L23. Neuroscience - Cytology of Neurons & Glia

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Questions and Answers

Which type of synapse is typically classified as inhibitory and formed between local circuit neurons?

Axodendritic synapse

Axospinous synapse

Axoaxonic synapse (correct)

Axosomatic synapse

What characterizes intrinsic neurons in the context of local circuit neurons?

They only form excitatory synapses.

They are primarily found in the white matter of the brain.

They are smaller and remain within the nucleus of origin. (correct)

They have long axons projecting out of the nucleus.

Which of the following statements is NOT true regarding local circuit neurons?

All local circuit neurons project their axons outside the nucleus. (correct)

Golgi cells are examples of local circuit neurons with localized intrinsic axons.

Most local circuit neuron synapses are inhibitory.

Local circuit neurons can have axonal morphology in their dendrites.

Which synapse type is generally considered excitatory?

Axospinous synapse Signup and view all the answers

Where are examples of intrinsic neurons typically found?

Cerebellum and olfactory bulb. Signup and view all the answers

Which type of neuron is characterized by having only one process that functions as both an axon and a dendrite?

Unipolar (pseudo-unipolar) neuron Signup and view all the answers

What is the primary role of astrocytes in the central nervous system?

Support and maintain neuronal function Signup and view all the answers

Which type of glial cell is responsible for myelinating neurons in the central nervous system?

Oligodendrocytes Signup and view all the answers

Dendrites are primarily specialized for which of the following functions?

Receiving synaptic contacts from other neurons Signup and view all the answers

Which of the following statements is true regarding the axons of neurons?

The axon usually originates from the cell body Signup and view all the answers

What distinguishes oligodendrocytes from Schwann cells in terms of myelination?

Oligodendrocytes myelinate multiple axons while Schwann cells myelinate a single axon Signup and view all the answers

Which characteristic of neurons is primarily responsible for their ability to respond to stimuli and transmit information?

Their electrical excitability Signup and view all the answers

What primarily composes the tissue found in the central nervous system (CNS)?

Gray and white matter Signup and view all the answers

Which structures in the white matter of the CNS are defined by their shared origin, destination, and function?

Fasciculi and tracts Signup and view all the answers

Which type of membrane specialization is characterized by distinct pre- and postsynaptic membrane thickenings?

Synapses Signup and view all the answers

How do cell bodies of neurons typically vary in size?

They can be as small as 4μm or as large as 50μm Signup and view all the answers

What is the primary role of the integral membrane proteins in the neuronal plasma membrane?

To function as receptors and channels for neurotransmitters and ions Signup and view all the answers

Which type of junction acts as an electrical synapse for ultra-rapid communication in neurons?

Gap junction Signup and view all the answers

What is a defining characteristic of gray matter in the CNS?

Rich in neuronal cell bodies and dendrites Signup and view all the answers

What provides the structural organization of axons in the white matter of the CNS?

The arrangement into tracts and columns Signup and view all the answers

Which of the following adhesion molecules is found in the plasma membrane of neurons?

Cadherins Signup and view all the answers

What is the primary function of the axon hillock in a neuron?

Acts as the initiation site for action potentials due to voltage-gated Na+ channels Signup and view all the answers

Which statement about myelinated axons is true?

Nodes of Ranvier serve to increase the speed of nerve impulse conduction via saltatory conduction Signup and view all the answers

What distinguishes unmyelinated axons from myelinated ones in terms of structure?

Unmyelinated axons lack organized myelin sheaths Signup and view all the answers

What term describes the branching of an axon at angles to its parent branch?

Axon Collaterals Signup and view all the answers

What role do voltage-gated Na+ channels in the initial segment of the axon play?

They allow for the initiation of action potentials Signup and view all the answers

In terms of action potential propagation speed, which factor is most influential?

The diameter and myelination of the axon Signup and view all the answers

Which type of neuron is most likely to have no axon?

Retinal amacrine cell Signup and view all the answers

What aspect of axon structure is critical for saltatory conduction?

Regular interval of nodes of Ranvier Signup and view all the answers

What cellular component is directly involved in the formation of myelin sheaths around axons?

Oligodendrocytes Signup and view all the answers

What is the significance of postsynaptic membrane densities in neuronal communication?

They anchor neurotransmitter receptors and scaffold proteins Signup and view all the answers

What is the role of Schwann cells concerning myelination of axons?

They myelinate axons with diameters larger than 0.6 microns. Signup and view all the answers

How do unmyelinated axons in the CNS differ from those in the PNS?

Unmyelinated axons in the CNS are ensheathed by astrocytes. Signup and view all the answers

What structures do varicosities contain within the axonal tree?

Mitochondria and synaptic vesicles. Signup and view all the answers

What characterizes the synaptic cleft in a typical synapse?

It fluctuates between 20-30 nm in width. Signup and view all the answers

Which type of fibers are categorized as C fibers?

Unmyelinated fibers associated with autonomic and pain sensation. Signup and view all the answers

What is the maximum number of troughs a single Schwann cell can provide to unmyelinated axons?

12-20 troughs. Signup and view all the answers

Which elements are present in the presynaptic membrane at a synapse?

Membrane density and synaptic vesicles. Signup and view all the answers

What function does the presynaptic membrane density serve?

