12.4 Nervous Tissue: Glial Cells and 12.4b Types of Glial Cells and 12.4c Myelination and 12.5 Axon Regeneration

Multiple sclerosis

is progressive demyelination of neurons in the central nervous system accompanied by the destruction of oligodendrocytes - progressive demyelination of neurons in CNS autoimmune disorder oligodendrocytes attacked by immune cells repeated inflammatory events causing scarring and permanent loss of function vision problems, muscle weakness and spasms, urinary and bladder problems, mood problems

Guillain-Barré syndrome

loss of myelin from peripheral nerves due to inflammation muscle weakness that begins in distal limbs advances to involve proximal muscles no specific infectious agent identified most function recovered with little medical intervention

Myelination

- is the process by which part of an axon is wrapped with myelin - This term also is completed by neurolemmocytes in the PNS and by oligodendrocytes in the CNS.

blood-brain barrier

- strictly controls movement of substances from exiting the blood and entering the nervous tissue in the brain - It also protects the delicate neurons of the brain from toxins, but at the same time allows needed nutrients to pass through

Myelin

- what is the insulating covering around the axon that consists of repeating concentric layers of plasma membrane of glial cells - This term also mainly consists of the membranes of these glial cells and contains a large proportion of lipids and a lesser amount of proteins - The high lipid content of the "This term" gives an axon a distinct, glossy-white appearance and serves to effectively insulate an axon.

Wallerian degeneration

Degeneration of the distal part of this axon

myelin sheath

What is the overlapping inner layers of the plasma membrane that can form into ______?

intro

(intro: answer) Four types of glial cells are found in the central nervous system. These different cells are called astrocytes, ependymal cells, microglia, and oligodendrocytes (figure 12.5a). They can be distinguished based upon size, intracellular organization, and the presence of specific cytoplasmic processes.

Intro

(intro:answer) (under:Glial Cells of the PNS) Two types of glial cells are found in the PNS. They are called satellite cells and neurolemmocytes

Intro

(intro:answer) Glial cells are the other distinct cell type within nervous tissue. These nonexcitable cells serve primarily to support and protect the neurons.

Astrocytes

(under: Glial Cells of the CNS) - One of 4 types of glial cells - star - exhibit a starlike shape due to projections from their surface. - These numerous cell processes touch both capillary walls and neurons. - are the most abundant glial cell in the CNS and constitute over 90% of the nervous tissue in some areas of the brain - Help form the blood-brain barrier - Regulate tissue fluid composition - Form a structural network - Assist neuronal development - Occupy the space of dying neurons

Factors influencing axon regeneration

(under:12.5 Axon Regeneration) PNS axons - vulnerable to cuts, trauma Regeneration possible if - cell body intact - enough neurilemma remains Regeneration success more likely if - amount of damage less extensive - smaller distance between site of damage and structure it innervates

Ependymal cells

- One of 4 types of glial cells in the CNS - What cells are ciliated simple cuboidal or simple columnar epithelial cells that line the internal cavities of the brain (ventricles) and the spinal cord (central canal). - Also, These cells have slender processes that branch extensively to make contact with other glial cells in the surrounding nervous tissue.

Oligodendrocytes

- One of 4 types of glial cells in the CNS - few - are large cells with a bulbous body and slender cytoplasmic extensions or processes - The processes of________ensheath portions of axons of many different neurons - Each process repeatedly wraps around an axon like electrical tape wrapped around a wire - This wrapping is called the myelin sheath - The protective covering around the axon insulates it and prevents the passage of ions through the axonal membrane. This allows for faster action potential propagation within the CNS.

Microglia

- One of 4 types of glial cells in the CNS - small - are typically small cells that have slender branches extending from the main portion of the cell. - They represent the smallest percentage of CNS glial cells with some estimates of their prevalence as low as 5% - They are classified as phagocytic cells of the immune system - These cells wander through the CNS and replicate in response to an infection. - They protect against microorganisms and other potentially harmful substances by engulfing infectious agents and removing debris from dead or damaged nervous tissue.

Neurolemmocytes

- One of the types of glial cells are found in the PNS - are also called Schwann cells - These flattened cells ensheath PNS axons to form a myelin sheath. - This allows for faster action potential propagation within the PNS

Satellite cells

- One of the types of glial cells are found in the PNS - are flattened cells arranged around neuronal cell bodies in a ganglion - For example, satellite cells surround the cell bodies of sensory neurons located in a posterior root ganglion - These cells physically separate cell bodies in a ganglion from their surrounding interstitial fluid - These cells also regulate the continuous exchange of nutrients and waste products between neurons and their environment.

neurilemma

- The delicate outer membrane sheath around an axon.

perivascular feet

- What is The ends of astrocyte processes are called? - it cover and wrap around capillaries in the brain - This term and the brain capillaries together contribute to a blood-brain barrier (BBB)

Glial cells

- are sometimes referred to as neuroglia (nū-rog′lē-a; glia = glue). - They are found within both the CNS and the peripheral nervous system - These cells are both smaller than neurons and capable of mitosis - also, these cells do not transmit nerve signals, but they do assist neurons with their functions - Moreover, theses cells cooperate to physically protect and help nourish neurons as well as provide an organized, supporting scaffolding for all the nervous tissue -Furthermore, these cells form the framework that guides young, migrating neurons to their final destinations. - To add, These cells are critical for the normal function at neural synapses, both maintaining the anatomic structure of synapses and modifying transmission that occurs there. - Also, nervous tissue of a young adult may contain 35 to 100 billion neurons and 100 billion to 1 trillion of "These cells" - and you can say these cells are account for roughly half the volume of the nervous system

ganglion

- is a collection of neuron cell bodies located outside the CNS

Steps of axon regeneration

1) Axon severed by trauma 2) Sealing off and swelling of proximal portion of severed axon disintegration of distal axon and myelin sheathtermed Wallerian degeneration If survival of neurilemma 3) Formation of regeneration tube • neurilemma and remaining endoneurium 5) Axon regeneration and remyelination • guided by regeneration tube • nerve growth factor released by neurolemmocytes 5) Innervation restored

Unmyelinated axons

Associated with neurolemmocytes No myelin sheath covers them Axon in depressed portion of neurolemmocyte Not wrapped in repeated layers In CNS, These term not associated with oligodendrocytes

CNS axon regeneration

Extremely limited - growth-inhibiting molecules secreted by oligodendrocytes - larger number of axons crowded within the CNS - regrowth obstructed by scars from astrocytes and connective tissue

neurofibril nodes

The gaps between the neurolemmocytes are called_____ nodes of Ranvier.