Chapter 9
Muscles and Muscle Tissue
311
9
CHARACTERISTIC
SKELETAL
CARDIAC
SMOOTH
Elaborate
sarcoplasmic
reticulum
Yes
Less than skeletal muscle (1–8% of
cell volume); scant terminal cisterns
Equivalent to cardiac muscle (1–8%
of cell volume); some SR contacts the
sarcolemma
Presence of gap
junctions
No
Yes; at intercalated discs
Yes; in unitary muscle
Cells exhibit
individual
neuromuscular
junctions
Yes
No
Not in unitary muscle; yes in multi
unit muscle
Regulation of
contraction
Voluntary via axon terminals of the
somatic nervous system
Involuntary; intrinsic system
regulation; also autonomic nervous
system controls; hormones; stretch
Involuntary; autonomic nerves,
hormones, local chemicals; stretch
Source of Ca
2
1
for
calcium pulse
Sarcoplasmic reticulum (SR)
SR and from extracellular fluid
SR and from extracellular fluid
Site of calcium
regulation
Troponin on actin-containing thin
filaments
Troponin on actin-containing thin
filaments
Calmodulin in the cytosol
Presence of
pacemaker(s)
No
Yes
Yes (in unitary muscle only)
Effect of nervous
system stimulation
Excitation
Excitation or inhibition
Excitation or inhibition
Speed of contraction
Slow to fast
Slow
Very slow
Rhythmic contraction
No
Yes
Yes in unitary muscle
Response to stretch
Contractile strength increases with
degree of stretch (to a point)
Contractile strength increases with
degree of stretch
Stress-relaxation response
Respiration
Aerobic and anaerobic
Aerobic
Mainly aerobic
Calmodulin
Myosin
(continued)
Table 9.3
Troponin
Actin
Troponin
Actin
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