Muscle Flashcards
What makes up antagonistic pairs?
flexor and extensor
What is isotonic muscle contraction?
muscle length changes and tension stays the same
define concentric
shortening
define eccentric
lengthening
What is isometric contraction?
tension develops and muscle stays the same length
What is the structure of myofibre?
large and cylindrical
multinucleated
packed with myofibrils
Summarise the mechanism of excitation-contraction coupling for skeletal muscle
AP propagates along sarcolemma and into T-tubules
depolarisation activates dihydropiridine receptors sarcolemma which causes a conformational change
linked to ryanodine receptors on SR which open and cause calcium influx
What are the z-lines?
defines the lateral boundaries of a sarcomere
What is actin?
polymeric thin filament composed of 2 twisted alpha helices that displays polarity
What is myosin?
thick filaments that contain numerous globular heads that interact with actin
What is titin?
very large spring-like filament that anchors myosin to the z-line
What is nebulin?
large filaments associated with actin
What is tropomyosin
elongated protein bound to actin
What is capZ?
associated with positive end of actin
What is tropomodulin?
associated with negative end of actin
Summarise the sliding filament theory
calcium presence causes troponin to move from the tropomyosin chain
this exposes a myosin binding site on actin surface and charged myosin heads bind
ADP released and myosin head pivots pulling actin filament
ATP binds to head and releases it from actin
ATP hydrolysed recharges the head
How does isotonic contraction relate to the sliding filament theory?
muscle tension greater than load force so muscle contracts and fibres shorten
How does isometric contraction relate to the sliding filament theory?
muscle tension = load forces so muscle doesn’t contract and myosin heads reattach to same point on actin
Name the two pacemaker cells and describe their structure
SA - small, empty, spindle shaped
AV - spend shapes network
Name the two conduction fibres
Bundle of His
Purkinje fibres
What kind of muscle are cardiomyocytes
striated muscle
What are intercalated disks?
specialised regions that connect individual cardiomyocytes
What do intercalated disks contain?
numerous gap junctions so AP spreads rapidly cell to cell
Summarise the mechanism of excitation-contraction coupling for cardiac muscle
AP propagates along sarcolemma and T-tubules
depolarisation opens vg-Ca2+ channels so calcium influx
calcium influx causes:
-calcium induced calcium release by binding to ryanodine receptor on SR
-initiates contraction binding to troponin
-further depolarisation
Summarise the mechanism of excitation-contraction coupling for smooth muscle
depolarisation activates VG-ca2+ channel
Ca2+-CaM complex forms which activates myosin light chain kinase
MLCK phosphorylates myosin light chains which then forms cross bridges with actin
How does smooth muscle differ from skeletal?
doesn’t contain regular arrangement of actin and myosin
How do cardiac muscle and skeletal muscle differ?
cardiomyocytes aren’t multinucleated
