1. Anatomy of Skeletal Muscle
The Muscular System
Anatomy of Skeletal Muscle

2. Part I: Macroscopic
In order to generate power, the muscle fibers must be tightly bound by connective tissue

3. Imagine… Imagine a muscle fiber as a single stalk of spaghetti
Several stalks of spaghetti are bundled together in a sheath
Those sheaths are also bundled together until you have a bundle of bundles

4. From Fiber to Epimysium
One muscle fiber is wrapped in an endomysium
Endo=within
Myo=muscle

5. From Fiber to Epimysium
Each endomysium-wrapped fibers is in turn bundled and called a fascicle
These fascicles are in turn wrapped in another layer of connective tissue called a perimysium
Peri=around (think “perimeter”)
I MISSPELLED “FASCICLE” ON THE CROSSWORD! CHANGE IT!
I spelled it “fasicle”. OOPS!

6. From Fiber to Epimysium
These perimysium-wrapped fascicles are bundled together and receive yet one more connective tissue covering: the epimysium
Epi=on top of
The epimysium blends together into a tendon, which in turn connects it to the bone
Question: You had an example of a muscle that was NOT attached to a bone. Which ones did this include?
The facial muscles!

8. Quiz Yourself Write the following in order of increasing “scope”
Muscle fiber, fascicle, epimysium, perimysium, endomysium

10. Let’s Make a Model Get in groups of 4! Green paper = endomysium
Pink paper = perimysium
Yellow paper = epimysium

11. Part II: Microscopic Muscle fiber = muscle cell
Long thin tube with many nuclei
Special names for organelles
Sarcolemma=plasma membrane

12. Muscle Fibers What causes muscle fibers to be striated? Myofibrils
long, ribbon-like organelles that fill the cytoplasm and run the entire length of the cell
Dark and light bands
Known as the A band and the I band

13. How are you going to remember?
In order to remember which band is dark and which is light, use this:
The dArk band is the A band
The lIght band is the I band

14. What about that other stuff?
Z disc
The half-way point right in the middle of the I line
Dark or light?
LIGHT!
There is also the H zone and the M line
I do not expect for you to know the locations, just that they exist.

15. Myofibrils
Myofibrils are actually the chains of contractile units of sarcomeres
Sarcomere = contractile unit of the muscle fiber
Sarcomeres reach from the center of the I band to the next center of the I band

16. Sarcomeres If we zoom in on sarcomeres, we see more banding patterns
Caused by thread-like proteins called myofilaments
These come in thick and thin varieties

17. Myofilaments
The thick filaments are composed of a protein called myosin
These are classified as an ATPase
means it is an enzyme that generates energy through breaking down ATP
The thin filaments are composed of a protein called actin
These anchor to the Z disc (the center of the I band)
This is why the I band is lighter-it only contains thin filaments!
The thick and the thin filaments overlap and are anchored to each other

19. Last but not least…
Also within the muscle fiber there is a special type of smooth endoplasmic reticulum
Called the sarcoplasmic reticulum
Surround each and every myofibril like a sweater surrounds your arm
Stores calcium
The “go” signal for muscle contraction

20. Worksheet #2!