lecture 1 - muscle physiology Flashcards
what are the universal characteristics of muscles
excitability, conductivity, contractility, extensibility, elasticity
excitability
responsiveness to chemical signals, stretch and electrical charges across plasma membrane
conductivity
electrical excitation initiates wave of excitation that travels along muscle fibre
contractility
shortens when stimulated
extensibility
capable of being stretched between contractions
elasticity
returns to original rest length after being stretched
features of skeletal muscles
voluntary, striated
voluntary action
usually subject to conscious control
striated
alternating light and dark bands due to internal contractile proteins
muscle
contractile organ, usually attached to bone by way of tendons
fascicle
bundle of muscle fibres
muscle fibre
single muscle cell
myoblasts
stem cells fuse and form muscle fibres early in development
satellite cells
unspecialised myoblasts between muscle fibre and endomysium
what is the role of satellite cells
regeneration of damaged skeletal muscle tissue
sarcoplasmic reticulum
smooth ER that forms a network around each myofibril
terminal cisterns
dilated end-sacs of SR that cross muscle fibre from one side to the other
T tubules
tubular infoldings of sarcolemma which penetrate through cell and emerge on other side
Triad
a T tubule and two terminal cisterns associated with it
when does muscle contraction begin
stored calcium is released into sarcoplasm
functional muscle units
sarcomeres
sarcomere
segment from Z line to Z disc
H band
thick filaments at the centre of the sarcomere
I bands
thin filaments
function sarcomeres
- stabilise the position of thin and thick filaments
- proteins that regulate interactions between thin and thick filaments
M line
proteins that connect neighbouring thick filaments
H band
region either side of M line
A band
thin and thick filaments overlap
fibrous actin
two intertwined strands
tropomyosin
actin binding protein
troponin
small, calcium binding protein on each tropmyosin molecule
what occurs when skeletal muscles contract
- sarcomere shorten
- H bands and I bands get smaller
- zones of overlap get larger
- Z lines move closer together as thick and thin filaments slide past each other
- A band remains constant
- sliding occurs in all sarcomeres in myofibril
- myofibril gets shorter
- muscle gets shorter
- tension is produced
somatic motor fibres
axons that lead to skeletal muscles
somatic motor neurons
nerve cell whose cell bodies lie in brainstem and spinal cord
motor unit
one nerve fibre and all muscle fibres innervated by it
characteristics of muscle fibres in a motor unit
- dispersed throughout muscle
- contract in unison
- produce weak contraction over wide area
- able to sustain long term contraction
- requires contraction of several motor units at once
synapse
where nerve fibre meets target cell
neuromuscular junction
when target cell meets a muscle fibre
axon terminal
swollen end of nerve fibre
synaptic cleft
gap between axon terminal and sarcolemma
basal lamina
thin layer of collagen and glycoprotein separating schwann cell and muscle cell from surrounding tissues
tetanus (lockjaw)
form of spastic paralysis caused by toxin Clostridium tetani
flaccid paralysis
muscles are limp and cannot contract
Botulism
food poisining caused by a neuromuscular toxin secreted by the bacterium Clostridium botulinium
What are the four major phases of contraction and relaxation
- excitation - nerve action potentials lead to muscle action potentials
- excitation-contraction coupling - events that link action potentials on sarcolemma to activation of myofilaments
- contraction - muscle fibre develops tension and may shorten
- relaxation - stimulation ends
length- tension relationship - amount of tension generated by muscle a muscle depends on how stretched or shortened it was before it was stimulated