It facilitates the release of neurotransmitters. Signup and view all the answers

What distinguishes the conduction velocity of C fibers?

They exhibit very slow conduction velocities. Signup and view all the answers

What is an essential feature of the axonal tree's structure?

It forms a highly branched structure called telodendria. Signup and view all the answers

Study Notes

Neurocytology Lecture Objectives

Neuronal Features in CNS and PNS:
- Contrast differences between the peripheral nervous system (PNS) and central nervous system (CNS).
- Detail the plasma membrane of neurons, including the characteristics of the cell body (soma).
- Outline the morphology of dendrites and axons, and their myelin sheaths
- Summarize the presynaptic terminals of neurons.
- Classify local circuit neurons (interneurons).
Neuroglia in CNS and PNS:
- Provide a summary of glial cells' general characteristics.
- List the morphology and function of astrocytes.
- Detail the morphology and function of oligodendrocytes and their role in myelination
- Detail the morphology and function of microglia
- Detail the morphology and function of ependymal and tanycytic cells.
- Discuss the differences between oligodendrocytes and Schwann cells in myelination.

Neuronal Features

Neuron Structure:
- Neurons are long-lived, electrically excitable cells specialized for receiving, integrating, and transmitting information to other target cells.
- Neuron morphology consists of a cell body (soma, perikaryon) with branching processes (dendrites, axon).
- Different types of neurons exist based on the number of processes originating from the cell body (bipolar, unipolar, multipolar).
- Dendrites receive signals; the axon transmits signals. The axon usually originates from the axon hillock.
Plasma Membrane:
- The plasma membrane of neurons is a phospholipid bilayer with integral proteins (receptors, ion channels, pumps, adhesion molecules).
- Synapses (junctions between neurons) are characterized by thickening of pre- and postsynaptic membranes.
- Junctions (adhesion, gap and punctum adherens) exist to facilitate neural transmission.

Cell Body Features

Cell body:
- The cell body (soma or perikaryon) contains cytoplasm and nucleus.
- Nissl bodies are aggregates of rough endoplasmic reticulum, crucial for protein synthesis.
- Smooth endoplasmic reticulum helps in ion sequestration and synthesis of membrane-bound vesicles.
- Mitochondria provide energy (ATP) for neuronal function.
- Other organelles essential for cellular function (lysosomes, microtubules, neurofilaments) are present inside the neuron.
- Lipofuscin pigment accumulates with aging.

Dendrites

Dendrites
- Dendrites taper and branch extensively, increasing receptive surface area.
- Membranes of dendrites contain receptors for neurotransmitters promoting excitatory or inhibitory activity.
- Dendritic spines (appendages) enhance the number of receptive sites.
- They contain microtubules and neurofilaments necessary for their structure and maintenance.

Axons/Myelin

Axons:
- Axons conduct nerve impulses away from the cell body.
- Axon hillock is the initial segment where the action potential originates.
- The Axon varies in diameter (0.7-25 microns)
- Myelination speeds up the rate of impulse conduction.

Axons and Myelin

Myelination:
- Myelinated axons are faster than unmyelinated axons.
- PNS myelination involves Schwann cells, forming a single segment of myelin on the axon.
- CNS myelination involves oligodendrocytes which create myelin segments on multiple axons.
- Nodes of Ranvier are important for saltatory conduction.

Presynaptic Terminals

Synaptic Terminals:
- Axon terminals branch forming axonal tree (telodendria or arborization).
- Varicosities (swellings) contain mitochondria and synaptic vesicles.
- The presynaptic membrane density is part of the axon varicosity membrane.

Neuroglia

Types of neuroglia:
- Astrocytes, oligodendrocytes, & microglia are the most abundant Glia in CNS.
- Ependymal, & tanycytes are neural supporting cells present in CNS.
- Schwann cells are found in PNS. They can form a myelin sheath around axons.
- Satellite cells are found in the PNS associated with neuronal cell bodies.
Neuroglia Functions:
- Provide structural support, insulation, and nutritional support to neurons. They help compartmentalize and isolate neuronal units.
- Buffer potassium, help regulate the extracellular potassium concentration and thus maintenance of transmembrane potential, and maintain the blood-brain barrier.
- Involved in neuronal repair, removing cellular debris, and maintaining the microenvironment.
- Support nutrient delivery to neurons, through blood-brain barrier maintenance.
- Glia can have roles in synaptic plasticity and neurogenesis.

Interneurons

Interneurons:
- Interneurons (local circuit neurons, LCN) have axons that remain within the nuclei of origin (or intrinsic neurons); different morphology according to the role.
- Several anatomical locations with varying degrees of axon localization.
- Their synapses are often inhibitory

Dendritic Morphology

Dendrites:
- Dendrites have receptive surfaces with numerous synapses and specific receptors.
- They contain microtubules and neurofilaments, crucial for their morphology.
- Spine-like structures on the dendrites help to improve the surface area to form synapses.

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Description

Test your knowledge on neuronal features and neuroglia within the CNS and PNS. This quiz covers the morphology, functions, and characteristics of neurons and glial cells, highlighting their differences and roles in the nervous system. Perfect for students studying neuroanatomy and neurophysiology.