smooth muscle Flashcards
single unit
hundreds to thousands of smooth muscle fibers that contracts together as a single unit
single unit features
fibers arranged in sheets/bundles
cell membranes are adhered to multiple points and joined by gap junctions. true/false
true
what excites single unit smooth muscle?
nerve signals, hormones, chemical factors, action potentials, ion flow
where are single unit smooth muscle located?
walls of viscera, ureters, uterus, urinary bladder, blood vessels
what characterizes multi unit smooth muscle?
discrete fibers separated by glycoprotein + collagen
what excites multi unit smooth muscle?
nerve signals
where is multi unit smooth muscle located?
ciliary muscles of the lens, iris muscles of the eye, erector pili muscles, bronchial muscles, ductus deferens, large arteries
multi unit smooth muscle
separate smooth muscle fibers that operate independently
what are the other names for single unit smooth muscle?
unitary/visceral/syncytial smooth muscle
dense bodies
bind to a large # of actin filaments and act like a z-disc
“side polar” cross bridges
efficient shortening that allows myosin to pull actin filaments in many different directions
latent period
time required for diffusion of calcium into cell + activation of enzymes to trigger muscle contraction
how long is the latent period in smooth muscle?
200-300 milliseconds
smooth muscle characteristics
small, thin, short, single/central nucleus, spindle shaped, no striations
what regulates contraction in smooth muscle?
calmodulin
what must happen to regulatory chains?
they must be phosphorylated
what are caveolae?
small invaginations of the cell membrane (resemble rudimentary t-tubules)
where are caveolae located?
in the SR
where does calcium for smooth muscle contraction come from?
extracellular fluid (ECF)
what innervates smooth muscle?
the ANS
smooth muscle resting membrane potential
-50 to -60 mV
varicosities
contain vesicles filled with neurotransmitters
diffuse junctions
autonomic nerve fibers that branch diffusely on top of a sheet of muscle fibers
contact junctions
varicosities that are close to the cell membrane that have rapid contraction
spike potentials
similar to skeletal muscle AP. drastic increase in mV
what causes spike potentials?
electrical stimulation, action of hormones, transmitter substances from nerve fibers, stretch, spontaneous generation
plateau potentials
repolarization is delayed allowing for prolonged contraction
slow wave action potentials
create rhythmical phases when the cells are self excitatory
where are slow wave APs used?
GI tract
pacemaker waves
repetitive sequences of APs that cause rhythmical contractions of smooth muscle
where are pacemaker waves contractions used?
specific GI organs. stomach (3/min) + duodenum (12/min)
what causes depolarization of smooth muscle?
influx of calcium by voltage gated Ca+ channels
does smooth muscle have a long or short latent period?
long
what is needed to relax smooth muscle?
dephosphorylation of myosin
parasympathetic postganglionic neurons
release ACH which binds to muscarinic receptors
what does parasympathetic ACH cause contraction of?
smooth muscle of GI tract, bronchi, iris sphincter, ciliary muscles, and some veins
what do sympathetic postganglionic neurons release?
norephinephrine which activates adrenergic receptors
what do sympathetic postganglionic receptors innervate?
sweat glands that release ACH
activation of alpha-1 recpetors causes?
smooth muscle to contract
activation of beta-2 receptors causes?
smooth muscle to relax
where are alpha-1 receptors found?
blood vessels for skin and GI
where are beta-2 receptors found?
cardiac muscle, skeletal muscles, bronchial muscles
junction potential
local depolarization occurs across the membrane to allow an influx of calcium for muscle contraction
why do junction potentials occur?
bc muscle fibers are too small to generate an AP
muscle stretch
smooth muscle is stretch generating spontaneous APs to contract smooth muscle
what cells are the pacemakers for GI smooth muscle?
interstitial cells of cajel
what causes small blood vessels to contract/relax?
chemicals released by the tissues they supply
vasodilation of small blood vessels
lack of oxygen. excess carbon dioxide. increased H+. increase in tissue temp. decrease in BP. lactic acid, adenosine, potassium ions, nitric oxide
vasoconstriction in small blood vessels
increased blood pressure
hormone gated excitatory receptors
open sodium or calcium channels
hormone gated inhibitory receptros
close sodium or calcium channels
slow cycling of myosin cross bridges
myosin attach to actin, release actin and reattachment is MUCH SLOWER
low energy requirement for smooth muscle contraction
conserves energy in intestines, urinary bladder, gall bladder, etc
total contraction time for smooth muscle
1-3 seconds
why is maximum force of contraction in smooth muscle greater than skeletal muscle?
because of prolonged periods of attachment of the myosin cross bridges to the actin filaments
latch mechanism
ability of smooth muscle to maintain prolonged tonic contraction for hours with little energy use
stress-relaxation of smooth muscle
ability to return to original force of contraction after muscle has been elongated/shortened
