Ligand gated ionotropic and metabotropic receptors 2

What are ionotropic receptors and their primary mechanism of action?

Ionotropic receptors are ligand-gated ion channels that open upon binding of a neurotransmitter, allowing ions to flow and rapidly change the membrane potential.

How does ligand binding affect ionotropic receptors?

Ligand binding induces a conformational change in the receptor, which opens an ion channel, allowing specific ions to flow through.

What is the speed of ionotropic signaling?

Ionotropic signaling is very fast, occurring within milliseconds.

What happens when positively charged ions like Na⁺ enter the cell?

It depolarizes the membrane, increasing the likelihood of an action potential.

What effect do negatively charged ions like Cl⁻ have on the cell?

They hyperpolarize the membrane, decreasing the likelihood of an action potential.

What is an example of an ionotropic receptor?

The AMPA receptor for glutamate, which permits Na⁺ inflow and causes rapid excitation.

What distinguishes metabotropic receptors from ionotropic receptors?

Metabotropic receptors do not contain ion channels themselves and work through G-proteins to activate second messenger pathways.

How is G-protein activated in metabotropic signaling?

The binding of neurotransmitters induces a conformational change in the receptor, activating a G-protein associated with it.

What is a second messenger in the context of metabotropic receptors?

A molecule produced as a result of G-protein activation that carries signals to effect changes within the cell, such as cyclic AMP (cAMP).

What are the downstream effects of metabotropic receptor signaling?

Second messengers can open nearby ion channels, alter enzyme activity, or modify gene expression.

Compare the ion flow mechanism of ionotropic and metabotropic receptors.

Ionotropic receptors allow direct ion flow in response to neurotransmitter binding, while metabotropic receptors influence ion flow indirectly via signaling cascades.

What are the effects of ionotropic receptors in the nervous system?

They mediate fast excitatory and inhibitory signals, crucial for rapid communication and reflexes.

Why are metabotropic receptors important for complex processes?

They can lead to long-term changes in neuronal structure and function, influencing processes such as learning and memory.

What types of channels do ionotropic receptors include?

They include voltage-gated Na⁺ channels, voltage-gated Ca²⁺ channels, and ligand-gated ion channels.

Describe the role of voltage-gated Ca²⁺ channels in neurotransmitter release.

They open during an action potential, allowing Ca²⁺ influx that triggers neurotransmitter release from vesicles.

What are Cys-loop receptors?

They are a type of ionotropic receptor composed of 5 subunits that mediate fast synaptic transmission.

Give examples of Cys-loop receptors.

Nicotinic acetylcholine receptors, GABA_A receptors, glycine receptors, and 5-HT3 receptors.

What neurotransmitter does the NMDA receptor specifically respond to?

The NMDA receptor specifically responds to glutamate.

What dual condition is required for NMDA receptor activation?

Both glutamate binding and postsynaptic depolarization are required for NMDA receptor activation.

What happens to the NMDA receptor at resting membrane potential?

At resting membrane potential, the NMDA receptor is blocked by a magnesium (Mg²⁺) ion.

What triggers the removal of the Mg²⁺ block from NMDA receptors?

Postsynaptic depolarization triggers the removal of the Mg²⁺ block.

What is the significance of calcium (Ca²⁺) entry through NMDA receptors?

Ca²⁺ entry serves as a second messenger that can initiate various intracellular signaling processes.

How do AMPA receptors contribute to synaptic transmission?

They allow Na⁺ to enter the cell upon glutamate binding, resulting in rapid depolarization.

Describe the selectivity of the AMPA receptor.

Most AMPA receptors are impermeable to Ca²⁺ due to the GluA2 subunit presence, allowing primarily Na⁺ to enter.

What role does acetylcholine play in the neuromuscular junction?

Acetylcholine binds to nicotinic receptors to induce muscle contraction.

What process terminates the action of acetylcholine in the synaptic cleft?

Acetylcholinesterase (AChE) breaks down acetylcholine into choline and acetic acid.

What is long-term potentiation (LTP)?

LTP is a lasting increase in synaptic strength, thought to underlie learning and memory.

How does GABA function as a neurotransmitter?

GABA acts as the primary inhibitory neurotransmitter in the CNS, hyperpolarizing neurons to reduce excitability.

What characterizes phasic GABA_A receptors?

Phasic GABA_A receptors respond rapidly to high, brief concentrations of GABA.

Define tonic GABA_A receptors.

Tonic GABA_A receptors respond to sustained, low concentrations of GABA, providing background inhibition.

What is the primary distinction between ionotropic and metabotropic receptors based on effects?

Ionotropic receptors cause fast and local effects, while metabotropic receptors lead to slower and longer-lasting effects.

What is the role of second messengers in metabotropic signaling?

Second messengers mediate a variety of cellular responses initiated by G-protein activation.

What are some examples of G-protein-coupled receptors (GPCRs)?

Dopamine receptors, serotonin receptors, and adrenergic receptors.

Describe the structural features of GPCRs.

GPCRs are characterized by a single polypeptide chain that spans the membrane seven times, forming seven transmembrane domains.

How does the activation of G-proteins influence signal transduction?

Activation allows G-proteins to dissociate into subunits that can activate downstream signaling pathways.

What are the two major signaling pathways activated by GPCR signaling?

The cAMP pathway and the phosphoinositide signaling pathway.

What is the outcome of the cAMP signaling pathway when activated?

The production of cAMP, which activates protein kinase A (PKA), leading to various cellular responses.

How does PLC (phospholipase C) contribute to signal transduction?

It hydrolyzes PIP2 to produce DAG and IP3, triggering intracellular calcium release and activation of specific kinases.

What is the significance of DAG in GPCR signaling?

DAG remains in the membrane and activates protein kinase C (PKC), influencing various signaling pathways.

How does endocannabinoid signaling affect neuronal excitability?

Endocannabinoids activate CB1 GPCRs, which can inhibit presynaptic calcium channels and reduce neurotransmitter release.

What are the effects of activating the M2 muscarinic receptor in the presynaptic terminal?

It promotes GIRK channel activation, leading to hyperpolarization and reduced excitability.

In what context does the mGluR pathway affect synaptic excitability?

Activation can lead to long-term depression (LTD), tuning excitability in synaptic responses.

What is a key characteristic of orphan GPCRs?

Orphan GPCRs are those for which the endogenous ligands or neurotransmitters are not yet identified.

Summarize the overall comparison between ionotropic and metabotropic receptors.

Ionotropic receptors mediate fast, localized responses to neurotransmitters, while metabotropic receptors entail slower, prolonged responses through secondary messengers.