Muscle Contraction Flashcards
Structure of skeletal
Striated, long, contain many nuclei and mitochondria
Structure of cardiac
striated, only one nucleus
Structure of smooth muscle
single nucleus, no t tubule system, irregular arrangement
t tubule system is
structural system of membrane folds characteristic of skeletal and cardiac muscle
ryanodine receptors are
calcium release channels in the sarcoplasmic reticulum
troponin is
calcium sensor in skeletal and cardiac muscle
tropomyosin is
protein associated with actin that prevents myosin binding
calmodulin
calcium sensor in smooth muscle cells
myosin light chain kinase (MLCK)
activated by calcium-calmodulin that converts smooth muscle myosin to more active form
organisation of skeletal muscle
-organised as group of bundles (fasciles).
-each fascile has many muscle cells (known as muscle fibre)
-within the muscle fibre (single cell), contains contractile units
neuromuscular junction (NMJ)
a synaptic connection between the terminal end of a motor nerve and a muscle
ACh is released and binds to receptor on muscle membrane. what happens when it reaches receptors?
-membrane channels open and contraction of relaxed muscle fibres begin
opening of what ion channels causes depolarisation?
sodium ion
ACh containing vesicles fuses with membrane. what is released and where does it bind?
acetylcholine is released and diffuses a short distance binding to nAChR
When do muscle fibres relax?
when nervous system signal is no longer present
one sarcomere runs from
one z disc to the next
thick filaments contain
mysoin
thin filaments contain
actin
sarcoplasmic reticulum is
big energy store for calcium
surrounds each myofibril
mechanism behind muscle contraction
role of myosin ATPase
allows myosin to consume ATP and convert it into ADP and pi
sliding filament model
- Both in skeletal and cardiac muscle rise in calcium will bind to troponin and remove tropomyosin from the myosin binding site on actin leaving them exposed
- Allows myosin head (on myosin filament), with hydrolysed ATP to then bind leading to power stroke when ADP released
-More ATP binding will cause detachment of myosin head and the subsequent hydrolysis will cause shape of myosin to change and move along another actin binding site - Causes muscle cell to shorten and contract
summarise muscle contraction
- Neuron AP leads to ca2+ influx
-ACh released
-Activate nAChR - Depolarisation open voltage gated Na+ ion channel
-T-tubule dihydropyridine activated
-Calcium released
-Calcium binds to troponin
-Sliding filament model
V SNAREs found in
vesicles
T SNAREs found in
cell membrane
Two main types of T SNAREs
syntax-1 and SNAP 25
How is a SNARE PIN created?
-Rise in calcium, Ca2+ binds to synaptotagamin
- The SNAP has higher afinity for phospholipids and stops interacting with VSNARE
-brings vesicle a little closer, allowing VSNARE (synaptobrevin) to interact with the TSNARE
what effect does botox have on SNAREs
degrades VSNARE/ TSNARE so vesicle for ACh cannot fuse
what is synaptotagamin?
calcium sensor
role of sarcoplasmic reticulum
big calcium store
function of ryanodine receptor, RyR
Calcium release channel, suppresses the opening and stops leak of calcium
mechanism for calcium release out of RyR
- activated of nAChR
-opening of voltage sodium channels
-passes excitation down the t tubules
-activated DHPR - molecular change thats caused, removes physical interaction
CICR
calcium induced calcium release
function of CICR
calcium influx induces RyR to release calcium
function of CICR
calcium influx induces RyR to release calcium
Summarise muscle contraction
- Neuronal A.P leads to calcium influx
-ACh release
activates nAChr
-depolarisation open voltage-gated Na+ channel - t-tubule DHP activated
- Calcium release
-Calcium ions bind to troponin, leading to removal
of inhibitory tropomyosin
-ATP hydrolysis by myosin
-This primed myosin binds to actin
-As ADP released , it moves the actin towards the middle of the cell leading to cell shortening
difference between skeletal and cardiac for excitation through t tubules
skeletal- voltage sensitive DHP protein leads to calcium release from SarcR
Cardiac- voltage- sensitive calcium channel leads to CICR from SR
What happens in the contractile cycle?
-Cross bridge formation releases pi
troponin bind to myosin head
-power stroke, ADP is released and myosin undergoes a conformational change
pulled towards centre of sarcomere
-ATP binds to myosin, causing detachment of myosin from actin, cross-bridge dissociates
-ATP hydrolysis occurs, cocking myosin head
T-tubule define:
structural system of membrane folds characteristic of skeletal and cardiac muscle
Ryanodine receptors define :
calcium release channels in the sarcoplasmic reticulum
Troponin define:
calcium sensor in skeletal and cardiac muscle
tropomyosin define:
A protein associated with actin that prevents myosin binding
calmodulin define:
calcium sensor in smooth muscle cells
Myosin Light Chain Kinase (MLCK) define:
Activated by calcium-calmodulin that converts smooth muscle myosin to a more active form
