Science Section 2 Flashcards
What is the postsynaptic density?
Area of the membrane that consists of clusters of neurotransmitter receptors and other molecular “machinery”
What are ionotropic receptors?
These ion channels have a central pore that allows ions to pass through when ligand is bound and are found across a membrane between a postsynaptic cell
What is synaptic integration?
The EPSPs and IPSPs coming in from all synapses across the cell are added (summed) together because one EPSP or IPSP cannot trigger a postsynaptic cell to fire an actionl or hyperpolarize the cell.
What is temporal summation?
This is when multiple EPSPs or IPSPs occur in rapid succession at the same synapse and are summed up over time
What is spatial summation?
When multiple EPSPs or IPSPs occur at the same time along different spatial locations and are then added together
Where in a neuron does the summation of EPSP or IPSP inputs happen?
At the axon hillock- this is where the cell assesses if the overall changes in charge bring it up to threshold
What are metabotropic receptors?
Another type of receptor that works much slower than ionotropic receptors but forms much more complex reactions
What are effector proteins?
Selectively binds to a protein to regulate its biological activity; can alter enzyme activity, gene expressionism, or other protein functions
Are metabotropic receptors ion channels?
No
What is the process by which metabotropic receptors are activated?
1). Binding of a neurotransmitter
2). Triggering the activation of the G proteins
3). Then the G proteins split into subunits which will then activate its own signal (effector) proteins
4). To modulate the channels, when the subunits bind to the channel it opens and allows an influx of ions
Or the G protein itself will bind to the channel and cause it to open
What is the metabotropic PKC pathway?
PKC stands for protein kinase C which is responsible for activating many important molecules by adding phosphate into them
Process of the metabotropic PKC pathway
1). Neurotransmitter binds to GPCR receptors which activate the G-protein subunits
2). The subunits then bind to the PLC (a membrane bound effector protein known as phospholipase C
3). This causes it to split into IP3 & DAG which will then (as a second messenger) impact\ other areas of the cell
How do potassium leak channels affect the voltage (charge) of the cell?
As they are always open, the positive potassium continually leaves the cell
True or False? The inside of the cell is often 60mV to 80mV more negative than the outside of the cell
True
What is resting membrane potential?
The electrical charge inside a neuron compared to the outside fluid when the neuron is at rest or not firing electrical signals
What is the inhibitory postsynaptic potential?
brief transiet hyperpolarization of the neuron as the mV becomes more negative
What are competitive agonists?
type of substance (agonist drug) that competes for the same binding site as the endogenous neurotransmitter but are much more concentrated
What are noncompetitive agonists?
- aka allosteric modulators
- increase the activity of the neurotransmitter without blocking the binding site which makes the neurotransmitter more effective
What is a second messenger and how does it relate to the Metabotropic PKC pathway?
A second messenger is a molecule, that is produced or activated by the effector protein, that diffuses away within the cystol to impact other areas of cell function.
In this case, IP3 and DAG are the second messengers of the pathway that are activated by the PLC which has PIP2 attached to it.
IP3 dissolves into the cystol to bind to specific ligond receptors (IP3-gated calcium channels) embedded in the membrane of the endoplasmic reticulum which causes calcium to flow into the cystol. The Calcim+ then binds to signaling molecules to cause effects leading to a cellular response.
While DAG stays bound to the membrane & activates protein kinase C (PKC) which then phosphorylates target protein which then causes a cellular response.
What are partial agonists?
Compete for the some binding site
- But have a smaller physiological effect on the receptor than endogenous neurotransmitter
Purpose of Prozac & Zoloft
- Treating mood disorders by inhibiting the function of reuptake transporter found in synapses that release the serotonin neurotransmitter
What is signal amplification?
process in which strength of a signal is increased after binding one molecule to a receptor
- the binding triggers a chain of events inside the cell that is also amplified
What is a reuptake transporter
featured in some presynaptic terminals
- It is a molecule that transports previously released neurotransmitter from the cleft bank into the presynaptic cell to be repackaged in vesicles and reused or degraded
How do SSRIs affect a person’s mood?
