L6: Synaptic Signalling

Question 1

What is the primary focus of the lecture on synaptic signaling?

Answer 1

Neurone-to-neurone communication, focusing on how one neurone talks to another and synaptic integration.

Question 2

What is a synapse?

Answer 2

The gap between a presynaptic neurone and a postsynaptic neurone where neurotransmitters are released and interact with receptors.

Question 3

What are the two main types of synaptic signaling mechanisms?

Answer 3

Isotropic (ligand-gated ion channels) and metabotropic (G-protein coupled receptors).

Question 4

What determines the excitability of the postsynaptic neurone?

Answer 4

The balance of excitatory (e.g., sodium influx) and inhibitory (e.g., chloride influx) synaptic inputs.

Question 5

What is spatial summation in synaptic integration?

Answer 5

The additive effect of excitatory postsynaptic potentials (EPSPs) from multiple synapses occurring simultaneously.

Question 6

What is temporal summation in synaptic integration?

Answer 6

The additive effect of EPSPs from the same synapse occurring in rapid succession.

Question 7

Why is the axon hillock an influential site in synaptic signaling?

Answer 7

Synaptic inputs closer to the axon hillock have a greater influence on action potential generation.

Question 8

What happens during the refractory period after an action potential?

Answer 8

Voltage-gated sodium channels enter an inactive state, preventing immediate firing of another action potential.

Question 9

How is stimulus strength encoded in neurones?

Answer 9

By the frequency of action potentials, not their amplitude.

Question 10

What is excitotoxicity and what condition is it linked to?

Answer 10

Excessive neuronal excitation leading to cell death, often associated with epilepsy.

Question 11

What is the role of inhibitory synaptic inputs in the brain?

Answer 11

To control excitability and prevent overexcitation, which can lead to conditions like seizures.

Question 12

How does the type of receptor influence synaptic response?

Answer 12

Isotropic receptors directly alter ion flow, while metabotropic receptors trigger slower, indirect effects through second messengers.

Question 13

What is the key threshold concept for action potential generation?

Answer 13

The membrane potential must reach a point where sodium influx exceeds potassium efflux to trigger voltage-gated sodium channel activation.

Question 14

What is meant by ‘frequency modulation’ in synaptic signaling?

Answer 14

The strength of a signal is communicated by the frequency of action potentials rather than their size.

Question 15

What is the ‘active zone’ in a synapse?

Answer 15

The region in the presynaptic terminal where neurotransmitter vesicles cluster and fuse with the membrane to release their contents.

Question 16

What is the postsynaptic density?

Answer 16

A thickened region of the postsynaptic membrane containing proteins, receptors, and intracellular signaling machinery.

Question 17

What are the different types of synaptic arrangements mentioned?

Answer 17

Axodendritic, axosomatic, and axoaxonic synapses.

Question 18

What is the significance of axosomatic synapses?

Answer 18

They are more influential in determining whether a neurone will generate an action potential.

Question 19

What is the relationship between synaptic location and influence?

Answer 19

Synaptic inputs closer to the axon hillock have a greater impact on action potential generation.

Question 20

How does the brain prevent overexcitation?

Answer 20

Through inhibitory inputs and control mechanisms that prevent excessive neuronal firing.

Question 21

What is the role of chloride ions in inhibitory signaling?

Answer 21

Chloride influx leads to hyperpolarization, reducing the likelihood of action potential generation.

Question 22

What is excitatory postsynaptic potential (EPSP)?

Answer 22

A depolarizing event caused by excitatory synaptic input, increasing the likelihood of an action potential.

Question 23

What is inhibitory postsynaptic potential (IPSP)?

Answer 23

A hyperpolarizing event caused by inhibitory synaptic input, decreasing the likelihood of an action potential.

Question 24

How do multiple EPSPs summate to generate an action potential?

Answer 24

Through spatial or temporal summation, where individual EPSPs combine to reach the threshold potential.

Question 25

What are quantum synaptic events?

Answer 25

The smallest unit of neurotransmitter release, involving a single vesicle of neurotransmitter.

Question 26

How does synaptic integration influence neural output?

