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Skeletal muscle composition
- smallest to largest:
- 1. actin and myosin
- 2. sacromere
- 3. myofibril
- 4. muscle fiber
- 5. bundles of muscle fibers
- 6. muscle
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Sliding-filament model
- 1. when the myosin head is in low configuration it is bound to ATP and the head is bent
- 2. the myosin head hydrolyzed to ATP to ADP and then it is in its high energy state, and it is lifted up
- 3. them myosin head binds to the actin filament
- 4. when the myosin head releases the ADP it returns to low energy configuration. this means it tries to re-bend, this causes the sliding
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The role of calcium
calcium must bind to the tropinin complex, which is located on the tropomyosin, so that it will expose the myosin binding site
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Regulation of skeletal muscle contraction
- 1. acetylcholine is released from the motor neuron and binds to the receptors on the muscle fiber
- 2. this causes the APs to travel down into the muscle fiber using the T-tubules
- 3. the AP triggers the sarcoplasmic reticulum to release calcium
- 4. the calcium binds to the troponin complex, exposing the myosin binding sites
- 5. the calcium is actively transported back to the SR
- 6. the tropomyosin covers the myosin sites
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The nervous system controls muscle contraction by...
- 1. controlling the number of muscle fibers contract
- 2. controlling the strength of the contractions
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Motor unit
- single motor neuron and all the muscle fibers it controls
- **each muscle cell is controlled by only one motor neuron**
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Types of muscles
- cardiac= only in the heart, striated=layers of actin and myosin
- smooth= found in the walls of hallow organs, contraction is involuntary, unstriated,
- intercalated disks= allows ions to pass b/w cells so APs pass quickly to all cells
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Calcium in smooth muscle contraction
- smooth muscle have no troponin or T tubules
- calcium enters through the plasma membrane
- the calcium binds to calmodulin
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Types of skeletal systems
- exoskeletons- in insets and arthropods, made from chitin
- hydrostatic skeletons- no hard parts, fluid cavity that protects the organs PERISTALSIS
- endoskeletons- aids in locomotion and to keep the shape
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Endoskeletons
- in mammals
- 2 types:
- cartilage= found in sharks; made of connective tissue
- bone= made from calcium carbonate; collagen; Hydroxyapatite
- 206 bones in humans
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Bone
- osteoblasts= build up ones
- osteoclasts= break down bones
- tendons= attach muscles to bone
- ligaments= bone to joints
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