Lecture 4 - Synaptic Communication

Question 1

What are the three types of voltage-gated ion channels?

Answer 1

Voltage-gated sodium channels, voltage-gated potassium channels, and voltage-gated calcium channels.

Question 2

What is the primary function of the voltage-gated sodium channel?

Answer 2

The primary function of the voltage-gated sodium channel is to help start and spread the action potential in neurons.

Question 3

What is the primary function of the voltage-gated potassium channel?

Answer 3

The primary function of the voltage-gated potassium channel is to quickly bring the membrane back to its resting state after the action potential.

Question 4

What is the primary function of the voltage-gated calcium channel?

Answer 4

The primary function of the voltage-gated calcium channel is to trigger the release of neurotransmitters.

Question 5

How do potassium ion channels selectively allow K+ ions but block Na+ ions?

Answer 5

The selectivity of potassium ion channels is based on a structure called the selectivity filter, which is specifically shaped to interact with potassium ions (K⁺) while preventing sodium ions (Na⁺) from passing through. When K⁺ ions enter the channel, the filter replaces the water molecules that typically surround them, known as the hydration shell, allowing them to pass easily. However, Na⁺ ions are smaller and have a different hydration shell configuration; they cannot fit through the filter properly without their surrounding water molecules. As a result, the channel preferentially allows K⁺ ions to flow through while effectively blocking Na⁺ ions.

Question 6

What modern techniques have helped us understand ion channels?

Answer 6

X-ray crystallography and mapping DNA sequences that code for ion channel proteins.

Scientists use X-ray crystallography to determine the three-dimensional structure of ion channel proteins, revealing how they function and interact with ions. Additionally, mapping DNA sequences helps identify the genes coding for these proteins, providing insight into their structure, function, and potential mutations that affect their operation. Together, these techniques enhance our understanding of ion channels’ roles in cellular communication and physiological processes.

Question 7

How can altering a DNA sequence help in studying ion channel selectivity?

Answer 7

By changing the amino acid coded for, researchers can determine if it affects the channel’s ability to selectively allow certain ions through.

Question 8

What is a hydration shell?

Answer 8

A layer of water molecules that surrounds an ion when it is dissolved in water.

Question 9

How many different genes in the human genome code for voltage-gated potassium channels?

Answer 9

40 different genes.

Question 10

What are the two main types of cells in the central nervous system (CNS)?

Answer 10

Neurons and glia.

Question 11

What is the role of astrocytes in the CNS?

Answer 11

They provide structural support, regulate ions, clear neurotransmitters, and control blood flow.

Question 12

What do ependymal cells do?

Answer 12

They line the brain’s ventricles and spinal cord, circulating cerebrospinal fluid.

Question 13

How do microglia function in the CNS?

Answer 13

They act as the brain’s cleanup crew, removing dead cells and debris and protecting against infections.

Question 14

What is the function of oligodendrocytes?

Answer 14

They create the myelin sheath around axons, which speeds up action potentials.

Question 15

What are nodes of Ranvier?

Answer 15

Tiny gaps in the myelin sheath where the axon’s charge can interact with the outside environment.

Question 16

How much faster does myelination speed up action potentials?

Answer 16

It can speed up the action potential by 20 times.

Question 17

What is a synapse?

Answer 17

The small gap between the axon terminal of one neuron and the cell membrane of another neuron.

Question 18

What is the role of neurotransmitters in synaptic communication?

Answer 18

They are released from the axon terminal and activate receptors on the receiving neuron, which can either excite or inhibit it.

Question 19

How are neurotransmitters stored before release?

Answer 19

They are stored in small sacs called synaptic vesicles.

Question 20

What are ionotropic receptors?

Answer 20

Ionotropic receptors are a type of neurotransmitter receptor that acts as ion channels, opening in response to a ligand (like a neurotransmitter). They allow ions to flow into or out of the cell, leading to rapid changes in the membrane potential.

Question 21

What are metabotropic receptors?

Answer 21

Metabotropic receptors are a type of neurotransmitter receptor that does not function as an ion channel. Instead, they activate signaling cascades inside the cell through G-protein signaling, resulting in slower, more prolonged effects on the cell’s activity.

Question 22

What is the difference between ionotropic and metabotropic receptors?

Answer 22

Ionotropic receptors act as ion channels and respond quickly, while metabotropic receptors trigger internal signaling cascades and are slower.

Question 23

What are the three methods the body uses to clear neurotransmitters?

Answer 23

Diffusion, enzymatic deactivation, and reuptake.

The neurotransmitter may be broken down by an enzyme, it may be sucked back up into the presynaptic neuron, or it may simply diffuse away.

Question 24

What is diffusion?

Answer 24

Diffusion is the passive spread of neurotransmitters from areas of high concentration to areas of low concentration, gradually reducing their presence in the synaptic cleft.

Question 25

What is enzymatic deactivation?

Answer 25

Enzymatic deactivation is when enzymes break down neurotransmitters (like acetylcholine being broken down by acetylcholinesterase), effectively inactivating them.

Question 26

What is reuptake?

Answer 26

Reuptake is when special transporters in the presynaptic neuron recycle neurotransmitters back into the cell, allowing them to be reused in future signaling (e.g., serotonin reuptake transporter).

Question 27

What are excitatory postsynaptic potentials (EPSPs)?

Answer 27

Changes that make the neuron more likely to fire an action potential by allowing positive ions (like Na+) to enter the cell.

Question 28

What are inhibitory postsynaptic potentials (IPSPs)?

Answer 28

Changes that make the neuron less likely to fire an action potential by allowing negative ions (like Cl-) to enter the cell or by causing positive ions (like K+) to leave the cell, thus hyperpolarizing the neuron.

Question 29

What is the difference between excitatory postsynaptic potentials (EPSPs) and inhibitory postsynaptic potentials (IPSPs)?

Answer 29

EPSPs occur when positive ions enter the neuron, making it more likely to fire an action potential, while IPSPs occur when negative ions enter, making it less likely to fire.

Question 30

How do inhibitory neurons influence behavior?

Answer 30

They can cause hyperpolarization, decreasing the likelihood of neuron firing, but may also inhibit other inhibitory neurons, allowing for movement.

Question 31

How do excitatory neurons influence behavior?

Answer 31

Excitatory neurons increase the likelihood of firing in the connected neurons, which can lead to the initiation of movements or behaviors by promoting action potentials.

Question 32

How does alcohol affect inhibitory control in the brain?

Answer 32

It reduces activity in areas controlling anxiety and self-restraint, leading to disinhibited behavior.