3.6.3 Skeletal muscles

They work in antagonistic pairs

Millions of myofibrils which are made up of two main proteins:
-Myosin(thicker) and actin(thinner) which form sarcromere

1)AP travels through system of tubules that branch through sarcoplasm
2)Tubules come in contact with sarcoplasmic reticulum
3)AP opens Ca$^{2+}$ channels on reticulum which calcium ions now diffuses into muscle cytoplasm
4)Ca$^{2+}$ causes trypomyosin to pull away from binding site on actin filament
5)ADP is attached to myosin head allowing it to bind to binding site on actin filament and form a crossbridge
6)Once attached myosin head changes their angle and pulls the actin filment along while releasing ADP
7)ATP molecule attaches to myosin head causing it to detach from actin filament
8)Ca$^{2+}$ then activate ATPase hydrolysing ATP to ADP releasing enough energy for myosin head to go back to original state
REPEAT UNTIL CALCIUM CONCENTRATION IS LOW IN MYOFIBRIL

Stored in muscles and supplies/ provides phosphate so ADP can reform ATP

A-band = total width of myosin
H- zone = Just the parts with myosin only
I - band = Just actin only
M line = middle point of myosin
z lines = start and beginning of sarcromere

Actin is much paler(thinner muscle) while myosin is darker(much thicker)

I- band becomes narrower and ends up closer together
H zone becomes narrower and smaller
Z lines closer
A band stays same width

Contain large store of myoglobin,rich blood supply and lots of mitochondria.
Contracts slower but can respire aerobically for long periods due to reasons above. Adapted for endurance work

Thicker than slow twitch with more myosin filaments,large store of glycogen and phosphocreatine and high concentration of enzymes involved in anaerobic respiration.
Contract faster to provide short bursts of powerful contractions. Adapted for intense exercise like sprinting