Final Review Deck - Lecture III - Smooth Muscle Flashcards
What is the main difference between skeletal and cardiac muscle?
cardiac muscle can get calcium throguh calcium channels not just the SR like skeletal muscle
Does smooth muscle have troponin and what kind of force does it generate?
no troponin and has low levels of force continuously
What are smooth muscle cells like?
mononuclear cells and they are spindle shaped cells and can contract into little balls from a long spindle shape
-very skinny and elongated
Over what range of lengths can smooth muscle contract?
over a very large range of lengths and there are actin thin filaments and myosin thick filaments and tropomyosin
Instead of z lines what does smooth muscle have?
dense bodies which anchor the thin actin filaments
What are the dense bodies linked to and what do they link together?
-linked to the plasma membrane and link together sarcoemres
How are myosin filaments arranged in thick filaments?
there is no longitudinal bundle like in skeletal muscle and in the middle of the thick filament there is no crossbridges
In smooth muscle compared to cardiac and skeletal muscle what does the arrangment of myosin in a 45 degree angle with no gaps do?
they can slide over a lot of distance and tehre is not limit in contraction lenght and can become l little ball
What is the duration and strength of contraction for smooth muscle?
the duration is always prolonged and weaker contraction more persistent
Are there t tubules and troponin in smooth muscel?
no
Where does calcium come into smooth muscle?
from the SR and calcium channels like cardiac muscle
In the single unit smooth muscle what are the cells joined by?
gap junctions so they behave as one and the aps propagate and calcium propagates and the innervation is through the autonomic nerve
Is there a nerve terminal for smooth muscles that are innervated by an autonomic nerve?
no there are just varicosities which release transmitter along the length of the axon and the transmitter release is greater because there is no small synaptic cleft
Why is the buildup of force so slow in smooth muscle?
because activation of force is through the diffusion of small molecules from varicosities
Smooth muscle in what parts of the body tends to be single unit?
blood vessels, intestines, uterus
What helps smooth muscle in uterus go from multi unit to single unit?
estrogen
How does multiunit smooth muscle behave?
not connected by gap junctions behave independently
What are some places in the body that have multi unit smooth muscle?
iris muscle and they control the pupil of eye and ciliary muscle controls the focal length and the non pregnant uterus
Can smooth muscle have no innervation?
yes smooth muscle can have no innervation and can be spontaneously active and have rhythymic APs
Can smooth muscle receive autonomic innervation?
yes both sympathetic and parasymathetic or just sympathetic like arterioles
What is histamine and where does it come from and what are basophils?
histamine is the main mediator of inflammation
-comes from mast cells
-basophils are in the blood
What can histamine and basophils do to vascular smooth muscle?
cause hyperpolarization to increase blood flow to an area
What kind of channels do smooth muscle have?
stretch activated channels which can depolarize the cell in response to stretch and the stretching of the smooth muscle causes more calcium entry so flow stays the same via contraction
There are receptor activated channels in smooth muscles and what do they bind to and cause?
bind to a transmitter or hormone and let calcium into the smooth muscle cell
What does the sodium potassium pump in smooth muscle do?
it is electrogenic and causes the cell to have a expulsion of one positive ion out every round
What do voltage gated sodium channels in smooth muscle do?
they allow for the influx of sodium into the cell causing an amplification of the depolarization seen in the muscle cell
What do voltage sensitive calcium channels do in smooth muscles?
come in during calcium depletion from SR and depolairzation or stretch activated in arterioles
What does the potassium channel do in smooth muscle?
hyperpolarizes the cell
How is calcium released from the SR?
there is a transmitter or hormone which binds to a GPCR and this causes PLC to be actuvated and it cleaves PIP2 into DAG and IP3 and IP3 goes to the SR and binds to a receptor there and causes calcium to be released
How is calcium removed in smooth muscle?
calcium atpase into the SR
-calcium pump in the membrane to pump into the ecf or a 3 sodium in one calcium out exchanger
What is the conductance?
1/R
-the inverse of resistance
How many IP3Rs are there in the membrane of a cell and how much calcium do they let in?
only 1 or 2 per cell
let in alot of calcium has a consductance of 200 picosiemens which is 1S = 1A/V
There are thousands of membrane Orai1 proteins per cell what does it do and how does STIM1 interact with it?
lets calcium into the cell when activated by the STIM 1 which is in the ER membrane and they have calcium sensors which bind calcium in the ER and when no calcium is present they aggregate and their cytoplasmic side reaches out to Orai1 and causes that channel to open and let calcium in
-Orai1 is store operated calcium channel which only open when calcium is depleted in the smooth ER
What is the subunit of myosin in smooth muscle?
it is a dimer with an alpha helical coil - and each myosin molecule contains three chains
What are the three chains of a myosin molecule in smooth muscle?
-essential light chain
-regulatory light chain
-heavy chain
What are the three domains of the myosin molecule in smooth muscle?
-head, neck, tail
What does the head have of the myosin molecule?
atpase and binding actin ability
What does the regulatory light chain control control>
cycling it must be phopshorylated to cause a contraction and dephosphorylated to stop it and the state of phosphorylation is regulated by calcium
What happens when the regulatory light chain get phosphorylated?
the crossbridge cycle occurs the myosin head goes from unattached to attached
Is there troponin and tropomyosin in smooth muscle?
there is no troponin but there is tropomyosin but it dos not block the actin binding site
How is the phosphorylation of the myosin light chain dependent on calcium?
the myosin light chain kinase is activated in a calcium clamodulin dependent manner
-when the chain is phosphorlated it is attached when it is unphopshorylated it is unattached by the myosin light chain phosphatase
Can the unattached head bind to ATP?
yes but it results in slower cycling
