Smooth muscle physiology Flashcards
is skeletal muscle striated or unstriated, voluntary or involuntary, and somatic or autonomic?
Striated
Voluntary
Somatic (a- and y- motor neurones)
is cardiac muscle striated or unstriated, voluntary or involuntary, and somatic or autonomic
Striated
Involuntary
Autonomic
is smooth muscle striated or unstriated, voluntary or involuntary, and somatic or autonomic?
Unstriated
Involuntary
Autonomic
describe skeletal muscle
Individual muscle fibres are large, elongated,cylindrical and possess multiple nuclei
describe cardiac muscle
Individual muscle fibers are large, cylindrical and possess multiple nuclei
describe smooth muscle
Individual muscle fibres are relatively small, spindle-shaped, and possess one nucleus
smooth muscle function of vasculature
controls diameter regulates flow and pressure
smooth muscle function of airways
controls diameter regulates flow and resistance
smooth muscle function of the urinary system
propulsion or urine into ureters, bladder tone, tone of intestinal sphincter of the bladder
smooth muscle function of gastrointestinal
controls tone, motility, opening/closing of sphincters
smooth muscle function of the male reproductive tract
secretion, propulsion of semen
smooth muscle function of the female reproductive tract
propulsion (fallopian tubes), parturition (uterus)
smooth muscle function of the skin
pili erection
what are the two types of smooth muscle
single-unit and multi-unit
what does the electrical isolation of cells allow
finer motor control
what do gap junctions permit
coordinated contraction
how does smooth muscle contract
like in skeletal muscle, smooth muscle relies on the sliding filament mechanism generated during actin-myosin cross-bridge formation
Cross-bridge formation and sliding filament in smooth muscle
- Driven by a rise in [Ca2+]i which binds to calmodulin
- Ca2+-calmodulin complex activates myosin light chain kinase (MLCK)
- Myosin light chain (MLC) is phosphorylated on the myosin head
- Phosphorylation of myosin head ‘cocks’ it and increases it’s ATPase activity readying it to interact with actin to form a cross-bridge
what are the factors affecting striated muscle cross-bridge formation
increased intracellular [Ca2+]
Stretch (frank-starling relationship)
what are the factors affecting smooth muscle cross-bridge formation
Increased intracellular [Ca2+]
Phosphorylation of myosin light chain kinase
Inhibition of myosin light chain phosphatase
what is calmodulin
a multifunctional Ca2+ binding protein present in the cytoplasm of all eukaryotic cells
relaxation of smooth muscle
relaxation involves a drop in [Ca2+]i and dephosphorylation
innervation of smooth muscle
innervated by the autonomic nervous system
→ Arterial smooth muscle – sympathetic innervation with noradrenaline
→ Other smooth muscle - sympathetic and parasympathetic innervation with acetylcholine
Vast networks of neural supply over the surface of the smooth muscle cells
by convention contraction of smooth muscle can be described as what
Pharmacomechanical coupling
Electromechanical coupling
what is Pharmacomechanical coupling
→ refers to 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
very important second messengers are:
→ inositol trisphosphate (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
in reality the two overlap to some extent
