Neurons: Structure and Function Quiz

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Questions and Answers

What structural components form the protofilaments of microtubules?

Alpha and beta tubulin heterodimers form the protofilaments of microtubules.

How do microfilaments contribute to synaptic plasticity in neurons?

Microfilaments allow for changes in neuronal shape and motility, which is crucial for synaptic plasticity.

Why are neurofilaments considered the 'bones' of the cytoskeleton?

Neurofilaments are referred to as the 'bones' of the cytoskeleton because they are strong and stable, providing structural support.

Describe the role of capping proteins in microtubule dynamics.

Capping proteins bind to one end of microtubules, preventing growth and allowing the other end to add or remove proteins. Signup and view all the answers

What is the diameter of microfilaments, and how do they form?

Microfilaments have an approximate diameter of 5 nm and are formed by the polymerization of G-actin monomers into F-actin. Signup and view all the answers

What components make up the ultrastructure of a neuron?

The ultrastructure of a neuron consists of the soma, dendrites, and axon. Signup and view all the answers

Describe the role of the nucleus in a neuron's soma.

The nucleus is responsible for protein synthesis within the neuron. Signup and view all the answers

What are Nissl bodies and where are they found?

Nissl bodies are clusters of rough endoplasmic reticulum and ribosomes found in the soma of neurons. Signup and view all the answers

What is the main function of mitochondria in neurons?

Mitochondria generate ATP, which is crucial for maintaining the sodium-potassium pump and overall neuron function. Signup and view all the answers

Explain the significance of the neuron doctrine.

The neuron doctrine states that neurons are discrete cells that are the basic structural and functional units of the nervous system. Signup and view all the answers

Identify the three components of the neuronal cytoskeleton.

The neuronal cytoskeleton comprises microtubules, microfilaments, and neurofilaments. Signup and view all the answers

What is the function of lipofuscin bodies in neurons?

Lipofuscin bodies contain lysosomal waste and increase with age, indicating cellular wear and tear. Signup and view all the answers

How do microtubules contribute to the structure of neurons?

Microtubules provide support and shape to neurons, allowing for intracellular transport. Signup and view all the answers

What role do synapses play in neuronal communication?

Synapses facilitate the transfer of information between neurons through electrochemical signaling. Signup and view all the answers

Describe the types of axonal transport found in neurons.

Axonal transport includes anterograde transport, which moves materials away from the soma, and retrograde transport, which moves materials toward the soma. Signup and view all the answers

What are neurofilaments composed of and what is their significance in neurodegenerative diseases?

Neurofilaments are composed of three protofibrils, each formed from dimers of monomers. They serve as biomarkers for neurodegenerative diseases like ALS, MS, and Huntington's when detected in cerebrospinal fluid (CSF). Signup and view all the answers

Explain the role of the sodium-potassium pump in maintaining the neuronal membrane potential.

The sodium-potassium pump actively transports 3 sodium ions out of the neuron and 2 potassium ions into it, utilizing ATP. This process helps to maintain a negative resting membrane potential of approximately -70mV. Signup and view all the answers

Describe what happens during depolarization of the neuronal membrane.

During depolarization, the membrane potential becomes less negative as voltage-gated Na+ channels open, allowing Na+ to flow into the cell. This influx of positive charge makes the cell membrane potential more positive. Signup and view all the answers

What occurs during hyperpolarization in a neuron?

Hyperpolarization occurs when the membrane potential becomes more negative than the resting state, primarily due to the delayed opening of voltage-gated K+ channels. K+ moves out of the cell, increasing negativity. Signup and view all the answers

What is the diameter of the neuronal membrane and its significance?

The diameter of the neuronal membrane is approximately 5nm. This semi-permeable barrier is crucial for controlling the selective passage of ions in and out of the neuron. Signup and view all the answers

What are neurofibrillary tangles and their association with Alzheimer's disease?

Neurofibrillary tangles are aggregates of hyperphosphorylated tau protein that accumulate in neurons. They are a characteristic feature of Alzheimer's disease and contribute to neurodegeneration. Signup and view all the answers

How does the action potential begin in a neuron?

The action potential begins when the membrane potential reaches -55mV, which opens sodium channels, leading to an influx of Na+ ions that causes rapid depolarization. Signup and view all the answers

What is the impact of voltage-gated channels during the action potential cycle?

Voltage-gated channels open during depolarization to allow Na+ influx and during repolarization to allow K+ efflux, restoring the membrane potential. These channels are essential for the generation and propagation of action potentials. Signup and view all the answers

What is the significance of dendritic spines in neuronal connectivity?

Dendritic spines are important for neuronal connectivity as each spine typically forms a single synapse, allowing for high neuronal connectivity and greater opportunities to form circuits with other neurons. Signup and view all the answers

Describe the role of the axon hillock in generating an action potential.

The axon hillock is where the summation of excitatory and inhibitory post-synaptic potentials occurs, determining whether the threshold potential is reached to generate an action potential. Signup and view all the answers

What distinguishes myelinated axons from unmyelinated axons in terms of conduction velocity?

Myelinated axons conduct impulses faster than unmyelinated axons due to the presence of myelin sheaths, which facilitate rapid saltatory conduction. Signup and view all the answers

How does synaptic plasticity relate to the shape of dendritic spines?

Synaptic plasticity is facilitated by the dynamic nature of dendritic spines, which can change shape due to microfilaments, allowing for the strengthening or weakening of synapses. Signup and view all the answers

Explain the mechanism of summation in the context of EPSPs and IPSPs.

