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Bio 385 Chapter 4 Summary
Chapter 4; neural condition and synaptic transmission Summary for Bio 385. Enjoy!!
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Chapter 4Neural 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
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