Neuroscience Chapter on Memory & Synapses

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Questions and Answers

What is the process called when several excitatory postsynaptic potentials (EPSPs) occur close together in time due to the successive firing of a single presynaptic neuron?

Spatial summation

Temporal summation (correct)

Desensitization

Inhibition

Which pathway allows many presynaptic neurons to influence a single postsynaptic neuron?

Threshold pathway

Divergent pathway

Convergent pathway (correct)

Synaptic pathway

What phenomenon occurs when an increase in the frequency of action potentials leads to a decrease in neurotransmitter release due to desensitization?

Long-term potentiation

Synaptic fatigue (correct)

Long-term memory

Neuronal integration

What type of memory is defined as the storage of knowledge from seconds to hours?

Short-term memory Signup and view all the answers

Which brain region is NOT typically involved in memory consolidation?

Amygdala Signup and view all the answers

What is the term for the process that transfers short-term memory into long-term memory?

Consolidation Signup and view all the answers

What allows the nervous system to change its anatomy and function in response to activity patterns?

Plasticity Signup and view all the answers

What is the result of repetitive stimulation of a synapse that strengthens the synaptic connection?

Long-term potentiation Signup and view all the answers

What role do the nodes of Ranvier play in saltatory conduction?

They are where sodium channels reinforce depolarization. Signup and view all the answers

Which of the following is NOT a characteristic of action potentials?

They vary in amplitude depending on signal strength. Signup and view all the answers

What effect does multiple sclerosis have on nerve transmission?

It leads to a loss of myelin. Signup and view all the answers

What is the primary function of dendrites in a neuron?

To receive signals from other neurons. Signup and view all the answers

Which mechanism is NOT a method for terminating synaptic transmission?

Re-uptake by the postsynaptic neuron. Signup and view all the answers

What neurotransmitter is promoted by cocaine leading to prolonged activation of neural pathways?

Dopamine Signup and view all the answers

What is the difference between EPSP and IPSP?

EPSP leads to an increase in action potential generation while IPSP decreases it. Signup and view all the answers

Which component of a synapse contains the neurotransmitters?

Axon terminal Signup and view all the answers

Which of the following is true regarding neurotransmitter release?

Each presynaptic neuron releases only one type of neurotransmitter. Signup and view all the answers

What primarily generates the resting membrane potential in a neuron?

The action of the Na+-K+ pump Signup and view all the answers

Which statement best describes action potentials compared to graded potentials?

Action potentials propagate nondecrementally along the axon. Signup and view all the answers

What is the role of voltage-gated Na+ channels during the action potential?

They rapidly depolarize the membrane. Signup and view all the answers

What mechanism leads to propagation of the action potential in myelinated fibers?

Saltatory conduction between nodes of Ranvier. Signup and view all the answers

During which phase of the action potential do K+ ions rush out of the cell?

Repolarization Signup and view all the answers

What is a characteristic effect of tetrodotoxin on neuronal function?

It blocks voltage-gated Na+ channels. Signup and view all the answers

Which of the following describes the absolute refractory period?

No new action potential can be initiated, regardless of stimulus strength. Signup and view all the answers

What role do oligodendrocytes play in the nervous system?

They produce myelin for CNS axons. Signup and view all the answers

What is hyperpolarization in the context of neuronal activity?

Membrane potential becomes more negative than the resting state. Signup and view all the answers

What defines the threshold potential in neurons?

The membrane potential at which action potentials are initiated. Signup and view all the answers

Which feature distinguishes myelinated axons from unmyelinated axons?

Presence of nodes of Ranvier. Signup and view all the answers

What occurs during depolarization of the neuron's membrane?

Na+ channels open, allowing Na+ to enter the cell. Signup and view all the answers

Which of the following describes the process of contiguous conduction?

Action potentials travel along every segment of the membrane in non-myelinated fibers. Signup and view all the answers

Study Notes

Human Physiology BIOL3205 - Neuronal Communication

Course instructor: Prof. Chi Bun Chan
Contact information: [email protected], 39173823
Location: 5N10 Kadoorie Biological Sciences Building
Course topic: Neuronal communication

Lecture Outline

Membrane potential
Action potential formation and conduction
Synapses and neurotransmitters
Neural integration and networking

Structure of a Neuron

Dendrites: Receive signals from other neurons, directed towards the cell body. Dendritic spines are also found in the cell body, forming synapses.
Cell body: Contains the nucleus and organelles, integrating signals.
Input zone: Receives incoming signals.
Axon: Conducts action potentials to other cells; variable in length triggered by the axon hillock.
Axon terminals: Release neurotransmitters influencing other cells.

Membrane Potential

Membrane potential: Voltage difference across a cell membrane.
Resting membrane potential of a neuron cell is -70 mV.
Expressed as a negative value due to a slight excess of anions inside the cell.
Maintained by the Na+-K+ pump, which expends energy.
K+ channels are always open (leaky channels).
Na+ and K+ ions are responsible for generating the resting membrane potential.

Change of Membrane Potential

Only nerve and muscle tissues are excitable.
Membrane potential can be changed through:
- Polarization: Separation of charges across the membrane.
- Depolarization: Decrease in membrane potential (less negative).
- Repolarization: Return to resting membrane potential.
- Hyperpolarization: Increase in membrane potential (more negative).
Ion movement is mediated by channels.

Ion Channels

Pores that open and close in an all-or-nothing fashion.
Types:
- Leaky channels
- Voltage-gated channels
- Chemically-gated channels
- Mechanically-gated channels
- Thermally-gated channels

Generation of Electrical Signals in Neurons

Electrical signals in neurons occur via changes in membrane potential.
Two basic forms of electrical signals:
- Graded potentials: Changes in membrane potential that are localized.
- Action potentials: Large, rapid changes in membrane potential that are used for long-distance signaling.

