Smooth Muscle Flashcards
Smooth muscle controls what?
Involuntary low force contractions
Name 5 places that smooth muscle is present
Skin Eyes Uterus Stomach Blood walls
Describe the structure of the smooth muscle
Spindle-shaped
Single nucleus
Actin and Myosin with thick and thin filament
Produce their own connective tissue, endomysium
NO T TUBLES OR SARCOMERE
After contraction what shape is the smooth muscle?
Globular shape
Skeletal muscle acts against the ____
Acts against the skeleton
What does smooth muscle requires what to contract?
requires an extracellular matrix which they secrete (collagen and glycoproteins)
This anchors the individual smooth muscle cell into functional units
Tension generated by contraction is transmitted through the focal adhesion densities to the surrounding connective tissue thus allowing groups of cells to act as one.
Contraction results in the cells becoming shorter and fatter.
Describe the smooth muscle contraction in 7 steps
Ca2+ ions released from SR or enter through caveolae.
Ca2+ ions form complex with calmodulin.
Ca2+-calmodulin complex activates myosin light chain kinase (MLCK).
MLCK phosphorylated and activates myosin ATPase activity.
Myosin is now able to bind to actin.
ATP-dependent contraction cycle ensues. Contraction continues as long as myosin is phosphorylated.
Phosphatase cleaves the phosphate group.
What is CaM?
What is its role?
Calmodulin (CaM or calcium-modulated protein).
CaM is an intracellular target of the second messenger Ca2+.
Once bound to Ca2+, CaM acts as part of a calcium signal transduction pathway by interacting with kinases and phosphatases
How is the smooth muscle adapted to function for long periods without rest?
Power output is relatively low
Some smooth muscle can maintain contractions even as Ca2+ is removed and myosin kinase is inactivated/dephosphorylated. This can happen as a subset of cross-bridges between myosin heads and actin, called latch-bridges, keep the thick and thin filaments linked together for a prolonged period, and without the need for ATP. This allows for the maintaining of muscle “tone” in smooth muscle that lines arterioles and other visceral organs with very little energy expenditure.
Describe varicosities
Unlike skeletal muscle fibres, smooth muscle cells do not have a specialized motor end-plate region. They have swollen regions known as varicosities.
Each varicosity contains many vesicles filled with neurotransmitter, some of which are released when an action potential passes the varicosity.
Varicosities from a single axon may be located along several muscle cells, and a single muscle cell may be located near varicosities belonging to postganglionic fibres of both sympathetic and parasympathetic neurons.
How is smooth muscle organised?
Single unit smooth muscle and muti-unit smooth muscle
Where are single unit smooth muscles?
Describe their structure
its muscle fibres joined by gap junctions so that the muscle contracts as a single unit. type of smooth muscle is found in the walls of all visceral organs except the heart, and so it is commonly called visceral muscle.
What response does visceral smooth muscle have?
stress-relaxation response. This means that as the muscle of a hollow organ is stretched when it fills, the mechanical stress of the stretching will trigger contraction, but this is immediately followed by relaxation so that the organ does not empty its contents prematurely.
What do multi-unit smooth muscle rarely contain?
And what does this involve
Multi-unit smooth muscle cells rarely possess gap junctions, and thus are not electrically coupled.
As a result, contraction does not spread from one cell to the next, but is instead confined to the cell that was originally stimulated.
Multi-unit smooth muscle is found where?
This type of tissue is found around large blood vessels, in the respiratory airways, and in the eyes.
