Neurology: Synapse and Chemical Synapse

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is a synapse?

A synapse is the region where a presynaptic neuron connects and transmits signals to a postsynaptic neuron.

What term is used to describe the connection between a neuron and a muscle?

The connection between a neuron and a muscle is called a neuromuscular junction.

What are the two main types of synapses?

The two main types of synapses are chemical and electrical synapses.

What is synaptic delay?

Synaptic delay is the minimum time for transmission across a synapse, typically around 0.5 ms. Signup and view all the answers

What are the three components of a synapse?

The three components of a synapse are the presynaptic terminal, synaptic cleft, and postsynaptic density. Signup and view all the answers

What are the types of synaptic vesicles and their contents?

Small, clear vesicles contain acetylcholine, glycine, GABA, or glutamate; small dense-core vesicles contain catecholamines; and large dense-core vesicles contain neuropeptides. Signup and view all the answers

How are synaptic vesicles transported within a neuron?

Synaptic vesicles are transported down the axon to nerve endings via fast axoplasmic transport. Signup and view all the answers

What process allows vesicles to release neurotransmitters?

Vesicles release neurotransmitters through a process called exocytosis. Signup and view all the answers

What is the kiss-and-run discharge process?

It is a method where vesicles release their contents through a small opening and quickly reseal. Signup and view all the answers

What role do voltage-gated Ca2+ channels play in neurotransmitter release?

They allow Ca2+ to enter the presynaptic neuron, triggering exocytosis of neurotransmitters. Signup and view all the answers

How do neurexins contribute to synaptic organization?

Neurexins are presynaptic cell-adhesion molecules that bind to neuroligins, helping to hold synapses together. Signup and view all the answers

What effect do neurotoxins from Clostridium tetani and Clostridium botulinum have on neurotransmitter release?

They block neurotransmitter release by inactivating proteins in the fusion-exocytosis complex. Signup and view all the answers

What occurs when Cl− ions enter a neuron?

The neuron undergoes hyperpolarization, making it less likely to fire an action potential. Signup and view all the answers

What characterizes slow EPSPs and IPSPs?

They have a delay of 100–500 ms and can last several seconds. Signup and view all the answers

What is the primary feature of electrical synapses?

They allow ions to pass freely between neurons through gap junctions. Signup and view all the answers

How do fast excitatory postsynaptic potentials (EPSPs) affect neuron excitability?

They cause brief depolarization, making the neuron more excitable. Signup and view all the answers

What is the primary effect of presynaptic inhibition on neurotransmitter release?

It decreases the amount of neurotransmitter released. Signup and view all the answers

Which neurotransmitter was first identified to cause presynaptic inhibition?

GABA. Signup and view all the answers

What role does Ca2+ play in presynaptic facilitation?

It increases neurotransmitter release by keeping Ca2+ channels open longer. Signup and view all the answers

What is the neuromuscular junction?

It is the connection point where a motor nerve meets a skeletal muscle fiber. Signup and view all the answers

What happens when acetylcholine binds to nicotinic receptors on the motor endplate?

It increases the flow of Na+ and K+ across the membrane. Signup and view all the answers

How does presynaptic inhibition affect K+ channels?

It opens K+ channels, allowing K+ to exit the neuron. Signup and view all the answers

What initiates the release of acetylcholine from synaptic vesicles?

An increase in permeability to Ca2+ upon receiving a nerve impulse. Signup and view all the answers

What is the role of baclofen in relation to presynaptic inhibition?

Baclofen is a GABAB agonist that treats spasticity. Signup and view all the answers

Study Notes

Synapse

Synapse: The point of connection between neurons, transmitting signals from one neuron to another.
Neuroeffector Junction: A specialized synapse where a neuron communicates with an effector organ (muscle or gland).
Neuromuscular Junction: A specialized type of neuroeffector junction where a neuron connects to a muscle fiber.
Synaptic Transmission: The process of signal transmission across a synapse.
Synaptic Delay: The minimum time required for synaptic transmission, typically 0.5 ms, attributed to neurotransmitter release and action on the postsynaptic neuron.

