Thin two strands twisted together,
globular protein
Tropomyosin forms long threads that that are wound around the Actin filaments
Myosin
Thick long rod- shaped
fibres with bulbous
heads that project
from it
Made up of two types of
protein; globular protein
which makes up the two
bulbous heads and fibrous
protein which are arranged
into a fillament
Contraction
Nervous control
A action potential activates the contraction
A action potential spreads across the actin filaments causing the tropomyosin molecules to pull away from the actin
This leaves the binding sites on the actin clear the the tropomyosin blocks the binding sites
Sliding filament mechanism
Actin
Used as the anchor for the
myosin molecule's bulbous
head
Myosin
Myosin head attaches
forms bonds to actin and
then pulls itself along
using them
Nervous impulses
move tropomyosin out
of the way of the
binding site
Now the myosin heads can
join with the binding sites on
the actin filament
The angle of the myosin head
changes thus moving the actin
filament as this happens the ADP
is released
ATP attaches to the myosin head
causing the it to detach from the
actin filament
Calcium ions activate ATPase, which
hydrolyses the ATP into ADP this releases
energy used to return the muosin head to its
orginal position
The myosin head, now attached to a ADP
molecule, will be reattached to the actin
filament and so the cycle will begin again
moving the actin filament further along
Neuromuscular Juction
Where a junction links a motor neuron and a skeletal muscle fibre
There are many of these junctions
across the muscle to help create
the contraction faster than if there
was only one junction
When a impulse arrives at the
junction the synaptic vesicles
fuse with the presynaptic
membrane and release their
acetylcholine
Acetylcholine diffuses to the postsynaptic
membrane, making it more permeable to
sodium ions which depolarise the membrane
Acetylcholine is then broken down by
acetylcholinesterase to ensure the muscle is
not over stimulated
The choline and ethanoic acid (acetyl) then diffuse back
into the neuron where they recombine into acetylcholine
using the energy produced by the mitochondria within the
neurone
Muscle Relaxation
Nervous stimulation ceases so calcium ions
are actively transported back into the
endoplasmic reticulum using energy from the
hydrolysis of ATP
The reabsorption of calcium ions allows the tropomyosin to block the actin filament again