Lecture 5 - Neurotransmitters

Question 1

What is a receptor protein?

Answer 1

A receptor protein acts like a sensor, reacting to various stimuli, such as neurotransmitters or sensory inputs like smell and taste.

Question 2

What are the two types of receptor proteins?

Answer 2

Ionotropic receptors and metabotropic receptors.

Question 3

What do ionotropic receptors do?

Answer 3

They are proteins which act as ion channels, allowing ions like sodium or chlorine to flow through and change the cell’s electrical charge almost instantly.

Ionotropic receptors are fast-acting. When a neurotransmitter binds to them, they directly open or close ion channels, allowing ions to flow in or out of the cell.

Question 4

What do metabotropic receptors do?

Answer 4

Metabotropic receptors activate a chain reaction inside the cell through signaling proteins rather than acting as ion channels. This process is slower because it involves signaling and diffusion.

Metabotropic receptors are G-protein-coupled receptors (GPCRs) that sit on the surface of the cell, and activate signaling pathways inside the cell.

Question 5

How do metabotropic receptors differ from ionotropic receptors?

Answer 5

Metabotropic receptors do not act as ion channels but instead activate a chain reaction inside the cell through proteins, which takes longer.

Question 6

What happens when sodium (Na+) enters a cell through ionotropic receptors?

Answer 6

The cell gets excited, making it more likely to send signals, resulting in an excitatory postsynaptic potential (EPSP).

Question 7

What effect does chlorine (Cl-) have when it enters a cell through ionotropic receptors?

Answer 7

It inhibits the cell, reducing signaling, which is known as an inhibitory postsynaptic potential (IPSP).

Question 8

What are G protein-coupled receptors (GPCRs)?

Answer 8

They are a major type of metabotropic receptor that relies on G proteins to transmit signals inside the cell.

Question 9

What does the term “tropic” refer to in metabotropic receptors?

Answer 9

“Tropic” means “to turn toward” something, indicating that metabotropic receptors influence metabolic processes inside cells.

Question 10

How do G proteins function in metabotropic signaling?

Answer 10

G proteins act as switches that turn ON or OFF based on whether they are bound to GTP (ON) or GDP (OFF).

When a neurotransmitter binds to a metabotropic receptor, it changes the receptor’s shape, allowing it to activate a nearby G protein. G proteins function as molecular switches that toggle between an active state (when bound to GTP) and an inactive state (when bound to GDP). Once activated, G proteins can trigger a series of biochemical reactions within the cell, leading to various cellular responses.

Question 11

What are G protein-gated ion channels?

Answer 11

These ion channels are controlled by G proteins and require a metabotropic receptor to be activated before they can open.

Question 12

Where can synapses form?

Answer 12

Synapses can form in various locations on a neuron, including smooth parts of dendrites, dendritic spines, and the soma (cell body). They can also occur at axoaxonic synapses, where one neuron’s axon influences the release of neurotransmitters from another neuron’s axon. This variety in synapse locations enhances the complexity of neural communication in the brain.

Question 13

What is presynaptic inhibition?

Answer 13

Presynaptic inhibition occurs when one neuron decreases the amount of neurotransmitter released by another neuron. This happens by making the second neuron’s axon terminal more negatively charged (hyperpolarized), which makes it less likely to trigger the release of neurotransmitters needed for communication between neurons. Essentially, it acts like a brake on the signal, making it harder for the second neuron to send its message.

Question 14

What is presynaptic facilitation?

Answer 14

It’s when one neuron increases neurotransmitter release by depolarizing the axon terminal of another neuron.

Question 15

What is an autoreceptor?

Answer 15

An autoreceptor is a receptor on a neuron that responds to the neurotransmitter released by that same neuron, usually reducing further release.

Question 16

How are signaling molecules classified based on their location?

Answer 16

In the brain, they are called neurotransmitters; in the blood, they are called hormones.

Question 17

What are neurotransmitters?

Answer 17

A neurotransmitter is a chemical messenger that transmits signals across the synapse from one neuron to another. They are released from the presynaptic neuron and bind to receptors on the postsynaptic neuron, influencing its activity and communication within the nervous system. Examples include dopamine, serotonin, and glutamate.

Question 18

Name some classical neurotransmitters.

Answer 18

Glutamate, GABA, dopamine, serotonin, norepinephrine, acetylcholine.

Question 19

What role does glutamate play in neurotransmission?

Answer 19

Glutamate is the main excitatory neurotransmitter that activates ionotropic receptors, allowing sodium to enter and excite cells.

Question 20

What role does GABA play in neurotransmission?

Answer 20

GABA is the main inhibitory neurotransmitter that activates ionotropic receptors, allowing chloride to enter and inhibit cells.

Question 21

How do neuromodulators differ from neurotransmitters?

Answer 21

Neuromodulators like serotonin and dopamine influence cell activity over a longer time and mainly act through metabotropic receptors.

