USMLE Step 1 Physiology Review 53 06 Neuronal Synapses (1 of 3)

USMLE Step 1 Physiology Review 53 06 Neuronal Synapses (1 of 3)

 

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Begin 53 06 Neuronal Synapses (1 of 3) Transcription

All right, now we’re going to talk about neuronal synapses.

Other than acetylcholine, what are the other neurotransmitters at the neuromuscular junction?

  • There are none.

Which is more complicated, nerve to nerve transmission or nerve to muscle transmission? 

  • Nerve to nerve transmission.

Activation of receptors at neuronal synapses produces changes in membrane conductance of what three ions?  List them alphabetically.

  • First, chlorine.  Second, potassium.  Third, sodium.

Postsynaptic potentials are graded potentials that have amplitudes that are proportional to the strength of what? 

  • The strength of the stimulus.

Graded potentials travel from the dendrites towards the soma of the postsynaptic neuron and then to the conical area of origin of the axon from the cell body.  The postsynaptic neuron summates the graded potentials both spatially and temporally.

 What is the term for the conical area of origin of the axon from the nerve body?

  • The axon hillock.

What occurs at the axon hillock to the summated potentials? 

  • They are integrated.

 The summated postsynaptic potentials bring the axon hillock region to threshold via what kinds of currents.  Local circuit currents.

  Student Doctor, please pause the tape and summarize the information discussed this far on neuronal synapses.

  • Acetylcholine is the only neurotransmitters at the neuromuscular junction.  Nerve to nerve transmission is more complicated than nerve to muscle transmission.  Activation of receptors at neuronal synapses produces changes in membrane conductance of what chlorine, potassium, and sodium.  Postsynaptic potentials are graded potentials that have amplitudes that are proportional to the strength of the stimulus.  Graded potentials travel from the dendrites towards the soma of the postsynaptic neuron and then to the axon hillock where the postsynaptic neuron summates the graded potentials both spatially and temporally.  The summated potentials are integrated at the axon hillock.  The summated postsynaptic potentials bring the axon hillock region to threshold via local circuit currents.

What kind of potential would be described as a one to ten millivolt depolarizing potential of several millisecond duration?

  • Excitatory Postsynaptic Potential, also referred to by its initials, EPSP.

 Excitatory Postsynaptic Potentials produce inwardly directed current that flows through channels in the postsynaptic neuron.  In what structure of the neuron are these channels located?

  • The membrane.

 What are two typical excitatory neurotransmitters?  One starts with an A and the other starts with a G? 

  • Aspartate and Glutamate.

 The EPSP equilibrium potential is close to the algebraic sum of the equilibrium potential of sodium and the equilibrium potential of potassium, and so is close to what number?

  • Zero.

Excitatory synapses produce EPSPs, or excitatory postsynaptic potentials, and Inhibitory synapses produce Inhibitory postsynaptic potentials, or IPSPs.

 Are IPSPs hyperpolarizing or depolarizing? 

  • Hyperpolarizing.

What is the range in millivolts of the hyperpolarizing potential? 

  • One to five millivolts.

Inhibitory neurotransmitters activate receptors that increase membrane conductance of what two ions? 

  • Chlorine and potassium.

 When the resting potential is close to the equilibrium potential for chlorine, then what effect does an increase in chlorine conductance have on the membrane potential?

  • Increased chlorine conductance effectively clamps the membrane potential at the equilibrium potential of chlorine and inhibits depolarization.

 Glycine and GABA are two examples of inhibitory transmitters.

 Student Doctor, please pause the tape and summarize the information discussed on neuronal synapses since the last summary.  We started with the description of EPSPs, or excitatory postsynaptic potentials.

  • An excitatory postsynaptic potential, or EPSP, is a one to ten millivolt depolarizing potential of a duration of several milliseconds.  EPSPs produce inwardly directed current that flows through channels in the postsynaptic membrane.  Aspartate and glutamate are two typical excitatory neurotransmitters.  The EPSP equilibrium potential is close to the algebraic sum of the equilibrium potential for sodium and the equilibrium potential for potassium, or zero millivolts.  Excitatory synapses produce EPSPs and inhibitory synapses produce Inhibitory postsynaptic potentials, or IPSPs. IPSPs are one to five millivolt hyperpolarizing potentials.  Inhibitory neurotransmitters activate receptors that increase membrane conductance of chlorine and potassium.  When the resting potential is close to the equilibrium potential for chlorine, increased chlorine conductance effectively clamps the membrane potential at the equilibrium potential of chlorine and inhibits depolarization.  Glycine and GABA are two examples of inhibitory transmitters.

 

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