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Questions and Answers
Which of the following contributed to the understanding of chemical transmission?
Which of the following contributed to the understanding of chemical transmission?
- Du Bois-Raymond's electrical theory of neurotransmission
- Elliot's suggestion that adrenaline acts as a chemical transmitter in the sympathetic nervous system
- Langley's observation of nicotine and curare's effects at the neuromuscular junction
- All of the above (correct)
By 1869 it was known that muscarine could mimic the effects of stimulating the vagus nerve.
By 1869 it was known that muscarine could mimic the effects of stimulating the vagus nerve.
True (A)
What is the primary site of information transfer between cells?
What is the primary site of information transfer between cells?
Synapse
The concept of neurotransmission, as described by Du Bois-Raymond in 1877, proposed that excitation could be passed on either through a ______ secretion or through an electrical process.
The concept of neurotransmission, as described by Du Bois-Raymond in 1877, proposed that excitation could be passed on either through a ______ secretion or through an electrical process.
Which of the following is NOT a characteristic of electrical synapses?
Which of the following is NOT a characteristic of electrical synapses?
Match the following scientists with their contributions to understanding chemical transmission:
Match the following scientists with their contributions to understanding chemical transmission:
Which of the following is NOT a type of chemical synapse?
Which of the following is NOT a type of chemical synapse?
Electrical synapses are typically faster than chemical synapses.
Electrical synapses are typically faster than chemical synapses.
What is the name of the gap between the presynaptic and postsynaptic membranes in a chemical synapse?
What is the name of the gap between the presynaptic and postsynaptic membranes in a chemical synapse?
The process by which synaptic vesicles are recycled is called ______.
The process by which synaptic vesicles are recycled is called ______.
Match the following neurotransmitter recovery mechanisms with their descriptions:
Match the following neurotransmitter recovery mechanisms with their descriptions:
Which type of receptor is directly linked to ion channels?
Which type of receptor is directly linked to ion channels?
Metabotropic receptors always lead to excitatory postsynaptic potentials (EPSPs).
Metabotropic receptors always lead to excitatory postsynaptic potentials (EPSPs).
What key role does calcium play in neurotransmitter release?
What key role does calcium play in neurotransmitter release?
The enzyme ______ breaks down acetylcholine in the synaptic cleft.
The enzyme ______ breaks down acetylcholine in the synaptic cleft.
Synaptic delay primarily results from the time required for neurotransmitter synthesis.
Synaptic delay primarily results from the time required for neurotransmitter synthesis.
What is the primary function of clathrin in the recycling of synaptic vesicles?
What is the primary function of clathrin in the recycling of synaptic vesicles?
The ______ system involves intracellular signaling cascades that amplify and extend the effects of neurotransmitters.
The ______ system involves intracellular signaling cascades that amplify and extend the effects of neurotransmitters.
Which of the following neurotransmitters acts at both nicotinic and muscarinic receptors?
Which of the following neurotransmitters acts at both nicotinic and muscarinic receptors?
Muscarinic receptors are always coupled to G proteins that activate adenylate cyclase.
Muscarinic receptors are always coupled to G proteins that activate adenylate cyclase.
Flashcards
Chemical transmission
Chemical transmission
The process where signals are transmitted between neurons using chemical substances called neurotransmitters.
Electrical transmission
Electrical transmission
The method of signal transfer in which electrical impulses travel along neurons directly via ion movements.
Neurotransmitters
Neurotransmitters
Chemical substances that transmit signals across a synapse from one neuron to another.
Synapse
Synapse
A junction between two neurons where communication occurs, either electrically or chemically.
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Muscarine
Muscarine
A chemical that mimics the effects of vagus nerve stimulation, discovered in 1869.
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Adrenaline as a transmitter
Adrenaline as a transmitter
The idea proposed in 1904 that adrenaline acts as a chemical messenger for the sympathetic nervous system.
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Historical evidence of chemical signaling
Historical evidence of chemical signaling
Observations by early physiologists that provided insights into chemical neurotransmission, especially around the actions of nicotine and curare.
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Eliot's observation
Eliot's observation
The finding that degeneration of sympathetic nerve terminals increased muscle sensitivity to adrenaline.
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Electrical synapses
Electrical synapses
Connections allowing direct current flow between excitable cells via gap junctions.
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Chemical synapses
Chemical synapses
Spaces where neurotransmitters transmit signals between neurons through a synaptic cleft.
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Gap junctions
Gap junctions
Low resistance pathways allowing ionic current flow between adjacent cells.
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Connexons
Connexons
Channels formed by six connexins that make gap junctions.
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Synaptic cleft
Synaptic cleft
The gap between presynaptic and postsynaptic membranes in chemical synapses.
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Neurotransmitter release
Neurotransmitter release
Process where neurotransmitters are ejected into the synaptic cleft.
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Synaptic delay
Synaptic delay
Time taken for neurotransmitter release and receptor binding, typically 0.3-5.0 ms.
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Desensitization
Desensitization
When receptors close despite the presence of a neurotransmitter, often after prolonged exposure.
