Transcript Muscle Contraction - Warren County Schools

Muscle Contraction
1. Acetylcholine (Ach) is released
from the axon terminal (nerve) into
the synaptic cleft and binds to Ach
receptors in the sarcolemma
(muscle cell)
2. Action potential is generated and muscle
fiber becomes excited
3. Calcium (Ca2+) is released from the
sarcoplasmic reticulum
4. Ca2+ binds to troponin, causing tropomyosin
on actin to shift and myosin binding sites
become exposed.
5. ATP binds to myosin head,
causing it to be in the “cocked”
position.
6. Actin and myosin bind,
forming a cross-bridge
7. Myosin head flexes, causing actin to be
pulled along the myosin, shortening
the sarcomere (remember, muscles
only pull/shorten/contract)
Muscle Relaxation
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Another ATP molecule releases myosin head
from actin.
Ca2+ is transported back to the sarcoplasmic
reticulum, causing tropomyosin to re-cover the
myosin binding site
Sarcomere “slides back” to its original position.