Glial Cells in the CNS

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Questions and Answers

What is the primary function of the ependymal cells' cilia?

To facilitate the movement of cerebrospinal fluid (correct)

To facilitate the absorption of cerebrospinal fluid

To facilitate the proliferation of astrocytes

To facilitate the phagocytosis of apoptotic bodies

What is the main difference between ependymal cells and epithelial cells?

Ependymal cells lack a basal lamina, while epithelial cells have one (correct)

Ependymal cells have a basal lamina, while epithelial cells do not

Ependymal cells are more numerous than epithelial cells

Ependymal cells have apical junctional complexes, while epithelial cells do not

What is the term for the barrier layer formed by astrocytes at the external CNS surface?

Glial limiting membrane (correct)

Ependymal layer

Microglial membrane

Astrocytic scar

What is the origin of microglia?

From circulating blood monocytes Signup and view all the answers

What is the function of microglia in removing apoptotic bodies and debris?

Phagocytosis Signup and view all the answers

What is the distribution of microglia in the CNS?

Evenly distributed throughout grey and white matter Signup and view all the answers

What is unique about the shape of ependymal cells?

They are elongated Signup and view all the answers

Why are microglia not typically visualized with H&E staining?

They do not express specific cell surface antigens Signup and view all the answers

What is the primary function of Schwann cells in the PNS?

To form myelin around a portion of only one axon Signup and view all the answers

What is the main component of white matter in the CNS?

Myelinated axons and oligodendrocytes Signup and view all the answers

Where are satellite cells typically found in the PNS?

In the ganglia of the PNS Signup and view all the answers

What is the function of oligodendrocytes in the CNS?

To form myelin around individual axons Signup and view all the answers

What is the term for the lipid-rich myelin-producing glial cells in the CNS?

Oligodendrocytes Signup and view all the answers

Where is gray matter primarily found in the CNS?

In the cortex of the cerebrum and cerebellum Signup and view all the answers

What is the purpose of the meninges in the CNS?

To protect the CNS from injury Signup and view all the answers

What is the main difference between Schwann cells and oligodendrocytes?

Schwann cells are found in the PNS, while oligodendrocytes are found in the CNS Signup and view all the answers

Where are the neuronal cell bodies of preganglionic fibers located in the sympathetic nervous system?

In the thoracic and lumbar segments of the spinal cord Signup and view all the answers

What is the neurotransmitter released by preganglionic fibers?

Acetylcholine Signup and view all the answers

Where are postganglionic neurons located?

In the peripheral ganglion system Signup and view all the answers

What is the function of neurotrophins?

To promote neuronal growth and survival Signup and view all the answers

Where are neural stem cells located in the adult CNS?

Among the cells of the ependymal Signup and view all the answers

What is the potential of neural stem cells?

To promote tissue regeneration and functional recovery Signup and view all the answers

What is the characteristic of the autonomic nervous system?

It has two parts: sympathetic and parasympathetic Signup and view all the answers

What is the characteristic of ganglia in the autonomic nervous system?

They are always located near or within the effector organs Signup and view all the answers

What is the primary function of the epineurium in peripheral nerves?

To fill the space between fascicles Signup and view all the answers

What type of neurons are typically found in autonomic ganglia?

Multipolar neurons Signup and view all the answers

What is the main difference between sensory ganglia and autonomic ganglia?

Direction of nerve impulse Signup and view all the answers

What is the role of the blood-nerve barrier in peripheral nerves?

To maintain the fibers' microenvironment Signup and view all the answers

What is the primary function of intramural ganglia?

To regulate digestion Signup and view all the answers

What is the characteristic of nerves that are classified as mixed?

They contain both sensory and motor neurons Signup and view all the answers

What is the role of the capsule surrounding ganglia?

To provide structural support Signup and view all the answers

What is the function of the neurons in sensory ganglia?

To transmit nerve impulses to the central nervous system Signup and view all the answers

What is the consequence of astrocytes proliferating at injured sites in spinal cord tracts?

Interface with successful axonal regeneration Signup and view all the answers

What is the term for the changes in the perikaryon that signal the onset of regeneration?

Chromolysis Signup and view all the answers

What is the role of new Schwann cells in regeneration?

Serving as guides for regrowing axons Signup and view all the answers

What is the result of the proximal segment of the axon degenerating after injury?

