NE203 Exam 1

What is the Neuron doctrine?

nerve cells are discrete, individual cells that are polarized to receive and transmit information

What is the difference between chemical and electrical synapses?

Chemical synapses use neurotransmitter molecules to send signals across a gap

Electrical synapses use physical channels called gap junctions to let electrical current flow

How is electrical activity among neurons synchronized?

because their transmissions are bidirectional

it minimizes the voltage differences between the connected cells

What are astrocytes?

in the CNS, forms the blood-brain barrier and acts like the immune system for the brain

What ae oligodendrocytes?

in the CNS, wraps myelin around axons in the CNS

What are Schwann Cells?

in the PNS, wraps myelin around axons in the PNS

What are microglia?

act like macrophages and removes cellular debris from sites of injury, also controls apoptosis

What is silver stain by Golgi and what can you visualize?

silver salts are injected to see dendrites, axons, and glial cells

What is the difference between Cresyl violet and Nissl staining?

although they are both purple, cresyl violet can only see RNA and nissl staining can visualize RNA, DNA, and ribosomes

Afferent

towards the brain from the body

Efferent

away from the brain to the body

Does the expression of CsChrimson require that both GAL4 and UAS be in the same cell in order to make the expression happen?

Yes

What is grey matter?

cell bodies, dendrites, unmyelinated axons, and other support cells of the brain

What is white matter?

has myelinated axons, hence the white color

What is an electroencephalogram (EEG)?

non-invasive analysis of the brain’s electrical activity using electrodes on scalp

• see where there is activity by mapping out the electrical activity

  • does not provide information about specific cortical areas and deeper structures

What is computerized tomography (CT)?

uses X-rays to visualize

• can create 3D images of deeper structures of the brain

• can distinguish grey and white matter

• low resolution

• high radiation exposure

What is positron emission tomography (PET scan)?

injected with radiolabeled metabolite and emit radioactive signal picked up by scanner

• measure metabolite uptake and map on brain image taken by CT or MRI

• detect differences in brain function in diseases

• has to be used immediately because of its rapid radioactive decay

What is magnetic resonance imaging (MRI)?

measures the physics of atomic motion in brain tissue

• generates high-resolution 3D image of living tissue

• deemed safe and versatile

What is Diffusion tensor imaging (DTI)?

variant of MRI that can visualize axon pathways

What is functional magnetic resonance imaging (fMRI)?

variant of MRI, measures the amount of magnetic distortion by oxygen

• essentially measures blood flow during a function

• can combine with MRI imaging

What is magnetoencephalography (MEG)?

used to map changes in brain function

• records magnetic consequences of brain electrical activity

Is the resting membrane potential positive or negative?

Negative

Is the action potential positive or negative?

positive

What is a receptor potential?

membrane potential changes due to activation of sensory neurons; changes the resting potential for fraction of a second

What is the synaptic potential?

signaling activated between neurons at synaptic contacts to transmit information

What is hyperpolarization?

making membrane potential more negative than its resting potential

What are passive electrical responses?

responses that do not need any unique property of neurons

What is depolarization?

making membrane potential more positive

What are active electrical responses and an example of it?

changes in neurons or any other aspect of neurons cause an electrical response

an example would be an action potential

Does an increase in intensity of a stimulus increase the amplitude of the action potential?

No, it increases the frequency of an AP

Are passive electrical signals strong enough to cover the distance of an axon?

No, it is not because axons have poor conductivity which leads to the electrical signals diminishing

What does local anesthesia do?

blocks APs from propagating because it blocks Na+ channels

which prevents depolarization

What does regional anesthesia do?

usually given with sedatives which enhance postsynaptic GABA receptors (inhibitory) so it increases inhibition of synapses

What does general anesthesia do?

causes unconsciousness, opens up K+ channels to hyperpolarize the resting membrane potential

What are active transporters?

proteins that actively move ions in and out of cells against their concentration gradients

What are ion channels?

proteins that allow ions to cross the membrane in the direction of their concentration gradient

What is the electrochemical equilibrium?

the exact balance between the concentration and electrical gradient

Which ion, K+ or Na+ is more abundant intracellularly at rest?

