Smooth Muscles Flashcards
troponin & T-tubules absent. in sm muscle
ya
thin filaments in sm muscle
thin filaments are anchored to the cell membrane or to cytoplasmic structures known as dense bodies (similar to z- lines).
what do intermediate filaments do in sm muscle?
non- contrac5le, form cytoskeleton
50 to 400 um in length
Smooth Muscle
smooth muscle is uninucleate
ya
major groups of sm muscle by location in humans
- vasculature; 2. GI tract; 3. urinary tract; 4. respiratory; 5. reproductive (uterus); 6. ocular
what are the categroies of sm muscles based on contraction patterns?
phasic and tonic
what is phasic sm muscle?
sm muscle that is usually relaxed; e.g. esophagus
what is tonic sm muscle?
usually contracted; relaxes to allow something to pass; e.g. sphincter
how is sm muscle categorized with neighbouring cells?
unitary (single unit sm muscle); multiunit sm muscle;
what is unitary sm muscle?
contains gap junctions; allows coordination of contraction of sm muscle cells as a single unit; usually makes up the walls of gi tract, bladder, e.g. visceral organs, it is called visceral sm muscle
what is multiunit sm muscle?
not electrically coupled–no gap junction; e.g. iris and ciliary of the eye, in male repro tract; and uterus except just prior to labour and delivery;
MOST smooth muscle is controlled by the ANS; -can be innervated by mul?ple neurons, capable of releasing different neurotransmitters
ya
how do APs differ in sm muscles?
- depolarization slower: Ca2+ channels propagate the AP instead of Na+
- repolariza?on also slower: Ca2+ channels inac?vate slowly and there is a delayed ac?va?on of voltage gated K+ and in some cases Ca2+ -ac?vated K+ channels
some sm muscle is capable of spon activity
ya
Action potentials usually do not occur in multiunit smooth muscle
ya
-autonomic neurons create a local depolariza?on that spreads electrotonically (graded fashion) throughout the muscle fibre triggering Ca2+ entry–the more APs in neuron–> bigger the GP in sm muscle
ya
how can Cai be increased in sm muscles?
through voltage-gated L type channels–> CICR from the SR; through IP3 pathway; stretch activated channels;
what are store operated channels?
when SR becomes depleted, store-operated channels are activated–>cause Ca to enter–> replenishes SR–>
what are the roles of STIM1 and Orai?
Orai proteins make up Ca channel in cell membrane; STIM1 activates the protein to alow influx of Ca
what is pharmacomechanical coupling?
drugs, excitatory neurotrans, hormones, can induce Ca release from the SR via the IP3 pathway (and Ca entry from store operated Ca channels in the plasma membrane)
