Task 3 Flashcards
What is a synapse?
A synapse consists of the specialized junction where one part of a neuron contacts and communicates with another neuron or cell type (such as a muscle or glandular cell)
What are the two sides of a synapse? And what is the usual direction of information flow?
Presynaptic side consists of an axon terminal
Postsynaptic side may be a dendrite or the soma of another neuron
The usual direction of information flows from pre to post
What is an axon terminal?(also called synaptic bouton)
Is the end of an axon or axon collaterals which grins a synapse on a neuron or other target cell
What is synaptic transmission
The transfer of information at the synapse from one neuron to another
How do synapses communicate?
Mostly chemically usually using chemical messengers
The action potential triggers the presynaptic neuron to release neurotransmitters
These molecules bind to receptors on the postsynaptic cell and make it more or less likely to fire an action potential
If not chemical synapses what is the other way?
Electrical synapses where ions flow directly between cells
How is a synapse constructed?
The axon terminals form synapses with the dendrites ir somata of other neurons
What are the three principal components of a synapse?
The presynaptic membrane of the axon terminal of the presynaptic neuron
The synaptic cleft gap (20-40 nanometers) that separates the presynaptic and postsynaptic membranes
Specialized postsynaptic membrane on the surface of the dendrite or cell body of the postsynaptic neuron.
What is inside the axon terminal of a sending cell?
Synaptic vesicles that are filled with neurotransmitter molecules
Each vesicles contains a neurotransmitter (chemical released from the presynaptic axon terminal that serves as the basis of communication between neurons
The neurotransmitter carries information from the presynaptic neuron (sending neuron) to the postsynaptic cell(receiving cell)
What are the two types of synapses again?
Electrical and chemical both types relay information but do se by very different mechanisms
What is signal transmission?
Steps required for the transmission of information from one neuron to another
Delay between arrival of information at presynaptic terminal and its transfer to the postsynaptic cell reflects this steps required
What is the presynaptic element?
The presynaptic side of the synapse.Consists of an axon terminal
What are synaptic vesicles?
Vesicles within within axon terminals that contain neurotransmitters
What are secretory granules,
Larger vesicles that contain soluble protein appearing dark so they are called dense core vesicles
What is the active zone?
Sites of neurotransmitter release
Synaptic vesicles are clustered in the cytoplasm adjacent to this zone
What is the postsynaptic element what the postsynaptic density?
Postsynaptic element is the postsynaptic side of te synapse
The postsynaptic density is the protein accumulated in and under the postsynaptic membrane
What are the two functions of the postsynaptic element?
1 to anchor receptors for neurotransmitters in the postsynaptic membrane
2 Transduction : the neurotransmitter receptors will convert intercellular chemical signal (neurotransmitter) into intracellular signal(change in membrane of potential/chemical change) in the postsynaptic cell
What does the nature of a postsynaptic response depend on?
Depends on the type of protein receptor activated by the neurotransmitter
What is te anatomy of a chemical synapse?
They lack cytoplasmic continuity
There’s an extracellular space between cells
The axon of the presynaptic cell is highly branched and terminates in terminal knobs aka synaptic buttons
Pre and postsynaptic cells have membrane specializations
What are the different types of chemical synapses in the CNS?
Axodendritic synapses
Axosomatic synapses
Axoaxonic synapses
Dendrodentric synapses
Location of axodendritic synapses?
Presynaptic neurons synapse along dendritic spines of the postsynaptic neuron
The presynaptic membrane is on axon
The postsynaptic membrane is on dendrite
Where are axosomatic synapses located?
Presynaptic neurons synapse along the cell body (soma) of the postsynaptic neuron
The presynaptic membrane is on axon
The postsynaptic membrane is in soma
Similitudes between axodendritic and axosomatic?
Chemicals released by presynaptic neurons at axodendritic and axosomatic synapses excite or inhibit the dendrites and cell body of the postsynaptic neuron
If sufficiently excited AP
Location of axoaxonic synapses?
Between the axon of a presynaptic neuron and the axon of a post synaptic neuron
Presynaptic membrane is on axon
Postsynaptic membrane is on axon
How can the effects of axoaxonic synapse be inhibited or facilitated?
When the axoaxonic synapse is on( or near) the terminal button
Presynaptic facilitation and ihibitionbcan selectivelyninfluence one particular synapse rather than the entire presynaptic neuron
Location of dendridentric synapses?
Between the dendrite of the presynaptic cell and the dendrite of postsynaptic cell
Presynaptic membrane is on dendrite
Postsynaptic membrane is on dendrite
What are dendrodendritic synapses capable of ?
