Flashcards in Lecture 19: Nervous Tissue II Deck (21)
Describe Glial Cells
(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.
- Schwann cells
- Microglial cells
- Ependymal cells (?)
* 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
What are the functions of astrocytes?
* 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
* Derived from neural crest (neuroepithelium)
* Found only in CNS
- 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.
Describe Schwann Cells
* Derived from neural crest
- Myelinate axons in the PNS, Each one myelinates a section of a single axon
Describe Microglial Cells
* Derived from macrophage precursors (bone marrow)
- 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.
Describe Ependymal Cells
- 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.
Describe Satellite Cells
- Derived from neural crest
- Form moons (crescents) around cell bodies in ganglia
- Function as insulators
What occurs during myelination of the PNS?
- Schwann cell plasma membrane wraps around axon.
- Schwann cell cytoplasm is “squeezed” out, leaving behind concentric layers of membranes
Describe the internal and external mesaxon
- 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)
Describe the intraperiod line
* 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.
Describe the Major Dense Line
* 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.
Describe the Schmidt-Lanterman Cleft
- Residual areas of cytoplasm within the major dense lines
Describe oligodendrocytes/nodes of ranvier
- 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
What are the two components of a synapse?
* Presynaptic Membrane
* Postsynpatic Membrane
Describe the presynaptic membrane
* Voltage-gated calcium channels
* Refer to Figure 8-6
* SNAPs bind synaptic vesicles to presynaptic membrane:
- Soluble NSF (N-ethylmaleimide-sensitive fusion protein)
- Found in cytosol of terminal
* Vesicle docking proteins:
- SNAP receptors found in presynaptic and synaptic vesicular membranes
* Synapsins : Filaments in the presynaptic membrane
Describe the Postsynaptic Membrane
...that's pretty much it.
See Slide 26
Describe the six types of synapses
* Axosomatic: Axon terminal synapses with the neuron cell body
* Axoaxonic: Axon terminal synapses with another axon terminal
* Axodendritic: Axon terminal synapses with a dendrite
* Axospinous: Axon terminal synapses with a dendritic spine
* Excitatory: More positive end-plate potential (closer to threshold)
* Inhibitory: More negative end-plate potential (farther from threshold)
- See Slide 28
Describe the meninges and spaces hierarchy
*Superficial to deep:
- Epidural space: Absent around brain, but present around the spinal cord
- Dura mater
- Subdural space
- Leptomeninx: Arachnoid membrane, Arachnoid villi, and Pia Mater
- See Slide 30
Describe the dura mater
(Also called Tough Mother)
- The dura mater is a tough thick sheet of dense fibrous connective tissue.
- In the cranial cavity it lines the inside of the cranial vault bone and serves as the periosteum.
- Around the spinal cord, the dura mater forms a connective tissue tube that is separated from the bone of the vertebral foramina by a space referred to as the epidural space.
- Within the dura mater are large, endothelial-lined venous sinuses that receive blood from the cerebral drainage as well as cerebrospinal fluid via the arachnoid villi.
- A layer of dural border cells separates the dura mater from the subdural space.