University:
Michigan State University
Course:
ANTR 211 | Human Tissues and Cells for Medical Illustrators
Academic year:

2019
Views:

259

Pages:

2
Author:

Arielle Armstrong

A Closer Look at Skeletal Muscles Fibers (Cells) and Myofibrils Each muscle fiber (cell) has tiny myofibrils running parallel in the cell. Myofibrils are the contractile elements of muscle cells. Each myofibril is made up of chains of sarcomeres. When you look at a myofibril, you can see dark and light bands. The dark bands are A-Bands. The light bands are I-Bands. These are the visible striations you see in skeletal muscle. This banding pattern of the myofibril is from protein filaments called myofilaments. The thick filaments extend the length of the A-Band. The thin filaments extend across the I-Band partway into the A-Band. In a relaxed muscle, inside the A-band there can be seen a light stripe called the H-Zone, which is lighter because the thick and thin filaments don’t overlap there. The M-Line in the center of each H-Zone is where the thick filaments connect. Down the center of the I-band there is a line called the Z-Line. This is the point of attachment of the thin filaments. The region of the myofibril, between two Z-Lines is called a sarcomere. This is the smallest contractile unit of a muscle cell. mitochondria sarcolemma multi-nucleate A-Band one skeletal muscle fiber (or cell) I-Band Myofibril A-Band (Dark Band) I-Band (Light Band) H-Zone Close up of a myofibril myofilaments: thin filament thick filament (Actin) (Myocin) sarcomere Z-Line M-Line An Even Look Closer at a Myofibril (Made up of Bundles of Myofilaments) Illustrated Reveiw: Each muscle fiber (cell) has tiny myofibrils running parallel in the cell. Myofibrils are the contractile elements of muscle cells. Each myofibril is made up of chains of sarcomeres. When you look at a myofibril, you can see dark and light bands. The dark bands are A-Bands. The light bands are I-Bands. These are the visible striations you see in skeletal muscle. This banding pattern of the myofibril is from protein filaments called myofilaments. The thick filaments extend the length of the A-Band. The thin filaments extend across the I-Band partway into the A-Band. In a relaxed muscle, inside the A-band there can be seen a light stripe called the H-Zone, which is lighter because the thick and thin filaments don’t overlap there. The M-Line in the center of each H-Zone is where the thick filaments connect. Down the center of the I-band there is a line called the Z-Line. This is the point of attachment of the thin filaments. The region of the myofibril, between two Z-Lines is called a sarcomere. This is the smallest contractile unit of a muscle cell. Close up of a Myofibril Myofilaments: thin filament thick filament (Myocin) (Actin) sarcomere I-Band (Light Band) A-Band (Dark Band) Z-Line M-Line H-Zone sarcomere sarcomere