NEUR3002 SAQs Flashcards
Explain synapse formation
Synapse formation is the intricate process through which neurons establish specialized connections for communication. During development, axons extend toward their target cells, guided by molecular cues. Upon reaching their targets, presynaptic terminals form at axon endings. These terminals contain synaptic vesicles filled with neurotransmitters. On the postsynaptic side, specialized regions called dendritic spines or postsynaptic densities develop to receive signals.
The synapse is a nanoscale structure where neurotransmitters are released from the presynaptic terminal into the synaptic cleft. These neurotransmitters bind to receptors on the postsynaptic membrane, causing ion channels to open or close. This generates postsynaptic potentials, transmitting information between neurons. Synapse formation is crucial for neural circuitry, learning, and memory.
explain chemical synapses
Chemical Synapses:
Chemical synapses involve the release of neurotransmitter molecules from the presynaptic neuron’s axon terminal into the synaptic cleft. These neurotransmitters bind to receptors on the postsynaptic neuron’s membrane, leading to changes in membrane potential and generating postsynaptic potentials. This process enables the transfer of information between neurons with a brief time delay. Chemical synapses are unidirectional and allow for complex signal integration and modulation.
explain electrical synapses
Electrical synapses, also called gap junctions, involve direct physical connections between the cytoplasm of adjacent neurons. Connexin proteins form gap junctions, creating channels that permit the flow of ions and small molecules. This allows for rapid and bidirectional communication between cells. Electrical synapses are less common than chemical synapses and are often found in specific brain regions requiring rapid synchronization, such as the cardiac conduction system.
explain chemical vs electrical synapses
In summary, chemical synapses involve the release and binding of neurotransmitters to transmit signals with synaptic delay, while electrical synapses provide rapid and direct communication through gap junctions. Each synapse type has distinct properties suited to different functional requirements in neural circuits.
explain pathways controlling axon pathfinding
Guidance Cues: Axons follow gradients of guidance cues, such as netrins, semaphorins, and ephrins. These cues are expressed in specific patterns along the pathway and at target areas.
Receptors: Axonal growth cones possess receptors that detect guidance cues. These include netrin receptors (DCC, UNC5), semaphorin receptors (neuropilins, plexins), and ephrin receptors (Eph kinases).
Attractive and Repulsive Signals: Guidance cues can be attractive or repulsive. Attractive cues attract axons toward their target, while repulsive cues steer axons away from inappropriate paths.
Cytoskeletal Dynamics: Signaling from guidance cues influences the cytoskeleton of axonal growth cones, altering actin and microtubule dynamics. This affects growth cone motility and axon extension.
Synaptic Specificity: Axons are guided to specific synaptic targets by recognition molecules, ensuring precise connections in neural circuits.
In essence, axon pathfinding involves a dynamic interplay between guidance cues, their receptors, and cytoskeletal changes, leading to the intricate wiring of the nervous system.
explain axon pathfinding and the growth cone
Axon pathfinding involves the growth cone, a dynamic structure at the tip of extending axons during development.
Growth Cone Function: The growth cone is responsible for sensing its environment and guiding the axon’s direction. It integrates information from guidance cues, allowing the axon to navigate toward its target.
Molecular Sensing: Growth cones possess receptors that detect attractive and repulsive guidance cues. These cues are expressed along the pathway and at target areas.
Cytoskeletal Dynamics: Guidance cues trigger changes in the growth cone’s cytoskeleton, specifically actin and microtubules. Actin-driven protrusions enable exploratory movement, while microtubules extend axon length.
Turning Responses: Attractive cues enhance growth cone movement toward the target, while repulsive cues induce turning or retraction, redirecting axon trajectory.
Synaptic Formation: Once the growth cone reaches its target, it transforms into a presynaptic terminal, establishing functional connections.
In summary, the growth cone is a specialized structure that directs axon pathfinding. It responds to molecular cues, orchestrates cytoskeletal changes, and guides axons to their precise targets, crucial for establishing neural circuits.
explain bipolar neurons
Bipolar neurons have two distinct processes extending from their cell body—an axon and a dendrite. They are commonly found in specialized sensory organs like the retina of the eye and the olfactory epithelium.
Explain unipolar neurons
Unipolar neurons have a single process extending from their cell body, which then branches into two distinct processes. One branch functions as an axon and the other as a dendrite-like structure. Unipolar neurons are often sensory neurons transmitting information from sensory receptors to the CNS.
