Lecture 10 - Physiology Of Smooth Muscle Flashcards
Where is smooth muscle mostly found
In the wall of hollow organs and tubes
What is the function of the smooth muscle within the walls and tubes of hollow organs
They are involved in mediating propulsive movements and exerting pressure within the blood vessels
What does smooth muscle control within the vessels
The diameter, blood flow and pressure
What does smooth muscle control within the lung airways
The diameter, airflow and air resistance
What does the smooth muscle control within the urinary system
The propulsion of urine through the ureters, bladder tone and the tone of the internal sphincter
What does the smooth muscle control within the gastrointestinal tract
the tone, motility and the opening/closing of the sphincers
What does smooth muscle do in the male reproductive system
It aids the secretion and propulsion of semen
What does smooth muscle do in the female reproductive tract
It aids propulsion within the fallopian tubes and aids child birth through the pressure exerted by the uyterus
What does smooth muscle do in the eye
It controls the pupil diameter and the lens shape
What muscles control pupil diameter of the eye
The iris muscles
What muscles control the lens shape of the eye
The ciliary muscles
What does smooth muscle do within the skin
It is involved in hair erectrion
What muscles cause hair erection
The pili muscles
What are the three types of filaments within smooth muscle
Thick myosin filaments, thin actin filaments and intermediate sized filaments
Within smooth muscle what do the actin filaments contain
Tropomyosin
What are the intermediate filaments involved in
Only involved in cytoskeletal elements but not contraction
What does smooth muscle respond to
An increase in cytosolic levels of Ca2+
How is smooth muscle arranged
In sheets
What does contraction occur by
The sliding filament mechanism
What is the cross bridge cycle regulated by
By intracellular Ca2+
Within smooth muscle what does Ca2+ bind to
Calmodulin
What are the differences between skeletal muscle and smooth muscle
Smooth muscle fibres do not form myofibrils and it also has no sarcomere pattern and no Z-line
What do the actin filaments in smooth muscle join to
The dense bodies
Where are dense bodies attached to
The inner surface of the plasma membrane
What proteins are the dense bodies made up of
Titin (the same protein that forms the Z line)
What are the dense bodies held in place by
The intermediate filaments
How many thin filaments surround each thick filament
10-15
What is smooth muscle innervated by
The autonomic nervous system
Are the thin filaments in smooth muscle all pulled in the same direction
No they are pulled in all different directions
Where does most of the calcium required to trigger contraction in smooth muscle come from
The extracellular fluid
The greater the volume of free calcium, the greater
The force of contraction
How can the volume of calcium be increased
By binding of extracellular chemical messengers to G-protein coupled receptors
What is an example of an extracellular chemical messenger
Noradrenaline
What happens when noradrenaline binds
It activates phospholipase C
What is attached to the myosin chain near the neck arean
The myosin light chain
What is the function of the myosin light chain
The myosin light chain prevents the myosin molecule from interacting with the actin molecule while it is unphosphorylated
What allows the interaction of actin and mysoin in smooth muscle
Th phosphorylation of the myosin light chain
What phosphorylates the myosin light chain
The myosin light chain kinase
What does contraction result from
The phosphorylation of the myosin light chain the the presence of elevated intracellular Ca2+ and ATP
What does relaxation occur from
The dephosphorylation of the myosin light chain
What dephosphorylates the myosin light chain
Myosin phophatase
What type of activity does myosin phosphatase have
Constitutive activity
What does it mean if a receptor has constitutive activity
The receptor is capable of producing a biological response in the absence of bound ligands
What allows the Ca2+ leve;s to return to a basal concentration
Primary and secondary active transport
What are the different classifications of smooth muscle
Phasic or tonic
Multiunit or single unit
Neurogenic or myogenic
What are the characteristic of phasic smooth muscle
It contracts in bursts, the action potentials trigger a rise in intracellular Ca2+, the contraction is phasic and vigorous
What body part are phasic contractions associated with
The walls of hollow organs
What does phasic smooth muscle contain
Specialised, non-contractile cells that display spontaneous changes in membrane potential, independent of neural input
Tonic smooth muscle is usually
Partially contracted at all times
What is open at relatively low resting potential of tonic smooht muscle cells
The voltage-activated Ca2+ channels
Ca2+ influx in tonic smooth muscle mediates a state of
Partial contraction or tone
In tonic smooth muscle what does contraction vary because of
Factors that alter cytostolic Ca2+
What body part is tonic smooth muscle usually associated with
The walls of arterioles
Single unit muscle cells characteristics
The muscle fibres are electrically coupled by gap junctions, it is self-excitable but autonomic innervation modifies its activity and it can be phasic or tonic
What is the single function unit of single unit muscle cells known as
A functional syncytium
What are the two categories of myogenic activity of single unit muscle cells
Pacemaker potentials and slow-wave potentials
Pacemaker potentials
The membrane potential gradually depolarises spontaneously to a value sufficient to reach the threshold for the generation of an action potential
How does excitation propagate throughout the smooth muscle sheet
Through gap junctions to cause a self-induced contraction
Slow-wave potentials
The membrane potential oscillates spontaneously between hyperpolarised and depolarised potentials but reaches the threshold for the generation of an action potential only in the presence of an external stimulus
How does gradation of tension occur in skeletal muscle
Motor unit recruitment and twitch summation
How does the gradation of tension occur in single unit smooth muscle cells
Through variations in the intraceullular levels of Ca2+ which regulates the number of cross bridges that are formed
Characteristics of multiunit smooth muscle cells
The muscle fibres are electrically isolated for each other, excitation/contraction of the fibres occurs independently of each other, contraction is usually driven by innervation autonomic nervous system and the muscles are usually phasic
