Flashcards in Physiology Chapter 2-Synapses and neuronal integration Deck (32):
What three structures can a neuron terminate on?
A neuron, muscle or gland.
What happens when the action potential reaches the axon terminals?
The axon terminals release a chemical messenger that alters the sodium-potassium pump activity of the cells on which the neuron terminates.
When a neuron terminates on a muscle or gland, the neuron is said to ________ the structure.
What are synapses?
Typically, involves a junction between an exon terminal of one neuron, known as the presynaptic neuron, and the dendrites or cell body of a second neuron, known as the postsynaptic neuron.
What is the synaptic knob?
A slight swelling at the end of the axon terminal of the presynaptic neuron.
The synaptic knob contains synaptic vesicles.
The synaptic knob comes into close proximity to, but does not actually directly touch the postsynaptic neuron.
What is the postsynaptic neuron?
The neuron whose action potentials are propagated away from the synapse.
What are synaptic vesicles?
Store a specific chemical messenger, a neurotransmitter that has been synthesized and packaged by the presynaptic neuron.
What is the synaptic cleft?
The space between the pre- and postsynaptic neuron;
Why does current not directly spread from the presynaptic membrane to the postsynaptic neuron?
No channels are present in the presynaptic membrane for passage for sodium and potassium.
How then, does an action potential propagate between neurons?
Instead, an action potential in the presynaptic neuron alters the postsynaptic neuron's potential by chemical means.
What occurs when an action potential in a presynaptic neuron has been propagated along the axon to the axon terminal?
The local change in potential opens voltage-gated calcium channels in the synaptic knob.
What are voltage-gated calcium channels?
Class of trans-membrane ion channels tat are activated by changes in electrical potential.
Calcium channels are critical in neurons, and are common in other cell types.
When the voltage-gated calcium channels open, what occurs?
Calcium is much more concentrated in the ECF and the electrical gradient favours its movement into the cell through the channels.
Calcium induces the release of a neurotransmitter from the synaptic vesicles into the synaptic cleft by exocytosis.
Once the neurotransmitter is released, what happens?
It diffuses across the cleft and binds with specific protein receptors on the subsynaptic membrane.
What is the subsynaptic membrane?
Postsynaptic membrane directly below the synaptic knob.
What happens after neurotransmitter binds to its specific receptor?
This binding triggers the opening of specific ion channels in the subsynaptic membrane, changing the ion permeability of the postsynaptic neuron.
What do motor neurons release?
What are the two different types of synapses?
Excitatory and inhibitory
What does the permeability changed induced at an excitatory synapse result in, concerning potassium and sodium?
Results in the movement of a few potassium ions out of the postsynaptic neuron and a larger number of sodium ions into this neuron.
What are excitation and inhibition dependent on?
The properties of the receptor and not the neurotransmitter.
What is an excitatory postsynaptic potential (EPSP)?
The postsynaptic potential change occuring at an excitatory synapse.
What does the binding of neurotransmitters to cause an inhibitory synapse cause, in the case of ions?
Increases the permeability of the subsynaptic membrane to either potassium or chloride.
Receptors coupled to chloride or potassium channels are ________ and receptors coupled to sodium or calcium are ________.
inhibitory and excitatory.
What is an inhibitory postsynaptic potential (IPSP)?
The small hyperpolarization of the postsynaptic neuron causing greater internal negativity.
How can a neurotransmitter be inactivated or removed?
It may diffuse from the synaptic cleft.
Be inactivated by specific enzymes within the subsynaptic membrane.
Be actively taken back up into the axon terminal by transport mechanisms in the presynaptic membrane.
EPSPs and IPSPs are what type of potentials?
Graded potentials which can be of varying magnitude, have no refractory period and can be summed.
What is the grand postsynaptic potential?
Sum total of all EPSPs and IPSPs occuring at approximately the same time.
What are the two different ways in which a postsynaptic neuron can be brought to threshold?
Temporal summation and spatial summation.
What is temporal summation?
The summing of several EPSPs occurring very close together in time because of successive firing of a single presynaptic neuron.
What is spatial summation?
The summation of EPSPs originating simultaneously from several different presynaptic inputs.
Can IPSPs undergo spatial and temporal summation?