Neuron Neuron Synapses (EPSP vs. IPSP)

Summary

This video script delves into the intricacies of synapses and neuron-to-neuron communication, highlighting the many-to-one relationship where one neuron receives input from several others. It explains how action potentials are transmitted via synaptic connections, primarily on cell bodies or dendritic membranes, and the role of neurotransmitters like acetylcholine and glutamate in generating excitatory postsynaptic potentials. The script also contrasts this with inhibitory postsynaptic potentials caused by neurotransmitters like GABA, affecting neuron excitability. Clinical implications of altered neuronal excitability, such as weakness or hyperreflexia, are also discussed, along with causes like ion imbalances, neuron loss, and the impact of toxins and drugs.

Takeaways

• 🧠 Synaptic connections are primarily on the cell body or dendritic membranes.
• 🔗 Neuron-to-neuron relationships are often many-to-one, with one neuron receiving input from several others.
• 💉 Action potentials at the synapse cause depolarization of the presynaptic membrane, leading to neurotransmitter release.
• 🚀 Sodium influx is the main current responsible for depolarizing the postsynaptic membrane.
• 🔑 Threshold potential at -10 millivolts is critical for initiating an action potential.
• 🏞️ The axon hillock is the only region near dendrites with a high density of fast voltage-gated sodium channels.
• 🌐 Synapses closer to the axon hillock have a greater influence on whether an action potential is generated.
• 📈 The sum of inputs from multiple presynaptic cells determines if a postsynaptic cell fires an action potential.
• 🏋️ Excitatory postsynaptic potentials (EPSPs) bring the membrane potential closer to the threshold, increasing neuron excitability.
• 🏃 Inhibitory postsynaptic potentials (IPSPs) hyperpolarize the neuron, decreasing its excitability and likelihood to fire an action potential.
• 🚑 Clinical signs of decreased neuronal excitability include weakness, ataxia, hyperreflexia, paralysis, and sensory deficit.

Q & A

What are the common types of neuron-neuron relationships?

The common type of neuron-neuron relationship is many-to-one, where one neuron takes input from several neurons, creating several synaptic regions.

Where are synaptic connections mainly located?

Synaptic connections are mainly located on a cell body or in dendritic membranes.

What happens when an action potential reaches a dendritic synaptic point?

The action potential depolarizes the presynaptic membrane, causing vesicles to release neurotransmitters like acetylcholine into the synaptic cleft.

How does the neurotransmitter acetylcholine affect the postsynaptic membrane?

Acetylcholine binds with its receptor on the postsynaptic membrane, opening channels that increase sodium and potassium conductance, leading to sodium influx and depolarization of the postsynaptic membrane.

What is the threshold potential in a neuron?

The threshold potential is at -10 millivolts, and when reached, it allows the current to travel along the dendritic and cell body membranes up to the axon hillock.

Why can't current flow at dendrites initiate an action potential?

Current flow at dendrites cannot initiate an action potential because they lack fast voltage-gated sodium channels.

What is the role of the axon hillock in generating an action potential?

The axon hillock has a high density of voltage-gated sodium channels, and when current flows up to it, it can take the membrane potential to the threshold potential, initiating an action potential.

How does the proximity of a synapse to the axon hillock affect its influence?

The closer the synapse is to the axon hillock, the greater its influence in determining whether an action potential is generated.

What is an excitatory postsynaptic potential (EPSP)?

An EPSP is a depolarization of the postsynaptic membrane, such as when glutamate is released and binds to its receptor, allowing sodium influx that makes the neuron more likely to fire an action potential.

What is an inhibitory postsynaptic potential (IPSP)?

An IPSP is a hyperpolarization of the postsynaptic membrane, such as when GABA is released and binds to its receptor, opening chloride channels and moving the membrane potential away from the threshold, decreasing the neuron's excitability.

What clinical signs might indicate decreased neuronal excitability?

Clinical signs of decreased neuronal excitability might include weakness, ataxia, hyperreflexia, paralysis, and sensory deficit.

What are some causes of decreased neuronal excitability?

Causes of decreased neuronal excitability include ion disturbances, loss of neurons, demyelination, and toxins or drugs that affect the neuromuscular junction.