Topic 3 Synaptic Communication

Question 1

Difference between chemical and electrical synapse

Answer 1

A chemical synapse uses neurotransmitters for communication, while an electrical synapse relies on direct electrical connections between neurons.

Question 2

Two Key Features of Chemical Synapses

Answer 2

1) Much larger synaptic cleft than gap junctions
2) Contain synaptic vesicles filled with neurotransmitters at the presynaptic axon terminal.

Question 3

Axodendritic synapses

Answer 3

These synapses occur between the axon of one neuron and the dendrites of another.

Question 4

Axosomatic synapses:

Answer 4

These synapses happen between the axon of one neuron and the cell body (soma) of another neuron.

Question 5

Axoaxonic synapses

Answer 5

Involve communication between the axon of one neuron and the axon of another neuron

Question 6

Steps in a chemical synapse

Answer 6

1) Action Potential Reaches Terminal (Axon Terminal or Bouton)
2) Calcium Influx and Voltage-Gated Calcium Channels:
3) Vesicle Movement and Neurotransmitter Storage
4) Neurotransmitter Release by Exocytosis:
5) Neurotransmitter Binding to Receptor
6) Induction of Postsynaptic Effect:

Question 7

Step 1) Action Potential

Answer 7

An action potential, which is an electrical signal generated at the cell body of the presynaptic neuron, travels along the length of the neuron’s axon.

Question 7

Step 2)Calcium Influx and Voltage-Gated Calcium Channels:

Answer 7

When the action potential reaches the axon terminal, it triggers the opening of voltage-gated calcium channels in the presynaptic membrane and calcium ions rush into the axon terminal

Question 8

Step 3) Vesicle Movement and Neurotransmitter Storage

Answer 8

Calcium influx triggers movement of synaptic vesicles (store NT) toward the presynaptic membrane.

Question 9

Step 4)Neurotransmitter Release by Exocytosis:

Answer 9

Synaptic vesicles fuse with the presynaptic membrane, releasing neurotransmitters into the synaptic cleft, happens through the process of exocytosis

Question 9

Step 5) Neurotransmitter Binding to Receptor

Answer 9

Neurotransmitters diffuse across the synaptic cleft and bind to receptors on the postsynaptic neuron’s membrane.
Binding can alter the postsynaptic membrane potential (depolarization or hyperpolarization).

Question 10

Step 6) Induction of Postsynaptic Effect:

Answer 10

Neurotransmitter binding initiates intracellular events in the postsynaptic neuron.
These events can lead to changes in membrane potential and potentially trigger an action potential, with effects depending on neurotransmitter and receptor types.

Question 10

The effects of neurotransmitters on the postsynaptic neuron depend on two critical factors:

Answer 10

The type of neurotransmitter (NT) involved and the type of receptor to which it binds.

Question 11

Explain how the effects of neurotransmitters on the postsynaptic neuron depend on the type of NT involved

Answer 11

Different neurotransmitters have distinct functions and can exert either excitatory or inhibitory effects on the postsynaptic neuron:

Question 12

What is the effect of excitatory neurotransmitters on the postsynaptic neuron?

Answer 12

Excitatory neurotransmitters promote depolarization, increasing the likelihood of an action potential.

Question 13

How do inhibitory neurotransmitters influence the postsynaptic neuron?

Answer 13

Inhibitory neurotransmitters induce hyperpolarization, decreasing the likelihood of an action potential.

Question 14

What happens when an excitatory neurotransmitter binds to an excitatory receptor?

Answer 14

It allows the influx of positively charged ions, leading to membrane depolarization and an increased likelihood of an action potential.

Question 15

What occurs when an inhibitory neurotransmitter binds to an inhibitory receptor?

Answer 15

It permits the entry of negatively charged ions, causing membrane hyperpolarization and reducing the likelihood of an action potential.

Question 16

What determines the overall impact on the postsynaptic neuron?

Answer 16

The balance between excitatory and inhibitory signals, which varies depending on the specific neurotransmitter and receptor interactions,

Question 17

Two Types of Post Synaptic Receptors

Answer 17

1) Ionotropic Receptors
2) Metabotropic Receptors

Question 18

What do ionotropic receptors trigger, and what is the result?

Answer 18

Ionotropic receptors trigger the opening of ion channels directly, leading to fast changes in postsynaptic potential.

Question 19

What is the primary function of ionotropic receptors?

Answer 19

The primary function of ionotropic receptors is to either excite (cause) or inhibit (prevent) an action potential in the postsynaptic neuron

Question 20

What do metabotropic receptors initiate, and what follows?

Answer 20

Metabotropic receptors initiate an enzymatic cascade that leads to changes in membrane permeability.

Question 21

How do metabotropic receptors differ from ionotropic receptors?

Answer 21

Metabotropic receptors are distinct from the ion channels they regulate, and their effects are slower and more prolonged.

Question 22

What is the typical role of metabotropic receptors in neural signaling?

Answer 22

Metabotropic receptors often serve a modulatory role, influencing the electrophysiological properties of the postsynaptic neuron in neural signaling.