Explain multipolar neurons
Multipolar neurons have multiple processes extending from their cell body—typically one axon and multiple dendrites. These neurons are the most common type and are found in the central nervous system (CNS) as interneurons and motor neurons.
explain Neuronal morphology
Neuronal morphology refers to the diverse shapes and structures of nerve cells (neurons) that allow them to perform their specialized functions in the nervous system.
explain electron microscopy for mapping neurological connections
Electron microscopy is a powerful technique used to visualize the ultrastructural details of neural connections at the nanoscale level. In the context of mapping neurological connections, electron microscopy allows researchers to observe the intricate morphology of synapses, dendrites, and axons, providing insights into the precise organization of neural circuits. This method involves fixing, embedding, and sectioning neural tissue, followed by staining and imaging using electron microscopes. The high resolution of electron microscopy enables the identification of synaptic vesicles, receptor densities, and other subcellular components, facilitating the detailed analysis of neural connectivity within the brain.
explain fluorescent dye labelling (Dil, DiO, LY, biocytin) for mapping neurological connections
Fluorescent dye labeling is a technique used to trace and visualize neural connections in biological tissues. Different dyes, such as Dil, DiO, LY, and biocytin, are employed for this purpose.
Process: Neurons are filled with or exposed to the fluorescent dye, which becomes incorporated into their membranes or cytoplasm. The dye emits fluorescence when exposed to specific wavelengths of light.
Labeling Specificity: Different dyes target different components. For example, Dil and DiO integrate into cell membranes, allowing visualization of axons and dendrites. LY (Lucifer Yellow) is often used for tracing dye-coupled neurons in intact tissue. Biocytin is used for whole-cell patch-clamp recording, revealing detailed morphologies of neurons.
Imaging: Fluorescently labeled neurons are imaged using fluorescence microscopy. Exciting the dye with specific wavelengths of light causes it to fluoresce, revealing the shape, trajectory, and connections of labeled neurons.
Applications: Fluorescent dye labeling helps researchers map neural circuits, identify connections, and understand the spatial organization of neurons within tissues.
In summary, fluorescent dye labeling involves incorporating dyes into neurons to visualize their structures and connections using fluorescence microscopy. Different dyes serve specific purposes in mapping neurological connections.
explain antibody labelling for mapping neurological connections
Antibody labeling is a technique that utilizes specific antibodies to target and visualize proteins or antigens within neural tissues, aiding in the mapping of neurological connections.
Process: Specific antibodies are designed to bind to particular proteins or antigens present in neurons or their components. These antibodies are often conjugated with fluorescent or other detectable markers.
Labeling Specificity: By targeting specific proteins, antibody labeling reveals the distribution and localization of these molecules within neurons, axons, dendrites, and synapses.
Imaging: After applying the labeled antibodies to tissue sections or cultured neurons, fluorescence microscopy or other imaging methods are used to visualize the labeled structures.
Applications: Antibody labeling helps researchers identify neural populations, study synaptic proteins, and map connections within brain regions.
In summary, antibody labeling involves using antibodies that specifically bind to proteins or antigens within neural tissues to visualize their distribution and connections, contributing to the understanding of neural circuitry.
explain genetically encoded labelling for mapping neurological connections
Genetically encoded labeling involves introducing genes that produce fluorescent or other markers into neurons, allowing visualization of neural connections in a targeted manner.
Process: Genes coding for fluorescent proteins (e.g., GFP) or other markers are introduced into neurons using viral vectors or transgenic techniques.
Labeling Specificity: Neurons expressing the introduced genes will produce the marker proteins, enabling visualization of their morphology and connections.
Imaging: Fluorescence microscopy or other imaging methods are used to visualize the labeled neurons and their connections.
Applications: Genetically encoded labeling provides precise control over which neurons are labeled, making it useful for tracing specific neural circuits and understanding connectivity patterns.
In summary, genetically encoded labeling involves introducing genes that produce markers into neurons, enabling visualization of their connections and aiding in the study of neural circuits.
explain trans-synaptic labelling for mapping neurological connections
Trans-synaptic labeling is a technique used to trace neural connections by exploiting the transfer of a labeled molecule from one neuron to another through synapses.
Process: A modified virus is used to deliver a genetically encoded marker, such as a fluorescent protein, into a specific target neuron. This marker is then transferred to connected neurons through synapses.
Labeling Specificity: As the marker spreads from the initially labeled neuron to its connected partners, it highlights the interconnected neural circuit.
Imaging: Fluorescence microscopy or other imaging methods are employed to visualize the labeled neurons and their connections.
Applications: Trans-synaptic labeling allows researchers to map neural circuits and identify connected regions within the brain.
In summary, trans-synaptic labeling involves the use of viral vectors to introduce markers into neurons, which are then transmitted through synapses to label connected neurons, aiding in the mapping of neural connections.
