Flashcards in Smooth muscle Deck (71):
Smooth muscle fibers are larger or smaller than skeletal muscle fibers?
Smaller (thinner and shorter)
Does smooth muscle contain striations?
True or false: all smooth muscle is largely the same
False- differs in innervation, packaging, organization
Where are nuclei found in smooth muscle?
What are multi-unit smooth muscle?
discrete smooth muscle fibers that contract independently
What are unitary smooth muscle?
a group of fibers that contract together as a single unit
Which type of smooth muscle utilizes gap junctions?
Unitary smooth muscle
Which type of smooth muscle is utilized for small movements?
Which type of smooth muscle are organized into sheets or bundles that contract together?
Which type of smooth muscle utilizes the ANS primarily?
Which type of smooth muscle utilizes hormones?
Do smooth muscles express troponin?
What is the difference in the myosin head in smooth muscle? What does this allow for?
that the myosin heads are not all arranged in the same direction. This allows for multi-directional contraction or force generation can in multiple in multiple planes.
What is the function of the dense bodies found dispersed throughout smooth muscle cells?
Like z discs
What replaces Z discs in smooth muscle?
What is the function of the dense bodies?
Allow for force of contraction to be transmitted from one cell to the next
What is the arrangement of myosin in smooth muscle?
Arranged in multiple planes
Which attaches to the dense bodies: actin or myosin?
What is the primary source of Ca in smooth muscle?
the extracellular fluid
How much Ca does the sarcoplasm contribute to smooth muscle cell contraction
What is the point of regulation for Ca in smooth muscle? (What does Ca bind to? What enzyme is affected? What does this cause?)
Binds to calmodulin, and activates myosin light-chain kinase (MLCK). This then phosphorylates the regulatory chain of myosin ATPase
In skeletal muscle ATPse is always on. Is this the case for smooth muscle? How?
No, must be activated by myosin light chain kinase
What forms the cross bridge between myosin head and actin?
Phosphorylation by from ATP, from myosin phosphorylase
Decreased MLCK activation and myosin phosphatase activity can lead to what?
Relaxation or tonic contraction
When intracellular [Ca] falls, what happens?
Prevents further MLCK activation,
Where can multi-unit smooth muscle be found?
Ciliary and iris muscle of the eyes, piloerector muscles
What is the action of MLCK?
Phosphorylate the regulator chain of myosin ATPase
What state is the myosin head in (in smooth muscle) when ADP + Pi is bound to it?
Actin and myosin are bound
What happens when myosin loses the ADP +Pi?
What is the chemical change in smooth muscle that allows myosin to detach?
ATP binds to the myosin head
How many molecules of ATP are needed for smooth muscle contraction?
2--One ATP molecule is needed for the phosphorylation of the regulatory chain of myosin and the second ATP molecule is needed for the cross bridge cycling.
What brings about relaxation of smooth muscle?
A decrease in [Ca], leading to a decrease in MLCK activation
What is the primary innervation of multiunit smooth muscles?
What is the primary innervation of unitary muscles?
Autonomics, as well as environmental factors
Which type of smooth muscle cells have gap junctions, unitary or multiunit?
Where are unitary muscles primarily found?
GI tract, bile ducts, ureters, uterus, blood vessels
Is ATPase regulated in skeletal muscle? How about in smooth muscle? What is the regulator in each (if any)?
No regulation in smooth muscle
Calmodulin/Ca complex turn it on for smooth muscle
How many inorganic phosphates are bound to myosin in skeletal muscle? Smooth muscle?
One is skeletal
Two in smooth
What causes the power stroke in smooth muscle?
The loss of ADP and one of the Pi
What recocks the myosin head in smooth muscle?
Binding of a new ATP
What must happen to the ATP on the myosin head to allow for attachment of the head to actin?
must be hydrolyzed to ADP
What are the two ways in which smooth muscles can relax?
1. Lower [Ca]
2. Dephosphorylation of myosin by myosin phosphatase
What are the two chemical changes that can lead to the "latch bridge" state?
Low MLCK and myosin phosphatase activity
Low ATPase activiy
What is the chemical state of myosin in the latch state?
ADP and Pi can be bound, but the regulatory Pi is not.
How many ATP molecules are needed for contraction in smooth muscle? What is the reason for this?
2-One ATP molecule is needed for the phosphorylation of the regulatory chain of myosin and the second ATP molecule is needed for the cross bridge cycling.
Which type of muscle can have rapid contraction and relaxation? Opposite?
Opposite = smooth
Which cross bridge cycling is fast: skeletal or smooth? Which is slow?
Fast = Skeletal
Slow = Smooth
What is the max force that skeletal muscle can generate?
What is the max force that smooth muscle can generate?
Which type of muscle is able to under a latch mechanism?
Which type of muscle has stress-relaxation?
Which muscle type exerts more energy for fast twitches? Slow?
Fast, smooth uses more
Slow, skeletal uses more
Why can smooth muscle require less energy to produce the same tension over an extended period of time, when it require more ATP per cycle of myosin movement?
Far less cycles occur to maintain contracted state
During smooth muscle relaxation, ATPase activity is relatively (large or small)? What is the consequence of this?
The actin-myosin cross bridge is not formed
There are no neuromuscular junctions in smooth muscle. How, then, is smooth muscle innervated?
Via diffuse branches of nerve fibers that lay over sheets of smooth muscle
What accounts for the slow onset of an action potential activating a smooth muscle?
There is more physical space between the neuron varicosities compared to a neuromuscular plate
What are the bodies along an axon terminal that innervate smooth muscles?
What are the primary neurotransmitters in smooth muscle control? Which is usually excitatory, and which is usually inhibiting?
Acetylcholine = excitatory
True or false: when acetylcholine plays an excitatory role in smooth muscle innervation, norepi always plays the exact opposite, and vice versa
"In some cases of (BLANK) smooth muscle, nerve fiber does contact the smooth muscle, forming a 'contact junction'".
What is electro-mechanical stimulation? How could this occur?
a change in membrane permeability that results in a depolarization of smooth muscle. This could occur if membrane sodium or calcium channels were opened.
What is electro-mechanical inhibition? How could this occur?
change in membrane permeability that results in a hyperpolarization of smooth muscle. This could occur if membrane sodium or calcium channels were closed or if potassium channels were opened.
What is pharmacomechanical stimulation? How could it occur?
stimulation of smooth muscle contraction by signaling molecules. For example, some hormones will activate the phospholipase C (PLC) pathway through their respective receptor.
What is pharmacomechanical inhibition? How could it occur?
as the inhibition of smooth muscle contraction mediated by signaling molecules. For example, some hormones will activate the protein kinase A (PKA) pathway, causing MLCK to be phosphorylated/deactivated
What are the three different regulator categories of smooth muscle?
What are the two roles of [Ca] in smooth muscle contraction?
Can cause action potential
What are the two types of action potentials in smooth muscles?
ACtion potentials ith plateaus
What is the resting membrane potential of smooth muscles? How does this compare to skeletal?
around -60 mV. Lower (absolute value) compared to skeletal muscle (~-90 mV)
What is responsible for the prolonged phase action potential (the pone with a plateau)?
Ca (channels are slower to open and close)
What is the slow wave potential? What is the consequence of this?
a basoelectrical rhythm of membrane potential that occurs at rest.
This means that a smooth muscle cell is more likely to be depolarized at peaks in the baseoelectric rhythm