Synapses and Neural Communication

Flashcards covering key concepts from the lecture notes on synapses and neural communication, including Sherrington's contributions, reflex arcs, synaptic delay, graded potentials (EPSP/IPSP), and neural summation and synchronization.

What was Charles Scott Sherrington's main contribution to neuroscience?

He discovered the synapse, coined the term 'synapse', and studied reflexes, building on Cajal's findings of there being separate neurons.

What is a reflex?

An involuntary, rapid, and automatic response to a specific stimulus, mediated by a neural pathway called a reflex arc. It allows for a quick reaction without conscious thought.

Name the steps and parts of a reflex arc.

1) Receptor detecting stimulus, 2) Sensory neuron transmitting signal to CNS, 3) Integration center (interneurons) where sensory neuron synapses with motor neuron, 4) Motor neurons carrying response to effector, 5) Effector (muscle or gland) carrying out response.

What is a reflecx arc?

The neural pathway that governs a reflex action.

What is the typical speed of an action potential along sensory or motor axons?

40 m/s (10 to 100 meters per second).

What is the speed of conduction through a reflex arc?

15 m/s.

Why is the speed of conduction through a reflex arc slower than the speed of an action potential?

Due to a delay that occurs when one neuron communicates with another at a synapse.

What is a synapse?

A junction between two nerve cells, consisting of a minute gap across which impulses pass by diffusion of a neurotransmitter.

What is the importance of synaptic delay?

The delay facilitates communication, allowing chemical signals to relay onto the postsynaptic terminals.

Which type of synapse is generally faster, chemical or electrical?

Electrical synapses.

Why are chemical synapses predominantly used over electrical synapses, despite being slower?

Neural communication depends on complex chemical signals for feelings, thoughts, and other complexities, which 'off-and-on' electrical signals cannot achieve.

What processes can rely on electrical signaling?

Regulation and action potentials (membrane potentials).

List some disadvantages of chemical signals.

Slowness, limited range, difficulty of pinpointing the source, slow fading times, potential loss of privacy, environmental interference, and the possibility of signal interference.

What is a graded potential?

A small, localized change in a cell’s membrane potential (can be depolarization or hyperpolarization) that does not propagate along the entire cell.

True or False: Graded potentials only be depolarization.

False, graded potentials can be both depolarization or hyperpolarization.

Do excitatory stimuli cause depolarization or hyperpolarization?

Depolarization (making the membrane potential more positive).

Do inhibitory stimuli cause depolarization or hyperpolarization?

Hyperpolarization (making the membrane potential more negative).

What is Excitatory Postsynaptic Potential (EPSP)?

A temporary graded depolarization of the postsynaptic membrane, making it more positive.

What causes an EPSP?

Sodium ions entering the membrane.

How does an EPSP contribute to action potentials?

It makes the cell more likely to fire an action potential by bringing the membrane potential closer to the threshold.

Why is an EPSP not considered an action potential?

The inner membrane potential of an EPSP does not reach the -55mV threshold required to prompt an action potential overshoot.

What is Inhibitory Postsynaptic Potential (IPSP)?

A temporary graded hyperpolarization of the postsynaptic membrane, making it more negative.

What causes an IPSP?

Potassium ions exiting the cell or chloride ions entering the cell.

How does an IPSP affect the likelihood of an action potential?

IPSP makes the cell less likely to fire an action potential because it makes the membrane potential more negative, moving it further from the threshold.

What is considered the most important inhibitory neurotransmitter and why?

GABA is the most important inhibitory neurotransmitter. It binds to receptors, prompting chloride channels to open and allow chloride ions into the membrane, making the cell more negative and less likely to react to stimuli.

Is it true or false that you need a lot of GABA to sleep well?

True, because GABA inhibits neurons from reacting to stimuli while resting, which is crucial for sleep.

How can GABA help with focus and attention?

GABA inhibits other neurons from firing off due to distracting stimuli, allowing for better focus and attention.

What is the most abundant neurotransmitter, and what is its importance?

Glutamate is an excitatory neurotransmitter that causes neurons to depolarize. It is essential for long-term potentiation (LTP), a process that strengthens synaptic connections and underlies memory formation.

Can both IPSP and EPSP occur in action potentials?

Yes.

Is it true or false that depolarization of the membrane always leads to an action potential?

False, not always, as the threshold potential must be reached.

What is spatial summation?

It occurs when multiple presynaptic neurons converge together to stimulate a singular postsynaptic neuron.

How might spatial summation differ from a neuron-to-neuron synapse?

Spatial summation requires the inputs to combine their effects to collectively increase the overall signal strength, reach the necessary threshold for the postsynaptic neuron to fire an action potential, or inhibit it from firing.

Is it true or false that the release of a neurotransmitter always prompts only an inhibitory synapse effect on a postsynaptic terminal?

False, the effect (inhibitory or excitatory) depends on the specific neurotransmitter being released.

What is a cumulative effect in neural signaling, and how does it happen?

It is the summation where multiple signals (excitatory or inhibitory) are combined over time or space to determine if a neuron will reach the threshold to fire an action potential. It can happen when there are repeated stimuli with very brief intervals between them.

Is it possible for a second excitation to combine with a delayed signal of a postsynaptic neuron to produce an action potential?

Yes, this is an example of the cumulative effect.

Can temporal and spatial summation occur together?

Yes.

What is the Spontaneous Firing Rate?

A periodic production of action potentials by neurons even without synaptic input or stimulation.

What does ongoing periodic activity refer to in the brain?

It refers to brain signals that repeat at regular or nearly regular intervals, typically detected using an electroencephalogram (EEG).

Can ongoing periodic activity vary from person to person? Provide examples.

Yes. Examples include the sleep-wake cycle (circadian rhythm), menstrual cycle, and heart rate variability.

What is ongoing activity important for?

Perception and cognition.

What does the perception of a weak stimulus depend on?

The phase and amplitude of spontaneous activity.

What do EPSPs do in the context of spontaneous firing rate?

They increase the frequency of action potentials.

What do IPSPs do in the context of spontaneous firing rate?

They decrease the frequencies of action potentials.

What is neural synchronization?

When brain waves from different regions synchronize, indicating network communication.

What can synchronized activity of neurons give rise to?

Oscillations.

What does oscillation of synchronized energy refer to?

Rhythmic, repeating patterns of activity within a system (like brain networks) that are temporally coordinated or 'in phase' with each other.

What is neural synchronization related to?

Neural summation.

What does synchronization mean in neural terms?

Intercommunication between neurons.