Lec 4 Muscle tissue Flashcards
What are the 3 types of muscle tissue
Skeletal/Striated voluntary
Cardiac/Striated involuntary
Smooth/non striated involuntary
What tissue is skeletal muscle surrounded by
What is skeletal muscle composed of (struc)
Skeletal muscle surrounded by epimysium
Composed of many muscle fascicles
What are muscle fascicles surrounded by
What is it composed of
Muscle fascicles are surrounded by perimysium
Composed of muscle cells - muscle fibres
What are muscle fibres surrounded by
What does it contain
Muscle fibres surrounded by endomysium
Composed of filamentous proteins, myofibrils
How is muscle bound to tendon
Collagen fibres in epi/peri/endomysium connect to tendon
How tendon-bone attach
Collagen fibres in tendon interwoven with periosteum
Then cemented in matrix as perforating/sharpey’s fibres
How muscles get nerve and blood
BV and nerves form neurovascular bundle that branch in CT to reach individual fibres
How do muscle cells form
Muscle cells develop from the fusion of myoblasts (mesodermal cells)
Skeletal muscle cells are multinucleate
Some myoblasts remain unfused to become satellite cells to provide some repair potential
- but usually dmg muscle replaced by fibrous tissue
How are muscle cells bound and why is it impt
Muscle fibers bound by endomysium and is not in direct contact with adjacent cells
But since is bound all by endomysium and CT, force is transferred so whole muscle contracts
Explain components of thin filament
Composed of actin
G-actin (globular): active site and binds myosin heads
F-actin: filamentous polymer of 300-400 G actin
Tropomyosin: covers actin active site
Troponin: Holds the tropomyosin in place
Explain components of thick filament
Composed of 2 elongated proteins - has a head and tail
500 of these bundled to form a thick filament
myosin heads spiral around
How are the myofilaments arranged in a sarcomere
Each thick filament is surrounded by 6 thin filaments
Adjacent thick filaments can share thin filaments as one of their 6
Sarcomere nomenclature
Z line: attachment for thin filaments, the midd line
M line: attachment for thick filamnets, the mid line
Zone of overlap: thick and thin filament parts
H zone: Thick filaments only
I band: Thin filaments only
A band: length of thick filament
Parts of the NMJ
How does signal pass
Synaptic terminal, Synaptic cleft, motor end plate
Synaptic vesicles in the terminal has ACh and is released onto the motor end plate binding AChRs (ligand gated ion ch) - depol sarcolemma
AChE clears ACh
Explain muscle contraction
Cells actively maintain low Ca levels
ACh release, AP goes down sarcolemma and t-tubes to get close and stim SR release of Ca.
Incr in cyto Ca binds troponin and tropomyosin slides off active sites for myosin heads to bind (crossbridging)
Myosin heads cock back and contracts muscle
Explain muscle relaxation and why is it passive
Ca will be pumped when signal dies
- back into SR and ECF
Troponin unbinds Ca and tropomyosin slides back on
Muscular relaxation is passive from elasticity of tissue, antagonist muscles, gravity
How many NMJ in a muscle fibre
What is a motor unit
ONE NMJ in each muscle fibre
A motor unit is a single motor neuron and ALL the muscle fibre it innervates
- # of muscle fibre/unit varies: small motor in eyes, for
small movements OR large motor units in antigravity
muscles (thighs)
- Force proportional to # of motor units
Explain muscle tone and how it functions
Resting tension in muscle - active motor units generate tension but not enough to shorten muscle
Avoids fatigues by rotating motor unit activation
Antigravity muscles for posture and balance
Give characteristics of Slow twitch muscle
Capillary supply, myoglobin content, color, mitochondria, glycolytic enzymes, Cross sec diameter, tension, fatigue resistance, substrate for atp
Capillary supply: High supply Myoglobin content: High Color: Red Mitochondria: lots Glycolytic enzymes: Low [] Cross sec diameter: Small Tension: Less Fatigue resistance: High Substrate for atp: Carbs, Lipids, Protein
Give characteristics of Fast twitch muscle
Capillary supply, myoglobin content, color, mitochondria, glycolytic enzymes, Cross sec diameter, tension, fatigue resistance, substrate for atp
Capillary supply: Low supply Myoglobin content: Low Color: Paler Mitochondria: Fewer Glycolytic enzymes: High [] Cross sec diameter: Large Tension: Greater Fatigue resistance: Low Substrate for atp: Glycogen
Explain what occurs from muscle hypertrophy
Increases: mito, glycogen reserve, [] of glycolytic enzymes, myofibrils and myofilaments
increases ATP capacity
Not more cells, cells get bigger
Cardiac muscle characteristics
Only in heart - striated involuntary muscle
Mononuclear, smaller than skeletal muscle
Cardiocytes form branching networks, joined at intercalated discs
Intercalated junc charcteristics
Has fingerlike projections: incr SA for better attachment
Gap juncs for intercellular comm - contact SIDE TO SIDE of muscle cells
FASCIA Adherens for anchorage of actin filaments and terminal sarcomeres
Desmosomes for connection of IFs of cytoskeleton
Pacemaker cells set rate - controlled by ANS
Cardiomyocytes characteristics
Aerobic metabolism - myoglobin, mito, cap network
Cannot regenerate
Smooth muscle tissue characteristics
Small spindle shaped non striated, involuntary - modulated by ANS Signal spread by gap juncs Can regen Elongated nuclei centrally placed
