Anatomy/Physiology: Muscle contraction Flashcards
explain the sliding filament theory
each sarcomere shortens as the thin filaments slide across the thick filaments so that Z-discs are pulled closer together.
outline the main events of the cross bridge cycle
4
1) Detachment occurs when ATP binds to myosin head
2) Hydrolysis Of ATP–>ADP+Pi brings the Myosin head to the ready position.
3) Myosin head binds to the actin filament causing a cross bridge to be formed
4) Power stroke occurs due to the loss of ADP+Pi causing actin filament to be pulled centrally towards the midline .
relate the siding filament theory to the length -tension relationship in muscle
(6)
Sliding filament theory :
1-thick and thin filaments slide past one another during cell contraction , supported by the fact that NONE of the filaments change shape.
2-many cross bridges are broken and formed
Length -tension relationship shows :
1- when muscle is too overstretched = low tension , and no overlap of the filaments
2-As overlap increases , the tension increases
3-UPTO a certain point when all the cross bridges have already been formed , then the thin myofilments start t interfere with each other and active force production decreases !
describe the 2 events responsible for excitation in contraction coupling in striated muscle
(7)
1) acetylcholine binds to receptor on sarcolema
2) Acetylcholine causes Na+ channel to open an eventually voltage gated Na+ channels open causing DEPOLARISATION AND AN AP
3) AP travels down T-tubule (in sarcoplasmic reticulum ), this causes DIHYDROPYRIDINE receptor to open Ca2+ channels
4) Ca2+ is released from terminal cicsternae of sarcoplasmic reticulum and ca2+ travel into the sarcoplasm
5) Ca2+ binds to troponin
6) this causes a conformational change in tropomyosin , (moving it out the way ) - leaving the actin binding site open
7) this mean that the myosin head can now bind to the actin —> contraction !
explain the functional classification of skeletal muscle fibres
(4)
Muscle ->Fasicle (portion of the muscle )->Muscle fibre (muscle cell) –>Myofibri (thick and thin filaments) / sarcomere/ mitochondria / T-tubules and the sarcoplasmic reticulum .
outline the similarities n differences in between skeletal , cardiac , and smooth muscle
(4)
similarities :
1- skeletal , cardiac muscle have striation and T-tubules
2-Skeletal, cardiac muscles have Troponin and Tropomyosin
3-they all have cross bridge cycling
Differences :
1-smooth muscle has no striations or T-tubule
2-Smooth muscle has no troponin or tropomyosin INSTEAD it has CALMODULIN &MLCK (myosin light chain kinase)
3-speed from fastest to slowest ( contraction) is:
skeletal>cardiac>smooth>slow
4-skeletal muscle is multinucleated and the nucleus is in the periphery of the cell
5-skeletal muscle is voluntary
6-cardiac and smooth muscle = nucleus in the centre of the cell
7-corkscrew shaped centrally located nuclei in contracted smooth muscle cell
8-Cardiac muscle contains intercalated discs made of :desmosomes , Fascia Adherins and gap junctions (nexus, allows communication)
explain the Excitation -contraction coupling in SMOOTH muscle (5)
1) Influx of Ca2+ ions from Sarcoplasmic reticulum or voltage gated channels
2) ca2+ binds to calmodulin
3) the ca2+ calmodulin complex activates an enzyme called Myosin Light Chain Kinase ( MLCK)
4) MLCK activates myosin by adding a phosphate group to inactive myosin —> ACTIVATED MYOSIN HEAD
5) cross bridge cycling can occur !
outline properties of a TYPE 1 muscle fibre
4
Type 1: red( myoglobin) known as slow twitch
- slow contraction ( spinal muscles , glutes for standing and walking )
- LOTS OF MITOCHONDRIA
- Long contraction ( it has enough energy to do so because of the mitochondria )
- FATIGUE resistance ( lots of ATP)
outline properties of type2a muscle fibre?
4
TYPE2A: fast twitch oxidative
- red ,contains myoglobin swell
- moderately prone to fatigue ( less mitochondria )
- found in calfs -soleus
Outline properties of a type 2b muscle fibre ?
4
Type 2b: fast twitch Glycolytic ( no oxygen )
- white ( NO MYOGLOBIN )
- VERY prone to fatigue
- hardly any mitochondria , hence ANAEROBIC respiration takes places
- RAPID / POWERFUL CONTRACTIONS ( limited glycogen), much quicker because they don’t have mitochondria
- eye muscles called EXTRAOCULAR muscles
Outline the main features of the skeletal muscle ?
5
1-Large cells with STRIATED ACTIN AND MYOSIN
2-Multinucleated
3-contains TRIADS ( 2 TERMINAL CISTERNAL of the sarcoplasmic reticulum and 1 T-TUBULE)
4- Satellite cells are able to differentiate and fuse to augment existing muscle fibers and to form new fibers. These cells represent the oldest known adult stem cell niche, and are involved in the normal growth of muscle, as well as regeneration following injury or disease.
5-VOLUNATRY
Outline the Main features of cardiac muscle - Myocardium?
6
1-INVOLUNTARY
2-central, singular nucleus in cells ( branched cells )
helps with heart beat
3-ACTIN /MYOSIN same as Skeletal muscle but they have DIADs with 1 terminal cistern and 1 T-TUBULE
4-LOTS OF MITOCHONDRIA /CAPILLARIES
5-INTERCALATED DISCS- join cells together to Make tight bonds and for RAPID communication of heart beat
6-Cells are connected side by side via : NEXUS( gap junctions which are communicating junctions ) / Top and bottom connections occur via DESMOSOMES AND FASCIA ADHERINS (mechanical junctions ) –> this all helps with rapid communication and synchronicity of the heart beat!
outline the main features of Smooth muscle (7)
- striated?
- shape of cell and nucleus ?
- Filaments
- organelles placement
- Mechanism for contraction
1-NOT STRIATED/INVOLUNTARY
2-Long spindly cells =long and tappered
3-can grow via hypertrophy
4-cork screw shaped nucleus
5-NO MYOFILAMENT , Actin and myosin filaments are not regular and they are anchored to DENSE BODIES (equals the Z-line )
6-Organelles are on the poles of the nucleus so that they don’t get in the way of contraction !
7-Equivalent of T-TUBULE = CAVEOLAE ( which import Ca2+ transport )
what're the connective tissues associated with : a) muscle fibre (cells) b) muscle fascicle c) Muscle (3)
a) muscle fibres (cells )-endomysium
b) Muscle fascicle- ( perimysium )
c) Muscle - epimysium
