Physio Ch 08 Flashcards
2 major types of smooth muscles
multi-unit smooth muscle and unitary (or single-unit) smooth muscle
discrete, separate smooth muscle fibers
multi-unit smooth muscle
major share of control is exerted by non-nervous stimuli
unitary smooth muscle
Where are some locations of multi-unit smooth muscle
ciliary muscle of the eye, iris muscle of the eye, piloerector muscles
mass of hundreds to thousands of smooth muscle fibers that contract together as a single unit
unitary smooth muscle
present in cell membrane of unitary smooth muscle wherein ions can flow freely from one muscle to the next
gap junctions
also known as syncytial smooth muscle because of its syncytial interconnections among fibers
unitary smooth muscle
visceral smooth muscle are found in these organs
GI tract, bile duct, ureter, uterus, blood vessels
It is mainly through these bonds that the force of contraction is transmitted from one cell to the next
dense bodies
serve the same role as the Z discs in skeletal muscle
dense bodies of smooth muscles
sidepolar of crossbridges in smooth muscles allows it to contract how many percent of their length
80 percent
major factor that determines the force of contraction in smooth muscles
fraction of time
these organs maintain muscle contraction indefinitely
intestines, urinary bladder, gallbladder
a typical smooth muscle reach full contraction in
0.5 seconds later
reaches full contraction about 0.5 second later, and then declines in contractile force in another
1 to 2 seconds
great force of smooth muscle contraction results from
prolonged period of attachment of the myosin cross bridges to the actin filaments
maintain prolonged tonic contraction in smooth muscle for hours with little use of energy
latch mechanism
Another important characteristic of smooth muscle, especially the visceral unitary type of smooth muscle of many hollow organs
stress relaxation of smooth muscle
allow a hollow organ to maintain about the same amount of pressure inside its lumen despite long-term, large changes in volume
stress relaxation or reverse stress relaxation
Factors that influence the increase of calcium ions in intracellular fluid
nerve stimulation, hormonal stimulation, stretch of the fiber, change in chemical environment of the fiber
In place of troponin, smooth muscle cells contain a large amount of another regulatory protein
calmodulin
calmodulin initiates contraction by?
activating myosin cross-bridges
the chain present in the light chains of myosin heads, that once phosphorylated attachment-detachment of myosin head with actin filament occurs
regulatory chain
calmodulin calcium complex binds with this enzyme that causes regulatory chain to be phosphorylated
myosin light chain kinase
located in the cytosol of the smooth muscle cell, which splits the phosphate from the regulatory light chain
myosin phosphotase
allows longterm maintenance of tone in many smooth muscle organs without much expenditure of energy
latch mechanism
innervate smooth muscle located on top of a sheet of muscle fibers
autonomic nerve fibers
autonomic nerve fibers forms this complex in order to secrete their transmitter subtance into the matrix through
diffuse junctions
axons in smooth muscle fiber do not have branching end feet type but have this instead distributed along their axes
varicosities
function in much the same way as the skeletal muscle neuromuscular junction
contact junction
rapidity of contraction of these smooth muscle fibers is considerably faster than that of fibers stimulated by the diffuse junctions
contact junction
most important transmitter substances secreted by the autonomic nerves innervating smooth muscle
ACH, norepinephrine
normal resting state of smooth muscle
negative fifty to negative sixty
action potential of this smooth muscle do not normally occur the same way as skeletal muscles
multi-unit smooth muscle
action potentials of visceral smooth muscle occur in one of two forms
spike potentials, action potential with plateus
spike potential duration
10 to 50 milliseconds
its importance account for the prolonged contraction that occurs in some types of smooth muscles
plateau
flow of these cations to the interior of smooth muscle fiber is mainly responsible for the action potential
calcium ions
a local property of the smooth muscle fibers that make up the muscle mass
slow wave rhythm
caused by waxing and waning of the pumping of positive ions outward through the muscle fiber membrane
slow wave rhythm
when strong enough, can initiate action potentials
slow wave rhythm
approximate threshold for eliciting action potentials in most visceral smooth muscle
negative 60 to about negative 35 millivolts
repetitive sequences of action potentials elicit rhythmical contraction of the smooth muscle mass
pacemaker waves
when stretched sufficiently, spontaneous action potentials generate
unitary smooth muscle
Excitation of visceral smooth muscle by muscle stretch is a result from
normal slow wave potentials; decrease in overall negativity of the membrane potential caused by the stretch itself
how many fibers must depolarize simultaneously before action potential ensues in multi-unit smooth muscle
30 to 40 smooth muscle fibers
local depolarization of multi unit smooth muscle caused by the nerve
transmitter substance
junctional potential
2 types of non nervous and non action potential stimulants
local tissue chemical factors, hormones
cause vasodilation
Adenosine, lactic acid, increased potassium ions, diminished calcium ion concentration, and increased body temperature
hormones affecting smooth muscle contraction in some degree
norepinephrine, epinephrine, acetylcholine, angiotensin, endothelin, vasopressin, oxytocin, serotonin, and histamine
hormone causes contraction of a smooth muscle when the muscle cell membrane contains
hormone gated excitatory receptors
time required for this diffusion of calcium ions into the cell occur averages 200 to 300 milliseconds before contraction begins
latent period
latent period is greater by how many times in smooth muscle compared to skeletal
50 times
Small invaginations of the cell membrane in smooth muscle
caveolae
rudimentary analog of the transverse tubule system of skeletal muscle
caveolae
When the extracellular fluid calcium ion concentration falls down into this number, smooth muscle contraction ceases
1/3 to 1/10 normal
removes calcium and pumps back into ECF or sarcoplasmic reticulum
calcium pump
Smooth muscle of each organ is distinctive from that of most other organs in several ways
- physical dimension
- organization into bundles or sheets
- response to different types of stimuli
- characteristics of innervation
- function
Major differences of smooth and skeletal muscles
- physical organization
- excitation-contraction coupling
- control of the contractile process by calcium
ions - duration of contraction
- amount of energy required for contraction
Control factors that influence smooth muscle contraction in response to local tissue chemical factors
- Lack of oxygen in the local tissues causes smooth muscle relaxation and, therefore, vasodilatation
- Excess carbon dioxide causes vasodilation
- Increased hydrogen ion concentration causes vasodilation
