Lesson 4: Synaptic Communication Flashcards
What happens to the electrostatic pressure when sodium comes in?
The electrostatic pressure dies
- at +40mV in the cell, there is no more sodium that comes in because the ball and chain blocks the sodium channel
What are the 3 voltage-gaited ion channel proteins involved in the action potential and what do they do?
- voltage-gaited sodium channel: initiates and propagates the action potential
- voltage-gaited potassium channel: restores the resting membrane potential
- voltage-gaited calcium channel: located at the end of the axon and causes the release of neurotransmitter-containing vesicles
How do we know about ion channels?
By using x-ray crystallography
- we purify proteins to crystallize them and observe the patterns to figure out how the molecules are arranged
How does nature evolve to let only the bigger ion (potassium) go through a channel and not the smaller ion (sodium)?
When dissolved in water, ions gain a hydration shell
- to go through the potassium channel, the potassium ion’s hydration shell breaks
- because the sodium ion is so small, the hydration shell does not break off, therefore the combination of the sodium ion and the hydration shell do not go through the potassium channel
What is a promoter in genetics?
A region of DNA that initiates transcription of a particular gene
- they indicate what kind of cells should read the gene and when
- they are usually located just before the gene
How many distinct genes does the human genome contain for voltage-gated potassium channels?
40
- we cannot mutate the channels, for they are too critical to life and functioning
What are neuroglia (or glial cells)? What do they do?
Glia are found all around neurons and even physically encapsulate some parts of them
- they help traffic nutrients and maintain molecular (ionic) stability in the extracellular space
What are the three types of neuroglia (glial cells)?
- Astrocyte
- Microglia
- Oligodendrocytes
What are astrocytes? What do they do?
They surround the synaptic connections between neurons
- go-to support staff of a neuron
- garbage man of the neuron (phagocytosis: cleaning up the debris in the brain)
- nourish the neurons and optimize neuronal function
What are microglia? What do they do?
They are very small cells
- immune system of the brain
What are oligodendrocytes? What do they do?
Produce myelin sheath that wrap around axons very tight to speed up the action potential
- myelin is a sheet of fat
- the cell membrane does not have access to other cells because it is secluded by the myelin sheath
What is the node of Ranvier?
The only place an axon can gain access to extracellular fluid, where the myelin sheath is not continuous
How do ions circulate in an action potential?
Positive ions come through the node of Ranvier, and go through the muelin sheath where the positive ions get pushed out at the next node of Ranvier
- there is decremental conduction under myelin sheath (positive ions get lost as the action potential goes through the myelin sheath)
- when the action potential reaches the next node of Ranvier, it is regenerated
T/F: There are almost no ion channels in myelinated areas.
True. There is no access to the extracellular fluid outside the membrane
What is saltatory conduction?
The conduction of action potentials by myelinated axons
- at each node of Ranvier, strength of the signal is regenerated with additional voltage-gated Na+ channels
What is a synapse?
A junction between the axon terminal of the sending neuron and the cell membraneof the receiving neuron
What is the presynaptic membrane?
Membrane of the terminal button (sending cell). This is where neurotransmitters are released from
What are synaptic vesicles?
They contain molecules of neurotransmitters. They attach to the presynaptic membrane and release neurotransmitters into the synaptic cleft
What is the synaptic cleft?
It is the space between the pre- and postsynaptic membranes. It is filled with extracellular fluid
What is the postsynaptic membrane?
The membrane of the receiving cell that is opposite to the axon terminal
What is electron microscopy?
It allows us to see small anatomical structures (e.g., synaptic vesicles and deatils of cell organelles) using a special electron microscope
What are signaling molecules (neurotransmitters) that bind to protein receptors called?
Ligands
What are the two categories of neurotransmitter recepters?
- Ionotropic receptors
- not gated by voltage, but by a ligand - Metabotropic receptors
- NOT ion channels
- they change in shape when fusing with neurotransmitters
Where can receptors be found?
On the cell membrane (surface receptors) or inside the cell (intracellular receptors)
What is the binding site?
Location on a receptor protein to which a ligand binds
What is a ligand-gated ion channel?
An ionotropic receptor
- a receptor that is an ion channel
- the ion channel opens when the ligand (e.g., the neurotransmitter) binds to it
What is enzymatic deactivation?
Destruction of a neurotransmitter by an enzyme after its release
What is reuptake?
Reentry of a neurotransmitter just liberated by a terminal button back through its membrane by the transporter, thus terminating postsynaptic potential
What is the postsynaptic potential?
Alterations in the membrane potental of a postsynaptic neuron, produced by neurotransmitter release into the synapse and receptor activation
- excitatory (influx of positive sodium ions depolarize the cell)
- inhibitory (influx of negative chloride ions hyperpolarize the cell)
What is depolarization?
When the membrane potential of a cell becomes more positive than it normally is at rest
- influx of positive ions such as Na+
What is hyperpolarization?
When the membrane potential of a cell becomes more negative than it normally is at rest
- influx of negative ions such as Cl-
What is excitatory postsynaptic potential (EPSP) caused by?
Caused by a neurotransmitter binding to a postsynaptic receptor protein
- mediated by receptor proteins that open ion channels permeable to sodium (which will depolarize the cell)
How does an action potential get triggered?
Many EPSPs must occur at nearly the same time
- sodium ions must come in at a faster rate than potassium ions leave
- this depolarization must reach the beginning of the axon (axon hillock), where tons of voltage-gated sodium channels are congregated
What causes inhibitory postsynaptic potential (IPSP)?
Caused by a neurotransmitter binding to a postsynaptic receptor protein
- mediated by receptor proteins that open ion channels permeable to chloride (hyperpolarizing the cell)
What is neural integration?
When EPSPs and IPSPs occur at the same time, the flux of negatively charged chloride ions diminish the impact of the positively charged sodium ions
- IPSPs decrease the likelihood that the cell will fire an action potential
What determines the direction of the postsynaptic potential (EPSP vs IPSP)?
The receptor
What is an ionotropic receptor?
A neurotransmitter receptor that is an ion channel. The properties of the pore of the ion channel will determine if it causes EPSPs or IPSPs (i.e., if it lets in sodium or chloride ions)
