Membrane and Action Potential

• Steps in muscle contraction:

  • Initiated by a depolarizing stimulus opening voltage-gated Na+ channels
  • Na+ influx depolarizes the membrane further, causing more Na+ channels to open
  • Positive feedback loop leads to rapid depolarization, the action potential
  • Terminated by inactivation of Na+ channels and opening of voltage-gated K+ channels
  • K+ efflux repolarizes the membrane, restoring the resting potential

  
• Image of a skeletal muscle fiber, the basic unit of skeletal muscle, with multiple nuclei beneath the sarcolemma

  
• Image of a skeletal muscle fiber seen with an electron microscope

  
• permit passage of certain ions

  Integral proteins
• An example of voltage-gated channel


  Activation and Inactivation gate of Sodium channel
• It balances the tendency for diffusion caused by

  concentration difference

  Equilibrium potential
• generated across a membrane because of a concentration difference of an ion

  potential difference
• No net diffusion occurs in Nernst Potential


  True
• Value of Normal nerve RMP

  -70mV
• exhibited by all cells

  RMP
• Causes of occurrence of RMP

  Nernst potential of Na and K

  K leak channels

  Na K ATPase pump
• Nerve membrane is more permeable to K+ than Na+


  True
• Why is nerve membrane more permeable to K+ than Na+?

  High resting conductance to K
• Exhibited only by excitable cells


  AP
• Characteristics of true Ap

  Stereotypical size and shape

  Propagating

  All or none
• Each normal AP for a given cell type looks identical,

  depolarizes to the same potential and repolarizes to the same RMP


  True
• AP at one cell causes depolarization of adjacent cells in a nondecremental

  manner

  Propagating
• If a threshold is reached, a full-sized AP will be produced, otherwise, none at all

  All or none principle
• Positive charges flow into the cell causing depolarization

  Inward current
• Positive charges flow out of the cell causing hyperpolarization


  Outward current
• Make the MP more positive

  Depolarization
• Make the MP more negative

  Hyperpolarization
• Occurs during an AP when MP>0mV

  Overshoot
• Occurs during an AP when MP<RMP

  Undershoot
• Non-propagated local potential due to local change in ionic conductance

  Electrotonic potential
• the larger the nerve fiber, the smaller the internal resistance, and

  the faster the conduction velocity


  True
• Where is conduction velocity is most dependent?

  Nerve diameter
• Where is AP is regenerated, which contains the highest concentration of Na+ channels per square micrometer of cell membrane?

  Nodes of Ranvier
• The basic working unit of CNS and PNS, and exhibits the characteristic of being electrically excitable

  Neurons
• Contains the nucleus, which is the neuron's metabolic center


  Soma
• bring signal away from the body (presynaptic terminal)

  Axon
• Brings and transmits signal towards the cell body

  Dendrite
• A protein-lipid complex that is wrapped around the axon

  Myelin sheath
• It is where action potentials cause the release of synaptic

  transmitters

  nerve endings
• It transmits propagated impulses to the nerve endings

  Axonal process
• minimal intensity of stimulating current needed to produce an action potential

  Threshold intesnsity
• weak stimulus needs a long duration.

  True
• A strong stimulus is sufficient at a short duration


  True
• No action potential occurs if the stimulus is subthreshold in magnitude, and the

  action potential has a constant amplitude and form at any stimulus strength above

  the threshold

  True
• Associated with the immune system; scavenger cells that resemble tissue macrophages

  Microglia