Z disks

Spike (typical): generated by an external stimulus (electrical, hormone, stretch, spontaneous)

Plateau: characteristic of more prolonged contractions (uterus, ureter, vascular smooth muscle)

Self-excitatory: generated without external stimuli (intestinal walls, gut)

Slow waves: aka pacemaker waves; low oscillation of RMP - don't reach threshold unless strong enough

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  • if threshold is reached (-35mV), train of action potentials occurs - rythmical contractions
  • Interstitial cells of cajal: pacemakers for the electrical and contractile activity of smooth muscle

• Action potential is carried out throughout the fiber
• calcium enters the cell from the ECF via voltage-gated Ca2+ channels
• calcium binds to calmodulin and activates it
• calmodulin then activates myosin kinase, which then phosphorylates myosin
• phosphorylated myosin is then able to bind to actin

• Multiunit: electrical isolation of cells allows finer motor control; each fiber contracts independently of each other
  • action potentials not common b/c fibers are too small
  • ANS stimulation w/ ACh and NE; local depolarization spreads over fibers causing contraction
  • found in Iris, ciliary muscle of eye, vas deferens, piloerector muscles
• Unitary (visceral): gap junctions b/t cells allows coordinated contractions
  • action potentials normall occur
  • 30-40 fibers must depolarize b4 action potential occurs
  • found in GI tract, bile duct, bladder, ureters, uterus, blood vessels

Phasic: characterized by twitch-like shortening of the muscle, followed by relaxation

Tonic: characterized by ability of muscle to sustain force of contraction with dec'd number of activated crossbridges, greatly reducing levels of energy consumption (ATP turnover); Calcium level doesn't drop back to intial level (unlike phasic) - they remain constant level above normal

List the ways calcium enters the smooth muscle during an action potential

1. Voltage-gated calcium channels open with AP depolarization (direct entry - main)
2. Ligand-gated channels are receptor-mediated by hormones and neurotransmitters (direct entry- main)
3. IP3-gated SR channels are receptor mediated and by hormones and neurotransmitters (indirect entry by 2nd messenger- main)
4. Leak channels (direct entry)

skin discoloration due to abnormal spasms of vascular smooth muscle of the peripheral tissues. Leads to diminished blood supply to local tissues

Discoloration is usually due to temperature or emotional changes: initially digits turn white due to dec'd blood supply; then they turn blue due to prolonged lack of oxygen; finally blood vessels reopen causing rush of blood "flushing", which turn digits red

Can ultimately lead to digital ulcerations

• underdeveloped SR
• T tubules run in both transverse and longitudinal directions
• cells function as syncytium (one unit)
• cells joined at intercalated disks
• cells held together by desmosomes
• cells connected by gap junctions
• cells are branched to form network
• fibers are morphologically different in different areas of the heart

The greater the end diastolic volume (preload), the greater the ventricular pressure that can be developed

The resting length of the muscle fiber corresponds to the period of end diastolic pressure

Describe contractility

How do you change contractility in cardiac muscle?

Contractility: the ability of myocardial cells to develop force at a given muscle length - correlates directly with calcium (internal)

Changing the strength of contraction without changing the length

To change: use Neurohumoral factors such as NE which increases sarcolemmal permeability to calcium; increase the frequency of contractons - can cause treppe, but not tetany due to long refractory period