Neurons and Glia

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Questions and Answers

Which of the following is NOT a primary function of the nervous system?

  • Serving as the main controlling and communicating center of the body
  • Coordinating essential bodily functions
  • Regulating body temperature (correct)
  • Processing environmental information

Neurons are capable of division once they are specialized.

False (B)

What is the primary role of the axolemma in a neuron?

The axolemma is the membrane that surrounds the axon, playing a crucial role in nerve impulse conduction.

The Nissl bodies, which are clusters of RER and free ribosomes, are essential for ______ in neurons.

<p>protein synthesis</p> Signup and view all the answers

Match the type of neuronal cytoskeleton element with its primary function:

<p>Microtubules = Transport of substances within the neuron Neurofilaments = Providing structural stability Microfilaments = Structural maintenance and movement of cargo</p> Signup and view all the answers

Which motor protein is primarily involved in retrograde axonal transport?

<p>Dynein (C)</p> Signup and view all the answers

Myelination slows down nerve conduction by increasing the resistance across the axon membrane.

<p>False (B)</p> Signup and view all the answers

Why is the node of Ranvier essential for saltatory conduction?

<p>It is the only place along a myelinated axon where ions can cross the membrane, regenerating the action potential.</p> Signup and view all the answers

In peripheral nerves, the ______ is the delicate connective tissue layer that immediately surrounds individual axons and their associated Schwann cells.

<p>endoneurium</p> Signup and view all the answers

Match the following terms related to peripheral nerve coverings with their descriptions:

<p>Endoneurium = Delicate connective tissue layer surrounding individual axons Perineurium = Connective tissue layer surrounding groups of axons forming fascicles Epineurium = Robust connective tissue layer surrounding multiple fascicles and forming the nerve itself</p> Signup and view all the answers

What cellular structure is characteristically stained by Nissl staining?

<p>Rough endoplasmic reticulum (D)</p> Signup and view all the answers

Chromatolysis, the dissolution of Nissl substance, indicates normal cellular function and health.

<p>False (B)</p> Signup and view all the answers

What key contribution did Santiago Ramón y Cajal make to the field of neuroscience?

<p>He proposed the neuron doctrine, stating that the nervous system is composed of individual cells.</p> Signup and view all the answers

Neurons that send signals towards the CNS are classified as ______ neurons.

<p>sensory/afferent</p> Signup and view all the answers

Match each neuron type with its typical location or function:

<p>Multipolar neuron = CNS (e.g., motor neurons) Bipolar neuron = Retina Pseudo-unipolar neuron = Primary somatosensory neuron in the DRG</p> Signup and view all the answers

Electrical synapses are characterized by which of the following?

<p>Physical connections between cells via gap junctions. (B)</p> Signup and view all the answers

In chemical synapses, the electrical signal is directly transmitted from the presynaptic neuron to the postsynaptic neuron without any conversion.

<p>False (B)</p> Signup and view all the answers

What are the three major types of synapses based on the location of contact?

<p>Axo-dendritic, axo-somatic, and axo-axonic</p> Signup and view all the answers

The post-synaptic density (PSD) is a protein-dense region found on the ______ side of a synapse.

<p>postsynaptic</p> Signup and view all the answers

Match each description with the correct term associated with synapse structure:

<p>Neurotransmitter vesicles = Structures in the presynaptic neuron Post-synaptic density = Specialized area on the postsynaptic membrane Dendritic spines = Protrusions where axo-dendritic synapses form</p> Signup and view all the answers

Neurons integrate multiple incoming signals into a binary output. What does this mean?

<p>The neuron decides whether or not to fire an action potential. (C)</p> Signup and view all the answers

Convergence in neuronal circuits refers to the process where one neuron diverges to influence many other neurons.

<p>False (B)</p> Signup and view all the answers

What is the general role of glial cells in the nervous system?

<p>Glial cells support neuronal function through various mechanisms, including structural support, insulation, and maintenance of microenvironment.</p> Signup and view all the answers

In the central nervous system, ______ are glial cells responsible for forming the myelin sheath around axons.

<p>oligodendrocytes</p> Signup and view all the answers

Match each glial cell type to its primary location:

<p>Astrocytes = CNS Schwann cells = PNS Satellite cells = PNS</p> Signup and view all the answers

Which type of astrocyte is primarily found in white matter and supports axons?

<p>Fibrous astrocytes (C)</p> Signup and view all the answers

Astrocytes are only involved in structural roles and do not participate in neurotransmitter regulation.

<p>False (B)</p> Signup and view all the answers

How do astrocytes contribute to the blood-brain barrier function?

