1. Functions of muscles
a. Feature of muscles is that they can conduct action potentials.
2. Similarities and differences between skeletal and cardiac muscles
a. Skeletal and cardiac muscle have striations.
b. Skeletal:
i. Long parallel multi-nucleated muscle cells.
ii. Cells often called muscle fibers.
iii. Voluntary and must be stimulated by nervous system.
c. Cardiac:
i. Shorter, wider and branched.
ii. Single nucleus.
iii. Intercalated discs that contain gap junctions.
iv. Involuntary.
3. Characteristics of muscles in relation to contraction, excitability, elasticity, distensibility etc.
a. Contraction:
i. Ability of muscle proteins to draw together.
ii. It means “shortening” but more accurately “increase in tension”.
iii. A muscle does not necessarily shorten.
b. Excitability:
i. Responsive to various stimuli.
ii. Stimuli may be chemical, mechanical (stretch) or electrical signals.
iii. Respond by generating electrical changes across plasma membrane.
c. Conductivity:
i. Ability of electrical changes to move or propagate along plasma membrane.
ii. Similar to electrical impulses in copper wire.
d. Extensibility:
i. Can be stretched up to three times their resting length without damage.
e. Elasticity:
i. Ability of muscle cells to return to original shape after being stretched.
4. Muscle cell components- Sarcolemma, Sarcoplasmic reticulum, T tubule, triad etc.
a. Plasma membrane is the sarcolemma.
b. Smooth ER is modified into a sarcoplasmic reticulum and stores Ca++.
c. Cytoplasm of a muscle cell is the sarcoplasm.
Sarcolemma form transverse
tubules that enter deep into
the muscle fiber. Transverse
tubules are flanked by enlarged
sacs of sarcoplasmic reticulum
called terminal cisternae.
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