Anatomy of Skeletal Muscle The Muscular System Anatomy of Skeletal Muscle

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

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

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

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!

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!

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

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

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

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

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

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.

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

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

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

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

Worksheet #2!