smooth muscle

Question 1

smooth muscles basics
- where found
- what does it allow
- how are contractions controlled
- how are they connected
- nature of contraction

Answer 1

• line walls of hollow visceral organs, eg. liver, pancreas, intestines)
• allows them to change shape
• the autonomic nervous system
• electrical and mechanical connections
• long sustained contractions, without fatigue when stimulated constantly

Question 2

properties
- striations?
- how are actin and myosin arranged
- how does actin attach to the cell
- where is mysoin
- how are cells mechanically connected
- how are some cells electrically connected

Answer 2

• no as have no sarcomeres so no z-lines
• form lattice (criss cross) allowing it to change shape
• specialised areas in cytoplasm called dense bodies
• between actin
• specialised areas in membrane called dense bands so movement of 1 cell impacts next
• gap junctions in membrane allowing sm to contract as a unit

Question 3

activation of smooth muscle
- where is neurotransmitter released from
- single unite sm activation
- multiunit sm activation

Answer 3

• from variscosities, it then binds and excites the cell
• connected by gap junctions, when 1 fibre excited, all are, so function as a unit
• cells not electrically couples so stimulated individually, allowing precision of movement

Question 4

mechanism of contraction
- actin and mysosin
- 2 reasons why important

Answer 4

• actin and mysosin slide without reaching end of sarcomere
• less myosin, more actin
• important as force of contraction is not all or none as can be graded due to calcium so can be varied over a range of lengths

Question 5

action potentials in sm
- pacemaker potential
- slow waves

Answer 5

• rhythmic contractions due to unstable resting potential
• influenced by excitatory and inhibitory inputs- when exc > inh membrane potential maintained above threshold and AP repeated + contractions sustained

Question 6

role of calcium in sm
- where is calcium stored
- impact of no troponin
- action of calcium
- what does it mean if calcium is present
- how/when is contraction stopped

Answer 6

• some extracellularly, some in SPR
• actin binding sites always available so calcium acts on myosin instead
• calcium activates calmodulin on myosin, so myosin light chain kinase uses atp to phosphorylate myosin light chains, so heads of myosin can interact with actin
• heads are energised, so can recycle and maintain contraction
• myosin light chain phosphatase active when calcium levels too low and removes phosphate so contraction stops (relaxation).