Lecture 19: Nervous Tissue II

Question 1

Describe Glial Cells

Answer 1

(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 (?)

Question 2

Describe astrocytes

Answer 2

• 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

Question 3

What are the functions of astrocytes?

Answer 3

• 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

Question 4

Describe oligodendrocytes

Answer 4

• 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.

Question 5

Describe Schwann Cells

Answer 5

• Derived from neural crest
• Functions:
• Myelinate axons in the PNS, Each one myelinates a section of a single axon

Question 6

Describe Microglial Cells

Answer 6

• 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.

Question 7

Describe Ependymal Cells

Answer 7

• 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.

Question 8

Describe Satellite Cells

Answer 8

Satellite cells:

• Derived from neural crest
• Form moons (crescents) around cell bodies in ganglia
• Function as insulators

Question 9

What occurs during myelination of the PNS?

Answer 9

• Schwann cell plasma membrane wraps around axon.

- Schwann cell cytoplasm is “squeezed” out, leaving behind concentric layers of membranes

Question 10

Describe the internal and external mesaxon

Answer 10

• 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)

Question 11

Describe the intraperiod line

Answer 11

• 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.

Question 12

Describe the Major Dense Line

Answer 12

• 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.

Question 13

Describe the Schmidt-Lanterman Cleft

Answer 13

Called incisures

• Residual areas of cytoplasm within the major dense lines

Question 14

Describe oligodendrocytes/nodes of ranvier

Answer 14

• 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

Question 15

What are the two components of a synapse?

Answer 15

• Presynaptic Membrane

* Postsynpatic Membrane

Question 16

Describe the presynaptic membrane

Answer 16

• 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

Question 17

Describe the Postsynaptic Membrane

Answer 17

Neurotransmitter receptors

…that’s pretty much it.

See Slide 26

Question 18

Describe the six types of synapses

Answer 18

• 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

Question 19

Describe the meninges and spaces hierarchy

Answer 19

• 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

Question 20

Describe the dura mater

Answer 20

(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.

Question 21

Incomplete:

Answer 21

Resume at slide 32