Histology of the Nervous System I: Neurons, Glia, and Myelin

Comprehensive practice questions covering the histology of nervous tissue, neuron structure, classification of neurons, types of glial cells, and myelin pathohistology.

What are the two main components of nervous tissue?

The two components are Neurons (excitable cells that conduct impulses) and Neuroglia or glial cells (non-excitable support cells).

Which structures constitute the Central Nervous System (CNS) and the Peripheral Nervous System (PNS)?

The CNS consists of the brain and spinal cord, while the PNS consists of nerves and ganglia.

Why is it specialized structures like neurons rarely divide or regenerate after death?

Neurons are highly specialized cells that rarely divide, with regeneration being very limited (except in specific areas like the hippocampus related to memory and learning).

What are Nissl bodies and how do they appear under a stain?

Nissl bodies are composed of rough endoplasmic reticulum (ER) and ribosomes; they stain basophilic and indicate active protein synthesis.

What is the significance of the axon hillock in a neuron?

The axon hillock is a clear area that lacks Nissl bodies and serves as the site for impulse generation (initiating the action potential).

How do Dendrites and Axons differ in the direction of signal conduction?

Dendrites conduct impulses toward the cell body, while the Axon conducts signals away from the soma toward the effector organ or another neuron.

Distinguish between anterograde and retrograde transport in an axon.

Anterograde transport moves materials from the soma to the axon terminal using the protein kinesin, while retrograde transport moves materials from the terminal to the soma using the protein dynein.

Where are Pseudounipolar neurons primarily located in the human body?

They are found in the dorsal root ganglia (sensory ganglia of spinal nerves) and sensory cranial nerve ganglia ($V$, $VII$, $IX$, $X$).

What is the structural characteristic of a Bipolar neuron and where is it found?

A bipolar neuron has one axon and one dendrite arising from opposite poles; it is found in the retina, olfactory epithelium, and vestibular/cochlear ganglia.

Identify the two types of Astrocytes and their specific locations.

Protoplasmic astrocytes are found in gray matter, and Fibrous astrocytes are found in white matter.

What are the primary functions of Astrocytes in the CNS?

They form the blood-brain barrier (via end-feet on capillaries), regulate ions and neurotransmitter uptake, and form glial scars during repair.

How do Oligodendrocytes and Schwann cells differ in their myelination capacity?

Oligodendrocytes myelinate several axons (up to $50$) at once in the CNS, whereas Schwann cells myelinate only a single axon segment in the PNS.

What is the embryological origin of Microglia and what is their role?

Microglia are derived from monocytes (mesodermal origin) and serve as the immune defense of the CNS through phagocytosis and antigen presentation.

What is the function of Ependymal cells in the CNS?

They line brain ventricles and the central canal of the spinal cord; their cilia and microvilli circulate and absorb cerebrospinal fluid (CSF).

What is the role of Satellite cells in the Peripheral Nervous System?

They surround neuronal cell bodies in ganglia to provide metabolic exchange, protection, and maintain the microenvironment.

Define Saltatory Conduction and the role of the Nodes of Ranvier.

Saltatory conduction is the process where action potentials jump from node to node between myelin segments; Nodes of Ranvier are rich in voltage-gated sodium channels and speed up conduction velocity up to $120\,\text{m/s}$.

Distinguish between Multiple Sclerosis (MS) and Guillain–Barr syndrome regarding the location of demyelination.

Multiple Sclerosis is an autoimmune demyelination occurring in the CNS (targeting oligodendrocytes), while Guillain–Barr Syndrome is an acute demyelination occurring in the PNS (affecting Schwann cells).