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Basic Science > Skeletal muscle > Flashcards

Skeletal muscle Flashcards

1
Q

Where are Skeletal muscle cells orginate?

A
  • Mesodermal origin
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2
Q

What are mature cells in adult skeletal muscle called?

A
  • Myotubes
  • these are differentiated multinucleated cells formed by cytoplasmic fusion of immature mononuclteated myoblasts
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3
Q

What are the muscle fibres bounded by ?

A
  • Plasma membrane - sarcolemma
  • they have cytoplasm- sarcoplasma
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4
Q

What is the name for many muscle fibres grouped together?

A
  • Fascicles
  • the fascicles are the smallest unit of structure visible to the naked eye
  • It is the ability if the fascicle to contract that determines the character of the muscle
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5
Q

What is the endomysium?

A
  • Connective tissue that surrounds individual fibres
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6
Q

What is the perimysium?

A
  • connective tissue that encloses the functional fascicular unit
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7
Q

What is the epimysium?

A
  • The connective tissue that surrounds the muscle in its entirety
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8
Q
A
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9
Q

What is surrounding each myofibril ?

A
  • A membranous sac = sarcoplasmic reticulum
  • it serves as a repository for calcium which is released to stimulate contraction
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10
Q

What do T tubules do?

A
  • They connect at a membranous junction with the sarcoplamic reticulum of each myofibril
  • the function is to carry depolarization of the surface membrane deep inside the muscle fibre
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11
Q

How does the arteriole entry the muscle fibre?

A
  • Perimysium - where the arterioles penetrate the sheath surrounding the fascicle
  • the arterioles enter obliquely or at 90 degrees to the muscle fibres then run parallel
  • terminal capillaries are associated with muscle fibre nuclei
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12
Q

what are the major contractile proteins in skeletal muscle?

A
  • Actin
  • Myosin
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13
Q

What is the grouped functional unit of actin/myosin filaments?

A
  • Myofibril
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14
Q

Myofibrils are segmented into functional contractile units called what?

A
  • Sarcomeres
  • visible under electron microscope
  • 2-2.5 microns in length
  • 1 micron in diameter
  • length varies with muscle activity but shows a variance along the length of the myofibril
  • sarcomeres in the myotendinous junction tend to be shorter
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15
Q

What is the A band?

A
  • Represents the Myosin filaments
  • Anisotrophic on light microscope
  • ***“AM”
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16
Q

What does the I band represent?

A
  • Actin filaments in adjacent sarcomeres where there is no overlap with myosin filaments
  • Isotrophic on light microscope
  • **IA**
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17
Q

What does the H band represent?

A
  • Myosin filament segment where there is no interdigitiating actin filaments
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18
Q

What do the M lines represent?

A
  • Connections between adjacent mysoin filaments in their central region
  • these are termed M band proteins
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19
Q

What do Z discs represent?

A
  • Attachment of adjacent sarcomeres
  • the disc lies between sarcomere
20
Q

What is the arrangement of actin and myosin filaments?

A
  • Hexagonal lattice in the centre of the sarcomere
  • ie each myosin filament is bounded by 6 actin filaments
  • this becomes more square towards the end of each sarcomere
21
Q

What other important proteins have a role in maintaining the structure of the sarcolemma?

A
  • Dystrophin ( absent in duchenne muscular dystrophy)
  • as a group called structural proteins as they maintain the overall architecture of the sarcomere during contraction
22
Q

What is actin?

A
  • A globular protein (molecular weight 42 000)
  • chief constituent of the thin filament of the sacromere
23
Q

What other proteins constitute the thin filament of the sarcomere?

A
  • Tropomyosin
  • Troponin subunits
    • troponin C
    • troponin T
    • troponin I
24
Q

What does tropmyosin do?

A
  • It exends across seven actin subunits
  • Blocks the bindings sites of the myosin head unit until unblocked by calcium binding to the troponin C subunit ( tropomysoin moves & mysoin- binding site exposed)
  • the activated troponin C subunit counteracts the inhibitory effect of the troponin I subunit
  • Troponin T assists toponin C binding to tropmyosin
25
Q

What is the myosin structure?

A
  • Made up of 6 distinct subunits
    • 2 heavy chains
      • S1 segment/cross bridge= articulate with actin
      • S2 segment= forms flexible neck which moves to allow articulation of the S1 head segment
    • 4 light chains - uncertain function
26
Q

Describe the sliding filament contraction/ cross bridge theory by Huxley?

A
  1. in rush of Ca 2+
  2. Ca 2+ binds to Troponin C
  3. Activated troponin C displaces inhibitory Troponin I from site on tropomyosin/actin complex
  4. Troponin T assists
  5. Tropomyosin undergoes conformational change to allow myosin head enagagement
  6. Myosin head engages
  7. Forced generation occurs due to S1 head segement rotation
27
Q

What is the force of a muscle is porportional to?

A
  • Cross sectional area
  • the more sarcomeres that are acting parallel to each other the higher the force generated
28
Q

What is speed of muscle related to ?

