Term
| Where is smooth muscle found? |
|
Definition
| In hollow organs and blood vessels |
|
|
Term
| Are smooth muscle contractions longer or shorter than skeletal muscle contractions? |
|
Definition
|
|
Term
| True or false: the shape of an organ changes when smooth muscle contracts. |
|
Definition
|
|
Term
| Are contractile fibers in smooth muscle arranged in sarcomeres? |
|
Definition
|
|
Term
| What are the two main types of smooth muscle cells? |
|
Definition
Single-unit smooth muscle cells
Multi-unit smooth muscle cells |
|
|
Term
| What are the qualities of single-unit smooth muscle cells? |
|
Definition
1.
cells
electrically
connected
via
gap
junctions
2.
functions
in
syncytial
fashion
3.
electrical
stimulation
of
one
cell
leads
to
stimulation
of
adjacent
cells
through
gap
junctions
4.
results
in
wave
of
contraction |
|
|
Term
| What are the qualities of multi-unit smooth muscle cells? |
|
Definition
1.
cells
not
electrically
connected
2.
each
cell
has to
be
individually
stimulated |
|
|
Term
| Where are the contractile muscle filaments in smooth muscle cells found? |
|
Definition
|
|
Term
| How does the actin-myosin ratio of smooth muscle cells compare to skeletal muscle cells? |
|
Definition
| The actin-myosin ratio is greater in smooth muscle cells |
|
|
Term
Which of the following do smooth muscle cells lack:
1. troponin
2. tropomyosin |
|
Definition
|
|
Term
| What is different in the myosin isoform in smooth muscle (compared to skeletal muscle) |
|
Definition
|
|
Term
| Does smooth muscle have a sarcoplasmic reticulum? |
|
Definition
| Yes, but it lacks T-tubules |
|
|
Term
|
Definition
| Anchoring points for actin filaments in smooth muscle |
|
|
Term
| What initiates smooth muscle contraction? |
|
Definition
| Increase in intracellular Ca2+ |
|
|
Term
| How does calcium enter smooth muscle cells? |
|
Definition
| Voltage-gated and ligand-gated calcium channels |
|
|
Term
| What causes calcium to be released from the SR? |
|
Definition
| The IP3 channel, which is activated IP3 that is generated due to G-protein coupled receptors activating PLC |
|
|
Term
| What leads to relaxation of smooth muscle? |
|
Definition
| removal of intracellular calcium |
|
|
Term
| What is required for continued contraction of smooth muscle? |
|
Definition
|
|
Term
| What does Ca2+ bind to when it enters the cell? |
|
Definition
|
|
Term
| What does the Ca2+-calmodulin complex activate? |
|
Definition
| myosin light chain kinase (MLCK) |
|
|
Term
| What is the function of MLCK? |
|
Definition
| it phosphorylates the regulatory light chains of myosin |
|
|
Term
| What happens when the regulatory light chains of myosin are activated? |
|
Definition
| myosin ATPase, binding to actin increases, muscle tension increases |
|
|
Term
| What causes the ratcheting movement of myosin heads? |
|
Definition
|
|
Term
| What causes release of myosin from actin? |
|
Definition
|
|
Term
| What causes continued cycling of binding of myosin heads to actin? |
|
Definition
| MLCK remains phosphorylated, Ca2+ in cell remains high |
|
|
Term
| Is cycling slower in smooth muscle or skeletal muscle? |
|
Definition
|
|
Term
What pumps Ca2+ back into the SR?
What pumps are present in the plasma membrane to remove calcium? |
|
Definition
SERCA (smooth ER calcium ATPase)
Calcium pump
Na/Ca exchanger |
|
|
Term
| What dephosphorylates MLCK after calcium is removed from within the cell? |
|
Definition
| MP (myosin light chain phosphatase) |
|
|
Term
| True or false: MLCK dephosphorylation leads to relaxation. |
|
Definition
|
|
Term
| Which signal and receptor are responsible for activating influx of Ca2+ in smooth muscle |
|
Definition
| binding of acetylcholine to muscarinic receptors |
|
|
Term
| What is phasic contraction? |
|
Definition
| intermittent or rhythmic contraction |
|
|
Term
| What is tonic contraction? |
|
Definition
|
|
Term
Is tonic contraction maintained by high or low MLC phosphorylation?
What is this state called? |
|
Definition
low; myosin
stays
attached
to
actin
and
force
continues
to
be
generated
Latch state |
|
|
Term
| What does the "latch state" depend on? |
|
Definition
| presence of enough Ca2+ to bind calmodulin and activate MLCK (muscle will relax in the case of too little Ca2+) |
|
|
Term
| What is the difference in the progression of force in tonic and phasic contraction? |
|
Definition
in tonic contraction, force builds and is then maintained
in phasic contraction, force peaks and then decreases |
|
|
Term
| What are the three types of membrane potentials that regulate smooth muscle contraction? |
|
Definition
slow wave potentials - cause action potentials when they reach threshold
pacemaker potentials - always reach threshold
pharmacomechanical coupling - chemical signals change muscle tension without changing membrane potential |
|
|
Term
| How is contraction of smooth muscle achieved? |
|
Definition
1. increase activity of Ca2+ channels
2. inhibit MP
3. Add Ach (makes membrane potential more positive) |
|
|
Term
| How does smooth muscle change its length-tension relationship? |
|
Definition
| length adaptation; thought to involve adding contractile units |
|
|
Term
| What does the force-velocity relationship depend on for smooth muscle? |
|
Definition
|
|
Term
| What are autonomic neuron varicosities? |
|
Definition
| swelling along nerve axons that contain neurotransmitter |
|
|
