NERVE IMPULSE TRANSMISSION  nerve cells are like no other cell in the body because they possess an electrical charge  the axon of a neuron has a cell membrane that is semipermeable

 imbedded in the membrane are specialized proteins called ION PUMPS that produce an unequal concentration of charged particles between the cell and its fluid extracellular environment

RESTING MEMBRANE POTENTIAL (Polarized RESTING MEMBRANE POTENTIAL (Polarized)  this refers to the charge of an axon that is waiting for a nerve impulse (resting)  Na + and K + ions are found both outside and inside the neuron

 there is a higher concentration of Na + in the extracellular environment than inside  K + is more highly concentrated inside than out

 a SODIUM POTASSIUM PUMP, in the membrane, is used to actively transport 3 Na + out of the axon for every 2 K + it moves in; this creates a charge of -70mV

ACTION POTENTIAL  an action potential is the name for the transmission of an electro- chemical stimulus through a nerve  in order for an action potential to occur the stimulus has to be strong enough, this is referred to as THRESHOLD LEVEL

 there are two stages to an action potential:  Depolarization and Repolarization

DEPOLARIZATION:  when the neuron is stimulated, its membrane becomes more permeable to Na + ions, and impermeable to K +, so Na + ions move into the neuron by diffusion and K + ions are not able to move out.

 this creates a reversal of charge in the neuron called depolarization, now the neuron is more positive than its surroundings (+40mV)

REPOLARIZATION:  is the return of the neuron to its resting state.  Na + channels close so Na + can no longer move into the neuron  K + rushes out of the axon and into the extracellular fluid by diffusion

 The Sodium Potassium Ion pump then begins functioning; it pumps 3 Na + ions out of the neuron and 2K + ions into the neuron, returning the cell to its polarized condition (-70 mV)

 depolarization and repolarization must be complete before a neuron can transmit another stimulus; this is called the REFRACTORY PERIOD

 a neuron transmits the electrical impulse in wavelike fashion, once a region of the axon becomes depolarized adjacent regions will also become depolarized.

 once a neuron’s threshold level has been reached it will respond totally, if it is not reached the neuron will not respond = ALL OR NONE RESPONSE

 neurons in your body have different threshold levels allowing for different intensities of response.  the more neurons that reach threshold levels the more intense the response.

w The more rapidly impulses are sent, the more intense the response as well

Graphing an Action Potential ChargemV Restingpotential Depolarization Repolariztion Restingpotential Time(us)