Question 23

What factors influence the response generated at a specific synapse?

Answer 23

The response elicited at a given synapse depends on several factors, including the neurotransmitter released, the postsynaptic neuron’s makeup, and the specific ion channels and receptors present on the postsynaptic membrane.

Question 24

Can a single neurotransmitter produce both fast and slow postsynaptic potentials (PSPs)?

Answer 24

Yes, a single neurotransmitter can elicit both fast and slow postsynaptic potentials, depending on the receptor type it activates and the intracellular signaling pathways it triggers.

Question 25

When does a postsynaptic potential (PSP) occur?

Answer 25

A postsynaptic potential (PSP) happens when the neurotransmitter (NT) opens channels in the postsynaptic membrane, allowing ions to flow and create an electrical signal.

Question 26

What is the typical outcome of an end-plate potential (EPP) at the neuromuscular junction?

Answer 26

At the neuromuscular junction, an EPP typically triggers an action potential, leading to muscle contraction.

Question 27

What does IPSP stand for, and what does it do?

Answer 27

IPSP stands for Inhibitory Postsynaptic Potential. It makes the postsynaptic neuron less likely to fire an action potential by hyperpolarizing the membrane (permits the entry of negatively charged ions)

Question 28

What neurotransmitters typically lead to the generation of IPSPs?

Answer 28

Inhibitory neurotransmitters like GABA and glycine often lead to the generation of IPSPs.

Question 29

What does EPSP stand for, and what is its function?

Answer 29

EPSP stands for Excitatory Postsynaptic Potential. It makes the postsynaptic neuron more likely to fire an action potential by depolarizing the membrane (allows the influx of positively charged ions (e.g., sodium or calcium)

Question 30

Which neurotransmitters are associated with the generation of EPSPs?

Answer 30

Excitatory neurotransmitters such as glutamate and acetylcholine are often associated with the generation of EPSPs.

Question 31

What factors determine whether a postsynaptic potential will be excitatory or inhibitory?

Answer 31

It depends on the type of channel coupled to the receptor, the concentration of ions inside and outside the cell, and which ions the neurotransmitter (NT) opens channels for (e.g., sodium or chloride).

Question 32

What is the usual relationship between post-synaptic potentials (PSPs) and the action potential threshold?

Answer 32

Most synapses have PSPs that are well below the action potential threshold.

Question 33

Are there exceptions to the typical PSPs being below threshold?

Answer 33

Yes, the neuromuscular junction is an exceptional case where PSPs can be at or near the threshold for action potential generation.

Question 34

Is an individual PSP typically sufficient to trigger an action potential in most synapses?

Answer 34

No, at most synapses in the central nervous system (CNS), an individual PSP is usually not enough to trigger an action potential.

Question 35

How can multiple PSPs influence the generation of an action potential in a neuron?

Answer 35

Typically, a neuron is innervated by thousands of synapses, and individual PSPs can sum up both spatially and temporally to potentially reach the threshold for action potential initiation. (think of button examples)- However, if many buttons are pressed together, or if they are pressed quickly one after the other, their effects can add up, like stacking blocks, and might eventually make the neuron ‘fire’ and send a message.”

Question 36

Spatial summation

Answer 36

The process by which multiple weak signals from different synapses on a neuron’s dendrites combine to reach the threshold for generating an action potential.

Question 37

Temporal summation

Answer 37

Process by which a neuron integrates multiple signals from the same synapse in rapid succession to reach the threshold for firing an action potential.

Question 38

How does the location of a synapse on the dendritic tree or cell body affect the likelihood of an action potential (AP)?

Answer 38

If a synapse is closer to the trigger zone (the area where the neuron decides to fire an action potential), it has a greater influence and makes it more likely for the neuron to fire an action potential.

Question 39

How does the distance between the presynaptic neuron and the trigger zone affect the potential change in the postsynaptic neuron?

Answer 39

The farther the signal has to travel from the sending neuron to the decision point (trigger zone) in the receiving neuron, the weaker the signal becomes along the way.”

Question 40

The net result of EPSP’s and IPSP’s summate at?

Answer 40

“The trigger zone is where the effects of excitatory and inhibitory signals add up, deciding whether the neuron will fire or not.”

Question 41

summary of synaptic communication

Answer 41

Neurotransmitter (NT) is released.
NT binds to receptors.
Ion channels open or close.
Conductance changes, allowing ions to flow.
Postsynaptic potential changes.
Postsynaptic cells may become excited or inhibited.
Summation of signals determines whether an action potential occurs or not.

Question 42

What is the function of axo-axonic interactions?

Answer 42

Axo-axonic interactions act like a volume knob at the end of an axon, where one axon can control how much NT gets released by the presynaptic terminal into the synapse.

Question 43

What are the two possible outcomes of axo-axonic interactions?

Answer 43

1) Presynaptic facilitation, where more NT is released 2) Presynaptic inhibition, where less NT is released, leading to either excitation or inhibition of the neuron.