K+

Which ion, K+ or Na+ defines the resting potential of the neuron?

K+

What can the Nernst equation predict?

the equilibrium potential for a single permeant ion by looking at both its intracellular and extracellular concentrations

What does the Goldman equation calculate?

the membrane potential looking at both permeabilities of the ions involved

Does the permeability of the membrane change or stay put during the process of an AP?

No it does not, it changes because the ions (K+, Na+) have different permeability

When is K+ permeability highest?

during resting period and hyperpolarization

When is Na+ permeability highest?

during depolarization

What happens to the Na+ channels during depolarization?

They open up to be permeable to Na+ and it causes the ions to rush into the cell and depolarizes it.

What is the voltage clamp method?

a technique that uses electronic feedback to control the membrane potential of a cell while also measuring the transmembrane currents created by the opening and closing of ion channels

An experiment was set up where a cell was hyperpolarized and depolarized. What happened to the cell during both of those times?

Hyperpolarization - didn’t do anything besides increase the negative potential

Depolarization - triggered an AP

What is the early/inward current?

the very brief inward flow of Na+ into cell, extracellular region becomes negative

What is the late/outward current?

the outflow of K+ into the extracellular space after the depolarization of the cell caused by the early flow

What happens to the early/inward current when the membrane potential increases to a higher voltage?

it is elimated because the membrane potential becomes the equilibrium potential of that ion, thus does not have net movement and change

What evidence is there that Na+ is the early current?

removing external Na+ concentration makes the extracellular area negative, and Na+ flows out and leaves the neuron. So, the Na+ is the early current because there is a lot of it extracellularly and rushes into the cell when the channel is open

What evidence is there to support that K+ and Na+ have different ion permeability mechanisms?

the start time of the flow of Na+ and K+ are delayed; Na+ channels open first and then K+ channels open later.

What does the toxin tetrodotoxin do?

alkaloid neurotoxin found in poisonous animals that block Na+ current without affecting K+ current

What does tetrodotoxin’s function prove about the independence of permeability pathways?

Since tetrodotoxin only affects Na+ channels without affecting K+ channels, it shows that they have independent pathways

What does tetraethylammonium do?

blocks K+ currents without affecting Na+ currents

What is membrane conductance?

the measure of how easily charged ions can flow across a cell membrane through open channels

Passive v.s. Active current flow

Passive current flow is the conduction of electrical charge through and down an axon

Active current flow is the explosive, energy-driven influx of ions through specialized voltage-gated channels

What is time-dependent activation?

opening of ion channels in response to a stimulus is dependent on the time

What is the refractory period?

the brief period after the generation of an AP where the next AP is difficult or impossible to trigger during this period

Why does the refractory period happen?

the persistence of Na+ conductance inactivation does not allow for Na+ conduction activation to happen right away.

Why is the action potential a positive feedback loop?

Activation of voltage-depended Na+ conductance —> increases Na+ entry into neuron —> membrane potential depolarizes —> activate more Na+ conductance … and continues

Why is K+ conduction activation is a negative feedback loop?

it restores the membrane to its resting state, disrupting the positive feedback loop

What is a characteristic that Na+ conduction has that K+ conduction does not have?

Na+ conduction is able to be activated and inactivated rapidly during depolarization, K+ conduction remains open during depolarization

What is patch clamp recording?

measures ionic currents flowing through an individual ion channel

Characteristics of the cell-attached patch clamp recording method

pipette suctions on a part of a neuronal membrane

Characteristics of whole-cell recording

membrane breaks open inside the pipette and interior of pipette is continuous with cell cytoplasm

Characteristics of inside-out patch recording configuration

pipette takes a small vesicle of membrane with it away from cell and exposes intracellular surface to air

• allows it to change the medium that the intracellular surface is exposed to

Characteristic of outside-out patch recording configuration

pipette takes a small vesicle membrane away from cell and exposes the extracellular surface to air

• allows it to change the medium that the extracellular surface is exposed to

What is a microscopic current?

a current flowing through a single channel

What are macroscopic currents?

