Structure and Function of Skeletal muscle Flashcards
skeletal muscle functions?
move body
control body posture
support and protect
control orifices (voluntary control)
participate in temp regulation
generate peristaltic movement
muscle fibre is enveloped by?
by a sheath of connective tissue
bundle of muscle fibres are enveloped by?
by a sheath of connective tissue
muscle is enveloped by ?
sheath of connective tissue
myofibrils are made up of what?
made up of myofilaments
what myofilaments are myofibrils made up from?
actin and myosin
smallest unit in a myofibril is?
a sarcomere, these are highly aligned
myosin filaments are made up of what?
several myosin molecules
where are myosin filaments located?
they are centred between z-discs and m-lines by Titin (protein that holds them in place)
actin molecules are attached to what protein? allowing?
nebulin, only present in skeletal muscle
ensuring uniformity in length
nebulin?
protein only present in skeletal muscle
T tubules?
transverse tubules
folds within muscle cell membrane
quick conduction of signals onto muscle cells to allow for quick response
correlated with z discs/run through fibres either side of the z-discs
close contact w/ sarcoplasmic reticulum
rapid conduction of action potentials
neuromuscular junction - NMJ?
where nerve cell terminates onto muscle fibre
NMJ?
post synaptic membrane is folded - more receptors so can pick up more of signalling molecule - Ach
when potential arrives at NMJ?
action potential arises on post synaptic side of membrane
when action potential arrives at pre synaptic membrane?
calcium influx due to voltage gated ca channels opening
ach released into synapse
bind to receptors
ion channels open mainly Na
depolarises membrane potential
more positive
forms excitatory post synaptic potential
opening of Na channels further along so ap (action potential) can propagate/move across the whole cell so muscle can start contracting
can only last as long as the ach is binded to receptors
muscle contractions - what causes sliding?
sliding filament mechanism - by binding the myosin heads to actin, followed by bending of the heads towards the sarcomere
muscle contraction - myosin and actin binding to each other?
form a cross bridge
myosin heads have an ATP binding site which hydrolyses ATP
this releases energy which is stored by myosin heads
calcium is released from sarcoplasmic reticulum allows heads to bind and bend = power stroke
when ADP is released following power stroke myosin heads bind to another ATP molecule, breaking the myosin/actin bond (breaks cross bridge)
what controls the muscle contractions?
tropomyosin and troponin
these prevent binding of myosin to actin in resting muscles
when tropomyosin binds?
myosin binding site becomes uncovered as troponin moves - so can bind to actin
slide 14, week 2 sem 2
summary of everything
ion pumps function>
get all calcium back into sarcoplasmic reticulum and can dissociate from troponin so tropomyosin returns to blocking the myosin binding site so muscle can relax
What happens during Rigor mortis?
ATP production ceases
ATP-dependent ion pumps in cells stop functioning
Ca levels no longer maintained
Ca leaks into cytosol
Within a few hours of death, Ca levels are high enough to causes binding of myosin heads
Low ATP means these bonds do not break
enzymes can then break muscle tissue down - this is what happens when you can come out of rigor mortis
hypocalcaemia in ruminants?
paresis (muscle paralysis)
hypocalcaemia in dogs?
tetany (muscle twitching)
what does calcium regulate?
regulates the release of Ach in the synapse between the motor neurone and the muscle cell
in cows, no calcium?
means no transmission of signals across NMJ
in dogs, no calcium?
amount of ACH produced normally is higher so transmission can still occur, only twitching not paralysis
spontaneous action potential generation?
low extracellular calcium depolarises all cells, in neurones this is what the result is
in dogs - hypocslcaemia?
involuntary contractions occur
in cows - hypocalcaemia?
this increased firing frequency of APs due to low extracellular Ca depolarising all cells does not lead to increased muscular activity as the NMJ is blocked
some of ATP produced by muscle fibres is used for what?
used to make creatine phosphate
reaction for the formation of creatine phosphate?
ATP + Creatine → ADP + Creatine Phosphate
What is
ATP + Creatine → ADP + Creatine Phosphate catalysed by?
creatine kinase
main energy substrate?
glucose from glycogen stores leads to glycolysis if not glycogen stores then use oxidative phosphorylation to get glucose
ATP is essential for what during muscle contraction?
energy for power stroke of the cross-bridge
ATP must bind to myosin heads to break cross bridge
Energy released by hydrolysis of ATP is necessary for pumping calcium back into sarcoplasmic reticulum
location of smooth muscle?
attached to bones
location of smooth muscle?
walls of hollow organs, blood vessels, eyes, glands, skin
location of cardiac muscle?
heart
functions of skeletal muscle?
body movements
functions of smooth muscle?
transport of food through the digestive tract, emptying of the urinary bladder, regulation of blood vessel diameter etc.
function of cardiac muscle?
pumping of blood
what is the calcium binding protein for skeletal muscle?
troponin
what is the calcium binding protein for smooth muscle?
calmodulin
what is the calcium binding protein for cardiac muscle?
troponin
Does skeletal muscle have voluntary control?
yes
Does smooth muscle have voluntary control?
No
Does cardiac muscle have voluntary control?
No
How do cells of skeletal muscle communicate?
via NMJ
neuromuscular junction
How do cells of smooth muscle communicate?
tight junctions
How do cells of cardiac muscle communicate?
Via gap junctions
What determines the direction of the reaction between ATP + Creatine in order to form ADP + Creatine Phosphate
concentrations of ATP and ADP
In resting muscles, describe the concentration of creatine phosphate compared to that of ATP:
Creatine phosphate concentration is much higher than ATP
As soon as muscular contractions start, what happens to ATP concentration?
it decreases
