Summary contraction and relaxation

1. 1. A WAVE of depolarization spreads
equally across the surface of the
sarcolemma in all directions.

2. 2. The depolarization wave follows the
surface of the transverse tubules which
brings the it deep inside the muscle fiber
and parallel to the terminal cisternae of the
sarcoplasmic reticulum.

3. 3. After the “signal” has completely
depolarized the sarcolemma, it enters the
sarcoplasmic reticulum.

4. 4. When the depolarization wave hits the
sarcoplasmic reticulum it causes the release
of Ca
+2
ions into the sarcoplasm.

5. 5. Chemical cross bridges form between
actin and myosin within the sarcomeres
whenever Ca
+2
ions are released into the
sarcoplasm.

6. 6. The cross bridges “jump” or “ratchet”
down the myosin thus sliding the actin
over the myosin.

7. 7. This causes the sarcomere to shorten,
thus the muscle is contracted.

8. 1. A WAVE of depolarization spreads equally across the surface of
sarcolemma in all directions.
2. The depolarization wave follows the surface of the transverse tubules
which brings the it deep inside the muscle fiber and parallel to the
terminal cisternae of the sarcoplasmic reticulum.
3. After the “signal” has completely depolarized the sarcolemma, it
enters the sarcoplasmic reticulum.
4. When the depolarization wave hits the sarcoplasmic reticulum it
causes the release of Ca
+2
ions into the sarcoplasm.
5. Chemical cross bridges form between actin and myosin within the
sarcomeres whenever Ca
+2
ions are released into the sarcoplasm.
6. The cross bridges “jump” or “ratchet” down the myosin thus sliding
the actin over the myosin.
7. This causes the sarcomere to shorten, thus the muscle is contracted.

9. 1. A WAVE of depolarization spreads equally across the surface of
sarcolemma in all directions.
2. The depolarization wave follows the surface of the transverse tubules
which brings it deep inside the muscle fiber and parallel to the terminal
cisternae of the sarcoplasmic reticulum.
3. After the “signal” has completely depolarized the sarcolemma, it
enters the sarcoplasmic reticulum.
4. When the depolarization wave hits the sarcoplasmic reticulum it
causes the release of Ca
+2
ions into the sarcoplasm.
5. Chemical cross bridges form between actin and myosin within the
sarcomeres whenever Ca
+2
ions are released into the sarcoplasm.
6. These cross bridges “jump” or “ratchet” down the myosin thus sliding
the actin over the myosin.
7. This causes the sarcomere to shorten, thus the muscle is contracted.

10. 1. A WAVE of depolarization
spreads equally across the
surface of the sarcolemma
(from the NMJ) in all
directions.
2. The depolarization wave
follows the surface of the
transverse tubules which brings it
deep inside the muscle fiber and
parallel to the terminal cisternae
of the sarcoplasmic reticulum.
3. After the “signal” has
completely depolarized the
sarcolemma, it enters the
sarcoplasmic reticulum.
1. A WAVE of repolarization
spreads equally across the
surface of the sarcolemma
(from the NMJ) in all directions.
2. The repolarization wave
follows the surface of the
transverse tubules which brings it
deep inside the muscle fiber and
parallel to the terminal cisternae
of the sarcoplasmic reticulum.
3. After the “signal” has
completely repolarized the
sarcolemma, it enters the
sarcoplasmic reticulum.

11. 4. When the depolarization
wave hits the sarcoplasmic
reticulum it causes the release of
Ca
+2
ions into the sarcoplasm.
5. Chemical cross bridges form
between actin and myosin
within the sarcomeres whenever
Ca
+2
ions are released into the
sarcoplasm.
6. The cross bridges “jump” or
“ratchet” down the myosin thus
sliding the actin over the myosin.
7. This causes the sarcomere to
shorten, thus the muscle is
contracted.
4. When the repolarization wave
hits the sarcoplasmic reticulum it
causes the absorption of Ca
+2

ions from the sarcoplasm.
5. Chemical cross bridges break
between actin and myosin
within the sarcomeres whenever
Ca
+2
ions are absorbed from the
sarcoplasm.
6. The cross bridges disappear
thus sliding the actin back over
the myosin.
7. This causes the sarcomere to
lengthen, thus the muscle is
relaxed.