Muscles 2 Flashcards
What is neuromuscular junction?
Small terminal swellings of the axon containing vesicles of ACETYLCHOLINE (Ach).
Nerve impulse causes release of acetylcholine - initiate action potential.
Explain the stages of skeletal muscle contraction from nerve impulse to contraction.
Nerve impulse arrives at neuromuscular junction.
Ach is released into the synaptic cleft, causing depolarisation of the sarcolemma.
Na+ enters the cell through voltage gated Na+ channels.
Depolarisation spreads of the T tubule.
Gated Ca2+ channels open and release the Ca2+ into the sarcoplasm.
Ca2+ binds to subunit of troponin.
Contraction is initiated and Ca2+ returned to the Sarcoplasmic Reticulum.
Name some visual properties of cardiac muscle.
Show striations.
Centrally positioned nuclei.
Show branching.
Have intercalated discs which provide electrical communication through gap junctions and to anchor cells.
What are T tubules and how do they differ between cardiac and skeletal muscle?
T Tubules lie in the sarcolemma and allow depolarisation to run along the cell.
In cardiac muscle they are bigger and wider and run along the Z disc.
In skeletal muscle they lie in the A-I band.
What is the difference between hypertrophy and hyperplasia?
Hypertrophy = enlargement of individual cells Hyperplasia = multiplication of cells
What is atrial distension?
Atrial = heart Distension = state of being enlarged / swollen from internal pressure.
What are natriuretic peptides and what are they marker for if large amounts are found in a blood test?
Natriuretic hormones are hormones released by the heart in heart failure, they decrease blood volume therefore decreasing blood pressure.
ANP (atrial natriuretic peptide) is released in response to atrial distension. High levels are found in patients with elevated blood volume and congestive heart failure (large heart + increased volume = high ANP)
BNP (brain type natriuretic peptide) is released by the ventricles. BNP and NT-pro-BNP are both markers for heart failure.
What are purkinje fibres and their function?
Located in the atrioventricular (AV) bundle of the heart,
Carry nerve impulses to the ventricles.
Abundant in glycogen (glucose) for energy.
Extensive gap junctions (allow impulses directly between cells).
Situated between the epicardium lining of the heart and the cardiac muscle.
What is proteolysis?
The breakdown of protein into smaller polypeptides.
What are some properties of smooth muscle?
Spindle shaped
Central nucleus
No sarcomeres or T tubules
Contractions are slower, larger, require less ATP.
Often form cavities (blood vessels, gut) which modify volume.
What are the role of intermediate filament bundles on smooth muscle?
Bundles are smooth muscle cells.
Ca2+ causes the filaments to squeeze tight, shortening the cells and causing a contraction.
What two types of cells are found in smooth muscle and what are their functions?
Myoepithelial cells - gather around glands, attraction assists secretion.
Myofibroblasts - gather at site of wound healing, cause wound contraction..
Can skeletal, cardiac or smooth muscle repair itself? Explain.
Skeletal - cannot divide however can regenerate through mitosis or fuse with other cells to causes hypertrophy.
cardiac muscle - cannot repair, if damaged fibroblasts lay down scar tissue.
Smooth muscle - Can from new muscle - hypertrophy and hyperplasia.
