Muscle Flashcards
Define myasthenia
Weakness of the muscles
Define myoclonus
sudden spasm of the muscles
What is the sarcoplasmic reticulum?
The SER of the muscle cells
What morphology defines skeletal muscle?
long, parallel cylinders with multiple peripheral nuclei and striations
What morphology defines cardiac muscle?
short, branched cylinders with a single, central nucleus and striations
What morphology defines smooth muscle?
spindle-shaped cells with tapering ends to cells, single, central nucleus and no striations
How is skeletal muscle derived?
mesodermally derived: myogenic stem cells produce myoblasts, formation of primary myotube, nuclei are displaced to periphery by newly synthesised myofilaments
What are the 2 types of muscle fibre?
red and white
What are the features of red muscle fibres?
smaller diameter, rich vascularisation, rich myoglobin, numerous mitochondria, contractions are slower and weaker, fatigue slowly, rich in oxidative enzymes, fewer neuromuscular junctions
What are the features of white muscle fibres?
larger diameter, poor vascularisation, poor myoglobin, few mitochondria, faster and stronger contractions, quickly fatigues, rich in ATP-ase, more neuromuscular junctions
Where are red muscle fibres found?
limb muscles and postural muscles
Where are white muscle fibres found?
extraocular muscles and fingers
Where is the epimysium found?
Surrounding the outside of the muscles
Where is the endomyosium found?
Surrounding individual muscle fibres
Where is the perimysium found?
Surrounding the fascicles of the muscle
What occurs at myotendinous junctions?
Skeletal muscle fibres interdigitate with tendon collagen bundles.
What are extrinsic muscles?
Muscles that have insertions in bone or cartilage.
What are intrinsic muscles?
Muscles that are not attached to bone.
Of the muscle bands A and I, which is dark and which is light?
A = dark I = light
What is the smallest unit of muscle?
Myofibrils
What happens to the bands during the sliding filament model?
H and I bands get smaller whilst the A band stays the same size
Which protein makes up the thin filaments?
Actin
Which protein makes up the thick filaments?
Myosin
What are the features of actin?
bistranded helix, tropomyosin wraps around actin, troponin complexes attach to tropomyosin
What can we use as a diagnostic for MI?
Troponin: released from ischaemic cardiac muscle within 1 hour of the MI
What are the features of myosin?
thick, rod-like structure with 2 protruding heads
How does calcium cause actin and myosin to join?
calcium binds to TnC of troponin, conformational change moves tropomyosin, exposes actin binding sites, myosin heads can attach to actin
What are the steps for contraction?
myosin cross bridges attach to actin, working stroke: myosin head pivots and pulls on the actin filament, sliding it towards the M line, ATP attaches to the myosin head and the cross bridge detaches, myosin head is cocked to start again
Why does rigor mortis occur?
The lack of ATP perpetuates the binding of the myosin cross bridge.
Where are the T tubules placed in skeletal muscle?
Where the A and I bands join
What is the sequence of events before muscle contraction occurs?
The nerve impulse arrives at neuromuscular junction and releases Ach into cleft. depolarisation of sarcomere, voltage-gated Na+ channels open, Na+ enters cells, depolarisation spreads over sarcolemma into T tubules, conformational change, gated calcium channels are activated, calcium released into the sarcoplasm, calcium binds to troponin and contraction cycle initiated.
How is calcium removed when the nerve impulse for contraction ends?
Calcium is removed via active transport into the sarcoplasmic reticulum.
What happens to myofibrils in cardiac muscle?
The myofibrils tend to fuse so that the myofilaments form continuous masses.
What are intercalated discs?
substitutes for Z lines where cells meet consisting of gap junctions and adherens-type junctions
Where are the T tubules in cardiac muscle?
Lie on the Z line
In which muscle do diads and triads occur?
Diads = cardiac Triads = skeletal
What are the features of the Purkinje fibres?
large cells with abundant glycogen, extensive gap junctions and extremely fast conduction
Where would you find smooth muscle?
contractile walls of passages or cavities: blood vessels, gut, respiratory tract, genitourinary system
Modified smooth muscle cells can occur as which 2 cells?
myoepithelial cells and myofibroblast cells
What are myoepithelial cells?
star shaped cells formed by dendritic processes that form a basketwork around the secretory units of some exocrine glands and contraction assists secretion
What are myofibroblast cells?
occur at wounds and produce collagenous matrix, draw wound edges together on contraction
Which nervous system innervates smooth muscle?
Autonomic NS
How are the filaments arranged in smooth muscle?
arranged diagonally within the cell, spiral down a long axis and contract in a twisting way
Can skeletal muscle repair itself?
The cells cannot divide but the tissue can regenerate by mitotic activity of satellite cells.
Can cardiac muscle regenerate?
No
Can smooth muscle regenerate?
Yes - the cells retain some of their mitotic activity and can form new smooth muscle cells.
How can muscle be remodelled?
actin and myosin filaments can be replaced, number of muscle fibres cannot change, just their size, number of myofilaments can increase or decrease
What happens in the muscle when amount of exercise increases?
SR swells, increase volume of mitochondria, increase Z band width, increase ATPase, increase number of contractile proteins
How often should you do high resistance exercise if you want to increase muscle mass?
2-3 days a week
3 sets of 8-12 reps
How does high resistance exercise change muscle?
stimulates contractile protein synthesis (more filaments) and increases muscle mass and strength (hypertrophy)
How often should you do endurance exercise?
5 days a week
30-60 minutes
How does endurance exercise change muscle?
increased endurance without hypertrophy, stimulates synthesis of mitochondrial proteins and vascular changes allow for greater oxygen utilisation
What is disuse atrophy?
The loss of protein and reduced fibre diameter which results in the loss of power.
What happens when muscles are denervated?
weakness, flaccidity and muscle atrophy
What is myasthenia gravis?
autoimmune destruction of end-plate ACh receptors, loss of junctional folds and widening of synaptic clefts
What are the symptoms of myasthenia gravis?
fatiguability, sudden falling, drooping eyelids, double vision
What is the treatment for myasthenia gravis?
acetylcholinesterase inhibitors and immune suppressants
What is plasmapheresis?
Removal of harmful antibodies from patient serum
What is conotoxin used for?
Painkiller used for patients who no longer respond to morphine.
What are muscular dystrophies?
genetic disorders, progressive muscle weakness and wasting and there are 6 types
What causes Duchenne muscular dystrophy?
Deficiency of dystrophin
What causes Becker type muscular dystrophy?
altered form (truncated) of dystrophy
What happens in muscular dystrophies?
muscle fibres tear apart on contraction, creatine kinase liberated into serum, calcium enters cells causing cell death (necrosis). Pseudohypertrophy occurs before fat and connective tissue replace muscle fibres
What are the 2 types of skeletal muscle disorders?
denervation and myopathies
Define myalgia
Muscle pain
