A&P Chapter 8
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How does smooth muscle differ from skeletal muscle under a microscope?
It lacks visible cross-striations
Z line : skeletal muscle ::________: smooth muscle
dense bodies in the cytoplasm
Does smooth muscle contain tropomyosin and troponin?
No, tropomyosin only
What are two characteristics of the sarcoplasmic reticulum in smooth muscle?
- 1) poorly developed
- 2) located near caveolae in the cell membrane
Does smooth muscle obtain most of its energy from ATP or glycolysis?
glycolysis. Smooth muscle has significantly less ATPase than skeletal muscle.
What are the two types of smooth muscle? what are the differences? give an example of each
- Unitary & Multiunitary
- coupled cells in large sheets
- spontaneously active
- contains gap junctions
- ex: walls of hollow viscera
- individual, independent cells
- react only in response to innervation
- ex: iris of eye
How does the ability of smooth muscle to shorten compare to skeletal muscle?
smooth muscle can shorten up to 75% whereas skeletal can only shorten 30%
How does oxygen consumption of smooth muscle compare to that of skeletal muscle?
MUCH LESS - 1% for the same tension
What is the biggest general difference in the receptors on smooth muscle vs skeletal?
smooth muscle has excitatory and inhibitory receptors, skeletal only has excitatory
How does the release of neurotransmitter differ in smooth and skeletal muscle?
- Skeletal: ACh from vesicles enter cleft via exocytosis
- Smooth: neurotransmitter is secreted into the matrix of the muscle cell
What binds to calcium as it enters the cell?
Is the regulation of smooth muscle contraction regulated by myosin or actin?
What are the steps to a smooth muscle contraction?
- 1) calcium enters cell and binds with calmodulin
- 2) calcium-calmodulin complex activates the myosin-light-chain-kinase
- 3) MLCK phosphorylates into myosin light chain
- 4) MLC --> contraction
- 5) calcium is removed via diffusion and ca pumps
- 6) muscle stays contracted until myosin phosphatase removes phos from MLC
How many ATP are required for one smooth muscle cross-bridge?
2 (phosphoylation and dephosphorylation)
How is a smooth muscle cell inhibited?
something closes the sodium and calcium gates and opens the K gates --> hyperpolarization
Can a smooth muscle contract without an action potential occurring?
yes - due to internal release of Ca from SR
How does extracellular [calcium] effect the contraction of smooth muscle?
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