muscle physiology Flashcards
1
Q
muscle types under involuntary control
A
- cardiac muscle, contains short striated cells and intercalated discs
- smooth muscle (in organ systems and blood vessels)
2
Q
myogenic muscle
A
- contract spontaneously, not from excitation from neurons
- specialised muscle cells produce electric potential
- e.g. autorhythmic fibres in vertebrate hearts
3
Q
skeletal muscles
A
- under voluntary control
- attached to skeleton, causes movement
- made from bundles of long striated muscle fibres
4
Q
properties of skeletal muscle fibres
A
- irritability
- conductivity
- contractability
- extensibility
5
Q
skeletal muscle fibres structure
A
- fibres are single cells with multiple nuclei arranged around outside
- each muscle fibre contains myofibrils that contain microfilaments arranged in repeating units called sarcomeres
6
Q
sarcolemma
A
muscle cell membrane
7
Q
sarcoplasm
A
- muscle cell cytoplasm
- contains sarcoplasmic reticulum
8
Q
sarcomere
A
- repeating units of microfilaments actin and myosin
- actin = thin filaments, binding site for myosin
- myosin = thick filaments, myosin heads extend towards actin
- contains regulatory proteins troponin and tropomyosin
- elastic filaments composed of titin
- non-elastic filament nebulin
9
Q
titin
A
- elastic filament
- anchors and stabilises myosin
- helps recover sarcomere length after contraction
10
Q
nebulin
A
- non-elastic filament
- stabilises actin
11
Q
sliding filament theory
A
- myosin head hydrolyses ATP
- converts to high energy form that can bind to actin, creating cross bridges
- pull actin towards centre of sarcomere each time ATP is hydrolysed (if more ATP and calcium provided in high levels)
12
Q
ATP sources for muscle contraction
A
- small amounts stored in cytoplasm (about 10s of contraction)
- stored creatine phosphate can convert ADP to ATP (30s contraction)
- stored glycogen
- aerobic respiration
13
Q
arrangement of sarcomeres in muscle fibres
A
- lots in parallel increases force generation
- lots in series increases degree of shortening
- optimal balance is mix of both, but depends on muscle type
14
Q
relationship between length of sarcomere and tension
A
- large overlap, little length means low tensions, as nowhere to pull actin filament
- optimal overlap has most tension
- little overlap, large length means low tension as lack of myosin heads available to form cross bridges
15
Q
neurogenic muscles
A
- stimulated by action of neurons across a neuromuscular junction (NMJ)
- e.g. vertebrate skeletal muscles
16
Q
troponin-tropomyosin complex
A
- regulatory protein tropomyosin binds to myosin binding site, covering it so mysoin cannot bind when the muscle is at rest
- troponin holds tropomyosin at rest
17
Q
muscle excitation
A
- ACh from motor neuron causes sarcolemma to depolarise
- electric potential conducts across sarcolemma and move through t-tubules into the sarcoplasmic reticulum
- activates Ca2+ channels, allow Ca2+ to move from the reservoir in the sarcoplasmic reticulum into the sarcoplasm
- Ca2+ binds to troponin and changes its configuration, tropomyosin-troponin complex slides away
- cross bridges can form, muscle contracts using stored ATP
18
Q
NMJ
A
- neuromuscular junction
- neurotransmitter is ACh (in vertebrates)
- postsynaptic cell is muscle fibre
- motor end plate is region of sarcolemma
19
Q
motor unit
A
- the motor neuron, its axon terminals and the skeletal muscles innervated by them
- strength of contraction depends on how many motor units stimulated
20
Q
muscle relaxation
A
- no inhibitory neurons in vertebrates
- muscle action potential ceases
- calcium ion channels close
- pumps and calsequestrin protein removes Ca2+ from sarcoplasm back into sarcoplasmic reticulum
- binding site recovered up by tropomyosin-troponin complex
