cardiac muscle

Question 1

myocardial infarction

Answer 1

a heart attack

Question 2

the heart is a dual-circuit pump

Answer 2

• ventricles fill the atria
• then there is a near-synchronous contraction of the ventricles to eject blood in the arteries
• at the same time the atria fill with venous return
• CO=HR X SV
• cardiac output increased by increased HR or stroke volume.

Question 3

adaptations for synchronous cell activity

Answer 3

gap junctions in intercalated disks act as leaky boundaries between cardiac muscle cells.
cardiac muscle cells are branched- have boundaries with several other cells
gap junctions- firm physical attachments between cells [via desosomes] and electrical activity [via gap junctions]

Question 4

cross-bridge cycle

Answer 4

1) splitting of ATP to ADP +Pi is required to ‘cock’ the myosin head
2) binding to of myosin to actin releases inorganic phosphate (Pi)
3) pulling on the actin by the myosin hear releases the ADP
4) thy myosin head is then in rigor
5) more ATP is required to detach the head and re-start the cycle

Question 5

how are cardiac cells adapted for metabolic demand?

Answer 5

40% of cell volume in cardiac muscles is mitochrondria. the cells are constantly synthesising and using ATP

Question 6

how cardiac cells differ from skeletal cells

Answer 6

• small cells
• single nucleus
• T-tubule and SR system less well developed than skeletal muscle
• mitochondria 40% of cell volume
• branched cells linked together by intercalated disks

Question 7

tetanus in cardiac muscle

Answer 7

tetanus is undesirable in cardiac muscle because the heart needs time to relax to allow blood to flow into the heart- once the ventricles have contracted they must relax to be able to fill with blood for the next heartbeat