13.6 The Nerve Impulse

• What is excitability in the context of plasma membranes?

  It is the ability of plasma membrane to respond to stimulus and generate action potential.
• Which types of cells have excitable membranes?

  Skeletal muscle fibers, cardiac muscle cells, some gland cells, and axolemma of most neurons.
• What does excitability allow plasma membranes to do?

  It allows plasma membranes to conduct electrical impulses.
• What is an action potential?

  It is a change in membrane potential that develops after axolemma is stimulated to a level known as threshold.
• What is membrane potential?

  It is the resting electrical change of the plasma membrane.
• How does membrane potential arise?

  It results from the uneven distribution of positive and negative ions across the plasma membrane.
• What happens when a stimulus is applied to an axon?

  It produces a temporary change in permeability of the axolemma.
• What is the effect of a temporary change in permeability on the axon?

  It changes the membrane potential of the axon.
• What is a threshold stimulus?

  It is the stimulus sufficient to start an action potential.
• What happens when an action potential develops in one location of an axon?

  It will propagate (spread) along the length of the axon toward the axon terminal.
• What factors affect the rate of impulse conduction in axons?

  The properties of the axon, such as its diameter and whether it is myelinated.
• If one axon conducts action potentials at 50 m/s and another at 1 m/s, which one is myelinated?

  The axon that conducts action potentials at 50 m/s is myelinated.
• How does myelination affect conduction speed?

  Myelination increases the conduction speed of a neuron.
• How is excitability defined?

  It is the ability of a plasma membrane to respond to an adequate stimulus and generate an action potential (AP).
• Excitability is ability of plasma membrane to respond to stimulus and generate action potential. Plasma membranes of skeletal muscle fibers, cardiac muscle cells, some gland cells, axolemma of most neurons (multipolar and pseudounipolar neurons) are examples of excitable membranes. 
• Excitability is ability of plasma membrane to conduct electrical impulses 
• Plasma membranes of skeletal muscle fibers and most neurons are excitable 
• Action potential, or nerve impulse, is change in membrane potential that develops after axolemma is stimulated to level known as threshold 
• Cells possess membrane potential, resting electrical change of plasma membrane 
• Membrane potential results from uneven distribution of positive and negative ions across plasma membrane
• When stimulus on axon, produced temporary change in permeability of axolemma
• Temporary change in permeability changes membrane potential of axon
• Stimulus sufficient to start action potential, stimulus termed threshold stimulus
• Action potential develops in one location of axon, it will propagate (spread) along length of axon toward axon terminal
• Rate of impulse conduction depends on axon’s properties, such diameter/myelinated
• Two axons are tested for conduction speeds. One conducts action potentials at 50m/s, the other at 1m/s. Which axon is myelinated?

  Myelination increases the conduction speed of a neuron, so the neuron that conducts action potentials at 50m/s would be myelinated.
• Define excitability.

  The ability of a plasma membrane to respond to an adequate stimulus and generate an action potential (AP).