Muscle 8 Flashcards
Smooth muscle is categorized by…
- location
- contraction pattern
- communication with neighbouring cells
In humans, smooth muscle can be divided in which 6 major (location) groups?
- vascular
- gastrointestinal
- urinary
- respiratory
- reproductive
- ocular
What are the 4 contraction patterns?
- a phasic smooth muscle that is usually relaxed
- a phasic smooth muscle that cycles between contraction and relaxation
- a tonic smooth muscle that is usually contracted
- a tonic smooth muscle whose contraction is varied as needed
unitary smooth muscle (single unit)
contains gap junctions that allow for coordinated contraction of many cells causing muscle to contract as a single unit
multiunit smooth muscle
-not electrically coupled
iris and cilliary body of eye, in male reproductive tract and in uterus except just prior to labor and delivery
What can alter smooth muscle tension?
hormones, stretch and local factors, paracrine signals, acidity, oxygen and CO2 conc, and osmolarity
Paps of smooth muscle can be initiated by…
neural, hormonal, or mechanical stimulation
slow wave potentials
fire action potential when they reach threshold
pacemaker potentials
always depolarize to threshold
in some smooth muscle Vm oscillations can lead to..
tonic contractions in absence of APs
electromechanical coupling
contraction due to electrical signaling
Autonomic AP initiation
- spikes or plateaus
- single unit
spontaneous AP
- slow wave
- pacemaker
- single unit
graded potentials
multiunit
Calcium conc is increased by what three different mechanisms?
- Ca2+ entry through voltage gated channels or ligand gated ion channels
- Ca2+ release from SR
- Ca2+ entry through voltage-independent channels
There is ____ SR in smooth than in skeletal and cardiac.
less
IP3 pathways
can cause contraction with minimal depolarization and negligible extracellular Ca2+ influx
Depletion of Ca2+ in the SR causes activation of…
store-operated channels
store-operated channels
cause a Ca2+ influx across the cell membrane. Allows [Ca2+]i to remain elevated and replenishes SR.
pharmacomechanical coupling
occurs when chemical signals change muscle tension through signal transduction pathways with little or no change in membrane potential
stretch of smooth muscle causes..
an internal release of Ca2+ from the SR through the ryanodine receptor causing phosphorylation of myosin light chain leading to contraction
myosin light chain kinase
phosphorylates the regulatory light chain near the myosin head which alters the conformation of the myosin head, increasing its ATPase activity and allows it to interact with actin
In smooth muscles, cross-bridge cycling is similar but…
occurs more slowly
During relaxation, the regulatory light chain must be…
dephosphorylated by myosin light chain phosphatase
latch state
when some smooth muscle can maintain force for an extended period of time with little ATP use
Neurotransmitters, hormones and paracrine molecules alter smooth muscle Ca2+ sensitivity by…
modulating light chain phosphatase