Graded Potentials

Depolarization of membrane in small, specialized regions.
Provoked by Na+ entry.
Bi-directional over a short distance.
Decreases ("current loss") gradually.
Signal for short distances only.
Magnitude depends on triggering event.

Action Potentials

Brief, rapid, large changes in membrane potential.
Initiated by a triggering event (membrane potential reaching threshold potential, often at the axon hillock).
Generated and propagated non-decrementally throughout the entire membrane.
Long-distance signals; fixed threshold.
All-or-none response: either generated or not.

Conformation of Voltage-gated Na+ and K+ Channels

Na+ channels:
- Open rapidly at threshold.
- Inactivated.
- Close slowly after depolarization.
K+ channels:
- Open more slowly than Na+ channels.
- Responsible for repolarization and then hyperpolarization.

Formation of Action Potentials

Caused by rapid fluxes of Na+ and K+.
Opening and closing of voltage-gated Na+ and K+ channels.
Positive feedback of Na+ channels (rapid depolarization).
Rapid K+ outflow (repolarization).
Hyperpolarization by the slow closure of K+ channels.

Propagation of Nerve Impulse

Once initiated, no further triggering is needed.
Conducted through:
- Contiguous conduction (non-myelinated).
- Saltatory conduction (myelinated).
- Depends on axon structure (myelinated or non-myelinated).

Contiguous Conduction

Occurs in non-myelinated neurons.
Spreads along every patch of membrane.
Active and inactive areas.
Self-perpetuating cycle.
Original action potential is not carried along, new action potentials are formed.

Refractory Period

Time when a new action potential cannot be initiated by a region that has just undergone one.
Types:
- Absolute refractory period: Impossible to generate another action potential.
- Relative refractory period: More difficult to generate an action potential.

Myelination

Myelin sheath surrounds axons, insulating them.
Produced by oligodendrocytes (CNS) and Schwann cells (PNS).
Concentrates Na+ and K+ channels at the nodes of Ranvier.
Saltatory conduction: Faster signal transmission.
Energy conservation.

Saltatory Conduction

APs produced only at Nodes of Ranvier.
Saltatory conduction: Current movement through the myelinated sheath diminished.
Na+ entry at the node reinforces depolarization to keep the magnitude at threshold for the next AP.
AP "jumps" between nodes.

Synaptic Transmission

Different localization of synaptic vesicles and neurotransmitter receptors.
One-way transmission.
Action potential triggers neurotransmitter release.Neurotransmitter binds to receptors, causing potential changes.

Termination of Synaptic Transmission

Endocytosis of neurotransmitter receptors by the post-synaptic neuron.
Re-uptake by the presynaptic terminal (re-use).
Enzyme destruction within the synaptic cleft.
Diffusion out of the cleft.

Blocking of Neurotransmitter Reuptake (Example: Cocaine)

Cocaine blocks neurotransmitter reuptake and prolongs the activation of neural pathways (e.g., pleasure).
Cocaine is a competitor of dopamine transporter.
Higher concentration of dopamine in synaptic cleft.

Types of Neurotransmitters

Endogenous chemicals that transmit signals across synapses.
Each Presynaptic neuron releases only one neurotransmitter.
Different neurons vary in neurotransmitter release.

Excitatory and Inhibitory Synaptic Transmission

Binding of neurotransmitters causes a membrane potential change in the post-synaptic neuron.
Can be excitatory (EPSP) or inhibitory (IPSP).
EPSP: Small depolarization.
IPSP: Small hyperpolarization.

Determination of Postsynaptic Potential

Temporal summation: Several EPSPs occurring close together in time.
Spatial summation: EPSPs originated simultaneously.
Cancellation of EPSPs by IPSPs.
Neuronal integration: Neuronal integration controls physiological activities. (e.g., urination).

Integration of Information Transfer between Neurons

Complex computational network.
Convergent pathway: Many pre-synaptic neurons input a signal to a postsynaptic neuron.
Divergent pathway: One presynaptic neuron branches to large numbers of postsynaptic neurons

What Determines Strength of Action Potential

Action potential frequency.
Neurotransmitter release, which may decrease during high frequency.

Memory

Memory is the storage of acquired knowledge.
Short-term memory (seconds to hours).
Long-term memory (days to years).
Consolidation: Process of transferring short-term to long-term memory, often in the hippocampus, cerebellum, and prefrontal cortex.
Structural changes: Elongation of dendrites and formation of new synapses.
LTP: Long-term potentiation.

Long-Term Potentiation (LTP)

Repetitive stimulation leads to an increase in synaptic strength.
Triggering an AP in the postsynaptic cell for prolonged period.
Distinguished from temporal summation.
Crucial for long-term memory formation.

LTP and Memory Formation

Related to the Morris water maze.
NMDAR (N-methyl-D-aspartate receptor) antagonist blocks this process.

After-Lecture Explanations

Students should be prepared to explain membrane potential, graded potential, action potential formation and transmission, information transmission between neurons, and neural integration.

Multiple Sclerosis

Autoimmune disease attacking the nervous system.
Loss of myelin.
Genetic/environmental factors.
Slows nerve impulse transmission.
Symptoms varied.
No cure.

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Description

Test your knowledge on key concepts in neuroscience, particularly those related to memory, synaptic transmission, and plasticity. From excitatory postsynaptic potentials to the roles of different brain regions, this quiz covers essential topics in the study of the nervous system.