Neuroscience: Synapses and Neurotransmission

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Questions and Answers

What type of synapse is formed between a neuron and a muscle cell?

Axodendritic synapse

Electrical synapse

Neuromuscular junction (correct)

Chemical synapse

Which type of synapse allows for the fastest transmission of signals?

Axosomatic synapse

Chemical synapse

Axoaxonic synapse

Electrical synapse (correct)

What is the primary function of neurotransmitters at chemical synapses?

To create gap junctions

To bind with receptors on the postsynaptic neuron (correct)

To maintain ion balance

To trigger an action potential

What type of junction is primarily responsible for forming electrical synapses?

Gap junctions (A) Signup and view all the answers

The distance between cells in an electrical synapse is typically how many nanometers?

2-4 nm (B) Signup and view all the answers

Which type of synapse involves a synaptic cleft that ranges from 20-40 nanometers?

Chemical synapse (A) Signup and view all the answers

Which of the following describes the role of calcium ions in chemical synapses?

They induce neurotransmitter release from vesicles. (A) Signup and view all the answers

What is the area of the postsynaptic structure referred to as in a neuromuscular junction?

Motor end plate (D) Signup and view all the answers

What is the primary effect of botulinum toxin on muscle contraction?

Blocks the release of acetylcholine (A) Signup and view all the answers

Which SNARE protein is specifically destroyed by Botulinum toxin A?

SNAP-25 (A) Signup and view all the answers

Which of the following is a clinical use of botulinum toxin?

Reduction of muscle spasms (B) Signup and view all the answers

What is a common source of botulinum toxin infection?

Homemade canned foods (C) Signup and view all the answers

What role does acetylcholine play in the central nervous system?

Involved in learning and memory (B) Signup and view all the answers

What condition is characterized by autoantibodies destroying voltage-gated Ca2+ channels?

Lambert-Eaton syndrome (C) Signup and view all the answers

What is one major difference between electrical and chemical synapses?

Chemical synapses use neurotransmitters (B) Signup and view all the answers

What is the mechanism of action of tetanus toxin?

Destroys synaptobrevin in inhibitory interneurons (A) Signup and view all the answers

How does myasthenia gravis lead to muscle weakness?

Autoantibodies against nicotinic acetylcholine receptors (B) Signup and view all the answers

Which protein is classified as a V-SNARE?

Synaptobrevin (C) Signup and view all the answers

How do V-SNARE and T-SNARE proteins contribute to neurotransmitter release?

They merge vesicles with target membranes (D) Signup and view all the answers

What compound is derived from tropical plants and has muscle relaxant properties?

Curare (D) Signup and view all the answers

Which condition is known to affect neuromuscular junction function?

Myasthenia Gravis (B) Signup and view all the answers

What is the mechanism of action of botulinum toxin?

Inhibits neurotransmitter release (D) Signup and view all the answers

What characterizes the transmission speed of electrical synapses compared to chemical synapses?

Electrical synapses are faster (A) Signup and view all the answers

What effect does synaptotagmin have in the SNARE complex?

It binds to Ca2+ and facilitates SNARE assembly (A) Signup and view all the answers

What initiates the opening of voltage-gated Ca+2 channels in the presynaptic neuron?

Depolarization of the presynaptic neuron (A) Signup and view all the answers

What causes neurotransmitter release into the synaptic cleft?

Vesicle fusion with the presynaptic membrane (A) Signup and view all the answers

Which neurotransmitter is primarily responsible for excitatory signaling in the CNS?

Glutamate (B) Signup and view all the answers

How does the binding of Ach to nAcHR affect ion flow in the postsynaptic cell?

Both Na+ enters and K+ exits the cell (B) Signup and view all the answers

What is the nature of the motor end plate potential formed when Ach binds to nAcHR?

Graded potential (D) Signup and view all the answers

What effect does an accumulation of excitatory postsynaptic potentials (EPP) have on the neuronal membrane?

It raises the resting potential to threshold (A) Signup and view all the answers

Which of the following channels opens as a result of reaching the threshold potential in the subneural parts of the membrane?

Voltage-gated Na+ channels (C) Signup and view all the answers

What role does GABA play in the central nervous system?

Inhibits neuronal excitability (D) Signup and view all the answers

What effect does curare have at the neuromuscular junction?

It prevents muscle contraction by blocking acetylcholine receptors. (C) Signup and view all the answers

What is the role of excitatory neurotransmitters in the generation of EPSP?

They make the postsynaptic membrane potential more positive. (A) Signup and view all the answers

What happens to acetylcholine due to the action of curare?

Acetylcholine accumulates in the synaptic cleft. (A) Signup and view all the answers

Which neurotransmitter is primarily associated with generating IPSP?

GABA (D) Signup and view all the answers

What is required for a postsynaptic neuron to reach the action potential threshold?

The sum of EPSP must exceed IPSP. (A) Signup and view all the answers

Which process involves multiple presynaptic neurons sending signals to a single postsynaptic neuron?

Convergence (D) Signup and view all the answers

What immediate result occurs when Na channels open in a postsynaptic neuron?

Depolarization of the membrane potential. (D) Signup and view all the answers

What happens to the postsynaptic neuron when the total of IPSP exceeds EPSP?