Because the reuptake transporters are blocked, the serotin hangs around the synaptic cleft giving it more time to have a bigger effect
What is agnoist drug?
a substance that binds to receptor and causes the same action as the substance (neurotransmitter) that normally binds to the receptor
- (neurotransmitter) these are known as endogenous or the naturally occurring neurotransmitter
Explain saltatory conduction
This is conduction down a myelinated neuron
_ It signals to be sent down the axon faster
Where does the name saltatory originate from & mean?
Originated from Latin word meaning “to jump”
How does the signal not degrade as it moves down the axon?
Sodium that has diffused into the axon because of AP causes the next set of sodium channels to open as that section of membrane reaches threshold. This process repeats, regenerating the AP. Only channels in front of the AP wave can open.
Where is AP initiated within a neuron?
The axon hillock before it travels down the axon (repeating each of the events)
What role do ions play in neural communication?
The state a neuron is in (whether it is excited or resting) determines if it’s transmitting electrical signals.
- However, the state it is in is determined by which ions are inside or outside of the cell. This is calculated by membrane potential.
How does the NA+/K+ pump use active transport?
Because the pump brings more potassium into the cell and more sodium out of the cell.
- This moves the molecules against the concentration gradient as the molecules move to areas with higher concentration of the same molecules (ie. potassium and/or sodium)
Why is the voltage-gated K+ channel referred to as a delayed rectifier?
Because it is slow to open/close and return the cell to resting membrane potential
Why are voltage-gated calcium channels vital in the axon terminal?
Once the AP reaches the terminal, voltage-gated calcium channels open. This causes an influx of calcium ions into the cell as those ions move down the concentration gradient. All this is important in initiating the release of neurotransmitters.
Why are electrical synapses much simpler than chemical?
Because the pre & post-synaptic cells are connected by gap junctions (single set of channels). Therefor positive ions flow directly from cell to cell.
Since the signal cannot be charged, these cells aren’t common in the brain.
What are the mitochondria and microtubules of the presynaptic cell?
The mitochondria at the axon terminal help produce ATP. Where there is no microtubules (cystoskeletal elements of the axon) is where the axon terminal begins
What is the synapse
signaling space between neurons
What is synaptic transmission?
process of neurons communicating with target cell
What pump restores the neuron to resting membrane potential during AP?
The sodium-potassium pump, as it works (always) to move potassium into the cell and sodium out of the cell
During AP, when do the K+ channels open/close?
When the peak is reached, the K+ channels are fully open, allowing for an efflux of potassium ions.
- This makes the cell more negative and causing the falling phase. It begins to close when potential membrane but isn’t fully closed until after hyperpolarization leading it to being more negative
What is the absolute refractory period?
This is the period in which it is impossible to open voltage gated channels or initiate AP as when the peak is reached NA+ channels become inactivated
How does the all-or-none principle apply to a neuron reaching threshold?
If threshold is reached, rising action of AP begins. Once threshold is reached there is no stopping rising action from occurring. It won’t occur if threshold isn’t reached.
What is the threshold of action potential?
This is the point when the neuron is slightly more positive than when it is at rest (between -65 and -50mV). Once threshold is reached, rising phase of AP begins as the voltage-gated sodium channels open.
What is the composition of the cystol and extra cellular fluid?
Mainly water but there are charged ions inside of it
What are the three main things that dictate resting membrane potential?
- the cystol (fluid inside)
- Extracellular fluid
- neuronal membrane
What is the neuronal membrane?
A phosophilid bilayer that separates the cystol and extracellular fluid.
It keeps the ion concentration different as ions cannot move freely across sides but the membrane has to be permeable to the ion.
What is the passive movement of ions?
When charged ions travel across the membrane because of a “natural force”.
- In other words, the ions move down the concentration gradient (from more concentrated to less; diffusion). This is known as ionic concentration
What is ionic concentration?
