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WEEK 6:
Smooth Muscle:
| Question | Answer |
|---|---|
| phasic smooth muscle | single unit of muscles which contract in response to AP which propagate from cell to cell creating rhythmic +intermittent (irregular) activity for short period |
| tonic smooth muscle | multi unit smooth muscle that is continuously active |
| normally contracted smooth muscle | sphincters (remain contracted + relax to close only for short period of time) |
| normally partially contracted (tone) smooth muscle | blood vessels (can sustain high force using low energy) |
| phasically active smooth muscle | stomach + intestines (needs to contract in response to signals) |
| normally relaxed smooth muscle | esophagus + urinary bladder (relaxed under normal conditions + contract in response to physiological stimuli) |
| structure | no striations, have actin + myosin (less myosin), not organised into sarcomeres |
| describe amount of myosin in smooth muscles | less |
| smooth muscle supported by and contains what | connective tissue (endomysium) |
| how can smooth muscle be structurally organised | single sheet or multiple sheets |
| how is SM organised as a single sheet | circularly orientated, tonically maintains vessel diameter + pressure, vary in diameter to control flow + pressure |
| how is SM organised as multiple sheets | 2 sheets perpendicular to each other, longitudinal + circular layers, vary in diameter + length |
| example of SM with multiple sheets | ileum for peristalsis |
| example of SM as a sheet | arterioles |
| single unit SM known as | visceral muscle |
| how are single unit SM myogenic | contraction originates in muscle tissue |
| how are multi unit SM neurogenic | relies on neuron to tell it to contract |
| what can a single-unit SM behave as | functional syncitium |
| syncitium meaning | all cells in area activated at once- all at once |
| properties of contraction | involuntary + innervated but do not need it to contract- neurotransmitters, hormones + stretching the muscle (stretch-relaxation response) can affect contraction |
| cause stretch-relaxation response of single unit SM | when muscle of hollow organ stretched (eg bladder filled) mechanical stress of stretching will trigger contraction + immediately relaxes |
| how is smooth muscle controlled when contracting | maintains muscle tone (tension- shape) |
| why is the muscle being toned and the stretch-relaxation response useful | prevents uncontrolled expulsion (eg bladder)m |
| compare contractile properties in SKM + SM | SKM smaller stretch + relaxation than SM |
| sources of Ca2+ | sarcoplasmic reticulum + extracellular fluid |
| describe the mechanism of smooth muscle contraction after AP (excitation coupling) | (1-Ca2+ enters) (2-Ca2+ bind to calmodulin) (3-Ca2+-calmodulin complex activates MLCK to phosphorylate light chains in myosin heads = active myosin heads + activates myosin ATPase ) (4- active myosin heads bind to actin + pull filaments = tension) |
| describe the relaxation mechanism of smooth muscle | (1- Ca2+ leaves) (2- Ca2+ unbinds from calmodulin, inactivating MLCK) (3- myosin phosphase enzyme removes Pi from myosin (decreasing myosin ATPase activity) (4- less myosin ATPase = decreased tension) |
| factors that control of smooth muscle contraction | depolarisiation response, ligands, stretch response |
| how do ligands control SM contraction | eg neurotransmitters like ACh can inititate contraction by interacting with membrane receptors/channels (ligand-gated channels) let Ca2+ín |
| how does the stretch response control SM contraction | stretch + open gated channels so Ca2+ enters |
| how does depolarisation control SM contraction | opens voltage gated Ca2+ channels so Ca2+ enters |
| compare single v multi unit 'electrically coupled + gap junctions' | single = electrically coupled to one another via gap junctions, multi = structurally independent |
| compare single v multi unit AP | single= AP propagate between cells, multi= not spread, only in original cell |
| compare how single v multi units act during contraction | single= fibres act in unison, multi= not unison |
| compare single v multi unit stimuli | single = ANS, neuronal cells + circulating hormones + stretching, multi = autonomic nerves/hormones but not stretching |
| single v multi unit innervation | single = few varicosities to spread info via gap junctions, multi = each fibre is individually innervated by multiple varicosities to spread info directly as no gap junctions |
| varicosities meaning | veins |
| compare function of SM and SKM | SM can contract involuntarily, SKM is voluntary |
| describe the movement when actin + myosin crossbridges form | actin filaments slide over myosin filaments (myosin stays in place) |
Created by:
kablooey
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