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Ionotropic receptors
Ionotropic receptors
Ligand-gated ion channels that open upon neurotransmitter binding, allowing ion flow.
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Metabotropic receptors
Metabotropic receptors
G-protein-coupled receptors triggering slower and more versatile responses in cells.
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Acetylcholine
Acetylcholine
A neurotransmitter involved in various functions in the PNS and CNS, and secretion from adrenal medulla.
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Muscarinic receptors
Muscarinic receptors
Five metabotropic ACh receptor types (M1-M5) with distinct effects based on their G proteins.
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Axo-dendritic synapse
Axo-dendritic synapse
A type of chemical synapse connecting an axon to a dendrite.
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Neurotransmitter recovery
Neurotransmitter recovery
Process of clearing neurotransmitters from the synaptic cleft for future transmission.
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Chemical Transmission in the Nervous System
- Chemical transmission is a fundamental process in the nervous system, crucial to how signals travel between cells.
- Key components of chemical transmission include synthesis, storage, and release of chemical transmitters, synaptic transmission, and signal termination.
- Early understanding of nervous function emerged from 19th-century experimental physiology, focusing on the peripheral and autonomic nervous systems. Observational studies showed that electrical nerve stimulation could trigger various physiological responses.
- Early studies showed that substances like muscarine and atropine could mimic or block the effects of vagus nerve stimulation.
- Du Bois-Reymond proposed two possible mechanisms for neurotransmission: either a stimulatory secretion at nerve endings (chemical) or an electrical phenomenon.
- In 1904, Elliott suggested adrenaline as a chemical transmitter for the sympathetic nervous system. Langley later demonstrated nicotine and curare's role at neuromuscular junctions, suggesting a chemical mediator from nerve terminals acting on muscle cells.
- Early interpretations of these findings often focused on nerve stimulation/inhibition rather than chemical transmission.
Synaptic Transmission
- Synapse: The specialized junction where information is transferred from one cell to another.
- Main categories:
- Electrical synapses: Current flows directly between cells through gap junctions.
- Gap junctions are formed by connexons, which are clusters of connexins that connect the membranes of two cells.
- Allows quick, bidirectional ion transfer facilitating communication
- Important in situations that require rapid signal integration
- Chemical synapses: Information transmission is mediated by neurotransmitters. They involve a synaptic cleft between the presynaptic and postsynaptic cells.
- Important in various parts of the nervous system.
- Chemical synapse types:
- Axodendritic (axon to dendrite)
- Axosomatic (axon to cell body)
- Axoaxonic (axon to axon)
- Dendrodendritic (dendrite to dendrite)
- Electrical synapses: Current flows directly between cells through gap junctions.
Principles of Chemical Synaptic Transmission
- Basic steps:
- Neurotransmitter synthesis
- Storage in synaptic vesicles
- Vesicle fusion with presynaptic membrane
- Neurotransmitter release into synaptic cleft
- Binding to postsynaptic receptors
- Postsynaptic response (biochemical/electrical)
- Neurotransmitter removal from the cleft
Retrograde Chemical Transmission
- In some cases, signals can travel from the postsynaptic cell back to the presynaptic neuron, modifying the latter's activity.
Neurotransmitter Synthesis & Storage
- Neurotransmitters are synthesized and stored in synaptic vesicles.
- Release occurs when an action potential reaches the nerve terminal:
- Vesicles fuse with plasma membranes.
- Influx of Calcium ions triggers neurotransmitter release.
- Exocytosis is incredibly rapid.
- Synaptic vesicles are recycled through endocytosis and refilling process.
- Key proteins like Clathrin are involved in vesicle recycling.
Neurotransmitter Recovery and Degradation
- Neurotransmitter removal is essential for subsequent synaptic transmission.
- Uptake into presynaptic terminals: Neurotransmitters re-enter via transporter proteins.
- Enzymatic degradation: Some neurotransmitters are broken down by enzymes in the synaptic cleft. Acetylcholine (ACh) is broken down by acetylcholinesterase (AchE).
Synaptic Delay
- Delay (0.3-5ms): Time required for neurotransmitter release, diffusion, and receptor binding.
- Rate-limiting step in neural transmission.
Synaptic Receptors
- Ionotropic receptors: Ligand-gated ion channels (e.g. ACh receptors) opening channels directly.
- Metabotropic receptors: G-protein coupled receptors, triggering slower, longer-lasting actions inside the cell.
Neurotransmitter Receptor Mechanisms
- Second messenger systems: Pathways activated by metabotropic receptors. Different neurotransmitters have different effects depending on receptor subtypes.
Specific Neurotransmitters
-
Acetylcholine(ACh): Plays vital roles in both the parasympathetic and sympathetic nervous systems. Found in various locations.
- Nicotinic ACh receptors: Ionotropic, mediate fast excitatory effects.
- Muscarinic ACh receptors: Metabotropic, mediate diverse effects, classified into 5 subtypes (M1 to M5). Each subtype has slightly different functions, influences diverse cellular processes.
-
Glutamate: Major excitatory neurotransmitter in the central nervous system.
- Several ionotropic receptor subtypes: AMPA, Kainate, NMDA, with variations in properties.
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