W2 Skeletal Muscle Flashcards
what are three functions of skeletal muscle?
any three of:
- move the body
- control body posture
- support and protect
- control orifice (voluntary control)
- participate in temperature regulation
- generate peristaltic movement
what are muscle fibers enveloped by?
a sheath of connective tissue
what bundles make up a muscle?
bundles of muscle fibers
what unit makes up muscle fibers?
myofibrils
what unit makes up myofibrils?
myofilaments
what unit makes up myofilaments?
sarcomeres
describe the structure of a sarcomere:
highly aligned, two Z-discs and and M-line containing myosin and actin filaments, Each muscle fibre has a light actin band (I-band) and a dark myosin band (A-band). The elastic fibre (Z-line) bisects each I-band, the thin filament is firmly anchored to the Z-line. The H-zone is the central part of the thick filament that is not overlapped by the thin.
what is myosin made up of and what are they centred by?
made up of several myosin molecules and centred between z-discs and m-lines by titin
what ensures uniformity in length of actin?
attachment to nebulin
what do T-tubules allow?
rapid conduction of AP
where are T-tubules found?
run through fibres either side of the z-discs
T-tubules are in close contact with what?
sarcoplasmic reticulum
what is a neuromuscular junction?
a synaptic connection between the terminal end of a motor nerve and a muscle, it is the site for the transmission of action potential from nerve to the muscle
describe the sliding filament theory:
during muscle contraction, myosin heads or cross-bridges come in close contact with the thin filaments of the actin bending the head towards the sarcomere, as a result the thin filaments are pulled towards the middle of the sarcomere, the Z-line attached to the actin filament is also pulled leading to the shortening of the sarcomere (the length of the bad remains constant as its original length but the I-band shortens and the H-zone disappears. this is caused by a serious of action potentials being reached in rapid succession
what is a cross bridge?
myosin heads binding to actin molecules
myosin have and ATP binding site which allows what?
hydrolysis of ATP (ATP -> ADP + P)
what is a power stroke?
when calcium is released from sarcoplasmic reticulum allowing the myosin heads to bind and bend
what happens following a power stroke?
ADP is released and myosin heads bind to another ATP molecule breaking the myosin/actin bond
what controls the contractions of muscle?
tropomyosin and troponin by preventing the binding of myosin to actin in resting muscle
what happens when an action potential arrives at the neuromuscular junction (NMJ)?
- calcium is released from sarcoplasmic reticulum
- the calcium then binds to troponin
- the tropomyosin changes position exposing the binding sites on the actin
- myosin heads bind and bend and the actin filament slides
- ATP binds to the myosin heads and breaks the bond to actin
- ATP is hydrolysed and the energy release straightens the myosin heads
- pumps in the sarcoplasmic reticulum pump calcium from cytosol back into the SR
- calcium dissociates from troponin
- tropomyosin blocks the myosin binding sites on actin
- the muscle relaxes
what is rigor mortis and what causes it?
when the body becomes stiff after death, this is due to ATP production ceasing causing ion pumps to stop, calcium leaking into cytosol, calcium levels are not maintained, eventually calcium levels are high enough to cause binding of myosin heads that do not break free
what is hypocalcaemia in ruminants and dogs respectively ?
paresis in ruminants and tetany in dogs
calcium regulates the release of what in the synapse between motor neurones and muscle cells?
ACH
low extracellular calcium depolarises all cells, what does this lead to in neurones?
spontaneous AP generation
