Bio 385 Chapter 4 Summary

Chapter 4
Neural Conduction and Synaptic Transmission



Resting Membrane Potential


 Membrane potential
o Difference in electrical charge between the inside and outside of cell
Recording Membrane Potential
 Microelectrodes
o Intracellur electrodes
o The top must be small enough to pierce neural membrane without damage
o When tip is inserted into neuron, potential is -70 millivolts
 Potential inside resting neuron is 70 mV less than outside neuron
o Resting potential - -70mV
 -70 mV built across membrane means it is polarized
Ionic Basis of Resting Potential
 Ions - salt in neuron tissues separate into positively and negatively charged particles
o Na+ and K+
 In resting neurons more Na+ on outside, more K+ on inside
 Pressure
o Pressure for Na+ to entire resting neurons
o Electrostatic pressure
 -70 mV attracts Na into resting neurons
o Pressure from random motion for Na+ to move down their concertation gradient
 Evenly distributed, more down concentration gradient than up
 Move from area to high concentration to areas of low
 Sodium potassium pumps
o Mechanism in cells membrane exchange three Na+ inside the neuron for two K+
outside neuron
o Allows resting membrane potential to stay fixed



Generation, Conduction, and Integration of Postsynaptic Potentials


Generation and Conduction
 Neurons release chemicals called neurotransmitters
o Bind to postsynaptic receptors, have different effect depending
 Depolarize receptive membrane- decrease resting membrane potential
 Excitatory postsynaptic potentials – postsynaptic depolarization
o Increase likelihood of neuron firing
 Hyperpolarize – increase resting potential

, Chapter 4
Neural Conduction and Synaptic Transmission
 Inhibitory postsynaptic potentials
o Decrease likelihood of neuron firing
 Graded responses
 EPSP and IPSP – amplitude of effect depends on signal that elicit
them
 Weak signals make for smaller potentials
o ESPS and IPSP
 Transmitted rapidly
 Transmission is decremental – decrease in amplitude as they travel
through neuron
Integration of Postsynaptic Potentials and Generation of Action Potential
 Threshold of Excitation
o If there is enough depolarization to the membrane, level referred to is threshold
of excitement – about 65 mV
o Creates action potential
 Action potential
o Massive reversal of membrane potential
o From -70 mV to +50mV
o Magnitude is not related to intensity of stimuli
o All or none responses – either occur to full extent or not at all


Conduction of Action Potentials


 Voltage active ion channels – ion channels that open or close in response to changes in
the level of membrane potential
o How Aps are produced and conducted along axon
Refractory Periods
 Absolute refractory period – brief period after action potential initiation where it is
impossible to elicit another AP
 Relative refractory period – period where it is possible to fire neuron again but only at
higher than normal stimulation
o The end of this period is the baseline stimulation
 AP travel along axon in one direction
 Rate of neural firing is related to intensity of stimulation
Axonal Conduction of Action Potential
 APs do not grow weaker as they travel along axon membrane
 Conducted more slowly than postsynaptic potential
 Action potential gets triggered in terminal buttons
 Conduction is a series of discrete events
o But, easier to think of as a single wave of excitation spreading actively as
constant speed along axon