Topic 19: The Muscular System (Vázizmok)

- while there are 3 types of muscle (skeletal, smooth and cardiac) found in the human body, the following section will only deal with skeletal muscle

- about 40% of the body's mass is muscle
- the human body contains more than 600 muscles

-skeletal muscles are attached to bones by tendons (ínak) at 2 points: the origin (eredet), which is attached to the bone that doesn't move when the muscles contracts or relaxes, and the insertion (tapadás), which is attached to the bone that moves

- Muscle pairs can be classified as antagonistic (when the function in an opposite manner) eg. bicep and tricep, or synergistic (when they "work together") eg. extensors and triceps

How muscles contract:

- first we must review the structure of muscles

- muscles are formed of bundles of muscle fibers (izomrost nyalábok)

- each muscle fiber is a single, giant cell.

- within each muscle cell or fiberthere are thousands of myofibrils (izomfonal)

- a myofibril is made up myofilaments, of which there are 2 kinds: myosin and actin

- myosin is referred to as the thick filament, while actin is the thin filament

- the myofilaments are arranged into segments called sarcomeres

Source:  http://www.biologycorner.com/anatomy/muscles/notes_muscles.html

- understanding the structure of the sacromere and the arrangement of myosin and actin allows us to understand the Sliding Filament Theory, which explains how muscle contraction occurs.

- if the video doesn't connect, go to this address:  http://www.youtube.com/watch?v=Ct8AbZn_A8A

Sliding filament theory (becsúszó mechanizmus elmélete)

1.  A nerve impusle causes calcium to be released from the sacroplasmic reticulum into the space around the myofilaments

2.  Calcium binds the troponin complex (which is wrapped around the actin filaments), causing it to shift position and expose the myosin binding sites on the actin filaments

3.  Myosin head binds to actin, ATP reacts to ADP and P

4.  Myosin releases, cocks back and ATP replaces ADP to start a new cycle of motion for myosin

5.  When the nerve impulse ends, calcium is pumped back into the sarcoplasmic reticulum, the troponin complex covers the binding site and the muscle relaxes.

For more explanation go here

Muscles function to let us move (locomotion).  They also produce heat energy as only a part of the energy in ATP is used for motion