<p>Astrocytes release factors that influence endothelial cells to maintain the blood-brain barrier.</p> Signup and view all the answers

Oligodendrocytes and astrocytes both inhibit axon regeneration in the ______.

<p>CNS</p> Signup and view all the answers

Match the glial cell type with their function.

<p>Microglia = Immune defence in the brain Ependymal cells = Aid in the circulation of cerebrospinal fluid</p> Signup and view all the answers

What happens to Microglia when activated?

<p>They retract their processes and become phagocytotic. (C)</p> Signup and view all the answers

The choroid plexus is responsible for secreting cerebrospinal fluid (CSF).

<p>True (A)</p> Signup and view all the answers

What is the main function of Schwann cells in the peripheral nervous system?

<p>Schwann cells myelinate axons in the PNS.</p> Signup and view all the answers

Satellite cells in the PNS provide ______ and ______ support to neurons.

<p>structural, metabolic</p> Signup and view all the answers

Match each glial cell type with the most accurate role:

<p>Oligodendrocytes = Myelination in the CNS Astrocytes = Electrolyte homeostasis Microglia = Immune defense Ependymal Cells = CSF circulation</p> Signup and view all the answers

Flashcards

The Nervous System

The main controlling and communicating center of the body, coordinating essential bodily functions, processing information, and enabling higher functions like memory and emotions.

Neuron Metabolic Activity

Neurons are transcriptionally and translationally very active cells with a prominent nucleolus, that do not divide once specialized.

Neuronal Cytoskeleton

Microtubules are tubulin dimers for transport. Neurofilaments are intermediate filaments for structure. Microfilaments are actin dimers for cargo movement.

Axonal Transport Motors

Kinesins transport cargo anterograde (forward) at 100-400 mm/day. Dyneins transport cargo retrograde (backward) at 50-250 mm/day.

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Myelination

Myelination speeds up nerve conduction through saltatory conduction.

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Peripheral Nerve Coverings

Endoneurium surrounds individual axons, perineurium surrounds fascicles, and epineurium surrounds the entire nerve.

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Nissl Staining & Chromatolysis

Nissl staining uses basic dyes to stain the cell body, particularly the ER. Chromatolysis is the dissolution of Nissl substance in response to cell injury.

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Neuron Functional Types

Sensory neurons send signals 'to' the CNS, motor neurons send signals 'away', and interneurons connect neurons within the CNS.

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Neuron Structural Types

Multipolar neurons are most common in the CNS, bipolar neurons are found in the retina, and (pseudo)unipolar neurons have a single process.

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Types of Synapses

Electrical synapses use gap junctions. Chemical synapses convert electrical signals to chemical signals using neurotransmitters.

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Synapse Location Types

Synapses can be axo-dendritic, axo-somatic, or axo-axonic, depending on where the axon terminal connects.

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Convergence and Divergence.

Neurons can receive numerous inputs but make a binary decision to fire or not.

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Roles of Astrocytes

Astrocytes provide structural support, regulate electrolytes, store energy, affect the BBB, uptake neurotransmitters, and modulate immunity.

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Astrocyte location and roles.

Fibrous astrocytes are in white matter, supporting axons. Protoplasmic astrocytes are in gray matter, with homeostatic functions.

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Oligodendrocyte function

Oligodendrocytes myelinate multiple axons and inhibit axon regeneration in the CNS.

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Microglia Functions

Microglia provide immune defense, remove debris, and become phagocytotic when activated.

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Ependymal Cells

Ependymal cells line the ventricular system and spinal canal, secreting and aiding in the circulation of cerebrospinal fluid.

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Satellite Cells

Satellite cells provide structural and metabolic support in the PNS, similar to astrocytes in the CNS.

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Study Notes

  • Lecture 6 covers Neurons and Glia
  • By the end of this lecture, you should be able to:
    • Describe the major classes of neurons
    • Identify the structural characteristics of a prototypical neuron
    • Understand the principles of convergence and divergence and how they can help build neural networks
    • Describe the classes of glia in the PNS and CNS
    • Explain how the different functions of glia provide support to the nervous system

The Nervous System

  • The main controlling and communicating center of the body
  • Coordinates and controls all essential bodily functions
  • Processes information from the environment and enables the body to respond accordingly
  • It provides us with higher functions such as memory, emotions, and learning

Neurons

  • The 'prototypical' neuron has specific structural elements
    • Including Dendrites, Axon, Axon hillock, Axolemma, Axoplasm, Nissl bodies, Mitochondrion, Nucleus, Nucleolus, Cell Body, Perikaryon, Neurofilament, Telodendria, and Synaptic terminals
  • It also involves a unidirectional flow of information
  • Neurons are transcriptionally and translationally very active
  • Possess a very prominent nucleolus
  • Postmitotic and have diffuse chromatin
  • Once specialized, they do not divide

