Smooth muscle physiology Flashcards
What would be the main components of the histology of smooth muscle?
Unstriated
Involuntary
Automonic innervation
How would you describe the structure of smooth muscle?
Individual muscle fibres are relatively small, spindle shaped, and possess a nucleus
What function does smooth muscle in the vasculature system have?
Controls diameter, regulates flow and pressure
What function does smooth muscle in the airways have?
Controls diameter, regulates flow and resistance
What function does smooth muscle in the urinary system have?
Propulsion of urine into ureters, bladder tone, tone of internal sphincter of bladder
What function does smooth muscle in the gastrointestinal tract have?
Controls tone, motility, opening/closing of sphincters
What function does smooth muscle in the male reproducitve tract have?
Secretion, propulsion of semen
What function does smooth muscle in the female reproductive tract have?
Propulsion (Fallopian tubes), partiuition (uterus)
What function does smooth muscle in the skin have?
Pill erection
What types of smooth muscle are there?
Tonic and phasic
What is the tonic type of smooth muscle based on their function. Give some examples?
Function ‘individually’ - Electrical isolatioon of cells allow fine motor control
Example: Iris and vas deferens
What is the phasic type of smooth muscle based on their function. Give some examples?
Function as a syncytium- Gap junctions permit coordinated contraction
Example: Stomach, urinary bladder and bronchioles
What are varicosities?
Synaptic contacts - in tonic smooth muscle fibres
What is the contractile machinery of smooth muscle. What do they rely on?
Sliding filament mechanism of genereated during actin-myosin cross-bridge formation to facilitate contraction
What is cross bridge formation and sliding filament in smooth muscle driven by?
A rise in [Ca+]i which binds to calmodulin
What does the Ca2+ -calmodulin complex activate?
Myosin light chain kinase (MLCK)
Where is the myosin light chain phosphorylated? And what occurs here?
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
To what length of [Ca2+] evokes maximal contraction?
1um
Elevated [Ca2+]i results from what?
Ca2+ release from the SR and Ca2+ influx across the plasma membrane
What are the factors that affect striated muscle cross-bridge formation?
- Increased intracellular [Ca2+]
- Stretch (Frank-starling relationship) law of heart (more stretched-more calcium uptake)
What are the factors that affect smooth muscle cross-brudge formation?
- Increased intracellular [Ca2+]
- Phosphorylation of myosin light chain kinase
- Inhibition of myosin light chain phosphatase
In smooth muscle cells, an increase in intracellular calcium conc. is sensed by what. What does this activate and phosphorylate. Then state what this allow, leads to and cause?
Sensed- CaM Activates- MLCK Phosphorylates- Myosin Allows- Actin-myosin Leads to- Crossbridge cycling Causes- Contraction
In striated muscle cells, an increase in intracellular calcium conc. is sensed by what. What does this move and expose binding sites to. Then state what this allow, leads to and cause?
Sensed- Troponin Moves- tropomyosin Exposes- Binding sites on actin Allows-Actin-myosin interaction Leads to- Cross bridge cycling Causes- contraction
What is calmodulin?
A multifunctional Ca2+ binding protein present in the cytoplasm of all eukaryotic cells
What does relaxation involve?
A drop in [Ca2+]i to pre-excitation concentrations
How is [Ca2+]i returned to its pre-excitation concentrations?
Membrane bound Ca2+ ATPase and Na+-Ca2+ exchangers expel calcium from the cell and calcium is sequestered into stores by Marco(endocrone)plasmic reticulum calcium ATPase (SERCA)
How does dephosphorylation occur in relaxation of smooth muscle?
Myosin light chain phosphatase (MLCP)
What nervous system is the smooth muscle innervated into?
Autonomic nervous system
Describe the innervation of arterial smooth muscle
Sympathetic innervation with noradrenaline
What are the anchor points in the sliding filament?
Plasma membrane- actin myosin filaments in between dense bodies
What is pharmacomechanical coupling?
Refers the process by which an agent causes a change in smooth muscle tone without a change in membrane potential
Pharmacomechanical coupling involces the production of intracellular second messengers that either contract, or relax, the muscle. What are the important second messengers?
- Inositol triphosphate (IP3) causing contraction
- Cyclic guanosine monophosphate (cGMP) and cyclic adenosine monophosphate (cAMP), both causing relaxation
What is electromechanical coupling?
Refers primarily to the opening of plasma membrane voltage-activated L-type Ca2+ channels in response to depolarisation with, or without, action potential generation
What is peristalsis?
Propulsive mmovements
What is arterial tone?
Exerts pressure
In pharmacochemical coupling, what activates the G-protein coupled receptor?
Transmitter or hormone activates GPCR
Myosin light chain phosphatase plays what role in pharmacochemical coupling?
Inhibitor
What will electromechanical coupling receptors respond to?
- Stretching in mechanosensitive stretch receptor allowing movement of ions into the cell
- Gap junction propagating a current
- Receptor-operated calcium channel- adrenergic or muscarinic
