Questions and Answers
Which mechanism allows for the reincorporation of catecholamines into presynaptic vesicles?
What type of synapse is formed between an axon and a dendrite?
Which neurotransmitter is broken down into acetate and choline in the synaptic cleft?
What is the distinction of an axoaxonic synapse?
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What treatment approach involves inhibiting the breakdown of norepinephrine?
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What component is not considered a morphotype of synapse?
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Which part of the neuromuscular junction consists of presynaptic vesicles containing acetylcholine?
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What process can occur to deactivated neurotransmitters besides recapture?
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Which structure in neurons is primarily responsible for signal conduction away from the cell body?
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What role do neurofilaments, microfilaments, and microtubules serve in neurons?
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Which of the following statements about the myelin sheath is correct?
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What is the significance of the axon hillock in neuronal function?
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Which neurons in the adult human body are known to regularly replace themselves?
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Which of the following is a characteristic feature of dendrites?
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What is the primary role of lysosomes within neurons?
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Which component of the neuron is involved in the formation of microtubules?
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What is the primary function of dendrites in nerve cells?
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Which characteristic does NOT describe dendrites compared to axons?
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What shape do dendritic spines typically resemble?
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What type of neurons are classified as pseudounipolar neurons primarily responsible for?
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Which component of the dendrites is responsible for the majority of postsynaptic receptors?
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In terms of cytoplasmic composition, which feature is characteristic of dendrites?
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Which structural feature differentiates dendrites from axons?
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What is the main implication of having up to 200,000 synapses in a single dendritic tree?
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What is the main effect of inhibitory synapses on the postsynaptic membrane potential?
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Which component of the synapse is responsible for releasing neurotransmitters into the synaptic cleft?
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How do neurotransmitters primarily influence the postsynaptic cell?
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What initiates the fusion of synaptic vesicles with the presynaptic membrane?
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Where are inhibitory synapses primarily located within a neuron?
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What happens to excess plasma membrane after the fusion of synaptic vesicles?
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What is the approximate width of the synaptic cleft?
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Which of the following describes the primary classification of neurotransmitters?
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Which support cell in the peripheral nervous system is responsible for the formation of myelin around nerve fibers?
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What type of synapse is characterized by communication directly between two neurons through gap junctions?
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Which type of glial cell in the central nervous system is primarily involved in the response to injury and repair?
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Which type of axonal transport involves transporting materials away from the cell body?
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What is the primary function of the synaptic cleft in a chemical synapse?
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Which type of neuron includes both sensory and motor neurons that are involved in reflex actions?
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Among the support cells of the peripheral nervous system, which cell type is responsible for providing structural support to neuronal cell bodies?
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Which type of synapse is responsible for the modulation of synaptic transmission and can either enhance or inhibit neuronal signals?
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Study Notes
Neurotransmitter Deactivation
- Released neurotransmitters are deactivated mainly through recapture and degradation.
- High-affinity reuptake allows up to 80% of catecholamines (e.g., dopamine, norepinephrine) to be recaptured into vesicles via endocytosis.
- Enzymes on the synaptic membrane break down remaining neurotransmitters; for instance, acetylcholine is converted into acetate and choline.
- Inhibiting norepinephrine breakdown or high-affinity reuptake is beneficial for depression treatment.
Morphotypes of Synapses
- Axodendritic synapses connect axons to dendrites.
- Axosomatic synapses link axons to neuron bodies (perikaryon).
- Axoaxonic synapses connect one axon to another axon.
- Motor end-plates are specialized synapses at neuromuscular junctions, containing presynaptic vesicles with acetylcholine.
- Type II inhibitory synapses hyperpolarize postsynaptic cells, reducing action potential likelihood.
Chemical Synapses
- Presynaptic knobs contain synaptic vesicles (40-60 nm), rich in neurotransmitters.
- Over 100 known neurotransmitters can induce depolarization or hyperpolarization, acting as either excitatory or inhibitory.
- The synaptic cleft is a narrow (~20 nm) gap between presynaptic and postsynaptic membranes.
- Action potential triggers calcium channel opening, facilitating neurotransmitter release into the synapse.
- Endocytosis removes excess plasma membrane after neurotransmitter release.
Dendrites
- Dendrites are numerous, short, tapered processes designed to convey signals toward the perikaryon.
- Dendritic trees can have up to 200,000 synapses, maximizing synaptic contact area.
- Dendritic spines, shaped like mushrooms, host most postsynaptic receptors.
- Dendrites lack myelin and contain ribosomes and rough endoplasmic reticulum but no Golgi apparatus.
Major Types of Neurons
- Neurons can be classified as pseudounipolar, bipolar, or multipolar based on shape and process number.
- Pseudounipolar neurons are primarily sensory, with one large process branching into peripheral and central processes that transmit sensory information to the central nervous system.
Axonal Transport
- Axonal transport occurs in two directions: anterograde (moving materials away from the cell body) and retrograde (moving materials toward the cell body).
- Anterograde transport includes both fast and slow transport mechanisms.
Neuron Structure
- Neurons feature distinct structures: one axon per cell, dendritic processes, and axon terminals.
- Axons vary in length (up to 1 meter), maintain a constant diameter, and lack Nissl bodies at the axon hillock.
- Myelinated axons enhance signal transmission speed, while myelin sheath formation abnormalities can lead to disorders.
Cytoskeleton of Neurons
- Neuronal cytoskeleton is well-developed, consisting of neurofilaments, microfilaments, and microtubules.
- Neurons generally lack centrioles, preventing cellular division, with limited neuroblast replacement in adults, notably in olfactory neurons.
Support Cells in Nervous System
- Peripheral nervous system support cells include Schwann cells (involved in myelination) and satellite cells.
- Central nervous system support cells encompass astrocytes (with multiple types), oligodendrocytes, microglial cells, and ependymal cells, each with distinct functions and clinical relevance.
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Description
Test your knowledge on the mechanisms of neurotransmitter deactivation, focusing on recapture and degradation. This quiz covers important neurotransmitters like catecholamines, including dopamine and norepinephrine, and their reuptake processes.
