1.3 Changes in Voltage of the Resting Membrane Potential

• What is the average resting membrane potential of smooth muscle?

  −56 millivolts
• What happens during depolarization of the membrane?

  The muscle fibers become more excitable
• What is hyperpolarization of the membrane?

  When the potential becomes more negative
• What are the factors that cause depolarization of the membrane?

  Stretching, acetylcholine, gastrointestinal hormones
• What factors hyperpolarize the membrane?

  Norepinephrine, sympathetic nerve stimulation
• How does calcium ion entry affect smooth muscle contraction?

  It activates myosin filaments to contract
• What do slow waves cause to enter the smooth muscle fiber?

  Sodium ions
• When do significant quantities of calcium ions enter the muscle fibers?

  During spike potentials at slow wave peaks
• What is tonic contraction in gastrointestinal smooth muscle?

  • Continuous contraction
  • Not associated with slow waves
  • Can last several minutes or hours
  • Intensity can vary
• What causes tonic contraction in smooth muscle?

  Repetitive spike potentials, hormones, calcium entry
• How does the frequency of spike potentials affect tonic contraction?

  Higher frequency increases contraction degree
• What is still unclear about tonic contraction mechanisms?


  The details of the mechanisms involved
• How can the baseline voltage level of the smooth muscle resting membrane potential change?

  Due to multiple factors affecting it
• What is the relationship between depolarization and muscle fiber excitability?

  Depolarization increases muscle fiber excitability
• What is the effect of continuous repetitive spike potentials on tonic contraction?

  It increases the degree of contraction
• What can cause continuous partial depolarization of the smooth muscle membrane?

  Hormones or other factors
• What is still unclear about the mechanisms of tonic contraction?

  The specific details of these mechanisms