Tissues 7 Flashcards
What are the features of skeletal muscle structure?
- Long and cylindrical cells
- Multinucleate
- Dark and light bands give striated appearance
What is the sarcomere?
The functional unit of muscle which lies between two Z lines.
What are T-tubules?
Invaginations of the myofibril that come into contact with the extracellular fluid
What is the sarcoplasmic reticulum?
Specialised network of intracellular calcium stores that surround each myofibril.
What is actin?
Thin polymeric filament that is composed of two alpha helices twisted together. It displays polarity.
What is myosin?
Thick filaments that contain globular heads that can interact with actin to facilitate muscle contraction.
What is titin?
Very large and spring-like filament that anchors actin to the Z lines.
What is nebulin?
A large filament associated with actin.
What is tropomyosin?
An elongated protein bound to actin.
What is CapZ?
Filament associated with positive end of actin.
What is tropomodulin?
Filament associated with negative end of actin.
How is calcium release initiated in muscle contraction?
1) AP propagates along myofibril
2) Depolarisation activates dihydropyridine receptors, causing conformational changes
3) Change is transmitted to ryanodine receptors on SR, opening ryanodine receptor causing Ca2+ to be released.
4) Depolarisation further increase Ca2+ influx.
What happens in the presence of calcium?
Troponin moves to the tropomyosin chain, exposing the myosin binding sites on the surface of actin.
How does the sliding filament theory work?
1) In the presence of calcium, calcium binds to the troponin, causing a conformational change of the troponin-tropomyosin complex, causing it to move into a groove of the actin chain, revealing open binding sites
2) Charged myosin heads bind to exposed actin sites
3) Discharge of ADP results in power stroke, pulling actin towards centre of sarcomere
4) ATP binding releases myosin from actin
5) ATP hydrolysis provides energy to re-energise and re-orientate the myosin heads for the next contraction
What is isotonic contraction?
Where the muscle length changes but tension remains the same.
What is isometric contraction?
Where the muscle length or tension does not change.
What are two types of pacemaker cells in the heart?
Sinoatrial node (spontaneously active) and the atrioventricular node (base of RA).
What are two types of conducting cells?
Bundle of His and Purkinje fibres.
What do they intercalated disks do?
Connect individual myocytes to one another.
What do gap junctions do?
Allow action potentials to spread rapidly from one cell to another.
How does EC coupling work in smooth muscle cells?
1) Depolarisation opens Ca2+ channels
2) Ca2+-CAM complex activates myosin light chain kinase (MLCK)
3) MLCK phosphorylates myosin light chains
4) Cross bridges are formed with actin, resulting in contraction
Where is smooth muscle found?
In the walls of hollow organs.
