Neuroscience - Neurotransmitters & Synaptic Transmission Flashcards

Question 1

What is a synapse?

Accepted Answer

The specialized junction where one neuron communicates with another neuron or an effector cell (e.g., muscle, gland). It typically consists of a presynaptic terminal, a synaptic cleft, and a postsynaptic membrane.

Question 2

What is the role of an action potential in synaptic transmission?

Accepted Answer

An action potential (electrical signal) arriving at the presynaptic terminal depolarizes the membrane, triggering the sequence of events that lead to neurotransmitter release into the synaptic cleft.

Question 3

What happens when an action potential reaches the presynaptic terminal?

Accepted Answer

The depolarization caused by the action potential opens voltage-gated $	ext{Ca}^{2+}$ channels in the presynaptic membrane, leading to an influx of $	ext{Ca}^{2+}$ ions into the terminal.

Question 4

How does calcium influx lead to neurotransmitter release?

Accepted Answer

The influx of $	ext{Ca}^{2+}$ ions acts as a signal, binding to proteins (e.g., synaptotagmin) on synaptic vesicles. This binding triggers the fusion of vesicles with the presynaptic membrane, releasing neurotransmitters into the synaptic cleft via exocytosis.

Question 5

What are synaptic vesicles?

Accepted Answer

Small, membrane-bound sacs within the presynaptic terminal that store neurotransmitters, protecting them from degradation and facilitating their rapid release upon stimulation.

Question 6

What is the role of SNARE proteins in neurotransmitter release?

Accepted Answer

SNARE (Soluble N-ethylmaleimide-sensitive factor Attachment protein Receptor) proteins are a complex of proteins (v-SNAREs on vesicles, t-SNAREs on the presynaptic membrane) that mediate the docking, priming, and fusion of synaptic vesicles with the presynaptic membrane, essential for exocytosis.

Question 7

How do neurotransmitters cross the synaptic cleft?

Accepted Answer

After release from the presynaptic terminal, neurotransmitters diffuse across the synaptic cleft, a small gap between the pre- and postsynaptic membranes, to reach receptors on the postsynaptic neuron.

Question 8

What are the two main types of neurotransmitter receptors?

Accepted Answer

The two main types are ionotropic receptors (ligand-gated ion channels) and metabotropic receptors (G-protein coupled receptors).

Question 9

Describe ionotropic receptors.

Accepted Answer

Ionotropic receptors are ligand-gated ion channels that, upon binding of a neurotransmitter, directly open an ion channel, leading to a rapid influx or efflux of specific ions and a change in the postsynaptic membrane potential.

Question 10

Describe metabotropic receptors.

Accepted Answer

Metabotropic receptors are G-protein coupled receptors that, upon neurotransmitter binding, activate an intracellular G-protein. This G-protein can then directly modulate ion channels or activate second messenger pathways, leading to slower, more prolonged, and diverse cellular responses.

Question 11

What is an Excitatory Postsynaptic Potential (EPSP)?

Accepted Answer

An EPSP is a transient depolarization of the postsynaptic membrane potential, typically caused by the influx of positive ions (e.g., $	ext{Na}^{+}$ or $	ext{Ca}^{2+}$), making the postsynaptic neuron more likely to fire an action potential.

Question 12

What is an Inhibitory Postsynaptic Potential (IPSP)?

Accepted Answer

An IPSP is a transient hyperpolarization or stabilization of the postsynaptic membrane potential, typically caused by the influx of negative ions (e.g., $	ext{Cl}^{-}$) or efflux of positive ions (e.g., $	ext{K}^{+}$), making the postsynaptic neuron less likely to fire an action potential.

Question 13

How are postsynaptic potentials integrated?

Accepted Answer

Postsynaptic potentials (EPSPs and IPSPs) are integrated through summation:
*   **Spatial Summation:** Multiple potentials from different synapses arriving simultaneously.
*   **Temporal Summation:** Multiple potentials from the same synapse arriving in rapid succession.
If the summed potential reaches the threshold at the axon hillock, an action potential is generated.

Question 14

What mechanisms terminate neurotransmitter action in the synapse?

Accepted Answer

Neurotransmitter action is terminated by:
1.  **Enzymatic Degradation:** Enzymes in the synaptic cleft break down the neurotransmitter (e.g., acetylcholinesterase for ACh).
2.  **Reuptake:** Neurotransmitters are actively transported back into the presynaptic terminal or glial cells.
3.  **Diffusion:** Neurotransmitters simply diffuse away from the synaptic cleft.

Question 15

What are the main classes of neurotransmitters?

Accepted Answer

Major classes include:
*   Amino Acids (e.g., Glutamate, GABA)
*   Monoamines (e.g., Dopamine, Serotonin, Norepinephrine)
*   Acetylcholine
*   Neuropeptides (e.g., Endorphins, Substance P)
*   Gases (e.g., Nitric Oxide)
*   Purines (e.g., ATP)

Question 16

What is Acetylcholine (ACh) and its primary functions?

Accepted Answer

ACh is a neurotransmitter found in both the central and peripheral nervous systems. It plays crucial roles in muscle contraction (neuromuscular junction), learning, memory, and attention.

Question 17

What is Dopamine (DA) and its primary functions?

Accepted Answer

DA is a monoamine neurotransmitter involved in reward, motivation, pleasure, motor control, and executive functions. Dysregulation is linked to Parkinson's disease and schizophrenia.

Question 18

What is Serotonin (5-HT) and its primary functions?

Accepted Answer

5-HT is a monoamine neurotransmitter that widely influences mood, sleep, appetite, digestion, learning, and memory. It is a target for many antidepressant medications.

Question 19

What is Gamma-aminobutyric acid (GABA) and its primary functions?

Accepted Answer

GABA is the primary inhibitory amino acid neurotransmitter in the CNS. It reduces neuronal excitability, promoting relaxation and reducing anxiety.

Question 20

What is Glutamate and its primary functions?

Accepted Answer

Glutamate is the primary excitatory amino acid neurotransmitter in the CNS. It is crucial for learning, memory formation, and synaptic plasticity. Excessive glutamate can be neurotoxic.

Question 21

What are Neuropeptides and provide an example?

Accepted Answer

Neuropeptides are short chains of amino acids that act as neurotransmitters or neuromodulators. They often have slower, longer-lasting effects than classical neurotransmitters. Example: Endorphins, which are involved in pain relief and pleasure.

Question 22

What is the difference between an excitatory and inhibitory neurotransmitter?

Accepted Answer

*   **Excitatory NTs:** Increase the likelihood of a postsynaptic neuron firing an action potential by causing depolarization (e.g., Glutamate, ACh at nicotinic receptors).
*   **Inhibitory NTs:** Decrease the likelihood of a postsynaptic neuron firing an action potential by causing hyperpolarization or stabilization (e.g., GABA, Glycine).

Neuroscience - Neurotransmitters & Synaptic Transmission

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