smooth muscle physiology Flashcards
what is the histology of skeletal muscle
striated
voluntary
somatic innervation (⍺- and 𝛾-motor neurons)
what is the histology of cardiac muscle
striated
involuntary
autonomic innervation (sympathetic and parasympathetic post-ganglionic fibres)
what is the histology of smooth muscle
unstriated
involuntary
autonomic innervation (sympathetic and parasympathetic post-ganglionic fibres)
what is skeletal muscle (basic)
individual muscle fibres are large, elongated, cylindrical, and possess multiple nuclei
what is cardiac muscle (basic)
individual muscle fibres are large, cylindrical and possess multiple nuclei
what is smooth muscle (basic)
individual muscle fibres are relatively small, spindle shaped and possess one nucleus
what is the function of smooth muscle in the vasculature
controls diameter
regulates flow and pressure
what is the function of smooth muscle in the airways
controls diameter
regulates flow and resistance
what is the function of smooth muscle in the urinary system
propulsion of urine into ureters
bladder tone
tone of internal sphincter of bladder
what is the function of smooth muscle in the gastrointestinal tract
controls tone, motility, opening and closing of sphincters
what is the function of smooth muscle in the male reproductive tract
secretion
propulsion of semen
what is the function of smooth muscle in the female reproductive tract
propulsion (fallopian tubes)
partuition (uterus)
what is the function of smooth muscle in the skin
pili erection
what are the types of smooth muscle
tonic
phasic
what is tonic smooth muscle
‘multi-unit’
electrical isolation of cells allows finer motor control
function ‘individually’
e.g. Iris and Vas deferens
what is phasic smooth muscle
‘unitary’
gap junctions permit coordinated contraction
functions as a syncytium
e.g. stomach, urinary, bladder and bronchioles
what is the contractile machinery of smooth muscle
smooth muscle relies on sliding filament mechanism generated during actin-myosin cross-bridge formation to facilitate contraction
smooth muscle cross-bridge formation and sliding filament
- driven by a rise in intracellular calcium which binds to calmodulin
> calcium release from the SR
> calcium influx across the plasma membrane - calcium-calmodulin complex activates myosin light chain kinase
- myosin light chain is phosphorylated on the myosin head
- phosphorylation of myosin head ‘cocks’ it and increases its ATPase activity readying it to interact with actin to form a cross bridge
what factors affect striated muscle cross-bridge formation
an increase in intracellular calcium concentration
stretch - frank-starling relationship
what factors affect smooth muscle cross-bridge formation
an increase in intracellular calcium concentration
phosphorylation of myosin light chain kinase
inhibition of myosin light chain phosphatase
what is calmodulin
a multifunctional calcium binding protein present in the cytoplasm of all eukaryotic cells
what is relaxation of smooth muscle
involves a drop in intracellular calcium concentration and dephosphorylation
how is intracellular calcium concentration returned to pre-excitation concentrations
membrane bound calcium ATPases and sodium-calcium exchangers expel calcium from the cell
calcium is sequestered into stores by sarcoplasmic, endoplasmic reticulum calcium ATPases (SERCA)
how does dephosphorylation work in relaxation of smooth muscle cells
myosin light chain phosphatase (MLCP)
how is smooth muscle innervated
innervated by the autonomic nervous system
vast network of neural supply over the surface of smooth muscle cells
how it arterial smooth muscle innervated
sympathetic innervation with noradrenaline
how is other (non-arterial) smooth muscle innervated
sympathetic and parasympathetic innervation with noradrenaline and acetylcholine
what is pharmacomechanical coupling
the processes by which an agent causes a change in smooth muscle tone without a change in membrane potential
involves the production of intracellular second messengers that either contract or relax the muscle
what second messenger causes contraction of smooth muscle
inositol triphosphate, IP3
what second messenger causes relaxation of smooth muscle
cGMP and cAMP
what is electromechanical coupling
the opening of plasma membrane voltage-activated L-type calcium channels in response to depolarisation with, or without action potential generation
how is relaxation caused in smooth muscle cells
NCX
PMCA
SERCA
how does NCX cause relaxation in smooth muscle cells
utilises the sodium electrochemical gradient to pump calcium out of the cell
how does PMCA cause relaxation in smooth muscle cells
utilises ATP hydrolysis to actively pump calcium out of the cell
how does SERCA cause relaxation in smooth muscle cells
utilises ATP hydrolysis to actively pump calcium into the sarcoplasmic reticulum
