- cytoplasmic - attachment for thin and intermediate filaments
- made of alpha actinin (Z disk protein)
- Allow for transmission of force from cell to cell in smooth muscle,
- found within lattice network of smooth muscle - external lattice interacts with membrane of other cells in response to what goes into internal lattice, allows smooth muscle to work in coordinated fashion
Convergent muscles?
- muscles where origin is wider than the point of insertion
- pec major
Parallel muscles?
- more force over long distance
- sartorius
Bipennate muscles?
- fascicles on both sides of central tendon
- Interossei
- rectus femoris
Multipennate muscles?
- more force over shorter distance
- deltoid
Vectors of muscle?
-muscle contraction is the sum of vectors generated by muscle
Effective distance vs force generated?
- small distance contraction = high force generated
- Gastrocnemius - large distance contraction= low force generated
- Lat Dorsi
