Smooth and cardiac muscle Flashcards
Describe physical characteristics of smooth muscle?
no striations like skeletal or cardiac
thinner
single celled
mono-nucleate
Filaments have a more diagonal arrangement and more random.
Filaments anchored to membranes and cell structures by dense bodies (like z lines)
What is the difference between smooth muscle (incl cardiac) and voluntary skeletal muscle system?
completely innervated by autonomic nervous system, NOT by voluntary somatic nervous system
What happens to smooth muscle cell appearance when relaxed and when contracts?
when muscle cell relaxed, thinner and filaments not overlapping as much
when muscle cell contracts, bulging areas form
Describe smooth muscle cross bridge cycle activation?
when calcium released into cellular environment- binds to calmodulin and forms calcium calmodulin complex
this complex interacts/binds with an enzyme called myosin light chain kinase
kinase phosphorylates myosin cross bridges with ATP and phosphorylated cross bridges bind to actin filaments
CONTRACTION AND TENSION
How does smooth muscle relax?
Smooth muscle relaxes via action of myosin light chain phosphatase - dephosphorylates X-bridges
Describe baseline tone?
low level contraction where some calcium released which helps maintain contraction for long time to keep blood vessel open
What are the features of smooth muscle that must have baseline tone?
Phosphorylated X-bridges may be dephosphorylated when still bound to actin
decreases rate of ATP splitting- don’t consume as much energy
Sources of cytosilic Ca2+?
sarcoplasmic reticulum
(less SR in smooth muscle than in skeletal, no T-tubules and randomly arranged)
Extracellular Ca2+
(voltage activated Ca2+ channels)
How would we get rid of calcium for cytosol to help cells relax?
pumping calcium back into SR and out of cell by calcium ATPases (slower)
Difference between skeletal and smooth muscle in activating troponin sites?
In skeletal muscle:
1 AP releases enough Ca2+ to saturate all troponin sites
In smooth muscle:
Only some sites activated
Can grade contraction depending on number of AP’s that reach cells
What does smooth muscle have tone and skeletal does not?
Designed to resist fatigue
Smooth muscle has tone i.e a basal level of Ca2+ in cells causes a constant level of tension
What are factors affecting contractile activity?
Spontaneous electrical activity in muscle membranes = Pacemaker activity
Autonomic (have to travel long distances) neurotransmitters from varicosities (bulges that exist along autonomic nerves
release autonomic neurotransmitters)- one autonomic nerve can regulate activity or contraction at different points of a big long sheet or tube of smooth muscle in one or organs.
Hormones- travelled from other sites in blood
Local factors (paracrine agents (released from neighbouring mols and tissues), pH, O2, osmolarity, ions, NO))
Stretch- contract back harder and faster
What are the different types of smooth muscle?
Single Unit (GIT, uterus, small blood vessels)
Many cells linked by gap junctions (allows chemical signals and ions to move between muscle cells)
Signals travel between cells
Contract synchronously
May contain pacemaker cells
Stretch evokes contraction
Multiunit (airways, large arteries, hairs)
Few or no gap junctions
Richly innervated by ANS
Don’t respond to stretch
