Key Points
Key Points: Mechanism of Muscle Contraction
- Muscle contraction follows the sliding filament theory, where thin (actin) filaments slide over thick (myosin) filaments.
- Contraction begins with a signal from the CNS through a motor neuron; the neuron and muscle fibres together form a motor unit.
- The neuromuscular junction (motor-end plate) is the point where the motor neuron connects to the muscle fibre.
- Acetylcholine is released, which generates an action potential and causes the release of Ca²⁺ from the sarcoplasmic reticulum.
- Calcium ions activate actin, allowing myosin heads to bind and form cross-bridges.
- Cross bridges pull actin filaments, causing sliding, shortening of the sarcomere, and muscle contraction (I-band shortens, A-band remains the same).
- ATP helps in breaking and reforming cross-bridges; when Ca²⁺ is pumped back, the muscle relaxes.
Key Points: Skeletal System
- The skeletal system consists of bones and cartilage and provides shape and support to the body.
- It plays an important role in movement, along with the muscular system (e.g., jaw for chewing, limbs for walking).
- Bones are hard due to calcium salts, while cartilage is flexible due to chondroitin salts.
- Humans have 206 bones in adulthood, while a newborn has about 300 bones that fuse during growth.
- The skeletal system is divided into two parts: the axial skeleton and the appendicular skeleton.
