Chapter 2: COMMUNICATION BETWEEN NEURONS Flashcards
What does the lock and key theory state?
Neurotransmitter molecules fit the binding sites of receptors like a key fits in a lock. Neurotransmitter binding conveys the neural message to the postsynaptic cell.
What are the two sides of the synapses?
- presynaptic cell (axon terminal of a neuron)
- postsynaptic cell (dendrite or soma)
- they are separated by a synaptic cleft.
Under what form is the synaptic transmission? (electrical or chemical)
- presynaptic: electrical to chemical (electrical impulse travel down the axon, then neurotransmitter release in extracellular fluid at the synaptic cleft)
- postsynaptic: electrical
What does synaptic transmission dysfunction lead to ?
It leads to mental disorders
What are the general characteristics of synaptic transmission?
- mostly chemical (what happens between presynaptic and postsynaptic)
- synaptic cleft: filled with a matrix of fibrous extracellular protein
- presynaptic: usually axon terminal
- postsynaptic: contains neurotransmitter receptors.
What different synaptic arrangements are there and what are they based upon?
- axodendritic, axospinuous, axosomatic, axoaxonic, dendrodendritic
- based upon which part of neurons is postsynaptic to the axon terminal
What are the different steps of chemical synaptic transmission?
- Neurotransmitter synthesis
- Load neurotransmitter into synaptic vesicles
- Vesicles fuse to presynaptic terminal
- Neurotransmitter spills into synaptic cleft
- Binds to postsynaptic receptors
- Biochemical/electrical response elicited in postsynaptic cell
- Removal of neurotransmitter from synaptic cleft
What does the presynaptic terminal contain?
- small spheres: synaptic vesicles, 50nm, store NT.
- larger vesicles: secretory granules, contains soluble protein, also called dense-core vesicles.
What is the site of NT release called?
-active zone: synaptic vesicles clustered in cytoplasm adjacent to active zone
How are NT released by vesicles?
-Released when synaptic vesicles fuse with membrane and break open, spilling contents into the synaptic cleft
How is NT release triggered?
- Arrival of AP
- Depolarization of terminal membrane causes voltage gated calcium channels to open
- Elevation in Ca+ triggers to be released
How is NT released via exocytosis?
- Basically what was explained earlier when vesicles fuse with membrane.
- Process in which intracellular vesicle moves to plasma membrane and fuse at the active zone.
How does exocytosis exactly happen?
- Rapid: 0.2 msec of Ca+ influx
- Ca+ enter at active zone (where voltage gates are located)
- synaptic vesicles ready and waiting
- calcium modifies snare proteins to initiate exocytosis
What is docking?
A molecular modeling technique that is used to predict how a protein (enzyme) interacts with small molecules (ligands).
What happens once binding occurs?
- the postsynaptic receptors open neurotransmitter-dependent ion channels (also called ligand-gated ion channels), which allow the passage of specific ions in and out of the cell
- NT open ion channels by at least 2 methods, direct and indirect.
What is the direct method in which NT open ion channels?
-ionotropic receptor: When a NT-dependent ion channel is equipped with it’s own binding site, a molecule of the appropriate NT attaches to it, and the ion channel opens.
What is the indirect method of opening ion channels?
- Metabotropic receptors are located close to G-proteins.
1. Molecule of NT binds to metabotropic receptor
2. Receptor activates G-protein
3. G-protein activates enzyme that stimulates the production of chemical second-messenger.
4. Second-messengers (molecules) travel through cytoplasm, attach themselves to ion channel and cause them to open.
What are the characteristics of the direct and indirect methods?
- Direct: transmitter-gated, fast, Amines and AAs.
- Indirect: G-protein-coupled, slower long-lasting and diverse actions, n type of NT can bind.
What determines the nature of the postsynaptic potential at a particular synapse? (EPSP or IPSP)
-determined by the particular type of ion channel the NT open.
What are the 4 major types of NT-dependent ion channels found in the post-synaptic membrane?
- sodium (Na+)
- potassium (K+)
- chloride (Cl-)
- Calcium (Ca2+)
What is an EPSP? (Excitatory Postsynaptic Potential)
-Excitatory depolarization of the postsynaptic membrane of a synapse caused by the liberation of a neurotransmitter by the terminal button.
What is an example of EPSP?
- NT-dependent Sodium channel is the most important source of EPSP.
- When sodium channels open, diffusion and electrostatic push Na+ in.
- Causes depolarization
What is IPSP? (Inhibitory Postsynapatic Potential)
An inhibitory hyperpolarization of the postsynaptic membrane of a synapse caused by the liberation of a NT by the terminal button.
What is an example of IPSP?
- Sodium-potassium transporters maintain a small surplus of K+ inside the cell.
- If K+ channels open, these positive ions will leave the cell, so inside of cell will become more negative: hyperpolarization.
