Muscle physiology L13 Flashcards
What are muscle stem cells called
satellite cells
When do satellite cells become activated
growth and muscle repair
Outer layer of muscle fascia
epimysium
What does the perimysium surround
the muscle fascicle
what surrounds the muscle fiber
endomysium
What are individual muscle fibres called
myofibrils
What surrounds myofibrils
sarcolemma membrane
A sacromere is between
2 Z lines
Difference between cardiac and skeletal muscle
cardiac= branched
What causes striations
overlap of actin and myosin
thick filament=
myosin
thin filament=
actin
2 proteins associated with actin
tropomyosin
troponin complex
troponin complex is made of
TnT
TnC
Tnl
What decreases during muscle contraction
distance between the Z lines
Calcium binds to
troponin C
What moves out of the myosin binding site
TnI
What does the myosin head act as
ATPase (hydrolysing ATP)
What is optimal resting length for a muscle
full overlap between thick and thin filaments
Decreased muscle length
Actin poking through M line; myosin bumping into Z disc
increased muscle length
decreased overlap
No overlap of myosin and actin?
Muscles are not naturally stretched to this point
Rigor mortis begins
3-4 hours after death
HOW LONG DOES RIGOR MORTIS LAST FOR
24 hours
Why does rigor mortis happen
Ca2+ diffuses out of SR and allows myosin to bind to actin, no ATP to detach cross bridges
What stops rigor mortis
proteolytic lysosomal enzymes decompose cells
3 things neuromuscular junction consists of
axonal terminal of a somatic motor neuron
synaptic cleft
Motor end plate
Why are muscle membranes highly folded
increase surface area
Neurotransmitters in skeletal muscle=
acetyl choline
Receptors in skeletal muscle=
nicotinic cholinergic receptors
In a neuromuscular junction what channels are opened on the motor end plate
Na/K+ channels (more sodium goes in )
Choline —>
retaken up by the nerve terminal
Acetate—>
goes into kreb cycle
What does curare do
blocks nicotinic acetylcholine receptors
What does botulinum toxin do
stops the release of the vesicles
Resting membrane potential of skeletal muscle=
-90mV
Threshold of skeletal muscle=
-50mV
What does suxamethonium do
depolarises the muscle membrane preventing end plate potentials
In skeletal muscle what is either side of the transverse tubule
terminal cisternae
A triad in skeletal muscle=
2 terminal cisternae either side of transverse tubule
What happens within the triad
excitation-contraction coupling
In cardiac muscle what is instead of a triad
a diad
why are L-type Ca2+ channels opened
membrane depolarisation (DHP binds to the channel)
What binds to the Ca2+ release channels
Ryanodine
What causes the release of Ca2+ from the SR
mechanical coupling between the L-type Ca2+ and the Ca2+ release channel
In skeletal muscle what isn’t released compared with cardiac
extracellular calcium
What pumps calcium back into the Sarcoplasmic reticulum
Calcium ATPase
What is a muscle twitch
muscle contraction in response to a stimulus that causes action potential in one or more muscle fibres
Three phases of muscle twitch
Lag phase
Contraction phase
Relaxation phases
What is temporal summation
before the muscle has relaxed from contraction it is stimulated again
Increase in contraction strength
what is unfused tetanus
stimulations very close together only a small amount of relaxation
What is fused tetanus
muscle stimulated so much no time for relaxation
What is a motor unit
Motor nerve + all muscle fibres it innervates
innervation ratio=
the number of muscle fibres innervated by a nerve
In a small stimulation what motor neurons are recruited first
small motor neurons innervating small muscle fibres
In a large stimulus what motor neurons are recruited
larger motor neurons and there motor units
isometric muscle contraction=
no change in muscle length
isotonic muscle contraction=
length shortens
As the force of a load increases contraction changes from
isotonic–> isometeric
3 types of skeletal muscle
slow-twitch (type 1) Fast-twitch (type 2b) Fast twitch (type 2a)
Facts about slow twitch type 1 (4)
always oxidative
resistant to fatigue
most myoglobin (red fibres)
Good blood supply
Which fibres have the most myoglobin
slow twitch type 1
What do slow twitch fibres control
posture
Fast twitch type 2b (3) facts
white fibres
poorer blood supply
susceptible to fatigue
Fast- twitch 2a facts
intermediate fibres
oxidative
intermediate myoglobin (pink-red)
Resistant to fatigue
2 types of muscle fibres resistant to fatigue
slow twitch
fast twitch 2a
3 sources of ATP in muscles
creatine
anaerobic respiration
aerobic respiration
Myopathy=
any muscle disease
Myositis =
muscle inflammatory
Muscular dystrophy is
weakening skeletal muscle over time (inherited)
Myasthenia=
increasing weakness on exercise
Myotonia=
failure of relaxation
Channalopathies=
abnormal Na+, K+, CL- channels