The Neuronal Cytoskeleton

  • Microtubules: composed of a and b tubulin dimers; aid in transport within the neuron
  • Neurofilaments (intermediate filaments): coiled-coil fibers which provide structural maintenance
  • Microfilaments: actin dimers; contribute to structural maintenance and cargo movement

Axonal Transport

  • Neuronal components are transported via motor proteins along axonal microtubules
  • Kinesins (anterograde) transport at 100-400 mm/day, carrying mitochondria and vesicles
  • Dyneins (retrograde) transport at 50-250 mm/day, carrying aging mitochondria and endocytic vesicles

Axon Myelination

  • Many axons are myelinated by specialized glial cells
  • De-myelination in multiple sclerosis is an autoimmune disease of unknown aetiology, has a UK prevalence of 1:1000, and involves genetic and environmental factors
  • Myelination speeds up nerve conduction = saltatory conduction

Coverings of Peripheral Nerves

  • Endoneurium: Delicate connective tissue layer surrounding the axon and associated Schwann cells
  • Perineurium: Connective tissue layer surrounding groups of axons forming fascicles
  • Epineurium: Robust connective tissue layer surrounding individual fascicles, contains blood vessels and forms the nerve itself

Nissl Staining and Substances

  • Nissl staining utilizes basic dyes (e.g., cresyl violet) to stain the cell body, particularly the ER
  • Nissl substance: Refers to rER
  • Chromatolysis: Dissolution of Nissl substance in response to ischemia, axotomy, cell toxicity, infections, etc

Foundations of Modern Neuroscience

  • Ramón y Cajal made significant contributions

Classes of Neurons

  • Functional classification:
    • Sensory/afferent neurons: send signals towards the CNS
    • Motor/efferent neurons: send signals away from the CNS, into the periphery
    • Interneurons: act locally, within the CNS, and connect neurons with each other
  • Structural classification:
    • Multipolar: most neurons in the CNS (e.g., motor neurons)
    • Bipolar: e.g., sensory neurons in the retina
    • (Pseudo)unipolar: neurons with a single process that often

Neuron Connectivity

  • Electrical synapses: Remember gap junctions
  • Chemical synapses: convert electrical signals to chemical signals, then back to electrical signals
  • Synapses can be:
    • Axo-dendritic
    • Axo-somatic
    • Axo-axonic

Synapses

  • Neurotransmitter vesicles in the pre-synapse
  • Post-synaptic density (PSD) present
  • Many axo-dendritic synapses form at dendritic spines

Convergence and Divergence

  • Neurons can receive inputs from tens of thousands of other neurons, but they can only make a binary decision: to fire or not

Glia

Major Classes of Neuroglial Cells

Astrocytes

  • Astrocytes can be fibrous in white matter, supporting axons, or protoplasmic in grey matter, contributing to homeostatic functions

Roles of Astrocytes

  • Structural support
  • Extracellular electrolyte homeostasis (ions, water, pH)
  • Energy storage (glycogen, glucose, lactate)
  • Effects on endothelial cells and angiogenic factors, influencing BBB regulation
  • Glia limitans
  • Uptake and regulation of neurotransmitters
  • Glutamate regulation (glutamate/glutamine transport)
  • Neurotrophic factors influence neuronal survival and myelination
  • Role in neurogenesis and synaptogenesis through ECM modification
  • Inhibition of axon regeneration
  • Immune modulation (together with microglia)
  • Have crucial roles in buffering K+ ions and preventing toxicity

Oligodendrocytes

  • A single oligodendrocyte can myelinate multiple different axons
  • Inhibit axon regeneration in the CNS, along with astrocytes

Microglia

  • Provides immune defense and remove cellular debris in the brain
  • Pro-inflammatory
  • Once activated, they retract processes and become phagocytotic

Ependymal Cells

  • Found in the lining of the ventricular system and spinal canal
  • Secrete, monitor, and aid in the circulation of cerebro-spinal fluid
  • Ependymocytes: have cilia and microvilli
  • Choroid plexus: Specialized cuboidal epithelium in all ventricles; secretes cerebro-spinal fluid (CSF)

Glia in the Peripheral Nervous System (PNS)

  • Schwann cells:
    • Myelinate PNS axons (one Schwann cell per axon)
    • Rapidly remove myelin debris by phagocytosis
    • Promote axon regeneration by producing permissive ECM components and neurotrophins
  • Satellite cells:
    • Provide structural and metabolic support, similar to astrocytes in the CNS

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