Neuroscience Chapter on Synapses

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Questions and Answers

What is the primary function of a synapse?

To regulate the metabolic rate of neurons.

To transmit information between neurons or between a neuron and another cell. (correct)

To produce neurotransmitters within neurons.

To provide structural support to neurons.

Which type of cell listed can be a postsynaptic cell in the peripheral nervous system?

Adipocyte

Muscle cell (correct)

Osteocyte

Epithelial cell

What characterizes an electrical synapse?

Slower signal transmission compared to chemical synapses.

Reliance on neurotransmitters to transmit signals.

Direct connection between neurons via gap junctions. (correct)

Use of a synaptic cleft that is 20-40 nanometers wide.

What role do calcium ions play in chemical synapses?

They trigger the release of neurotransmitters from synaptic vesicles. Signup and view all the answers

Which of the following best describes the width of the synaptic cleft in a chemical synapse?

20-40 nm Signup and view all the answers

What is formed between cells through gap junctions?

Syncytium Signup and view all the answers

What is the name of the entire postsynaptic structure in a chemical synapse?

Motor end plate Signup and view all the answers

In electrical communication, what is nerve conduction based on?

An ion balance Signup and view all the answers

Which of the following neurotransmitters is primarily responsible for initiating muscle contractions?

Acetylcholine Signup and view all the answers

What is the primary difference in signal transmission between electrical and chemical synapses?

Electrical synapses transmit signals faster than chemical synapses. Signup and view all the answers

Where are T-SNARE proteins located?

On the target cell or organelle membrane Signup and view all the answers

What is the role of synaptotagmin in the SNARE complex?

It senses calcium ions ($Ca^{2+}$), enhancing SNARE complex assembly. Signup and view all the answers

Which of the following conditions is caused by the blockage of neurotransmitter release at the neuromuscular junction?

Botulism Signup and view all the answers

What is the initial step in the merging process facilitated by SNARE proteins?

V-SNARE and T-SNARE proteins locking together. Signup and view all the answers

Which of the following is a V-SNARE protein that binds with syntaxin and SNAP-25 to form the 'SNARE complex'?

Synaptobrevin Signup and view all the answers

In a chemical synapse, what directly causes the synaptic delay?

The diffusion time for neurotransmitters across the synaptic gap Signup and view all the answers

What is the direct consequence of the action potential reaching the presynaptic terminal?

Opening of voltage-gated $Ca^{+2}$ channels and $Ca^{+2}$ influx. Signup and view all the answers

Which of the following accurately describes the role of SNARE proteins in neurotransmitter release?

They mediate the fusion of synaptic vesicles with the presynaptic membrane. Signup and view all the answers

What is the immediate effect of acetylcholine (ACh) binding to nicotinic ACh receptors (nAChRs) on the postsynaptic cell?

Opening of a nonselective cation channel permeable to both $Na^+$ and $K^+$. Signup and view all the answers

What determines the quantity of acetylcholine released into the synaptic cleft?

The amount of $Ca^{+2}$ influx into the presynaptic terminal. Signup and view all the answers

How is the motor end plate potential classified?

Graded potential. Signup and view all the answers

What triggers the opening of voltage-gated $Na^+$ channels in the subneural parts of the postsynaptic membrane?

The accumulation of EPPs to reach the threshold potential. Signup and view all the answers

Which of the following neurotransmitters is primarily responsible for inhibitory neurotransmission in the CNS?

GABA. Signup and view all the answers

Which of the following plays an important role in learning and memory?

Glutamate Signup and view all the answers

Which of the following is the primary mechanism of action of botulinum toxin?

Preventing synaptic vesicles from releasing neurotransmitters from nerve endings to muscle cells. Signup and view all the answers

Which of the following SNAP-25 is destroyed by?

Botulinum toxin A-E Signup and view all the answers

A patient presents with severe muscle contractions and spastic paralysis. Which toxin is most likely responsible for these symptoms?

Tetanus toxin Signup and view all the answers

Why is honey not recommended for babies?

It may contain botulinum spores, which can produce toxins in the baby's digestive system. Signup and view all the answers

Which of the following proteins is destroyed by Botulinum toxin C?

Syntaxin Signup and view all the answers

What is the primary defect in Lambert-Eaton Syndrome (L-E Syndrome)?

Autoantibodies destroy voltage-gated $Ca^{2+}$ channels, reducing acetylcholine release. Signup and view all the answers

Which of the following best describes how tetanus toxin affects neuronal function?

It blocks the release of inhibitory neurotransmitters from interneurons, leading to overactivity of motor neurons. Signup and view all the answers

How does Curare cause muscle relaxation?

