Muscle Contraction!
Using the word or words provided, create a sentence or sentences that explains each step of the muscle contraction.
Step 1: Creating muscle contraction
1. Brain, motor neuron, axon terminal
a. The brains sends an electrical impulse (action potential) down a motor neuron until it reaches and axon
terminal
2. Vesicle, neurotransmitter
a. Inside the axon terminal there are vesicles containing the neurotransmitter (Acetylcholine)
3. Synaptic cleft, receptor proteins
a. The electrical impulse triggers the vesicles to move to the end of the axon terminal and dump the
neurotransmitter into the synaptic cleft
b. The Neurotransmitter crosses the synaptic cleft by diffusion and binds to the receptor proteins on the
sarcolemma
4. Sarcolemma, sodium, depolarization
a. When the acetylcholine binds to the receptor proteins the sarcolemma becomes permeable to Sodium
(found in high concentration outside the cell)
b. Sodium rushes through the sarcolemma into the cell causing depolarization of the membrane
5. Action potential, t-tubules
a. When the sarcolemma is depolarized a second action potential is created
b. The action potential travels the length of the sarcolemma and deep into the cell by way of the T-Tubules
6. Sarcoplasmic reticulum, Calcium ions
a. The action potential reaches the sarcoplasmic reticulum and releases stored calcium ions
7. Troponin, Tropomyosin, Actin
a. The calcium ions bind to the troponin and tropomyosin complex found on the thin Actin filament
b. The troponin tropomyosin complex moves
8. Myosin heads, binding sites, ATP
a. Because the troponin tropomyosin complex moved the Myosin binding sites on actin open up and
myosin binds to actin
b. Using ATP the myosin heads pull on the actin filaments
9. Sarcomere, contraction, z-lines
a. When myosin pulls on actin the z-lines move closer together causing contraction of the sarcomere
10. Endomysium, muscle fiber, myofibril
a. The shortening of the myofibril shortens the muscle fiber which pulls on the endomysium (connective
tissue surrounding the muscle fiber)
11. Perimysium, fascicle
a. The shortening of the muscle fiber shortens the fascicle which pulls on the perimysium (connective
tissue surrounding the fascicle)
12. Epimysium, muscle
a. The shortening of the fascicle shortens the muscle which pulls on the epimysium (connective tissue
surrounding the muscle)
13. Tendon, bone, movement
a. The shortening of the muscle pulls on the tendon (connective tissue connecting the muscle to the bone)
b. The muscle pulling on the bone causes movement
Step 2: Restoring resting state to repeat muscle contraction (these things must occur before the muscle can contract
again)
1. Reabsorption, Calcium, sarcoplasmic reticulum
a. Calcium is reabsorbed in the sarcoplasmic reticulum which moves troponin and tropomysoin back onto
the myosin binding sites on actin
2. Active Transport, Sodium, Potassium, repolarization
a. In order to repolarize the membrane 3 sodium have to be pumped out of the cell for every 2 potassium
that are pumped in by way of active transport (active transport pumps ions from low to high
concentration across the membrane and requires energy and a transport protein)
3. Reabsorption, neurotransmitter, enzyme, decomposition
a. The neurotransmitter (acetylcholine) must be removed from the synaptic cleft in order to depolarize the
membrane
b. This is accomplished by reabsorbing some of the acetylcholine back into the axon terminal
c. The remainder of the acetylcholine is broken down by an enzyme
4. Lengthening, Sarcomere, Relaxation
a. Once the above listed mechanisms occur, the myosin heads release the actin filament leading to
lengthening of the sarcomere and therefore relaxation of the muscle