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.
What is the stimuli of multi-unit smooth muscle
Stimuli for multi-unit smooth muscles come from autonomic nerves or hormones but not from stretching.
How can some smooth muscles maintain contractions even if Ca2+ is removed and myosin kinase is inactivated
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.
Is smooth muscle responsive the hormones?
Yes
In the fight, flight or freeze response what changes involve smooth muscle activity?
Skin – smooth muscle in follicles
Eye – iris smooth muscle
Stomach, intestines and bladder
Bronchodilation
Describe how inhalers work?
Beta2 agonist (salbutamol (inhalers) ) target Beta2 receptors (GPCR) located on bronchial smooth muscle, resulting in bronchodilation. Due to increased intracellular cAMP and increased phosphorylation
What is the name of the smooth muscle in the uterus?
What happens to this during pregnancy?
Myometrium
It increases in size due to oestrogen
During birth the strong contractions are reinforced. by oxytocin
How is the oesophagus an example of smooth and skeletal working together?
Swallowing is voluntary
but peristalsis is involuntary
Describe the structure of the Ureter and bladder
Ureter is a tube and the bladder is a bag
The ureter is a tube made of smooth muscle fibres, that propel urine from the kidneys to the urinary bladder
Urine is squeezed into the bladder by peristalsis
The bladder has three layers of smooth muscle: inner longitudinal, middle circular and outer longitudinal
What has been used to delay labour?
Intravenous Salbutamol relaxes the smooth muscle walls. SAME MECHANISM AT BRONCHODILATION
Describe the 4 steps of smooth muscle excitation
1- increased cytosolic [Ca2+]
2- Ca2+ binds to calmodulin which binds to myosin light chain kinases
3- phosphorylation of myosin cross bridges in thick filament
4- binding of actin and myosin at cross bridges
Describe the 4 steps of skeletal muscle excitation
1- increase cytosolic [Ca2+]
2- Ca2+ binds to tropnin
3-physical repositiioning of troponin and tropomyosin- uncovering of cross bridges binding sites in actinin thin filaments
4- binding of actin and myosin at cross bridges
