1. 2. Striation Pattern of Sarcomere
A band: Thick myofilaments extend across this band, but thin filaments extends only to H Zone
I band: Contain only Thin myofilaments
Z disc: Beginning of Sarcomere, anchor Thin Myofilam.
H zone: Contains only thick Myofilaments
M line: middle of Sarcomere
Sarcomere
Z Disc
H Zone M
Portion of a Myofibril I I
A Band

2. Arrangement of the Filaments in a Sarcomere
Longitudinal section within one sarcomere
Figure 9.4d

3. Microscopic Anatomy
Sarcomere
Thick Myofilament
Thin Myofilament

4. III. Physiology of Skeletal Muscle Fibers A
III. Physiology of Skeletal Muscle Fibers A. OVERVIEW OF STEPS TO MUSCLE CONTRACTION
* Brain: message to move  spinal cord  nerve  Axon Terminal
1. Events at Neuromuscular Junction: pp
Axon of Motor Neuron sends Action Potential to Sarcolemma
2. EXCITATION-CONTRACTION COUPLING: 289
A second Action Potential moves along sarcolemma
Sarcoplasmic Reticulum releases Calcium
Calcium binds to troponin and then Myosin Head binding site is uncovered
Contraction begins
3. CROSS BRIDGE CYCLE: (Sliding Filament Model):
Myosin Heads attach to Actin and pull it inward 
Myofibrils shorten 
Muscle fibers shortens = Muscle contracts

5. Major external ion = Na+ Major intracellular ion = K+
Physiology of Skeletal Muscle Fibers … B. Events at Neuromuscular Junction– Details
Action Potential #1 travels down Axon to Terminals = Caused by ion movement
Major external ion = Na+
Major intracellular ion = K+
a) Resting Membrane: initially inside of cell is negative due to having more negative Chemicals
a) Na+ enters axon = Depolarization and inside of cell becomes positive
b) K+ leaves axon = Repolarization and inside of cell goes back to negative
Figure 9.7 (a-c)

6. 2. Synaptic Vesicles release Ach via exocytosis
3. Ach diffuses across synapse
4. Ach binds with Ach receptors of motor end plate
Axon Terminal
Receptor

7. Run the Muscle Contraction Video- part 1

8. Initially Sarcolemma is in the Resting Membrane state
Physiology of Skeletal Muscle Fibers … Binding of Ach to Receptors on Sarcolemma then triggers changes in Muscle Fibers and leads to C. Excitation-Contraction Coupling: events from transmission of action potential along sarcolemma to the beginning of contraction
Initially Sarcolemma is in the Resting Membrane state
2. #2 Action Potential
Receptors allow Na+ ions to enter and K+ ions to leave the muscle fiber; but more Na+ enters making the inside of the cell positive
More Positive outside
Negative inside
Outside Cell
Inside Cell
Figure 9.8a

9. Initially Sarcolemma is in the Resting Membrane state
Physiology of Skeletal Muscle Fibers … Binding of Ach to Receptors on Sarcolemma then triggers changes in Muscle Fibers and leads to C. Excitation-Contraction Coupling: events from transmission of action potential along sarcolemma to the beginning of contraction
Initially Sarcolemma is in the Resting Membrane state
2. #2 Action Potential
Receptors allow Na+ ions to enter and K+ ions to leave the muscle fiber; but more Na+ enters making the inside of the cell positive
More Positive outside
Negative inside
Outside Cell
Inside Cell
Figure 9.8a

10. Excitation-Contraction Coupling …
2. #2 Action Potential …
Charge inside cell changes from negative to positive
If enough Na+ enters, an action potential travels down Sarcolemma
It moves out in all directions via Depolarization and Repolarization
Outside Cell + + + + + + +
Inside Cell +
Na++ K+
Figure 9.8b

11. Excitation-Contraction Coupling … 2. Action Potential …
©2007 Thomson Higher Education
After Action Potential has ended, the Resting state is restored by the Na+-K+ pump
Na+
Figure 9.8d

12. Excitation-Contraction Coupling … Action Potential …
Action potential travels down the T-tubules
The Sarcoplasmic Reticulum releases Ca+2 into the cell
High Ca+ in the Sarcoplasm ultimately leads to muscle contraction
Figure 9.8c

13. Run the Muscle Contraction Video-part 2

14. END