Lesson 4: Synaptic Communication

Question 1

What happens to the electrostatic pressure when sodium comes in?

Answer 1

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

Question 2

What are the 3 voltage-gaited ion channel proteins involved in the action potential and what do they do?

Answer 2

1. voltage-gaited sodium channel: initiates and propagates the action potential
2. voltage-gaited potassium channel: restores the resting membrane potential
3. voltage-gaited calcium channel: located at the end of the axon and causes the release of neurotransmitter-containing vesicles

Question 3

How do we know about ion channels?

Answer 3

By using x-ray crystallography
- we purify proteins to crystallize them and observe the patterns to figure out how the molecules are arranged

Question 4

How does nature evolve to let only the bigger ion (potassium) go through a channel and not the smaller ion (sodium)?

Answer 4

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

Question 5

What is a promoter in genetics?

Answer 5

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

Question 6

How many distinct genes does the human genome contain for voltage-gated potassium channels?

Answer 6

40
- we cannot mutate the channels, for they are too critical to life and functioning

Question 7

What are neuroglia (or glial cells)? What do they do?

Answer 7

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

Question 8

What are the three types of neuroglia (glial cells)?

Answer 8

1. Astrocyte
2. Microglia
3. Oligodendrocytes

Question 9

What are astrocytes? What do they do?

Answer 9

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

Question 10

What are microglia? What do they do?

Answer 10

They are very small cells
- immune system of the brain

Question 11

What are oligodendrocytes? What do they do?

Answer 11

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

Question 12

What is the node of Ranvier?

Answer 12

The only place an axon can gain access to extracellular fluid, where the myelin sheath is not continuous

Question 13

How do ions circulate in an action potential?

Answer 13

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

Question 14

T/F: There are almost no ion channels in myelinated areas.

Answer 14

True. There is no access to the extracellular fluid outside the membrane

Question 15

What is saltatory conduction?

Answer 15

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

Question 16

What is a synapse?

Answer 16

A junction between the axon terminal of the sending neuron and the cell membraneof the receiving neuron

Question 17

What is the presynaptic membrane?

Answer 17

Membrane of the terminal button (sending cell). This is where neurotransmitters are released from

Question 18

What are synaptic vesicles?

Answer 18

They contain molecules of neurotransmitters. They attach to the presynaptic membrane and release neurotransmitters into the synaptic cleft

Question 19

What is the synaptic cleft?

Answer 19

It is the space between the pre- and postsynaptic membranes. It is filled with extracellular fluid

Question 20

What is the postsynaptic membrane?

Answer 20

The membrane of the receiving cell that is opposite to the axon terminal

Question 21

What is electron microscopy?

Answer 21

It allows us to see small anatomical structures (e.g., synaptic vesicles and deatils of cell organelles) using a special electron microscope

Question 22

What are signaling molecules (neurotransmitters) that bind to protein receptors called?

Answer 22

Ligands

Question 23

What are the two categories of neurotransmitter recepters?

Answer 23

1. Ionotropic receptors
   - not gated by voltage, but by a ligand
2. Metabotropic receptors
   - NOT ion channels
   - they change in shape when fusing with neurotransmitters

Question 24

Where can receptors be found?

Answer 24

On the cell membrane (surface receptors) or inside the cell (intracellular receptors)

Question 25

What is the binding site?

Answer 25

Location on a receptor protein to which a ligand binds

Question 26

What is a ligand-gated ion channel?

Answer 26

An ionotropic receptor
- a receptor that is an ion channel
- the ion channel opens when the ligand (e.g., the neurotransmitter) binds to it

Question 27

What is enzymatic deactivation?

Answer 27

Destruction of a neurotransmitter by an enzyme after its release

Question 28

What is reuptake?

Answer 28

Reentry of a neurotransmitter just liberated by a terminal button back through its membrane by the transporter, thus terminating postsynaptic potential

Question 29

What is the postsynaptic potential?

Answer 29

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)

Question 30

What is depolarization?

Answer 30

When the membrane potential of a cell becomes more positive than it normally is at rest
- influx of positive ions such as Na+

Question 31

What is hyperpolarization?

Answer 31

When the membrane potential of a cell becomes more negative than it normally is at rest
- influx of negative ions such as Cl-

Question 32

What is excitatory postsynaptic potential (EPSP) caused by?

Answer 32

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)

Question 33

How does an action potential get triggered?

Answer 33

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

Question 34

What causes inhibitory postsynaptic potential (IPSP)?

Answer 34

Caused by a neurotransmitter binding to a postsynaptic receptor protein
- mediated by receptor proteins that open ion channels permeable to chloride (hyperpolarizing the cell)

Question 35

What is neural integration?

Answer 35

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

Question 36

What determines the direction of the postsynaptic potential (EPSP vs IPSP)?

Answer 36

The receptor

Question 37

What is an ionotropic receptor?

Answer 37

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)