Neurons and Glia Flashcards
Anterograde transport
A cellular process responsible for the movement of substance from the cell body to the distal parts of a cell
Aspinous neuron
A neuron lacking dendritic spines
Astrocyte
A star-shaped glial cell of the central nervous system
Axon
The long thread-like part of a neuron along which impulses are conducted from the cell body to other cells
Axon collateral
Branches off a neuron’s main axon
Axon hillock
The site in the soma where membrane potentials propagated from synaptic inputs are summated before being transmitted to the axon
Axon terminal (bouton)
The enlarged club-shaped endings by which axons make synaptic connections with other neurons or effector cells
Axoplasmic transport
A cellular process responsible for the movement of substances from the soma down the axon
Bipolar neuron
A neuron with two neurites extending from the soma
(“Reticular theory”) by Camillo Golgi (1843-1926)
Golgi proposed that neurons were fused together to form a continuous reticulum (or network)
(“Neuron doctrine”) by Santiago Ramon y Cajal (1852-1934)
Cajal proposed that neurons were not continuous but communicated by neuron-neuron contact
Nissl stain
comprised of a basic dye (e.g. cresyl violet) – stains the nuclei and Nissl bodies of neurons
Golgi stain
comprised of a silver chromate solution – stains neurons and their projections
Light microscopy
- Standard light microscopy has a limit of resolution of 0.1 𝝻M
- Space between neurons approximately 0.02 𝝻M (or 20 nM)
Electron microscopy
- Electron microscopy has a limit of resolution of 0.1 nM
* Our insights into the fine structure of neurons have come from electron microscopy
Structure of simple prototypical neuron
- Cell body (soma)
- Axon
- Dendrites
Cell body organelles
- Nucleus
- Rough endoplasmic reticulum (RER)
- Smooth endoplasmic reticulum (SER)
- Golgi apparatus
- Mitochondrion
Microtubules
• A polymer of the protein tubulin – located in axons and dendrites and important in axoplasmic transport
Microfilaments
• A polymer of the protein actin – found throughout the neuron but particularly abundant in axons and dendrites
Neurofilaments
- A type of intermediate filament – particularly abundant in axons and important in regulating axonal shape
- Promising biomarker for neurodegenerative disorders (e.g. Alzheimer’s)
What are axons?
Axons are highly specialised neuronal projections that conduct nerve impulses (or action potentials) within the nervous system
What are axons comprised of?
- Axon hillock – tapers away from the soma to form the initial segment of the axon
- Axon ‘proper’ – axon can branch to form axon collaterals (and recurrent collaterals)
- Axon terminal – site at which the axon meets other neurons at a synapse
Glial cells
- Myelin is a membranous sheath that wraps around and insulates axons
- Gaps in myelin sheath are Nodes of Ranvier – highly enriched in voltage-gated Na+ ion channels
What are dendrites?
- Dendrites are highly specialised neuronal projections that receive synaptic inputs from other neurons
- Dendritic spine structure is sensitive to type and amount of synaptic activity
Different dendrites?
Stellate
Pyramidal
Neuron projects
Unipolar
Bipolar
Multipolar
Connections
Sensory
Motor
Interneurons
Axon length
Golgi type I and Golgi type II
What are astrocytes
Astrocytes are star-shaped glial cells that function to regulate – in a number of ways – the extracellular environment of the brain.
Astrocytes
• Astrocytes regulate the extracellular environment in the brain by, for example, enclosing synaptic junctions and actively removing neurotransmitters from the synaptic cleft
Microglia
Phagocytosis of neuronal and glial debris (e.g. sites of injury)
• Synaptic connection remodelling
• Directing neuronal migration during brain development
Ependymal cells
- Osmotic regulation of cerebrospinal fluid
- Flow of cerebrospinal fluid
- Directing cell migration during brain development
What are ependymal cells?
Ependymal cells are a type of glial cell that provides the lining of the ventricular system of both the brain and spinal cord.
Ependymal cells line the ventricular system and act as a physical barrier separating brain tissue from cerebrospinal fluid (CSF)
What are microglia?
Microglia are a type of glial cell that function as phagocytes within the nervous system to remove neuronal and glial debris.
Microglia – which account for approximately 5-15% of total CNS cell number depending on anatomical region – are broadly distributed in the brain and spinal cord
4 types of glial cells
Astrocytes Microglia Ependymal cells Oligodendrocytes/Schwann cells Glial cells are the “support cells” within the nervous system and can be classified into four categories based on structure and function.
Oligodendrocytes
Oligodendrocytes (pictured) are situated in the central nervous system (CNS)
Schwann cells
Schwann cells are situated in the peripheral nervous system (PNS)