Summation involves combining multiple excitatory (EPSPs) and inhibitory (IPSPs) input signals to determine if the overall potential reaches the threshold for action potential generation. Signup and view all the answers

What is the role of microtubules in axonal transport?

Microtubules serve as 'tracks' for the fast and slow transport of secretory proteins and organelles between the soma and axon, ensuring cellular components are delivered where needed. Signup and view all the answers

How many types of dendritic spine shapes are identified and what distinguishes them?

There are three main types of dendritic spine shapes: thin, mushroom, and stubby, distinguished by their neck and head structure. Signup and view all the answers

What factors influence action potential conduction velocity in axons?

Action potential conduction velocity is primarily influenced by the axon diameter and whether the axon is myelinated or unmyelinated. Signup and view all the answers

Study Notes

The Neuron

Neurons are the fundamental units of the nervous system, responsible for receiving, processing, and transmitting information via electrochemical signaling.
Camillo Golgi developed a silver staining method that made the entire neuron (soma, axon, and dendrites) visible under a microscope. He believed neurons were interconnected, forming a continuous network.
Santiago Ramon y Cajal used Golgi's staining method to visualize brain circuitry, highlighting the distinct structures of neurons. He proposed the Neuron Doctrine, stating that neurons are discrete units that communicate via synapses but are not physically connected.
The soma (cell body) contains the nucleus and surrounding cytoplasm (perikaryon). It is responsible for protein synthesis and other cellular functions.
Organelles of the soma:
- Nucleus: involved in protein synthesis but not replication in adult neurons.
- Ribosomes: sites of protein translation, either free or associated with the endoplasmic reticulum (ER).
- ER: present in both smooth and rough forms (Nissl bodies). Nissl staining reveals the abundance of ER in neurons, indicative of their high metabolic activity.
- Golgi apparatus: involved in post-translational processing of proteins.
- Mitochondria: responsible for ATP generation, crucial for maintaining the membrane potential.
- Lysosomes: contain enzymes that break down cellular organelles.
- Lipofuscin bodies: accumulate lysosomal waste, appearing yellow/brown and increasing with age.
The cytoskeleton provides structural support and shape to neurons, but it’s dynamic and constantly reorganizing.
Microtubules: composed of alpha and beta tubulin proteins, they are dynamic structures that can grow or shrink. They are organized in a longitudinal manner and can branch to form new microtubules.
Microfilaments: the thinnest cytoskeletal fibers, composed of actin polymers. They are responsible for changing neuronal shape and motility, especially important in dendrites.
Neurofilaments: intermediate filaments made up of three protofibrils. They are less dynamic than microtubules and microfilaments, providing strong structural support, often referred to as the ‘bones’ of the cytoskeleton.
Neurofibrillary tangles: abnormal accumulations of neurofilaments, associated with Alzheimer's disease.

The Neuronal Membrane

The neuronal membrane is a phospholipid bilayer that forms a barrier, isolating the cytosol from the extracellular fluid. It contains transmembrane proteins that control the passage of ions in and out of the neuron.
Transmembrane proteins:
- Receptor proteins: bind to signaling molecules.
- Channel proteins: allow the passage of specific ions.
- NA-K pump: uses ATP to actively move 3 sodium ions out of the cell and 2 potassium ions in, contributing to maintaining the membrane potential.
- Voltage-gated channels: open or close based on changes in membrane potential, allowing the passage of specific ions.
The neuronal membrane is semi-permeable, allowing controlled movement of ions to maintain the resting membrane potential, which is approximately -70mV.
Depolarization: Stimulus causes the membrane potential to become less negative; voltage-gated sodium channels open, and sodium ions move into the cell, making it more positive.
Repolarization/Hyperpolarization: Sodium channels close, and potassium channels open. Potassium ions move out of the cell, driving the membrane potential back down to negative values. Hyperpolarization refers to the potential becoming even more negative than the resting potential.

The Action Potential

The action potential is a rapid, short-lasting change in membrane potential that propagates down the axon. It is triggered when the membrane potential reaches a threshold of -55mV.
The axon hillock is the site where EPSPs and IPSPs summate, determining whether an action potential is generated.
The initial segment is where the action potential is generated.
Conduction velocity: The speed at which an action potential travels down the axon, determined by the axon diameter and myelination.

Dendrites

Dendrites are branching extensions of the neuron that receive synaptic input from other neurons.
Dendritic spines: small projections on dendrites, typically forming one synapse each. A high number of spines indicates higher connectivity.
Synaptic plasticity: the ability of dendrites to modify their shape and structure over time, altering the strength of synapses.

The Axon

The axon is a specialized structure for transmitting electrical impulses (action potential) from the cell body to other neurons or target cells.
Myelination: insulation of the axon by a sheath of myelin, greatly increasing conduction velocity (Group A and B fibers).
Unmyelinated axons: lack myelin, conduction is slower (Group C fibers, e.g., pain signals).
Axon collaterals: branches of the axon that allow a single neuron to communicate with multiple other neurons.

Axonal Transport

Axonal transport: the movement of materials between the soma and the axon terminal, relying on microtubules as “tracks”.
Fast transport: transports materials at speeds of 50-400 mm/day.
Slow transport: transports materials at slower speeds.

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Description

This quiz covers the fundamental aspects of neurons, including their structure, functions, and key contributions from scientists like Camillo Golgi and Santiago Ramon y Cajal. Explore the roles of different neuron components and their importance in the nervous system.