Goals of neuronal communication Flashcards
Why is neuronal communication important?
- essential for the proper functioning of the nervous system.
- neurons are specialized cells that transmit information throughout the body, and they rely on chemical and electrical signals to communicate with each other and with other cells.
What are the goals of neuron communication?
- To transmit information: Neurons transmit information about the external environment, the internal state of the body, and the activity of other cells. This information is critical for coordinating the activities of different cells and tissues and for allowing the organism to respond appropriately to stimuli.
- To process and integrate information: Neurons receive input from multiple sources and must integrate this information to generate an appropriate response. Communication between neurons allows them to process and integrate complex patterns of input and to generate highly specific responses.
- To adapt and learn: Communication between neurons allows the nervous system to adapt to changing environments and to learn from experience.
For example, neurons can modify their synapses, or the junctions between cells, in response to activity, leading to changes in the strength and efficacy of communication between neurons.
Signal Transduction
is the process by which a cell receives and responds to a signal from its environment (extracellular stimuli) (within a cell).
It is a crucial process that allows cells to communicate with their surroundings, and it is essential for the proper functioning of many physiological processes in the body.
What are the steps involved in signal transduction?
- Signal reception: A signal, such as a hormone or neurotransmitter, is received by the cell. This signal is usually in the form of a chemical or physical stimulus.
- Signal transduction: The signal is then transmitted into the cell through a series of chemical reactions. These reactions involve the activation or deactivation of enzymes and other proteins, and they are mediated by signaling pathways.
- Signal amplification: The signal is amplified as it is transmitted through the cell, allowing it to have a greater impact on the cell’s behavior.
- Signal response: The cell responds to the signal by activating or deactivating specific genes, producing proteins, or altering its metabolism
G protein receptors
G protein-coupled receptors (GPCRs) are a class of proteins that are involved in many signaling pathways in the body. They are called “G protein-coupled” receptors because they are activated by G proteins, which are proteins that transmit signals between the cell surface and the inside of the cell.
What do they do?
When a GPCR is activated, it causes the G protein to exchange GDP for GTP, which triggers a conformational change in the G protein that allows it to interact with downstream effector proteins.
What do they do?
When a GPCR is activated, it causes the G protein to exchange GDP for GTP, which triggers a conformational change in the G protein that allows it to interact with downstream effector proteins.
What are second messengers
Second messengers are molecules or ions that transmit signals within cells in response to a stimulus, such as a hormone or neurotransmitter binding to a receptor on the cell surface.
What is the amplification cascade?
a series of reactions that amplify the initial signal generated by a receptor. Amplification is important because it allows a small initial signal to be converted into a larger response, allowing the cell to respond more robustly to stimuli.
One example of an amplification cascade is the cAMP system, which is activated by G protein-coupled receptors that bind to extracellular ligands such as hormones or neurotransmitters.
= amplification cascade ensures that a small number of signaling molecules can lead to a large cellular response. This is important for cells to respond appropriately to small changes in the concentration of signaling molecules and to amplify the signal in order to produce a robust response.
Amplification Cascade in short
o Agonist (Neurotransmitter; Hormone) activates membrane bound receptor
o The membrane bound receptor activates G-Protein which produces effector (Adenylyl Cyclase; Guanylate Cyclase; Phospholipase; Ion Channel)
o Effector stimulates 2nd messenger synthesis (cAMP; cGMP; IP3; Ca2+)
o Second messenger activates intercellular process (the protein kinases)
What are glutamergic synapses?
Glutamatergic synapses are chemical synapses that use glutamate as their primary neurotransmitter.
Glutamate is an excitatory neurotransmitter, meaning it tends to increase the likelihood that a postsynaptic neuron will generate an action potential.
Glutamatergic synapses are important for fast, excitatory signaling in the nervous system, and they play a key role in learning and memory.
-> Dysregulation of glutamate signaling has been implicated in several neurological and psychiatric disorders, including Alzheimer’s disease, schizophrenia, and addiction.
What are the steps involved in glutamergic synapses?
o Presynaptic action potential reaches the synaptic terminal
o Electrical signal stimulates vesicles to release Glutamate into the synaptic cleft
o Glutamate binds to Receptors in the Postsynapse (Processes at Postsynape later below)
o Glutamate in the synaptic cleft gets reuptaken by the Glia and Neuron with help of EAAT (exciatriry amino acid transporter)
Inside the synapse: Glutamate gets packed into vesicles again by VGLUT (vesicular glutamate transporters)
Inside the Glia: Glutamate is synthesized again to Glutamine
o The Glia cell then supplies the pre synapse again with Glutamine
o Glutamine in the Pre Synapsis gets synthesized to Glutamate by Glutaminase (mitochondiral enzyme)
o The Glutamate is then packed again in to Vesicles by VGLUT
o (The gabaergic synapse works similar as Gaba is also synthesized by glutamine and both reuptaken into the synapse and the glia but other enzymes are involved in the steps between)
glutamate receptors, including ionotropic receptors and metabotropic receptors.
3. Ionotropic glutamate receptors are ion channels that open in response to the binding of glutamate, allowing ions to flow into or out of the cell and changing the membrane potential of the postsynaptic cell. There are three main types of ionotropic glutamate receptors: AMPA receptors, NMDA receptors, and kainate receptors.
4. Metabotropic glutamate receptors are G protein-coupled receptors that activate intracellular signaling pathways in response to the binding of glutamate. There are three main types of metabotropic glutamate receptors: mGlu1, mGlu5, and mGlu7.
What are AMPA receptors
- AMPA receptors are a type of ionotropic glutamate receptor that are activated by the neurotransmitter glutamate.
-> Glutamate binds to AMPA receptor and allows the influx of ions
-> Are independent to voltage (as they are ligand gated)
-> Permeable to Sodium and Potassium Ions (Na+ and K+)
-> Fast opening and closing
Kainate
similar to AMPA receptors (activated by glutamate)
- Rise and decay times of Kainate receptors is a little slower than of AMPA receptors
NMDA
-> Are slightly different than the other ones above
(e.g. when there is ion influx through the AMPA receptor and rising positive charge in the cell, NMDA receptor might not be activated yet)
-> Has a Magnesium (Mg2+) blocker
-> Just after a certain threshold of positive charge inside (due to ion influx via AMPA), the magnesium is removed and ions can flux inside
-> NMDA receptor is also permeable to calcium ions (so to Na+; K+ and Ca2+)
-> The receptor is more voltage dependent (almost no conductance at negative voltage, conductance appears when positive voltage is reached => close to 0mv and higher)
-> Fast opening but sustained/delayed closing
- More specifity/details:
-> Detects synchrony between pre- and post-synaptic activity
-> Can prevent LTP (e.g. when you block the receptor via a pharmaceutical drug, even after 100hz stimulation you won’t see a potentiation of the synapse)
-> Therefore, important for regulating synaptic strength
-> They are also associated with memory formation and plasticity (=> Mouse experiment with hidden platform. When the receptor is blocked, no learning effect in finding the hidden platform)
