Nerve Impulse

• Nerve Impulse - electrical message that is transmitted down the axon of a neuron.
• Nerve Impulse - does not travel directly down the axon but is regenerated at points along the axon so that is is not weakened.
• Speed - of nerve impulse ranges from less than 1 meter/second to 100 meter/second.
• Messages in a neuron develop from disturbances of the: resting potential.
• RESTING POTENTIAL - the membrane maintains an Electrical Gradient, also known as polarization
• polarization - a difference in electrical charge between the inside and outside of the cell.
• polarization - a difference in the electrical charge of two locations.
• Resting Potential - refers to the state of the neuron prior to the sending of a nerve impulse.
• The membrane is "selectively permeable" allowing some chemicals to pass more freely than others.
• When membranes are at REST:

  • Sodium Channels are: Closed
  • Potassium Channels are: Partially Closed
• Sodium-potassium pump - a protein complex, repeatedly transports three sodium ions out of the cell while drawing two potassium ions into it.
• Three - number of sodium ions out of the cell during sodium-potassium pump
• Two - number of potassium ions in during sodium potassium pump
• Sodium-potassium pump - Helps to maintain the electrical gradient
• resting potential - invests much energy to prepare the neuron to respond rapidly
• action potentials - messages sent by axon
• Hyperpolarization - which means increased polarization.
• Depolarization - refers to decreasing the polarization towards zero
• threshold of excitement - refers to a level above which any stimulation produces a massive depolarization.
• Action potential - rapid depolarization of the neuron
• Depolarized - state of polarization during action potential
• Action Potential - triggered during stimulation of neuron past the threshold of excitation
• Outside - where sodium ions are at the start of the action potential
• Inside - mostly where potassium ions are during action potential
• At the peak of action potential Sodium Channels are: closed
• propagation - describes the transmission of an action potential down an axon.
• action potential "don't" directly travel down the axon
• Axon Hillock - Where the action potential begins
• Axon Hillock - swelling where axon exits the soma
• Myelin Sheath - increase the speed still more, vertebrate axons evolved a special mechanism
• Myelin Sheath - an insulating material composed of fats and proteins.
• nodes of Ranvier - interrupt the myelin sheath of axons
• Saltatory conduction - The jumping of action potentials from node to node.
• Saltatory conduction - Provides rapid conduction of impulses
• Saltatory conduction - Conserves energy for the cell
• Multiple sclerosis - disease in which the myelin sheath is destroyed and

  associated with poor muscle coordination and sometimes visual impairments
• Refractory Period - Happens after action potential where the neuron resists the production of another action potential
• Absolute - the first part of refractory period in which the membrane cannot produce an action potential
• Relative - the secondary part of the refractory period where it takes a stronger than usual stimulus to trigger an action potential
• Local Neurons - Small neurons that have no axon