1. Prayer
Homework
Attendance

2. Musculoskeletal-System-Part-1-4
Ms. Doshi

3. Sarcomere Made of thin and thick filaments Thin filaments:
Made of actin molecules and two other proteins, troponin and tropomyosin.
Thick filaments:
Made of myosin molecules
Each myosin molecule has a head and a tail.

4. Memorize

5. Name It! 2 1 6 4 7 5 3

6. Sarcomere Sarcomere under electron microscope: Z lines M line I band
borders (국경) one sarcomere
Anchors (Verb: 닻으로 고정시키다) the thin filaments
M line
Center of the sarcomere
I band
Has thin filaments only
H zone
Has thick filaments only
A band
Has all of the thick filaments and any overlapping (중복 Verb: 몰고 멀리 육로로 가다 , 가축 떼를 몰고 멀리 육로로 가다) parts of the thin filaments

7. Memorize

8. Name It! 1 5 5 6 4 3 2 1

9. Questions Part 4-1

10. Contraction 3 steps of contraction:
Intiation, Shortening of the Sarcomere, and Relaxation
Initiation occurs in the Neuromuscular Junction:
the area between the sarcolemma of the muscle fiber (plasma membrane of muscle fiber) and the nerve axon terminal

11. Contraction: Initiation
message from motor neuron
Motor neuron depolarizes
Neurotransmitters (ex. acetylcholine) are released from the axon terminal
Neurotransmitters diffuse across the synaptic cleft
Neurotransmitters bind to receptor sites on the sarcolemma
If enough receptors are stimulated, an action potential is made

12. Contraction: Shortening of the Sarcomere1 2 3

13. Contraction: Shortening of the Sarcomere
Calcium binds to the troponin molecules.
The tropomyosin molecules move.
Myosin-binding sites on the actin filaments are exposed (shown).

14. Contraction: Shortening of the Sarcomere
The heads of the myosin molecules move toward and bind to the binding sites on the actin molecules.
Cross bridges are made.
The myosin pulls on the actin molecules.
The thin filaments move toward the center of the H zone and shorten the sarcomere.

15. Contraction: Shortening of the Sarcomere
ATPase activity in myosin head:
allows for powerstroke
steps 4-7
at end of powerstroke:
myosin head separates from actin
The myosin head binds to another actin molecule and repeats the process
myosin crossbridges pulls actin towards the H zone

16. Contraction: Shortening of the Sarcomere

17. Relaxation When stimulation of the sarcolemmic receptors end:
Calcium is pumped back into the sarcoplasmic reticulum
Myosin binding sites are covered by tropomyosin molecules
A new ATP binds to the myosin head
Myosin separates from actin
sarcomere returns to normal width

18. Questions Part 4-2