January 9, 2015

Journal: Name three muscles that can be found in your leg.

Muscle Anatomy

Macroscopic Anatomy

- Tendons connect the muscles to bone and are made up of numerous fascicles all clustered together surrounded by epimysium

-Fascicle: a bundle of muscle fibers all put together surrounded by perimysium

-Muscle fiber (muscle cell): a cluster of myofibril surrounded by endomysium

-Myofibrils: long proteins chains that make up muscle cells

- Myofilaments: filaments within the myofibrils

Muscle Coverings Deep Fascia – layer that surrounds the

muscles that allows for communication and connection between them

Epimysium - layer of connective tissue beneath the fascia that decreases the friction between muscles

Perimysium – connective tissues that group muscle fibers into bundles

Endomysium – connective tissue that encloses a single muscle fiber

What is a muscle fiber (cell) made out of?

Microscopic Anatomy:

• The plasma membrane around a muscle fiber is called the sarcolemma.

• Multiple nuclei and mitochondrion are found within the cell

• Cytoplasm, called sarcoplasm, is almost completely filled with long protein chains called myofibrils.

What does each myofibril look like?

• Each myofibril has an alternating light (I) and dark (A) band.

• Each light I band has a darker midline called a Z line.

• Each dark A band has a lighter central area called the H zone.

• Middle area of the H zone is called the M-line.

• One Z line to another Z line is called a Sarcomere.

Myofibril Structure

• Composed of long proteins called myofilaments.

2 Types:1.Thick (myosin) filament – filled with myosin protein heads (act like hands).

2.Thin (actin) filament – made of a protein called actin which allows myosin heads to grab onto it.

Let’s take a closer look at a Sarcomere

Let’s take a closer look at Myosin

Let’s take a closer look at Actin

How do muscles work? Contraction & Relaxation

“The Sliding Filament Theory”

Shortening of sarcomeres =

muscle shortening

1.Nervous system tells a muscle to contract by releasing a chemical messnager acetylcholine (Ach) into the synaptic cleft

2. This causes sodium ion channels to open and sodium rushes into the muscle fiber and excite the muscle producing muscle action potential.

3. Increased sodium levels inside the muscle fiber causes the Sarcoplasmic Reticulum (SR) to release calcium into the sarcoplasm.

SR is a specialized organelle in muscle cells used to store calcium.

4. The presence of calcium causes ATP to interact with the actin and myosin filaments by changing their shape.

5. Myosin heads make crossbridges to actin filaments which pulls the sarcomeres together, contracting the muscle.

6. When an enzyme removes the chemcial messanger ACh from receptors on the sarcolemma, ATP detaches myosin heads and calcium is pumped back into the SR and the muscle relaxes

What happens to our muscles when we die?

Ca+2 leaks out and muscle contract – no ATP to release contraction =

Rigor Mortis

Macroscopic Anatomy of Skeletal Muscle Review

4 7

1

3256