The Muscular System Flashcards
What are the functions of the skeletal muscles
movement, support, communication, posture
What are the characteristics of skeletal muscle
contractility, extensibility, elasticity, conductivity
What are myofibrils rich in
blood vessels and nerves
What type of cell are myofibrils
multi-nucleate - syncytium
What formed myofibrils
fusion of myoblasts
What are t tubules
invaginations of muscle fibre membrane in the cytoplasm
What do t tubules allow
electric depolarisation of membrane - propagation
What does the myofibril cytoplasm contain
bundles of protein and mitochondria
What are sacromeres
repeated units in myofibrils
What are sarcomeres responsible for
contraction of muscle
What does the dark A band of myofibrils contain
myosin filaments
Which band is dense in myofibrils?
dark A band
What is the I band in myofibrils composed of
actin - thin filament
What does the I band in myofibrils span across
sarcomere
How is actin made stable in myofibrils
plus ends anchored into the Z line
What does anchoring of actin into the Z line prevent
polymerisation at the plus end
What is nebulin
large protein
What is nebulin made of
repeating actin binding domains
What is the process of muscle contraction driven by
myosin heads
What is contraction
thick filament of actin moves towards thin filament
What does contraction obtain
shortening of sarcomere without changing length of filaments
What is the myosin head normally attached to
specific binding site on actin filament
What happens when the actin filament binds ATP
change in conformation, myosin head slides along actin filament
What happens when the myosin head attaches to new binding site
phosphate is released - change in head conformation - power stroke
What does the power stroke allow
actin filament to slide against myosin filament
What does contraction require
energy - ATP
How is contraction initiated
membrane depolarisation allows entry of calcium
What is the starting point of contraction
calcium
What has the ability to bind calcium
troponin
What does the binding of calcium allow
conformational change - releases tropomyosin
What is the function of calcium in contraction initiation
unmasks myosin binding sites on thin filament
What is the function of releasing tropomyosin
unmasks binding site for myosin head
What happens when a nerve impulse reaches the nerve terminal
Ca2+ released - causes release of ACh by exocytosis
When does muscle contraction stop
when nerve impulses stop
What can toxins cause
muscle paralysis
What can botulinum toxin cause
muscle weakness, paralysis, death
What can BOTOX be used for?
cosmetically, medically for cross eyedness
What does botulinum toxin degrade
SNAP25
What does botulinum toxin prevent formation of
complex needed for fusion of excitatory vesicles with membrane
What is the function of SNAP25
promotes fusion of excitatory vesicles with membrane
What does BOTOX cause to be retained inside the cell
ACh
What happens if ACh is retained inside the cell
X muscle contraction
What muscles are fatigue resistant
oxidative muscles
What is the difference between slow and fast fibres
slow fibres - sustain contract for longer periods of time, fast fibres - contract rapidly
Which muscle fibres are anaerobic
glycolytic
Which muscle type has the highest concentration of mitochondria
slow oxidative
How do cells generate ATP
aerobic metabolism in mitochondria
What does aerobic muscle metabolism typically stimulate
slow fibres
What muscle metabolism is anaerobic
glycolytic
What does anaerobic muscle metabolism rely on
degradation of glycogen
What does anaerobic muscle metabolism produce
lactic acid
What is the NET production of anaerobic muscle metabolism
2ATP
What does anaerobic muscle metabolism stimulate
fast fibres
What does phosphocreatine allow production of
phosphate and ATP
What do fast muscle fibres use heavily
phosphocreatine
What happens to creatine in mitochondria
recycled into P-creatine at rest
What metabolism do slow fibres use
aerobic
What metabolism do fast fibres use
anaerobic
What happens in the muscles during fatigue
lactic acid, pH decreases
