Ch. 5 - Glia and Myelination

Neuroglia

supporting cells of the nervous system that are intimately related to neurons and their processes

Some types of neuroglia are involved in

excitation, inhibition, or propagation of the nerve impulse

3 CNS Types of Neuroglia

1. Astrocytes

2. Oligodendroglia

3. Microglia

1 PNS Type of Neuroglia

1. Schwann cells

Astrocytes

• form the structural support of the CNS

  • blood-brain barrier

• remove necessary nutrients from blood to nourish neurons

  • basically helping to feed the nerve

How do astrocytes contribute to neuronal signaling?

by releasing Ca2 which increases or decreases communication between neurons

T or F? Astrocytes remove NTs, debris, and K from synapse, remove debris, and dead tissues, and proliferates following a CNS injury.

T, if you have an injury → astrocytes get rid of the bad cells

Microglia

• are similar to macrophages as they clean the CNS when it is afflicted by injury or disease

• may play a role in protecting CNS from viruses, microorganisms, and the formation of tumors

Myelin

substance of proteins and fats that surround an axon, insulating it, and supporting the flow of the action potential

Nodes of Ranvier

gaps in the myelin where sodium channels can open and can generate more action potentials

Myelin is essential during the first few years of development. What happens if there is dysfunction?

significant problems regarding nerve conduction

Two Types of Myelin

1. Oligodendroglia - CNS

2. Schwann Cells - PNS

Oligodendrolgia - CNS

• produce and maintain myelin sheaths in CNS

• each process provides myelin of one internode (myelinated interval between two nodes of ranvier) of one axon

Schwann Cells - PNS

• produce and form the myelin of peripheral nerves

• each cell form one internede of myelination of only one axon

What is PNS demyelination caused by?

• neuropathies

• autoimmune or metabolic disorders

• viruses

• trauma

• toxic chemicals

Guillian Barre

• PNS Demyelinating Disorder

• occurs 2-3 weeks after a mild infection

• in 2/3 of cases, it is preceded by an intestinal infection which activates the immune system causing production of antibodies that mistakes the Schwann cells and attacks them

• results in inflammation and demyelination of peripheral sensory and motor fibers

• symptoms: muscle weakness, trouble breathing

Multiple Sclerosis

• CNS demylineating disorder

• destroyed oligodendrocytes in brain or spinal cord producing areas of demyelination called plaques

• may involve crnaial nerves

• results in action potentials being unable to depolarize

• symptoms: dysfunction in

  • vision

  • sensation

  • clumsiness

  • loss of balance

  • brain fog

Leukodystrophies

• hereditary demyelination disorders

• symptoms:

  • sight

  • hearing

  • speech

  • ambulation

• results in death within a few years