• Neuron :• Supporting cells :

– CNS : neuroglia (glia)– PNS : Schwann cells and satellite cells– Functions :

• physical support• electrical insulation• metabolic exchange• blood-brain barrier

Composition of Nervous Tissue

Types and Functions of GliaName of Glial

CellFunction

Astrocyte (Astroglia)

Star-shaped cells that provide physical and nutritional support for neurons: 1) clean up brain"debris"; 2) transport nutrients to neurons; 3) hold neurons in place; 4) digest parts of dead neurons; 5) regulate content of extracellular space

Microglia Like astrocytes, microglia digest parts of dead neurons.

Oligo-dendroglia

Provide the insulation (myelin) to neurons in the central nervous system.

Satellite Cells Physical support to neurons in the peripheral nervous system.

Schwann Cells Provide the insulation (myelin) to neurons in the peripheral nervous system.

Neuroglia in the CNS

• Able to replicate!• Importance in nervous system function is

VASTLY underestimated!• Evidence is mounting:

1. Nurturing role2. Signaling role (Memory?)3. Inflammation4. Pain5. Many more to come!

Neuroglia: Distinguishing Feature

s

1. Presence of tight junctions between the endothelial cells2. One of the notable features of endothelial cells in compa

rison to other cell is the lack of pinocytic vesicles3. Selective permeability to molecules based on their mole

cular weight and lipid solubility4. Presence of specific markers

• Rich in two enzymes: gamma glutamyl transpeptidase (GGTP) (for amino acid transport) and alkaline phosphatase (transport of phsopahte ions) used as marker for BBB.

• Others: glucose transporter (GLUT-1); endothelial barrier antigen (EBA; unknown function) and antigen recognized by the MRC OX-47 monoclonal antibody (important for cell-to-cell adhesion); transferrin receptor (transport of ferric ions).

Properties of Blood Brain Barriers

BBB

1. Neurons have TWO "processes" called axons and dendrites. Glial cells only have ONE.

2. Neurons CAN generate action potentials. Glial cells CANNOT, however, do have a resting potential.

3. Neurons HAVE synapses that use neurotransmitters. Glial cells do NOT have chemical synapses.

4. Neurons do NOT continue to divide. Glial cells DO continue to divide.

5. There are many MORE (10-50 times more) glial cells in the brain compared to the number of neurons.

Glia are different from neurons:

Nerve Cells

Neurons, Glia, Extracellular Space, and Bloo

d

Bidirectional Communication Partners in the CNS

• Receiving signals from neighboring neurons and responding to them with release of neuroactive substances

• Express receptors for almost all neurotransmitters and neuromodulators

• Increase of intracellular calcium concentration• Membrane depolarization in astrocytes are common

responses to neural activity• Metabolically coupled to neural activity

Metabolism of Astrocytes and their Metabolic Cooperation with Neurons

• Glucose• Amino acid metabolism• Enzymes:

• glutamine synthetase(glutamate-glutamine cycle);• glycogen phosphorylatase (glycogen mobilization); • pyruvate carboxylase (anaplerotic synthesis of oxal

oacetate); • cysteine sulfinate decarboxylase (synthesis of tauri

ne); • glycine cleavage system, glycine metabolism.

•

Three Types of Metabolic Cooperation of Astrocytes and

Neurons1. Supply of the energy substrate lactate t

o neurons2. The recycling of neuronal glutamate b

y the glutamate-glutamine cycle3. The supply by astrocytes of precursors

for neuronal glutathione (GSH) synthesis