antomy 25 muscle

Sheet of connective tissue that surrounds individual muscle cells.

Sheet of connective tissue that surrounds bundles of muscle cells ( fascicles ).

Sheet of dense irregular connective tissue that surrounds outside of entire muscle. It is continuous with tendon.

Fascicles are bundels of muscle cells.

Myofibers are muscle cells that make up skeletal muscles. They are very long, have many nuclei in them, and kind of taper at their ends. The nuclei are located just below the cell membrane.

The cell membrane of the muscle.

The cytoplasm of muscle cells.

A sarcomere is a section of muscle cell spanning between two Z-lines.

Attached to the z-lines and extending toward the center of the sacromere are myofilaments called thin filaments ( it's actually actin ) made up mostly of the protein actin.

At the center of the sacromere are thick filaments ( its actually myosin ) made mostly of myosin which overlap the inner ends of the actin filaments. These thick filaments also contain ATPase enzymes that turn ATP into ADP +P to produce energy. The ends of myosin filaments have myosin heads on them.

The origin attachment of a muscle is the point at which the muscle attaches to the bone that does not move much.

The insertion point of attachment on a muscle is the point at which the muscle attaches to the bone that does move.

Muscles that span more than one joint and cause more than one joint to bend.

Myofillament - myofibril - myofiber.

The A-band in a muscle cell is the length of the thick / myosin fillament at the center of the sacromere plus the internal ends of the thin / actin fillaments.

At the center of the a-band is the H-zone, this is between the internal ends of the thin - actin fillaments.

At the center of the H-zone is the M-line which is made up of tiny rods ( what are the rods? ) that keep the bundles of thick filaments / myosin held together.

I bands are the bands between A-Bands, they appear light / less dark under magnification, these bands contain just the thin / actin filaments.

In the center of the I-bands are z-lines. Two z-lines border a sacromere. Z-lines are points at which elasitn and actin connect to each other.

Myofillaments are contractile proteins.

Actin: G-actin attached to more g-actin to make F-actin chains, two F-actin chains to make an Actin molecule.

Tropomyosin: Two polypeptide chains make a tropomyosin molecule.

Troponin: TnC binds Ca+ ions, TnT links troponin to tropomyosin, TnI inhibits actin-myosin binding.

Myosin molecule is made of a tail + hinge area and two heads. The head area has actin bingind site and ATP binding site. These two binding sites allow the the head to move back and forth, pulling the myofilament along with it.

The thick myofilament is bundled myosin molecules with heads projecting out in a kind of spiral.