Heart

Histology
  • Striated muscle but fibres divide and recombine.
  • Though each cell is dictinct withits own nucleus, the cells are joined end to end by specialised cell junctions called intercalated disks. These junctions offer a veru weak resistance to electrical flow and thus the heart muscle acts as a syncetium.
  • In contrast with skeletal muscle, the heart muscle tissue can contract without a nervous stimulation.

Other differences between cardiac and skeletal muscle tissue

  • Sarcoplasmic Reticulum is less extensive in cardiac muscle.
  • Calcium sensitivity of intact cardiac muscle is greater than skeletal muscle. Because of this increased sensitivity, cardiac muscle contraction is longer than skeletal muscle.
  • Cardiac muscle cannot undergo tetanisation. This occurs as the absolute refractory period in the cardiac muscle cell is longer than for skeletal muscle. In fact absolute refractory period is almost as long as the contraction period - 200 msecs.
  • Cardiac muscle resists wear and tear better than skeletal muscle. This is important as cardiac muscle contracts som 100,000 times/day (in 70 years this totals to 2.5 billion times).
  • Cardiac muscle is very susceptible to oxygen lack - can withstand not more than 30secs without oxygen before they stop working.
  • The cardiac muscle as a whole, and not only the single muscle fibre, obeys the all or none rule i.e. if one muscle cell in the syncetium contracts, the rest contract at the same time.