Muscle Pt. 3 Flashcards
How is smooth muscle activated?
Involuntarily.
What are the 2 types of smooth muscle?
- Single unit/unitary/visceral.
- Multiunit.
How does smooth muscle compare to skeletal muscle fiber in size? Length?
- Smaller.
- Much shorter.
How are multiunit smooth muscle fibers described?
Individual fiber that each have their own motor neuron terminals w/ few gap junctions between neighboring fibers.
What happens when multiunit smooth muscle fibers are stimulated?
Only that fiber is stimulated.
Where are multiunit smooth muscle fiber found?
- Airways to lungs.
- Ciliary body.
- Muscles of iris.
- Pilo-erector muscles.
- Walls of large arteries.
How are visceral smooth muscle fibers described?
Auto-rhythmic fibers connected by gap junctions that allow for the communication of an action potential to permit contraction in unison.
How are visceral smooth muscle fibers arranged?
A tubular fashion in the form of either circular or longitudinal sheets.
What happens when a signal (autorhythmic, hormone, neurotransmitter) stimulates one fiber?
The muscle action potential would be transmitted to neighboring fibers, leading them to contract in unison.
Where are visceral smooth muscle fibers found?
- Hollow organs.
- Walls of small arteries.
- Walls of veins.
What does an individual smooth muscle fiber look like?
- Contains dense bodies.
- Contains intermediate filaments.
- Lacks T-tubules.
- Less organized sarcomere.
- Single, centrally located nucleus.
- Small amount of SR, caveolae instead.
What are dense bodies?
Structures that thin and intermediate filaments are attached to that are similar to Z-discs.
What are caveolae?
Small pouch-like plasma membrane invaginations that contain extracellular Ca2+.
Where are dense bodies found?
- Sarcolemma.
- Sarcoplasm.
How does the smooth muscle contract?
The sliding filament mechanism generates tension that is transmitted to intermediate filaments that pull on the dense bodies to cause a lengthwise shortening of the muscle fiber. This shortening causes a corkscrew rotation of the muscle as the fibers twist in a helix pattern.
How does the contraction of smooth muscle differ from that of skeletal muscle?
- Contracts more slowly (due to Ca2+ taking longer to reach the filaments) and lasts much longer.
- Can shorten and stretch to a greater extent.
What initiates the contraction?
Increased Ca2+ in the cytosol that flows in from the interstitial fluid, SR, and caveolae.
What is calmodulin and what is its function?
A regulatory protein that binds to Ca2+ in the cytosol and activates myosin light chain kinase to phosphorylate the myosin head and allow for binding to actin.
What rate does myosin light chain kinase function at?
Slowly, contributing to the slower rate of contraction.
What rate does Ca2+ move out of smooth muscle?
Slowly, delaying relaxation.
What does the prolonged presence of Ca2+ contribute to?
- Smooth muscle tone.
- The state of continued partial contraction.
What does the prolonged presence of Ca2+ in the smooth muscle aid with in the GIT?
Maintenance of steady pressure on contents in GIT.
What does the prolonged presence of Ca2+ in the smooth muscle aid with in the arterioles?
Maintenance of steady blood pressure.
What do the smooth muscles contract/relax in response to?
- Action potentials from the ANS.
- Hormones.
- Ion concentrations.
- pH change.
- Stretching.
- Temperature change.
