Nervous System Physiology Part 3 Flashcards
What are Chemical Synapses?
Interaction between cells occurs via chemical intermediaries known as neurotransmitters.
What does Unidirectional transmission of signals involve?
Unidirectional transmission of signals.
Involves the release of chemical messengers from one neuron to affect another.
What event arrives at the axon terminal of the presynaptic neuron?
Action potential
What type of channels open in the presynaptic neuron membrane upon arrival of the action potential? What ion passes through these channels?
Voltage-gated Ca2+channels open.
Ca2+calcium ions) pass through the channels
Where does Ca{2+}enter after the voltage-gated channels open?
The presynaptic neuron (specifically, the axon terminal).
What do Ca2+ signals trigger within the presynaptic neuron?
signals the neurotransmitter vesicles.
What happens to the neurotransmitter vesicles as a result of the Ca$^{2+}$ signal?
Vesicles move to the membrane and dock.
How are neurotransmitters released from the presynaptic neuron into the synaptic cleft?
Via exocytosis.
What do neurotransmitters do once they are released into the synaptic cleft?
Neurotransmitters bind to receptors on the postsynaptic cell.
What is initiated in the postsynaptic cell upon neurotransmitter binding?
A graded potential (which may or may not lead to an action potential).
Many receptors on postsynaptic membranes at chemical synapses are specialized to
open ion channels, converting chemical signals to electrical signals.
What do neurotransmitter receptors do for graded potentials?
Neurotransmitter receptors mediate graded potentials.
What are graded potentials?
Graded potentials are local changes in membrane potential that vary in strength.
What does the strength of a graded potential depend on?
- The strength of a graded potential depends on the amount of neurotransmitter released and how long it remains in the
Where does Graded Potential occur and where does Action Potential occur?
- Graded Potential: Usually dendrites and cell body
- Action Potential: Trigger zone through axon
Types of gated ion channels involved in graded potential and action potential
Graded Potential: Mechanically, chemically, or voltage-gated channels
* Action Potential: Voltage-gated channels
Ions involved in graded potential and action potential
Graded Potential: Usually Na ion K ion Cl ion
* Action Potential: Na ion and K iona
Type of signal used in graded potential and action potential
Graded Potential: Depolarizing (e.g., Na$^+) or hyperpolarizing (e.g., K^+$ or Cl$^-$)
* Action Potential: Depolarizing
Strength of signal in graded potential and that of action potential
Graded Potential: Depends on initial stimulus; can be summed
* Action Potential: All-or-none phenomenon; cannot be summed
What initiates the signal in graded potential and action potential
Graded Potential: Entry of ions through channels
* Action Potential: Threshold stimulus graded potential at the trigger zone
Unique characteristics of graded potential and action potential
Graded Potential:
* No minimum level required to initiate
* Two signals coming close together in time can summate
* Initial stimulus strength is indicated by frequency of a series of action potentials
* Action Potential:
* Threshold stimulus required to initiate
* Refractory period: two signals too close together in time cannot summate
What can increase the amplitude of graded potential?
Stimulus responses can summate to increase the amplitude of the graded potential.
What is the difference between temporal and spatial summation?
Temporal Summation: Increased frequency of stimuli from a single presynaptic neuron can add together.
* Spatial Summation: Stimuli from multiple sources (different presynaptic neurons) arriving at the same time can add together.
What are the two main types of postsynaptic potentials?
Excitatory Postsynaptic Potentials (EPSPs)
* Inhibitory Postsynaptic Potentials (IPSPs)
At excitatory synapses, what happens when neurotransmitters bind to the postsynaptic membrane? What is the result?
Neurotransmitter binding depolarizes the postsynaptic membrane.
What type of ion channels are opened during an EPSP? What ions flow and in what direction?
Opens chemically gated channels that allow simultaneous Na$^+$ and K$^+$ fluxes.
* Each channel allows Na$^+$ and K$^+$ to diffuse simultaneously through the membrane but in opposite directions.
* Na$^+$ influx is greater than K$^+$ efflux, resulting in a net depolarization.
EPSP Effect on Membrane Potential: What is the typical change in membrane potential during an EPSP?
The membrane potential depolarizes, moving toward 0 mV from the resting potential (e.g., -70 mV).
What do most inhibitory neurotransmitters cause in the postsynaptic membrane? How do they achieve this?
Most inhibitory neurotransmitters hyperpolarize the postsynaptic membrane by making the membrane more permeable to K$^+$ or Cl$^-$.
If K$^+$ channels open during an IPSP, in which direction does K$^+$ move? What effect does this have on the membrane potential?
If K$^+$ channels open, K$^+$ moves out of the cell. This causes the inside of the membrane to become more negative, resulting in hyperpolarization.
If Cl$^-$ channels open during an IPSP, in which direction does Cl$^-$ move? What effect does this have on the membrane potential?
If Cl$^-$ channels open, Cl$^-$ moves into cell. In either case (depending on the initial membrane potential and Cl$^-$ concentration), the charge on the inner face of the membrane becomes more negative (hyperpolarization) or it stabilizes the membrane potential preventing depolarization.
What is the typical change in membrane potential during an IPSP?
The membrane potential hyperpolarizes, moving toward a more negative value (e.g., -90 mV) from the resting potential (e.g., -70 mV).
