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.
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