The number of ions in a particular volume of water forming a solution (such as the cystol or the extracellular fluid)
True or False. Positive ions attract, therefore, they’ll move across the membrane toward one another.
False. If a positively charged ion is on the side of the membrane with lots of other positive ions, the ion will be repelled to the other side by electrical potential as long as the membrane is permeable to that ion.
How do ligand gated channels open?
They open when a particular molecule binds to a specific location on the channel.
This changes the shape of the channel causing it to open. The chemical molecule is only bound for a certain amount of time before it is released and the channel closes.
When do voltage-gated ion channels open?
They open or close when membrane potential is at a certain voltage (no longer at rest)
What is sodium potassium pump (NA+/K+ pump)?
It is crucial for establishing resting membrane potential
- Breaks down ATP to change its shape/conformation
*Go to page 28 in the guide for more details
What is the difference between the Nernst and Goldman Equation?
While both equations calculate the exact value of equilibrium potential, the Nernst equation only factors in that there is only permeability to ONE ION. However, the Goldman equation factors in MULTIPLE IONS and it does build off the work of the Nernst equation
What is “gating” in regards to ion channels?
a process by which environmental factors or changes causes an ion pump to open or close
What is action potential?
Also known as nerve impulses, spikes, or APs
- action potential is the electrical potential across the membrane when the cell is active
What is the undershoot or after hyperpolarization?
This is when the membrane potential does not stop falling or becoming more negative once, membrane potential is reached as it decreases before stopping around -80mV
What is the second phase of action potential?
The overshoot or peak. This is when the membrane potential continues to become more positive even after reaching equilibrium, it continues until +30mV to +40mV
What is the falling phase of action potential?
This is when the cell becomes more negative because of positive ions leaving the cell. It is known as repolarization or hyperpolarization as the cell becomes more polarized
What is the purpose of SNARE proteins and where are they located?
SNARE proteins are located at the active ne which is the membrane facing the synaptic cleft
-SNARE proteins are membrane bound proteins that lock the vesicle in place
Describe exocytosis.
The process of releasing neurotransmitters via synaptotagmin & voltage-gated CA+ channels.
1. Calcium binds to synaptotagmin which changes its shape to then bring the vesicle closer to the membrane to then fuse.
2. A pore fuses, allowing neurotransmitters to diffuse into synaptic cleft to the post synaptic cell.
What is endocytosis?
The process by which the vesicle membrane is recovered and separated from the neuronal membrane.
Why is endocytosis important?
It makes sure the neuronal membrane stays a consistent size and does not get too large
Can vesicles be recycled?
Yes, they’re also refilled with neurotransmitters by transport proteins
What happens to the neurotransmitters?
It’ll be cleared out of the synaptic cleft by enzymatic digestion, uptake by a glial cell, or it may just diffuse over time
Can neurotransmitters be recycled?
Yes. Some transport proteins will remove the transmitter from the synaptic cleft and into the presynaptic cell to be repackaged or recycled
What is excitory postsynaptic potential (EPSP)?
A short period of time of depolarization that results from positive ions entering the cell through permeable channels.
Ex: When neurotransmitters bind to the receptors, sodium ion channels open allowing positive ions to diffuse into the cell which will temporarily depolarize the cell.
What are SSRI’s?
acronym for Selective Serotonin Reuptake Inhibitors
- a class of drugs that inhibit the function of the reuptake transporter found in synapses that release serotonin as their neurotransmitter
- Used as an antidepressant
Ex: prozac
What is serotonin?
A neurotransmitter, aka 5-hydroxytryptamine, that deals with mood and emotion
True or False. The metabotropic PKC pathway is an example of signal cascades and signal amplification.
True
What is signal cascade?
a series of chemical reactions that occur within a biological cell when initiated by a stimulus
What does IP3 stand for?
Inositol-1, 4, 5, - triphosphate
What does DAG stand for?
Diacylglycerol
