Lecture 19: Nervous Tissue II Flashcards
1
Q
Describe Glial Cells
A
(Also Called Glue Cells)
- Glial cells are non-neuronal cells typically derived from embryonic neural crest tissue (except microglia).
- Glial cells serve in various support functions in the PNS and especially in the CNS.
- Capable of cell division under appropriate conditions.
- Types:
- Astrocytes
- Oligodendrocytes
- Schwann cells
- Microglial cells
- Ependymal cells (?)
2
Q
Describe astrocytes
A
- Derived from neural crest (neuroepithelum)
- Found only in CNS
- Have numerous processes with expanded feet (pediceles) that terminate on capillaries or the pia mater
- Fibrous astrocytes
- Found predominantly in white matter
- Have long processes with few branches
- Protoplasmic astrocytes
- Found predominantly in gray matter
- Have shorter processes with many short branches
3
Q
What are the functions of astrocytes?
A
- Regulate composition of intercellular environment or entry of substances into it
- Structural support
- Blood-brain barrier
- Mediate exchange of nutrients and metabolites between blood and neurons
- End feet form glia limitans
- Development of cerebral cortex
- Potassium sink
- Secretion of neuron trophic factors
- Refer to Figure 8-9.
- Uptake/metabolism of neurotransmitters
- Help form noncollagenous scar tissue after injury to CNS
4
Q
Describe oligodendrocytes
A
- Derived from neural crest (neuroepithelium)
- Found only in CNS
- Functions:
- Closely associated with neuron cell bodies in gray matter and function as satellite cells
- Surround axons of unmyelinated fibers in gray matter
- Myelinate axons in the CNS, Each one myelinates several axons
- Refer to Figure 8-10.
5
Q
Describe Schwann Cells
A
- Derived from neural crest
- Functions:
- Myelinate axons in the PNS, Each one myelinates a section of a single axon
6
Q
Describe Microglial Cells
A
- Derived from macrophage precursors (bone marrow)
- Functions:
- Phagocytic in the PNS
- Recruit leukocytes across the blood-brain barrier
- Modulate initiation and progression of immune responses along with astrocytes
- Refer to Figure 8-17.
7
Q
Describe Ependymal Cells
A
- Ciliated cuboidal cells
- Derived from neuroepithelium and line ventricular system of CNS
- Function in transport
- In choroid plexus, may be principal cell type that secretes cerebrospinal fluid
- Refer to Figure 8-18.
8
Q
Describe Satellite Cells
A
Satellite cells:
- Derived from neural crest
- Form moons (crescents) around cell bodies in ganglia
- Function as insulators
9
Q
What occurs during myelination of the PNS?
A
- Schwann cell plasma membrane wraps around axon.
- Schwann cell cytoplasm is “squeezed” out, leaving behind concentric layers of membranes
10
Q
Describe the internal and external mesaxon
A
- Outer and innermost points of fusion between the outer leaflets (extracellular leaflets)
- Refer to Figures 8-11, 8-12, and 8-13. (19, 20, 21)
11
Q
Describe the intraperiod line
A
- Electron-dense line created by extracellular space between adjacent outer leaflets
- Major protein zero is a transmembrane protein that forms homodimers.
- Found only in the PNS
- Homodimers form homotetramers with the opposing outer leaflets.
- Cytoplasmic domains may have signaling functions.
- Mutations are related to Charcot-Marie-Tooth diseases.
- In the CNS this protein is replaced by the proteolipid protein which has four homophobic domains. Mutations in this protein result in Pelizaeus-Merzbacher disease.
12
Q
Describe the Major Dense Line
A
- Electron-dense line created by cytoplasmic space remnant between adjacent inner leaflets
- Myelin basic protein (also found in the PNS) is an abundant protein associated with the inner leaflets.
- It may function to stabilize lipids in the leaflet.
- There are a number of forms created by splicing of a single gene.
13
Q
Describe the Schmidt-Lanterman Cleft
A
Called incisures
- Residual areas of cytoplasm within the major dense lines
14
Q
Describe oligodendrocytes/nodes of ranvier
A
- Compare cytoplasmicaxon contacts in PNS and CNS.
- Note contact by astrocyte end-foot in node of Ranvier in CNS.
- Note role of tight junctions and connexin 32 in PNS nodes.
- Compare autotypic and heterotypic junctions.
- See Slides 20-23
15
Q
What are the two components of a synapse?
A
- Presynaptic Membrane
* Postsynpatic Membrane