Answer 26

The neurone integrates all excitatory and inhibitory inputs to determine if it reaches the threshold to fire an action potential.

Question 27

What is the absolute refractory period?

Answer 27

The time during which no new action potential can be initiated, regardless of the stimulus strength.

Question 28

What is the relative refractory period?

Answer 28

The time during which a stronger-than-normal stimulus is required to trigger another action potential.

Question 29

Why are action potentials considered ‘all-or-nothing’ events?

Answer 29

Because their amplitude does not vary with the strength of the stimulus once the threshold is reached.

Question 30

What is meant by ‘frequency encoding’ in neuronal signaling?

Answer 30

The strength of a stimulus is conveyed by the frequency of action potentials rather than changes in their size.

Question 31

What limits the maximum frequency of action potentials?

Answer 31

The duration of the absolute refractory period.

Question 32

What is the role of G-protein coupled receptors in synaptic signaling?

Answer 32

They trigger slower, longer-lasting intracellular responses through secondary messenger cascades.

Question 33

How does synaptic diversity contribute to neural function?

Answer 33

Different synaptic arrangements and mechanisms allow for varied and precise control of neuronal communication.

Question 34

What are ligand-gated ion channels?

Answer 34

Ion channels that open in response to the binding of a neurotransmitter, allowing specific ions to flow through the membrane.

Question 35

What causes depolarization in an excitatory synaptic event?

Answer 35

Sodium influx into the postsynaptic neurone through ligand-gated ion channels.

Question 36

How does an inhibitory synapse affect the postsynaptic membrane potential?

Answer 36

It causes hyperpolarization, making the membrane potential more negative and reducing excitability.

Question 37

What is meant by ‘integration of synaptic inputs’?

Answer 37

The process by which a neurone combines multiple excitatory and inhibitory inputs to determine its output.

Question 38

What role does the dendritic tree play in synaptic input?

Answer 38

It collects and processes signals from synaptic inputs across its branches, influencing neuronal activity.

Question 39

What is the significance of the threshold potential?

Answer 39

It is the critical level of depolarization needed to trigger an action potential.

Question 40

What happens when the threshold is reached in a neurone?

Answer 40

Voltage-gated sodium channels open, causing a rapid influx of sodium and the generation of an action potential.

Question 41

How does epilepsy relate to synaptic signaling?

Answer 41

It involves excessive neuronal excitation and synchronization, leading to seizures.

Question 42

What is the role of voltage-gated sodium channels in action potentials?

Answer 42

They allow sodium ions to enter the neurone during depolarization, driving the action potential.

Question 43

What happens to voltage-gated sodium channels during the absolute refractory period?

Answer 43

They become inactivated and cannot open, preventing another action potential.

Question 44

How do spatial summation and temporal summation differ?

Answer 44

Spatial summation combines inputs from multiple synapses, while temporal summation combines inputs from repeated activity at the same synapse.

Question 45

What is excitotoxicity?

Answer 45

Neuronal damage or death caused by excessive stimulation and calcium influx.

Question 46

What is the role of neurotransmitter vesicles in synaptic transmission?

Answer 46

They store and release neurotransmitters into the synaptic cleft during exocytosis.

Question 47

How does chloride influx contribute to inhibitory signaling?

Answer 47

It increases the negative charge inside the neurone, hyperpolarizing the membrane and reducing excitability.

Question 48

Why is frequency modulation important in neuronal communication?

Answer 48

It encodes the strength of a stimulus through the frequency of action potentials.

Question 49

How does the relative refractory period allow for action potentials to occur?

Answer 49

With a strong enough stimulus, sufficient depolarization can occur to reach the threshold despite the hyperpolarized state.

Question 50

What is a neuromuscular junction?

Answer 50

A specialized synapse where a motor neurone communicates with a muscle fiber.

Question 51

What is the difference between excitatory and inhibitory postsynaptic potentials?

Answer 51

Excitatory potentials depolarize the membrane, while inhibitory potentials hyperpolarize it.

Question 52

What mechanisms prevent overexcitation in the brain?

Answer 52

Inhibitory synapses, chloride influx, and control of excitatory inputs.