current flowing through a large number of channels in a specific region of PM

What does saxitoxin do?

similar to tetrodotoxin, blocks Na+ channels

What does μ-conotoxin do?

paralysis by blocking the pore of Na+ channels

What does α-toxin do?

slows the inactivation of Na+ channels —> prolongs AP

What does β-toxin do?

causes Na+ channels to open at potentials much more negative than normal which causes uncontrollable AP firing

What are thermosensitive ion channels?

responds to changes in temperature and contribute to the senses of pain and body temperature

Where are voltage sensors of ion channels located and how are they connected there?

sensors are on the side of the transmembrane structure subunits by helical linkers that push out and pull in the sensors when needed

What is the Na+/K+ ATPase pump?

maintains the transmembrane gradients for Na+ and K+ that is powered by ATP

What is the ratio for the Na+/K+ pump?

2 K+ into cell, 3 Na+ out of cell

What was discovered by the experiment that examined the release of acetylcholine at neuromuscular junctions?

EPPs (end plate potentials) are made up of individual units equivalent to MEPP (miniature end plate potentials) to start an AP

What is the role of calcium in neurotransmitter secretion?

Ca2+ concentration affects the amount of neurotransmitter released and it is a second messenger.

It binds to calmodulin which triggers a cascade that eventually leads to the release of a neurotransmitter

Explain the exocytosis process that is done by SNARE proteins.

1. SNARE proteins synaptobrevin on the vesicle binds with syntaxin and SNAP-25

2. SNARE complex works to pull vesicle to dock

3. Synaptotagmin binds with the SNARE protein which triggers Ca2+ release

4. Curvature of plasma membrane brings membrane together, fusion of membranes to release neurotransmitters

What does endocytosis look like?

a cyclic cycle that takes around 1 minute to recycle a vesicle by coating it and putting it back into endosomes

What is a synapsin?

protein that binds to synaptic vesicles and keeps them tethered within the reserve pool

What does Ca2+/calmodulin-dependent protein kinase type II do?

it phosphorylates synapsin and releases the synaptic vesicles from reserve pool to make their way to the PM

What do SNARE proteins do?

they dock the vesicles to the membrane

What primes synaptic vesicles for fusion?

NSF and SNAPs

What does priming synaptic vesicles entail?

organizing the different SNARE proteins into correct conformation for membrane fusion between the vesicle and PM

What are the SNARE proteins?

Synaptobrevin, synatxin, and SNAP-25

What happens if toxins cleave SNARE proteins?

blocks neurotransmitter release

What do synaptotagmins do?

proteins that are found in the membrane of synaptic vesicles that bind with Ca2+

• acts like a Ca2+ sensor to trigger vesicle fusion

What is clathrin and what does it do?

most important protein for endocytotic budding of vesicles

triskelion assembles a cagelike coating around vesicle membrane

What is dynamin and what does it do?

involved in the pinching off of membranes during endocytosis

• forms a ringlike coil that surrounds the lipid stalk and pinches off membrane and rounds out the vesicle

What is actin and what does it do during endocytosis?

cytoskeletal protein that carries vesicle away from the PM

Which proteins uncoat the vesicles?

Hsc70, auxilin, synaptojanin

Explain the flow of endocytosis

1. Clathrin assemble into a coat that curves membrane to form a coated pit

2. Clathrin then pulls the coated pit away from the membrane, making a lipid stalk

3. Dynamin comes in and rings around the lipid stalk and pinches it off

4. Actin carries the vesicle away

5. Hsc70, auxilin, and synaptojanin uncoates the vesicle

What is paracrine signaling?

longer range chemical communication that secretes chemical signals onto a group of nearby target cells

What is endocrine signaling?

secretion of hormones into bloodstream

What is intracellular signal transduction?

chemical signals that happen within the cell that usually triggers a cascade of events

What is signal amplification?

intercellular or intracellular signal transduction that involves reactions that generate a much larger number of products than the number of molecules that initiated the process

What are the three classes of signaling molecules?

Cell-impermeant

Cell-permeant

Cell-associated signaling molecules