By blocking acetylcholine receptors on muscle cells Signup and view all the answers

What is the primary mechanism by which curare leads to muscle paralysis?

Preventing muscle contraction by blocking acetylcholine receptors. Signup and view all the answers

What is the effect of an IPSP on the postsynaptic neuron's membrane potential?

It causes hyperpolarization, making the membrane potential more negative. Signup and view all the answers

Which of the following neurotransmitters is most likely to produce an EPSP?

Glutamate Signup and view all the answers

If the total postsynaptic potential in a neuron is high in IPSP, how will this affect the neuron?

It will be inhibited, reducing the likelihood of an action potential. Signup and view all the answers

What is the term for the process where many presynaptic neurons send signals to one single postsynaptic neuron?

Convergence Signup and view all the answers

Which of the following describes the immediate effect of curare on acetylcholine levels in the synaptic cleft?

Increased levels due to prevention of binding to receptors Signup and view all the answers

Which of the following accurately describes the effect of opening potassium ($K^+$) and chloride ($Cl^−$) channels on the postsynaptic membrane?

Hyperpolarization and IPSP production Signup and view all the answers

Which of the following events is characteristic of EPSP?

Influx of sodium ($Na^+$) ions into the cell Signup and view all the answers

Study Notes

Nervous System Physiology Essentials 3

This chapter covers the essentials of nervous system physiology, focusing on synapses.

Synapses

A synapse is the connection between two neurons, muscle cells, or gland cells.
The presynaptic cell is positioned before the synapse, and the postsynaptic cell is after the synapse.
Synapses in the central nervous system (CNS) are connections between two neurons, while synapses in the peripheral nervous system (PNS) connect neurons to muscle or gland cells.
The synapse between a neuron and a muscle cell is called a neuromuscular junction.

Synapse Types

Synapses are categorized based on structure and function.
Structural features: Axodendritic, axosomatic, axoaxonic.
Functional features: Excitatory and inhibitory.
Electrical and chemical synapses are the major types.

Electrical Synapses

Establish a direct connection between neurons, letting ions flow freely.
Communication happens through gap junctions, which allow direct ion flow.
Very rapid transmission.
Found in smooth muscle and heart muscle.
Transmission is bidirectional.

Chemical Synapses

More prevalent compared to electrical synapses.
A gap called a synaptic cleft separates the presynaptic and postsynaptic cells.
Neurotransmitters are released from vesicles in the presynaptic terminal across the synaptic cleft.
Neurotransmitters bind to receptors on the postsynaptic cell, sending signal
Transmission is unidirectional, slower than electrical synapses.
This type involves a chemical messenger.

Neurotransmitters

Chemical messengers that transfer signals between nerve cells.
Stored in synaptic vesicles.
Released by exocytosis upon arrival of an action potential.
Bind to receptors on postsynaptic membrane.
Examples include glutamate, GABA, acetylcholine.

Important Neurotransmitters/Conditions affecting Neurotransmission

Glutamate is a major excitatory neurotransmitter in the CNS and has roles in learning and memory.
GABA is a major inhibitory neurotransmitter in the CNS and has a role in calming effects and preventing nerve cell overstimulation.
Acetylcholine is essential for muscle contractions and has roles in learning and memory.
Various diseases and conditions, such as Lambert-Eaton Syndrome, Botulism, Tetanus, Myasthenia Gravis and Curare, can affect synaptic transmission and neuromuscular junction.

V-SNARE and T-SNARE

These proteins (V-SNARE and T-SNARE) play pivotal roles in exocytosis.
V-SNAREs are located on vesicles, while T-SNAREs are on the target cell membranes.
Their interaction forms a SNARE complex, mediating vesicle fusion.

SNARE Proteins

Synaptotagmin, syntaxin, SNAP-25, and synaptobrevin are types of SNARE proteins.
SNARE proteins are needed for neurotransmitter release via regulated exocytosis.

Summation

Temporal summation: rapid arrival of successive signals from a single presynaptic neuron.
Spatial summation: simultaneous stimulation from multiple presynaptic neurons.
These types of summation are critical for the postsynaptic neuron responding appropriately.

Facilitation

The temporary increase in the excitability of a neuron due to repeated stimulation.

Convergence and Divergence

Information gathering at a single postsynaptic neuron from several presynaptic neurons (Convergence).
Signal dispersal from a presynaptic neuron to several postsynaptic neurons (Divergence).

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Test your knowledge of synapses with this comprehensive quiz. Explore key concepts including electrical and chemical synapses, the role of neurotransmitters, and the significance of calcium ions. Perfect for students studying neuroscience and nervous system functions.