The axon grows distally Signup and view all the answers

What is the final outcome of axonal regeneration in peripheral nerves?

Motor axons reestablish synaptic connections with muscles Signup and view all the answers

What occurs to the Nissl substance during chromatolysis?

It is initially diminished Signup and view all the answers

Study Notes

Glial Cells

Astrocytes:
- Extend fibrous processes with expanded perivascular feet that cover capillary endothelial cells and modulate blood flow
- Help move nutrients, wastes, and other metabolites between neurons and capillaries
- Form a barrier layer of expanded protoplasmic processes called the glial limiting membrane, which lines the meninges at the external CNS surface
- Fill tissue defects after CNS injury by proliferation to form an astrocytic scar
Ependymal cells:
- Line the fluid-filled ventricles of the brain and the central canal of the spinal cord
- Have cilia and long microvilli that facilitate the movement of cerebrospinal fluid and absorption
- Joined apically by apical junctional complexes, but lack a basal lamina
- Have elongated basal ends that extend branching processes into the adjacent neuropil
Microglia:
- Origin: From circulating blood monocytes, belonging to the same family as macrophages and other antigen-presenting cells
- Small cell bodies with many long, branched processes
- Relatively static, but their processes continuously probe and interact with neuropil, synapses, and other cells in an area up to 10-fold that of the cell body
- Function: Remove apoptotic bodies and debris from damaged or remodeled synapses by phagocytosis, and constitute the major mechanism of immune defense in the CNS

Glial Cells of the PNS

Schwann cells (neurolemmocytes):
- Origin: From precursors in the neural crest
- Found only in the PNS, considered as the counterpart to oligodendrocytes of the CNS
- Have trophic interactions with axons and form their myelin sheathes
- Unlike oligodendrocytes, each Schwann cell forms myelin around a portion of only one axon
Satellite cells of ganglia:
- Origin: From the embryonic neural crest
- Form a thin, intimate glial layer around each large neuronal cell body in the ganglia of the PNS
- Exert a trophic or supportive effect on these neurons, insulating, nourishing, and regulating their microenvironments

Central Nervous System (CNS)

Composed of three major structures: cerebrum, cerebellum, and spinal cord
CNS tissue is covered with a connective tissue layer called meninges, which is relatively soft and easily damaged by injuries
Arranged into two areas: white matter and gray matter
- White matter: Main components are myelinated axons, myelin-producing oligodendrocytes, astrocytes, and microglia
- Gray matter: Contains abundant neuronal cell bodies, dendrites, astrocytes, and microglial cells, and is where most synapses occur

Nerve Organization

Peripheral nerves have a dense, irregular fibrous coat called the epineurium, which extends deeply to fill the space between fascicles
Nerves can be afferent/sensory or efferent/motor, and can be motor, sensory, or mixed
Ganglia:
- Ovoid structures containing neuronal cell bodies and their surrounding glial satellite cells
- Serve as relay stations to transmit nerve impulses
- Divided into sensory or autonomic ganglia based on the direction of the nerve impulse
- Associated with both cranial nerves (cranial ganglia) and the dorsal roots of the spinal nerves (spinal ganglia)

Autonomic Ganglia

Autonomic nerves control the activity of smooth muscle, secretion of some glands, heart rate, and involuntary activities that maintain a constant internal environment (homeostasis)
Autonomic ganglia:
- Contain multipolar neurons
- Located within certain organs, especially in the walls of the digestive tract, where they constitute the intramural ganglia
- Have two neuron circuits: preganglionic and postganglionic fibers
- Autonomic nervous system has two parts: sympathetic and parasympathetic nervous systems

Neural Plasticity and Regeneration

The nervous system exhibits neuronal differentiation and formation of new synapses even in adults
Neural stem cells are present in the adult CNS, located in part among the cells of the ependymal
Astrocytes can proliferate at injured sites, but can interfere with successful axonal regeneration
In peripheral nerves, injured axons have a much greater potential for regeneration and return of function
The onset of regeneration is signaled by changes in the perikaryon, including chromatolysis
The new Schwann cells align to serve as guides for the regrowing axons and produce polypeptide factors that promote axonal outgrowth

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Description

This quiz covers the functions and characteristics of astrocytes and ependymal cells, including their roles in modulating blood flow, facilitating nutrient exchange, and forming scar tissue in the central nervous system.