The neuron is inhibited and less likely to fire an action potential. (D) Signup and view all the answers

Study Notes

Nervous System Physiology Essentials 3

This chapter covers the fundamentals of synapses, specifically neuromuscular junctions, and different synapse types, including electrical and chemical synapses, along with various neurotransmitters.

Synapse

A synapse is the connection between two neurons, a neuron and a muscle cell, or a neuron and a gland cell.
In the CNS, both cells involved in a synapse are neurons.
In the PNS, either a neuron, muscle, or gland cell can be the second cell.
The synapse between a neuron and a muscle cell is called a neuromuscular junction (NMJ).

Presynaptic and Postsynaptic Cells

The cell before the synapse is the presynaptic cell.
The cell behind the synapse is the postsynaptic cell.

Muscle Neuromuscular Junction

The presynaptic cell is the neuron.
The postsynaptic cell is the muscle cell.

Synapse Types (Structural)

Axodendritic: Neuron to dendrite
Axosomatic: Neuron to cell body
Axoaxonic: Neuron to axon

Synapse Types (Functional)

Excitatory: Stimulate the postsynaptic cell.
Inhibitory: Suppress the postsynaptic cell.

Electrical Synapse

Direct connection between neurons.
Ions flow freely through gap junctions between cells.
Transmission is very fast and bidirectional.
No synaptic delay.
Found in smooth muscle and heart muscle.
Gap junctions are relatively close (2-4 nm).

Chemical Synapse

Indirect connection between neurons.
Neurotransmitters are released from the presynaptic neuron to transmit signals across a synaptic cleft.
Transmission is unidirectional (one way).
Synaptic delay exists (time it takes for neurotransmitter release and receptor binding).
Found in most synapses in the nervous system.
Synaptic cleft is wider, 20-40 nm apart.

Neurotransmitters

Chemical messengers that transmit signals between neurons.
Stored in synaptic vesicles in the presynaptic neuron.
Released via exocytosis when an action potential reaches the axon terminal of the presynaptic neuron.
Bind to receptors on the postsynaptic cell, initiating a response.
Examples: Glutamate, GABA, Acetylcholine.

Neurotransmitters and Their Functions in CNS

Glutamate: Excitatory, crucial for learning and memory.
GABA: Inhibitory, plays a role in reducing anxiety.
Acetylcholine: Excitatory, important for muscle contractions, learning, and memory.

Conditions Affecting the Neuromuscular Junction

Lambert-Eaton Syndrome: Autoimmune disease affecting voltage-gated Ca2+ channels, reducing acetylcholine release.
Botulism: Blocks the release of acetylcholine, leading to muscle paralysis.
Tetanus: Blocks the release of inhibitory neurotransmitters causing overactivity of motor neurons, leading to muscle contraction.
Myasthenia Gravis: Autoantibodies attack acetylcholine receptors at the neuromuscular junction decreasing its function.
Curare: Competes with acetylcholine for receptor sites, blocking muscle stimulation.

Botulinum toxin (Botox)

Released by Clostridium botulinum.
Blocks the release of acetylcholine.
Used to treat wrinkles, muscle spasms, and other conditions.

Common Ways to Get Botulism Toxin Infection

Poorly preserved/sterilized/sealed homemade canned foods.
Commercial foods.
Honey (for infants as they lack bacteria in stomach for proper digestion)

Tetanus

Caused by Clostridium tetani.
Destroys synaptobrevin in inhibitory interneurons.
Blocks release of inhibitory neurotransmitters.
Leads to muscle contraction and spastic paralysis.

Lambert-Eaton Syndrome (LES)

Autoimmune disease attacking voltage-gated Ca2+ channels in the presynaptic terminal.
Less ACh release by presynaptic neuron.
Leads to muscle weakness.

Myasthenia Gravis (MG)

Autoimmune disease attacking ACh receptors.
Less ACh reception.
Causes muscle weakness.

Curare

Plant-derived compound that blocks acetylcholine receptors.
Causes muscle weakness/paralysis.

Postsynaptic Potentials

EPSP (Excitatory Postsynaptic Potential): Makes it more likely that the postsynaptic neuron will fire. Increases membrane potential.
IPSP (Inhibitory Postsynaptic Potential): Makes it less likely that the postsynaptic neuron will fire. Decreases membrane potential.

Summation

Temporal Summation: Successive rapid stimuli from one presynaptic neuron.
Spatial Summation: Simultaneous stimulation from multiple presynaptic neurons.

Convergence and Divergence

Convergence: Multiple presynaptic neurons converging onto a single postsynaptic neuron (information from multiple sources collected in one place).
Divergence: Information from one neuron diverging to multiple postsynaptic neurons (information from one source going to several).
Facilitation: Temporary increase in the neuron's excitability from repeated stimulation/activation.

###V-SNARE and T-SNARE

Proteins that are essential for neurotransmitter release from synaptic vesicles into the synaptic cleft. Essential for V-SNARE proteins and T-SNARE proteins to properly fuse.

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Description

Test your knowledge on types of synapses, neurotransmitters, and their functions at chemical and electrical synapses. This quiz covers various aspects including the role of calcium ions, botulinum toxin effects, and the neuromuscular junction. Enhance your understanding of synaptic mechanisms and their implications in neuroscience.