Glia:

Quantity

Glia:

Physical Characteristics

Glia:

Mitosis

Retain mitotic ability - repair CNS lesions (gliosis).

CNS cancers can be caused by this.

Astrocytes:

Physical Characteristics

Largest, most numerous glial cells.

Have end-feet (foot-processes) which contact and surround blood vessels, line ventricles and contact neurons.

Star-shaped bodies with many processes

Astrocytes:

Types

Fibrous: long, thin processes, found in white matter.

Protoplasmic: shorter, thicker processes, found in gray matter.

Astrocytes:

Functions (6)

1) Support and Repair: glial fibrillary acidic proteins (GFAP)fill in empty spaces (CT of the CNS).

2) K+ spatial buffering: K+ ions released during APs are taken up to reestablish neuronal Em. Astrocytes respond to changes in [K+], but are not excitable.

3) Neurotransmitter and metabolite removal: surround synapses to terminate synaptic signal.

4) Neurotransmitter receptors: cause electrical and biochemical changes in glial cells.

5) Communication via gap junctions.

6) Glial guides for neurons during development.

Oligodendrocytes:

Physical Characteristics

Smaller, fewer processes, round nuclei.

Cytoplasm is electron-dense in EM.

Oligodendrocytes:

Function

Myelination of axons in CNS.

One may myelinate many axons by extending a process to each axon.

Oligodendrocytes:

Associated Proteins

Schwann Cells:

Function

Myelinate single axons in PNS (but one axon can be myelinated by many Schwann cells).

Also surround ALL peripheral axons (may wrap multiple axons if they are unmyelinated).

Microglia:

Physical Characteristics

Small, oval cell bodies with many short processes.

Few in number unless neurons are degenerating.

Microglia:

Function

Ependymal Cells:

Physical Characteristics

Cuboidal or columnar epithelial lining of neural tube and choroid plexus, where they secrete CSF.

Can have cilia or microvilli.

Ependymal Cells:

Function (2)

1) Form barrier between brain and CSF. Form desmosomes, so CSF can penetrate brain.

2) Cilia aid CSF circulation.

Myelination:

CNS

Oligodendrocytes extend cytoplasmic tongue.

No outer mesaxon.

Bare nodes.

Myelination:

PNS

Schwann cells envelop a segment of one axon.

Has both inner and outer mesaxon.

Nodes covered by Schwann cells.

Myelination:

General Structure

High lipid content.

Major dense lines: apposed IC faces.

Minor dense lines: apposed EC faces.

Thickness increases with axon diameter.

Often targets of autoimmune diseases.

Myelin Basic Protein: major structural protein in CNS and PNS.

Myelin-associated glycoprotein (MAG): in both CNS and PNS.

Myelin-oligodendrocyte glycoprotein (MOG): CNS only.

Exposed asolemma that facilitates saltatory conduction.

Lots of voltage-gated Na+ channels.

Axon branching only occurs at nodes.

Clefts:

PNS

Clefts:

CNS

Myelination:

Function (2)

1) Decreased ionic flux across axolemma conserves ATP

2) Saltatory conduction increases velocity (2m/s -> 120m/s).

Chronic demyelinating disease of CNS that affects sensory and motor neurons, which causes gliosis.

This causes abnormal AP conduction, leading to paralysis.

Marked by remission and relapse. May be autoimmune.

Acute, inflammatory demyelinating disease of PNS that affects muscle and skin innervation.

This causes problems with sensory perception and motor coordination.

Autoimmune attack against myelin proteins.