Rucete ✏ Biology In a Nutshell
1. Muscle Fiber Structure
- Sarcolemma: the cell membrane of a muscle fiber
- T-tubules (Transverse tubules): extensions of the sarcolemma that carry impulses into the muscle cell
- Sarcoplasm: the cytoplasm of a muscle cell
- Sarcoplasmic Reticulum (SR): stores and releases Ca²⁺, which is essential for muscle contraction
- Myofibrils: long, rod-like structures within the muscle fiber that contain the contractile elements
a) Thin Filament
- Made of actin, troponin, and tropomyosin
b) Thick Filament
- Composed of myosin
c) Z-line
- The boundary of a sarcomere, which is the functional unit of muscle contraction
- Actin (thin) filaments are anchored here
2. Sliding Filament Model of Muscle Contraction
- ATP binds to the myosin head
- Myosin hydrolyzes ATP into ADP + Pi, becoming energized
- Ca²⁺ is released from the SR, binding to troponin, exposing binding sites on actin
- Myosin head binds to actin, forming a cross-bridge
- ADP + Pi are released, and the myosin head pulls the actin filament, sliding it inward
- A new ATP binds to myosin, causing it to release the actin and repeat the cycle
3. Three Types of Muscles
a) Skeletal Muscle
- Voluntary
- Attached to bones
- Responsible for movement of the body
b) Smooth Muscle
- Involuntary
- Found in walls of internal organs (e.g., intestines, blood vessels)
- Controls movements like peristalsis
c) Cardiac Muscle
- Involuntary
- Found only in the heart
- Has characteristics of both skeletal and smooth muscle, including striations and intercalated discs
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Biology in a nutshell