Skeletal Muscle Fiber Contraction

Introduction: Now for the last section of Unit Three! We are going to be taking a closer look at how a muscle contracts as well as the different parts of a muscle. First, let's look at some vocabulary.

Slide to the left, then slide to the right (vocabulary):

~Sarcolemma: Plasma membrane of muscle fiber; can generate or carry action

Potential along the length

~Sarcoplasmic Reticulum: Endoplasmic Reticulum of muscle that holds calcium

Ions

~T (Transverse) Tubules: Dip down into the cell and come into contact with

Sarcoplasmic reticulum at calcium storage sites

~Myofibrils: Contractile part of the muscle fibers

*Sarcomere: bundle of myofibrils that has two types of protein

Myofilaments

1. Myosin: thick filaments made up of protein

2. Actin: thin filament made up of protein

~Myosin is shaped like a golf club, with the head sticking out (cross-bridge)

*act as ores during contraction

~Actin contains tropomyosin and troponin

Below is a picture from http://www.mhhe.com that shows the structure of a muscle fiber.

Sliding:

From http://www.mhhe.com, here is a picture that gives a general idea as to how a muscle contracts. Continue further to learn more about myosin and actin and what role they play.

1. Muscle is stimulated

2. Impulse travels down a T tubule

3. Calcium is released from the sarcoplasmic reticulum

4. Muscle fiber contracts

5. Myosin, in a way, pulls the actin past it with its “ores,” going through a

Cycling shape change in the presence of calcium

6. The sliding of myosin and actin past each other is called

The sliding filament model

Below is a picture of myosin and actin at work with calcium attaching to it. This picture was found at http://www.niaaa.nih.gov.

7. Uses a lot of energy

8. Energy is extracted in three different ways

a. Fermentation

b. Aerobic in Kreb’s Cycle

c. Anaerobic using creatine; quick way to produce ATP but
can’t do it very long

Control of Muscle Fiber Contraction:

~Neuro-Muscular Junction: Region where an axon terminal approaches a muscle

Fiber; the synaptic cleft separates the axon terminal from the sarcolemma

Of a muscle fiber.

~Axon terminals have synaptic vesicles filled with acetylcholine

~When nerve impulses get to the axon terminal, the synaptic vesicles release

Acetylcholine into the synaptic cleft.

~When acetylcholine is released, it diffuses and binds to receptors in the

Sarcolemma, down T tubules, to the sarcoplasmic reticulum releasing

Calcium, thus ending in sarcomere contraction

Below is the picture of a neuromuscular junction from http://www.shelfieldpeonline.co.uk.




Conclusion: That about wraps it up! Explore further and you will see a simple lab about muscle workings (which turned out a little different for me!) as well as a lab that includes an egg cell body! Enjoy!