smooth muscle physiology Flashcards
describe individual smooth muscle fibers
small, spindle shaped and have a single nucleus
what is smooth muscle innervated by
Autonomic - parasympathetic and sympathetic
function of smooth muscle in the vasculature
Controls diameter, regulates flow and
pressure
function of smooth muscle in the airways
Controls diameter, regulates flow and
resistance
function of smooth muscle in the urinary system
Propulsion of urine into ureters, bladder
tone, tone of internal sphincter of
bladder
function of smooth muscle in the GI tract
Controls tone, motility, opening/closing
of sphincters
function of smooth muscle in the male reproductive tract
secretion, propulsion of semen
function of smooth muscle in the female reproductive tract
propulsion (fallopian tubes) and partuition (uterus)
function of smooth muscle in the skin
pili erection
what are the two types of smooth muscle ?
multiunit and single unit (or unitary)
multiunit smooth muscle
-each muscle fiber can contract individually
-capable of fine control
where is multiunit smooth muscle found ?
iris, ciliary body, vas deferens and piloerector muscles of the skin
unitary smooth muscle
group of muscle cells work as a syncytium because gap junctions provide electrical and chemical communications between cells
where is unitary smooth muscle found
is the most predominant.
found in GI tract, urinary tract, uterus and many blood vessels
what is unitary smooth muscle also referred to as
visceral smooth muscle
what mechanism facilitates contraction in smooth muscle ?
sliding filament mechanism, which is generated during actin- myosin cross bridging
dense bodies
serve as anchoring points for actin filaments during muscle contraction
describe cross-bridge formation in smooth muscle
1) rise in intracellular Ca2+ which binds to Calmodulin
2)Ca2+-calmodulin complex activates myosin light chain kinase
3) Myosin light chain is phosphorylated on the myosin head
4)phosphorylation of myosin head ‘cocks’ it and increases ATPase activity readying it to interact with actin to form a cross-bridge
what concentration does intracellular Ca2+ need to be to evoke maximal contraction
1um
what is basal intracellular Ca2+ levels ?
100nm
what factors affect smooth muscle cross bridge formation ?
-increased intracellular Ca2+
-phosphorylation of MLCK
-inhibition of myosin light chain phosphatase
calmodulin
multifunctional Ca2+ binding protein present in the cytoplasm of all eukaryotic cells
what is involved in the relaxation of smooth muscle ?
-drop in intracellular Ca2+ concentration : Membrane bound Ca2+ ATPases and Na+-Ca2+ exchangers expel calcium from from the cell and calcium is sequestered into stores by SERCA
-dephosphorylation of Myosin light chain phosphatase
what is Arterial smooth muscle innervated by?
sympathetic innervation with noradrenaline
pharmacomechanical coupling
-process by which an agent causes a change in smooth muscle tone without a change in membrane potential
-involves production of intracellular second messengers that either contract or relax the muscle
what second messenger causes the contraction of smooth muscle
inositol triphosphate (IP3)
what second messengers cause the relaxation of of smooth muscle?
cyclic guanosine monophosphate (cGMP) and cyclic adenosine monophosphate (cAMP)
Electromechanical coupling
refers primarily to the opening of plasma membrane voltage-activated L-type Ca2+ channels in response to depolarization with, or without, action potential generation