Question 22

What triggers the release of neurotransmitters?

Answer 22

Neurotransmitters are released when calcium ions enter the axon terminal, causing vesicles to release their contents.

Question 23

Why are serotonin, dopamine, and norepinephrine classified as monoamine neuromodulators?

Answer 23

They are classified as monoamines due to their similar chemical structure, which can lead some drugs to affect them all.

Question 24

What are catecholamines?

Answer 24

Catecholamines are a subgroup of monoamines that include dopamine and norepinephrine, known for their close chemical relationship.

Question 25

What distinguishes classical neurotransmitters from neuropeptides?

Answer 25

Classical neurotransmitters are small molecules (like glutamate and GABA), while neuropeptides are small proteins that can exceed 70 different types.

Question 26

What are lipid-based neurotransmitters?

Answer 26

These are signaling molecules that are lipid-derived, such as endocannabinoids.

Question 27

What are gasotransmitters?

Answer 27

Gasotransmitters are gaseous signaling molecules, such as nitric oxide, that can influence neurotransmission (the transfer of information between neurons).

Question 28

What happens after a neurotransmitter activates a metabotropic receptor?

Answer 28

The activated metabotropic receptor swaps GDP for GTP on the G protein, triggering the G protein to initiate various cellular responses.

Question 29

Can metabotropic receptors affect ion channels?

Answer 29

Yes, some metabotropic receptors can open ion channels through G protein activation, influencing the cell’s electrical activity indirectly.

Question 30

What are some functions of metabotropic receptors?

Answer 30

Metabotropic receptors can open ion channels, change gene expression, release substances, and control cell growth or division (though not in neurons).

Question 31

What is a presynaptic receptor?

Answer 31

A presynaptic receptor is a receptor located on the presynaptic neuron that responds to neurotransmitters released by that neuron, often involved in feedback mechanisms to regulate neurotransmitter release.

Question 32

What is the presynaptic membrane?

Answer 32

The presynaptic membrane is the part of the neuron’s membrane that faces the synaptic cleft and contains proteins that release neurotransmitters into the synapse.

Question 33

What is a postsynaptic receptor?

Answer 33

A postsynaptic receptor is a receptor located on the postsynaptic neuron that binds to neurotransmitters released from the presynaptic neuron, leading to changes in the postsynaptic cell’s activity.

Question 34

What is the postsynaptic membrane?

Answer 34

The postsynaptic membrane is the part of the neuron’s membrane that faces the synaptic cleft and contains receptors that respond to neurotransmitters from the presynaptic neuron.

Question 35

What is the difference between a presynaptic receptor and a postsynaptic receptor?

Answer 35

A presynaptic receptor is located on the neuron that releases neurotransmitters and regulates that release, while a postsynaptic receptor is located on the neuron that receives neurotransmitters and mediates the effects of those neurotransmitters on the postsynaptic cell.

Question 36

What is the difference between a presynaptic membrane and a postsynaptic membrane?

Answer 36

The presynaptic membrane is the membrane of the neuron that releases neurotransmitters into the synapse, while the postsynaptic membrane is the membrane of the neuron that contains receptors to receive those neurotransmitters.

The presynaptic membrane has vesicles and release machinery, whereas the postsynaptic membrane has neurotransmitter receptors and signaling proteins.

Question 37

What is the primary function of the presynaptic membrane in synaptic transmission?

Answer 37

Its primary function is to transmit the signal by releasing neurotransmitters.

Question 38

What is the primary function of the postsynaptic membrane in synaptic transmission?

Answer 38

Its primary function is to process the signal by detecting and responding to neurotransmitters.

Question 39

What is a membrane in the context of neurons?

Answer 39

A membrane is a thin layer that surrounds a cell, acting as a barrier that controls what enters and exits the cell.

Question 40

What is a receptor in the context of neurons?

Answer 40

A receptor is a specific type of protein that resides within or on the surface of a membrane and detects and responds to signaling molecules like neurotransmitters.

Question 41

How does a membrane function in neuron communication?

Answer 41

The membrane houses various proteins, including receptors, and facilitates communication between cells.

Question 42

What is the role of receptors in neurons?

Answer 42

Receptors specifically bind to signaling molecules and initiate cellular responses when activated.

Question 43

How does the structure of a membrane differ from that of a receptor?

Answer 43

A membrane is a broad structure that encloses the cell, while a receptor is a specific protein or molecule within the membrane with a distinct function.

Question 44

What analogy can help differentiate between a membrane and receptors?

Answer 44

Think of the membrane as the outer wall of a building (the cell), while the receptors are the windows and doors that allow communication with the outside when they interact with specific signals.

Question 45

In terms of function, how do membranes and receptors differ?

Answer 45

Membranes act as barriers and facilitate communication, while receptors specifically bind to signaling molecules and trigger cellular responses.