Transmission on either direction
CNS synapses can further be classified in two general categories based on the appearance of their presynaptic and postsynaptic membrane differentiation’s
Thank u!
What is a membrane differentiation?
Dense accumulations of protein adjacent to and within the membranes on either side of the synaptic cleft
What are the two types of synapses we can distinguish based on membrane differentiation?
Asymmetrical synapses (=grays type 1 synapses) -Membrane differentiation on the postsynaptic side is thicker than that in the presynaptic side
Symmetrical synapses where membrane differentiation’s are of similar thickness
What is another way to classify synapses?
Directed synapses where the neurotransmitter release site and the site of reception are in close proximity
Non directed synapses at which the site of release is at some distance from the site of reception
What are neurotransmitters?
Chemical messengers released into the synaptic cleft by neurons that allow signals to pass between a neuron and another cell
How can neurotransmitters be classified?
Excitatory : Activates receptors on the postsynaptic membrane and enhances the effects of AP —> triggering depolarization and increasing likelihood of a response
Inhibitory —> reverse mechanism triggering hyperpolarization and decreasing the likelihood of a response
What are the theee classes of small molecule neurotransmitters?
Amino acids
Monoamines
Acetylcholine
Peptides
What are neuropeptides?
Large molecule neurotransmitters
What is a neuromodulator?
Naturally aerated substance that acts like a neurotransmittter except that it is not restricted to the synaptic cleft but diffuses through the extracellular fluid
What are the steps in chemical synapses?
Synthesis
Storage
Release
Binding
Inactivation
How does synthesis work?what are the two general classes of neurotransmitters?
Neurotransmitters are synthesized from precursors under the influence of enzymes
Large peptides - synthesized in the cell body of the neuron and the transported to the synaptic terminal through the axon
Smaller amines/amino acids - synthesized at the presynaptic terminal itself
How does storage work?
Once neurotransmitters are synthesized they need to be put into small groups (stored in vesicles) ready to be launched across the synaptic cleft
How does release work?
When electrical signal (AP) reaches the presynaptic terminal depolarization of the terminal membrane occurs causing voltage gated calcium channels in the active zone to open
The content is released by a process called Exocytosis
What is binding?
Molecules of neurotransmitter diffuse (swim) across the synaptic cleft until they reach the postsynaptic neuron
The membrane of the postsynaptic membrane contain a few channels (= receptors) that control how a neurotransmitter can be translated into an electrical signal
The they bind to postsynaptic receptors which lead to opening or closing of ion channels in the cell membrane
This can be depolarizing or hyperpolarizing
What does it mean to be depolarizing?
Making the inside of the cell more positive
Likelihood of response
What does it mean to hyperpolarize?
Making the inside of the cell more negative
Decreases likelihood of response
What is inactivation?
Once neurotransmitter signal has been translated into an electrical signal, postsynaptic receptors need to be cleared so that they can receive new transmitters from new signals
Some neurotransmitters will be degraded some will be transported back to the presynaptic terminal to be recycled, and sometimes they are absorbed by the postsynaptic terminal
What happens to the vesicles after the release of neurotransmitters,”?
There’s two things that happen:
Kiss and run:
Merge and recycle
What do we understand as the kids and run proccess?
The vesicles fuse with the presynaptic membrane
Release of neurotransmitter reseals leaves the docking site becomes refilled with the neurotransmitter and mixes with the other vesicles in the terminal button
What do we know as merge and recycle ?
The vesicles completely fuses with the postsynaptic membrane losing its identity. Extra membrane from fuses vesicles pinched off into the cytoplasm and forms vesicles which are filled with the neurotransmitter.
What is bulk endocytosis?
Procaces through which the membrane of vesicles in the reserve pool are recycled
What are two mechanisms for terminating neurotransmitter action?
Reuptake and enzymatic degradation
How does reuptake work?
Neurotransmitters are recycled directly
This mechanism is common to the small molecule neurotransmitters (except acetylcholine)
What is enzymatic degradation?
Enzymes in extracellular fluid in synaptic cleft break the neurotransmitters down into their building blocks
Building blocks are partially taken up again through the presynaptic membrane where they can be recycled
What are the two types of postsynaptic receptors
Ionotropic receptors
Metabotropic receptors
What is psychopharmacology?
The study of the effects of drugs on the nervous system and on the behavior
What is a drug ?
Any substance that is used or is intended to be used to modify or explore ohysiological systems or pathological states for the benefit of the recipient
What dodrugs do?
They mimic actions of a neurotransmitter binding to both types of receptors and have effects in a more or less impulse way
