Muscle Flashcards
What is the structure of skeletal muscle?
Flexor/extensor antagonistic pairs attached to bone
Differentiate between the different types of contraction?
Isotonic contraction: shortening relates to flexor
Eccentric: lengthening relates to extensor
- Both able to contract through both forms
Isometric Contraction: tension changes but the length remains the same
- Change in muscle tone e.g carrying shopping back
What is the structure of myofibers?
- Large and cylindrical
- Multinucleate
- Packed with myofibrils extending around the length of the structure
What are t-tubules?
T tubules: membrane invaginations that contact ECF
- CM of myofiber in more contact with myofibrils
What is the sacroplasmic recticulum?
Sarcoplasmic reticulum: intracellular Ca stores surrounding each myofibril
- In close contact with membrane and t tubules
How does excitation contraction coupling occur in skeletal muscle?
- Z lines come closer together
- Increased Calcium concentration
- Myosin heads pivot
- AP propagates along myofiber T tubules
- Depolarisation activates dihydropiridine receptors (DPHR) so conformational change
- DPHR is on T tubules on sacrolemma (membrane of myofibre) - Change in shape allows DHPR to make contact with ryadine receptors (RyR) on SR
- Opening of RyR so Ca2+ released from intracellular stores in scarolemma
- Depolarisation causes increase in intracellular Ca
AP–>conformational change on DPHR–>touch RyR–>release intraceulluar Ca
What is the structure of a sarcomere?
Z line: defines SM lateral boundaries
Actin: polymer of thin filament of two twisted alpha helices, displays polarity
Myosin: thick filament–> “motor proteins”
- Contains "globular heads" that interact with actin Titin: very large "spring like" filament anchoring myosin to Z line, keeps myosin in bplace Nebulin: large filament associated with actin, doesn't really do anything Cap Z and tropomodulin: associated with positive and negative ends of actin respectively
Tropomysoin: forms a chain along each actin filament and associated with the tropomyosin is another protein, troponin.
Explain the sliding filament theory?
- In calcium presence troponin moves (forms helix around actin) from tropomyosin chain
- Movement exposes myosin binding site on actin chain
- Charged myosin head binds to exposed site on actin filament (head has ADP bound)
- The binding and ADP discharge causes myosin head to pivot –> pulls actin filament towards centre of sarcomere
- ATP binds releasing myosin head from actin chain
- ATP hydrolysis to ADP provides energy for myosin head to recharge
What is the structure of cardiac muscle?
- Cardiomyocytes are striated
- Unicellular and uninuclear
- Intercalated disk: specialised disc connecting individual cardiomyocytes
○ Have desmosomes (hold membrane structures together) and gap junction (allows electrical communication between cells) - Contraction mechanism is the same as skeletal muscle
How does EC coupling occur in cardiac muscle?
- AP generated by pacemaker cells in nodes
- AP moves down T tubules and opens VGCC so Ca influx
- no contact between the VGCC and RyR
- Ca binds to RyR to cause calcium induced calcium release (CICR)
- Initiates contraction by binding to troponin
- Further depolarisation
- The rest is the same except there is a different type of troponin
AP–>VGCC–>RyR–>CICR–> further depolarisation
What is the structure of smooth muscle?
- Present in walls of hollow organs e.g blood vessels, GIT
- Multiplies and gets bigger without gym so doesn’T need as much attention as caridac and skeletal
- Smooth because no striated actin-myosin pattern, although the filaments are still present
- Contracts much more slowly than other two
- do not express voltage-gated Na+ channels
- irregular actin and mysoin arrangment
How does EC coupling occur in smooth muscle?
- Depolarisation opens VGCC (slightly different than those in cardiomyocytes) so Calcium influx
- Calcium moves into cell and binds to Calmodium (CAM)
- Activates Myosin Light chain kinase (MLCK)
- MLCK phosphorylates myosin light chains (MLC20) allowing them to form cross-bridges with the actin filaments
- Contraction
- Also causes vasoconstriction
VGCC–>CAM–>MLCK–>change in appearance of MLC20–>contraction
how does muscle maintain low Ca concentration?
Ca2+- ATPase that continuously pumps Ca2+ from the cytosol into the sarcoplasmic reticulum (SR).
