Neurobiology Quiz: Glial Cells and Myelin Sheath

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Questions and Answers

What is the main function of oligodendrocytes in the CNS?

To maintain the blood-brain barrier

To regulate blood flow in the brain

To produce myelin (correct)

To support neurons by providing nutrients

What type of glial cell is primarily responsible for removing debris through phagocytosis?

Ependymal cell

Astrocyte

Microglia (correct)

Oligodendrocyte

Which type of astrocyte is mainly found in gray matter?

Fibrous astrocyte

Microglia

Oligodendrocyte

Protoplasmic astrocyte (correct)

What is the main function of ependymal cells?

To control the production and flow of cerebrospinal fluid Signup and view all the answers

In which part of the nervous system are Schwann cells primarily found?

Peripheral Nervous System (PNS) Signup and view all the answers

Which of the following glial cells has a star-shaped morphology?

Astrocyte Signup and view all the answers

What is the main function of astrocytes in the CNS?

To support neurons by providing nutrients Signup and view all the answers

How many types of glial cells are present in the Central Nervous System (CNS)?

4 Signup and view all the answers

What is unique about the way oligodendrocytes form the myelin sheath in the CNS?

Different branches of one oligodendrocyte can envelope segments of several axons. Signup and view all the answers

What is the main function of a node of Ranvier?

To transmit nerve impulses Signup and view all the answers

What type of glial cell is responsible for forming the myelin sheath in the PNS?

Schwann cell Signup and view all the answers

What is the main difference between sensory and autonomic ganglia?

Sensory ganglia receive afferent impulses, while autonomic ganglia transmit efferent impulses Signup and view all the answers

What is the term for the gaps in the myelin sheath where nerve impulses can jump from one node to the next?

Nodes of Ranvier Signup and view all the answers

What type of neuron is found in sensory ganglia?

Pseudounipolar neuron Signup and view all the answers

What is the term for the type of glial cells that support neurons in the CNS?

Astrocytes Signup and view all the answers

What is the name of the type of autonomic ganglia located just ventral and lateral to the spinal cord?

Sympathetic ganglia Signup and view all the answers

What is the function of the myelin sheath in nerve fibers?

To electrically isolate the axon and increase the rate of action potential transmission Signup and view all the answers

Which type of glial cell forms myelin sheaths on axons in the CNS?

Oligodendrocytes Signup and view all the answers

What is the name of the gaps between myelin sheath cells?

Nodes of Ranvier Signup and view all the answers

How do myelinated fibers differ from unmyelinated fibers in terms of action potential transmission?

Myelinated fibers are faster than unmyelinated fibers Signup and view all the answers

What is the name of the structure formed by the cytoplasm of Schwann cells wrapping around the axon?

Lamellate membrane Signup and view all the answers

Which type of glial cell is found in craniospinal and autonomic ganglia?

Capsular or satellite cells Signup and view all the answers

What is the function of the Schwann cell in the PNS?

To produce myelin on axons Signup and view all the answers

What is the length of an internode in the largest nerve fibers?

Up to 1.5 mm Signup and view all the answers

Study Notes

PNS

5-6 capsular or satellite cells are found in craniospinal and autonomic ganglia, forming a one-cell thick covering over the cell body of neurons with spherical nuclei.
Schwann cells accompany the PNS fibers, produce myelin in myelinated fibers, and still ensheath unmyelinated fibers.

Myelin Sheath

Myelin sheath is formed by two types of glia: Oligodendrocytes (in CNS) and Schwann cells (in PNS).
Myelinated fibers can conduct electrical signals much faster than unmyelinated fibers (about 150 times faster).
Gaps between myelin sheath cells are the Nodes of Ranvier.

Nerve Fiber

Consists of an axon enveloped by a special sheath that protects the axon and electrically isolates it, increasing the rate of action potential transmission.
In PNS, unmyelinated fibers are covered by a sheath of Schwann cell (neurilemma).

Formation of Myelin Sheath (PNS)

Cytoplasm of Schwann cell wraps around the axon several times, forming a lamellate membrane that unites to form a lipo-protein complex called MYELIN.
The enfolding are called mesaxon (internal and external).

Schwann Cell

Each Schwann cell myelinates a single internode.
Internode length can be up to 1.5 mm in the largest nerve fibers.
Myelination of axons is not continuous along its length, leaving gaps called Node of Ranvier, where no myelin is present, but still covered by folds from Schwann cell.

Myelination in CNS

There are no Schwann cells; the myelin sheath is formed by the processes of oligodendrocytes.
The differences from Schwann cells are:
1. Different branches of one cell can envelope segments of several axons in CNS.
2. The cell body is not directly opposite to the myelin sheath.
3. Neurolemma is not found.

Nodes of Ranvier

Nodes of Ranvier are gaps between myelin sheath cells.
They are covered by folds from Schwann cell.

Ganglia

Ganglia are collections of neurons outside the CNS (in PNS) or inside the white matter of CNS (called Nuclei).
Two types of ganglia: Sensory and Motor.
Ganglia are ovoid structures containing neuronal cell bodies, glial cells, and supported by connective tissue.
They act as a station to transmit nerve impulses.

Sensory Ganglia

Receive afferent impulses that go to the CNS.
Two types: spinal ganglia (associated with spinal nerves) and cranial ganglia (associated with cranial nerves).
Type of neuron is pseudounipolar, with a centrally located nucleus surrounded by several capsular glial cells (satellite cells).
The center of the ganglia is occupied by nerve fibers, while the neurons are placed at the periphery.
Surrounded by a capsule, they have a sensory function.

Autonomic Ganglia

Sympathetic ganglia are located just ventral and lateral to the spinal cord.
They are called paravertebral ganglia.

Neuroglial Cells

Functions: support, protection, neural nutrition, and viability, removing debris (phagocytosis), formation of myelin, defense, and participating in the Blood-Brain Barrier.
Six types of neuroglial cells are present: four in CNS (Astrocyte, Oligodendrocyte, Microglia cell, and Ependymal cell) and two in PNS (Schwann cell and Satellite cell).

CNS Neuroglial Cells

Astrocytes: the largest, with a large spherical and granulated nucleus, star-shaped, and multiple processes.
- Functions: support, maintaining the integrity of the Blood-Brain Barrier, regulating blood flow in the brain, and maintaining synapses.
- Two types: protoplasmic (found mainly in gray matter) and fibrous (found mainly in white matter).
Oligodendrocytes: much smaller, less processes than astrocyte, and produce myelin in CNS.
Microglia: small, elongated cells with a dense oval or elongated nucleus, short irregular processes, and less numerous; involved in inflammation and repair in the adult CNS.
Ependymal cell: epithelium-like cuboidal-columnar, lining the cavities of the brain and the central canal of the spinal cord, with apical microvili and cilia; controlling the production and flow of cerebrospinal fluid (CSF), brain metabolism, and waste clearance.

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Description

This quiz covers the functions and characteristics of glial cells, including oligodendrocytes and Schwann cells, and their role in forming the myelin sheath in the central and peripheral nervous systems.