PSYCO275 Chapter Notes - Chapter 4: Saltatory Conduction, Catecholamine, Nitric Oxide
6 Jun 2018
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PSYCO 275 - Chapter 4
Resting Membrane Potential
●Recording The Membrane Potential
○Position the tip of one electrode inside the neuron and the tip of another electrode
outside the neuron in the extracellular fluid
○The tip of the intracellular electrode should be fine enough to pierce the neural
membrane without severely damaging it
■Microelectrodes
: the intracellular electrodes
○Steady potential of -70 mV is recorded when the intracellular electrodes are
inserted in the neural membrane
■Means that the potential inside the resting neuron is about 70 mV less than
the outside
■This is called the resting potential
■In its resting state, the neuron is polarized (separation of charges)
●Ionic Basis of the Resting Potential
○Ions
: The salts in neural tissue separate into positively and negatively charged
particles
■Na+ and K+
○In resting neurons: more Na+ outside than inside and more K+ inside than outside
■Ions can go through ion channels
■These ion channels are specific to which ions pass through
○2 types of pressure put on Na+ to enter neurons:
■Electrostatic pressure
●This is from the resting membrane potential
●The -70 mV attracts the Na+ into resting neurons (opposites
attract)
■Pressure from random motion
●Motion for Na+ ions to move down their concentration gradient
●The ions in the neural tissue are in constant random motion
●Particles in random motion tend to become evenly distributed
because they’re more likely to go down their concentration
gradients than up them (high concentration to low concentration)
○The Na+ ion channels are closed during rest while the K+ ion channels are open
during rest
■But only a small amount of K+ go out because they’re held tightly by the
negative resting membrane potential
○Sodium-Potassium Pumps
■Discovered by Hodgkin & Huxley
■Rate of Na+ going out = Rate of Na+ going in (same for K+)
■3 Na+ in and then 2 K+ out
○Transporters
: mechanisms in the cell membrane of a cell that actively transports
ions or molecules across a cell
Generation, Conduction and Integration of Postsynaptic Potentials
●Generation and Conduction of Postsynaptic Potentials
○Neurotransmitters:
released from the neuron when they fire
■These are chemicals
■They diffuse across the synaptic clefts and interact with specialized
receptor molecules on the receptive membranes of the next neurons in the
circuit
■Two effects once these bind to postsynaptic receptors:
●Depolarize the receptive membrane
○Decrease the resting membrane potential from -70 to -65
mV for example
●Hyperpolarize the receptive membrane
○Increase the resting membrane potential from -70 to -72
mV for example
○Excitatory Postsynaptic Potentials (EPSPs)
■Increase the likelihood that the neurons will fire
○Inhibitory Postsynaptic Potentials (IPSPs)
■Decrease the likelihood that the neurons will fire
○EPSPs and IPSPs are graded responses
: their amplitudes are proportional to the
intensity of the signals that elicit them
■Weak signals, small postsynaptic potentials (same with strong signals)
■Usually travel passively from their sites of generation at synapses, usually
on the dendrites/cell body, in much the same way as electrical signals
travel through a cable
○Transmission of postsynaptic potentials has 2 important characteristics
■It’s rapid
●Don’t confuse the duration of the EPSPs and IPSPs with their rate
of transmission
●All postsynaptic potentials are delivered at great speed
■The transmission of EPSPs and IPSPs is decremental
●EPSPs and IPSPs decrease in amplitude as they go through the
neuron
●Most of them don’t travel the whole axon
●Integration of Postsynaptic Potentials and Generation of Action Potentials
○A neuron fires depends on the balance between the excitatory and inhibitory
signals reaching its axon
○Axon hillock
: it was believed that action potentials were generated here BUT NO
○Axon initial segment
: where the action potentials actually get generated
○The graded EPSPs and IPSPs are conducted instantly and decrementally to the
axon initial segment
○Threshold of excitation:
sufficient sum of depolarizations and hyperpolarizations
from the axon initial segment to depolarize the membrane
■Usually -65 mV
■Once this threshold is reached, an action potential (AP) is created
Document Summary
Position the tip of one electrode inside the neuron and the tip of another electrode outside the neuron in the extracellular fluid. The tip of the intracellular electrode should be fine enough to pierce the neural membrane without severely damaging it. Steady potential of -70 mv is recorded when the intracellular electrodes are inserted in the neural membrane. Means that the potential inside the resting neuron is about 70 mv less than the outside. In its resting state, the neuron is polarized (separation of charges) Ions : the salts in neural tissue separate into positively and negatively charged particles. In resting neurons: more na+ outside than inside and more k+ inside than outside. These ion channels are specific to which ions pass through. 2 types of pressure put on na+ to enter neurons: This is from the resting membrane potential. The -70 mv attracts the na+ into resting neurons (opposites attract)