A
  • Length of the muscle
  • Upon stimulating a muscle all sarcomeres contract at the same time.
  • for long muscle there will be a greater change in length per unit time ie the greater the muscle velocity
  • the sarcomeres act in series
29
Q

What is the power of the muscle a product of ?

A
  • Force x velocity
  • short fat muscles produce high force but low max velocity
  • long thin muscles produce low force but high max velocity
30
Q

What is the name given to all muscles fibres innervated by the same motor neuron?

A
  • Motor unit
31
Q

Can you draw a neuromuscular junction?

A
32
Q

Describe what happens at the Neuromuscular junction?

A
  • Motor neurone, action potential propagates an influx of Ca2+ thru voltage- sensitive channels
  • Increased concentrations of intracellular Ca2+ cause preformed vesicles of acetylcholine to fuse with presynaptic nerve membrane
  • Acetylcholine in the synaptic cleft binds to the postsynaptic receptors on the sarcolemma
  • Binding of acetylcholine depolarises the muscle fibre membrane
  • Depolarisation is dependent on the amount of acetylcholine releases into the synaptic cleft
  • Also dependent on the rate of release of acetylcholine into the cleft as it is broken down rapidly by cholinerases from the post synaptic membrane
33
Q

What is the myotendinous junction?

A
  • An area where insertion of every skeletal muscle fibre into its tendon occurs
  • specific morophology
    • shorter sarcomere lengths
    • greater no of organelles per cell
    • greater synthetic ability
    • interdigitation of the cell membrane
    • extracellular connective tissue
    • high degree of membrane folding- increases resistance to stress by increasing the surface area and reducing the angle of the force vector applied
    • net result junction very strong
34
Q

Describe the different types of muscle?

A
  • Type 1 “Slow Red Ox”
    • Slow fibres
    • Large conc of myoglobin ( red in colour)
    • Oxidative
    • Very fatigue Reisistance
  • Type 2a
    • Fast fibres
    • Oxidative
    • Glycolytic ( realtively white in colour)
    • Fatigue resistant
  • Type 2b
    • Fast fibres
    • Glycolytic ( white in colour)
    • Fatiguable
35
Q

What is the single most important factor in fibre type expression?

A
  • Pattern of activity imposed on the muscle
  • ie atheletes who train for endurance can reach proportions of up to 80% of type 1 fibres in their muscles
36
Q

What causes damage to muscle cells in truama?

How does this continue?

A
  • Raised calcium concentrations
  • Once cell damaged the process continues via a calcium-activated enzymes - Proteases and phospholipids
  • also by free-radicals and oxidation of liberated free fatty acids
37
Q

What are the modes of muscle injury?

A
  • Muscle belly tear
  • Muscle laceration
  • Musculotendinous junction injury
  • Ischaemic damage and compartment syndrome
  • Denervation
  • Crush injury and rhabdomyolysis
  • Malignant hyperpyrexia
    • skeletal muscle reaction to halothane with prolonged muscle contraction -> metabolic distintegration of muscle
    • K is released first so risk of MI, followed by myoglobin release and renal failure
  • Delayed muscle soreness
    • muscle soreness that develops 24-72hrs following intense exercise
38
Q

What is the prognosis of a proximal belly tear?

A
  • Worse the prognosis
  • As more bullk is denervated
39
Q

What do muscle lacerations result in ?

A
  • Dense fibrous scars
  • Myotubes regenerate across scar tissue in small no
  • Partial lacerations have better functional outcomes cf complete belly lacerations
  • complete lac- distal portion wastes rapidly.
  • muscle regeneration can occur with a nerve supply but permanent muscle atrophy will develop if regeneration fails
  • A complete lac in mid-substance can recover only 50% of previous force that was generated by the muscle
40
Q

Where do complete tears normally occur?

A
  • Myotendinous junction, with a segement of adjacent muscle avulsed when stretched to failure
41
Q

Where do incomplete tears occur?

A
  • Near the myotendinous junction in an area of relatively stiffer sarcomeres
42
Q

Describe the EMG of skeletal muscle?

A
  • is a recording of electrical activity in skeletal muscle
  • Needle electrodes are inserted into muscle to be studied
  • The electrode records any spontaneous activity within the muscle are rest and the signal given by firing of motor units when the muscle is activated
  • normally no spontaneous activity at rest in a healthy muscle after the needle is inserted
  • the patterns of motor activity ( motor unit action potentials) are related to the nerve supply to the muscle in question
43
Q

What is the EMG findings of acute degenerative injury?

A
  • Spontaneous activity of Sharp waves
44
Q

What is the EMG findings of chronic degenerative injury?

A
  • Fasiculations
45
Q

What is seen on EMG with early re-innervation?

A
  • Reduced amplitude motor action potentials
  • Longer duration
  • Poor recruitement
  • the new sprouts conduct slowly , producing temporary dispersion ( prolonged MUAP) adn MUAP polyphasicity
46
Q

What is seen on EMG with late re-innervation?

A
  • Large ampitude, stable consistent firing Motor action potentials
  • Good recruitement of units gives polyphasic signal

Basic Science (31 decks)

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