Chemical Synapse

Presynaptic Terminal: The terminal end of the neuron that releases neurotransmitters.
Synaptic Cleft: The space separating the presynaptic and postsynaptic membranes, about 20-40nm wide.
Postsynaptic Density: An organized structure on the postsynaptic neuron containing receptors, binding proteins, and enzymes for receiving and processing neurotransmitters.
Neurotransmitters: Chemical messengers stored in synaptic vesicles, released into the synaptic cleft to transmit signals.
Types of Synaptic Vesicles:
- Small, clear synaptic vesicles: Contain acetylcholine, glycine, GABA, or glutamate.
- Small dense-core vesicles: Contain catecholamines.
- Large dense-core vesicles: Contain neuropeptides.
Exocytosis: The process of releasing neurotransmitters from vesicles into the synaptic cleft by fusing with the cell membrane.
Endocytosis: The process of recycling synaptic vesicles after release, refilling them with neurotransmitters.
Kiss-and-Run Discharge: A mechanism where vesicles release contents through a small opening and quickly reseal, without full fusion with the membrane.
Voltage-gated Ca2+ Channels: Located near the release sites, opening upon depolarization, allowing Ca2+ influx and triggering exocytosis.
Neurexins: Presynaptic cell-adhesion molecules that bind to neuroligins on the postsynaptic membrane.
Neuroligins: Postsynaptic cell-adhesion molecules that bind to neurexins on the presynaptic membrane.
Neurexin-Neuroligin Interaction: Helps maintain synapse structure and ensure precise communication between neurons.

Electrical Synapse

Gap Junctions: Low-resistance pathways formed between presynaptic and postsynaptic neurons, allowing direct ion flow.
Fast Transmission: Enables faster communication between neurons compared to chemical synapses due to direct ion flow.

Presynaptic Regulation

Presynaptic Inhibition: Decreases neurotransmitter release by reducing action potential strength at the presynaptic terminal.
Presynaptic Facilitation: Increases neurotransmitter release by prolonging the action potential at the presynaptic terminal.
Axoaxonal Synapse: A synapse where one neuron connects to the axon of another neuron, involved in presynaptic inhibition.
GABAA Receptor: Activation increases Cl− conductance, contributing to presynaptic inhibition.
GABAB Receptor: Activation increases K+ conductance, also involving presynaptic inhibition.

Neuromuscular Junction

Terminal Boutons: Branching endings of the motor neuron, containing acetylcholine-filled synaptic vesicles.
Motor Endplate: A specialized region of the muscle fiber membrane, receiving signals from the motor neuron.
Sequence of Events at the Neuromuscular Junction:
1. Depolarization of the motor nerve ending.
2. Ca2+ influx into the nerve terminal.
3. Acetylcholine release from synaptic vesicles via exocytosis.
4. Acetylcholine binding to nicotinic receptors on the motor endplate.
5. Na+ influx into the muscle fiber, causing depolarization.
6. Triggering of muscle contraction.

Additional Information

Deadly Toxins: Zinc endopeptidases can block neurotransmitter release by inactivating proteins in the fusion-exocytosis complex.
Clostridium Tetani and Clostridium Botulinum: Bacteria producing toxins that disrupt neurotransmitter release, causing tetanus or botulism, respectively.
EPSP: Excitatory postsynaptic potential, a brief depolarization, making the neuron more excitable.
IPSP: Inhibitory postsynaptic potential, a brief hyperpolarization, making the neuron less excitable.
Slow EPSPs and IPSPs: Occur in autonomic ganglia, cardiac and smooth muscle, and cortical neurons, with longer durations and distinct mechanisms involving K+ channels.
Spasticity: Increased muscle tone and stiffness, potentially treated with baclofen, a GABAB agonist.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

This quiz explores the fundamental concepts of synapses in the nervous system, covering key terms like synaptic transmission, neuroeffector junctions, and the structure of chemical synapses. It aims to enhance your understanding of how neurons communicate and the specifics of synaptic connections.