Muscle 2 Flashcards
Semester 1 year 1
What is cardiac muscle made up of?
-cardiomyocytes
-myocytes are shorter + more branched
-intercalated disks - where myocytes join together
How do cardiomyocytes appear?
Striated
How is each cardiac muscle cell coupled to its neighbour?
-electrically
-by gap junctions
Is smooth muscle striated or non-striated?
Non-striated
What is smooth muscle involved in and is its control more complex?
-involved in mechanical control of organ system
-more complex - can involve hormones, autonomic nervous system or inflammatory mediators
What are dense bodies?
Where actin fibres join together
What are the 2 classes of smooth muscle?
Multiunit + unitary
Describe multiunit smooth muscle
-cells aren’t coupled to each other
-each cell receives individual innervation
-electrical isolation of cells allows fine motor control
Describe unitary smooth muscle
-some cells have their own nerve supply
-the rest receive information from other cells via gap junctions
How is intracellular calcium increased in skeletal muscle?
-depolarisation activates L-type calcium channels in T-tubule membrane to open
-influx of calcium into cell
-causes mechanical tethering between L-type calcium channels in T tubules + calcium release channels (ryanodine receptors) in SR membrane
-calcium release channels in SR open and calcium moves into cytoplasm
How is intracellular calcium increased in cardiac muscle?
-have T tubules, but only close to 1 branch of SR - Dyad
-lie at Z line region of sarcomere
-no mechanical interaction between voltage gated calcium channels in T-tubule + Ryanodine receptors in SR
-influx of calcium through T-tubules activates ryanodine receptors (calcium induced calcium release - CICR)
How is intracellular calcium increased in smooth muscle?
-no T-tubules + Triad/Dyad structure, have shallow invaginations (cave)
-peripheral SR encircles caveolae
-central SR runs through cell
-changes in action potential can activate L-type calcium channels
-leads to CICR via activation of ryanodine receptors in SR membrane
-activation of Gq coupled receptors leads to IP3 production + stimulation of IP3 receptors in SR membrane
-causes increase in intracellular Ca2+
How is calcium removed from calcium terminated muscle contraction?
-removed from cytoplasm
-across cell membrane by means of plasma membrane calcium ATPase (PMSA) or electrogenic sodium/calcium exchanger (NCX)
-back into SR via sarco/endoplasmic reticulum ATPase
How does the sarcomere contract?
-calcium binding occurs on troponin complex
-initiates a change in shape of the molecules, exposing binding sites
-myosin head has high ATPase activity but very low at resting conditions
What is the troponin complex made up of and what does each part do?
-troponin C - calcium binding part of complex
-troponin I - lies over active myosin binding site
-troponin T - couples to troponin myosin
