Chapter 9 - Nerve

I'm nervous :s

What are the two main anatomical divisions of the nervous system?

• Central Nervous System (CNS): Brain and spinal cord

• Peripheral Nervous System (PNS): All other nervous tissue

What are the two main functional divisions of the nervous system and how do they differ?

• Somatic nervous system: Voluntary, under conscious control

• Autonomic nervous system: Involuntary, regulates automatic functions like heartbeat and digestion

True or False: The CNS includes the brain, spinal cord, and peripheral nerves.

False.
Explanation: The CNS includes only the brain and spinal cord; peripheral nerves are part of the PNS.

Fill in the blank: Histologically, nervous tissue consists of __________ and __________.

Cells and cell processes

What are the three major groups of stains used in nervous tissue histology?

1. Stains for neuronal cell bodies and processes

2. Stains for glial cells and their processes

3. Stains for the myelin sheath

About how many neurons are estimated to be in the human brain?

At least 14 billion neurons

Fill in the blank: A neuron consists of a cell body, also called the __________, and one or more processes called __________ and __________.

• Cell body: Perikaryon

• Processes: Axon and dendrites

True or False: Neuron cell bodies are generally smaller than other cells.

False.
Explanation: Neuron cell bodies are generally larger, ranging from 4–135 μm in diameter.

What is characteristic of the neuron’s nucleus?

• Usually singular

• Contains predominantly euchromatin

• Has a very prominent nucleolus

What is another name for Nissl substance?

Tigroid substance or chromidal substance

What does Nissl substance consist of at the ultrastructural level?

Large aggregates of rough endoplasmic reticulum with high RNA content

Which dyes are commonly used to stain Nissl substance and why?

• Basic aniline dyes such as thionin and cresyl echt violet

• These dyes bind to the RNA content, making the basophilic material visible

Fill in the blank: The loss of Nissl substance due to neuronal injury is called __________.

Chromatolysis

True or False: Chromatolysis begins with the disappearance of Nissl substance at the axon hillock.

False.
Explanation: Chromatolysis begins around the nucleus, not at the axon hillock.

What are the two types of neuronal processes and their roles?

• Dendrites: Short, branched; receive information

• Axons: Long, single; transmit impulses

Fill in the blank: The axon originates from a cone-shaped region of the cell body called the __________.

Axon hillock

What is a synapse?

The point where an axon terminates on the dendrites or cell body of another neuron or on an effector organ

What are neurofibrils composed of?

Aggregates of microtubules and neurofilaments

Which staining method is used to demonstrate both nerve fibers and neurofibrils?

Silver staining methods

What are neuroglia and what is their primary role?

• Supporting cells in the nervous system ("nerve glue")

• Provide structural and metabolic support, insulate neurons, regulate the environment

True or False: Connective tissue proper is found throughout the CNS alongside neuroglia.

False.
Explanation: Connective tissue proper is not found in the CNS except in meninges and blood vessels.

What are the four main types of glial cells?

• Oligodendroglia

• Astroglia (Astrocytes)

• Microglia

• Ependymal cells

What is the primary function of oligodendroglia?

Produce and maintain the myelin sheath in the CNS

Where are oligodendroglia found?

In both gray matter (nerve cell bodies) and white matter (nerve fibers) of the CNS

What are the two types of astrocytes and where are they located?

• Protoplasmic astrocytes: Gray matter

• Fibrous astrocytes: White matter

What role do astrocytes play in response to CNS injury?

• Proliferate and form scars (gliosis)

• Support nerve fiber tracts

• Regulate exchange of fluids, gases, and metabolites

True or False: Traditional histochemical stains for astrocytes are commonly used today in pathology labs.

False.
Explanation: These methods have largely been replaced by immunohistochemical techniques.

What is the primary function of microglia?

Fixed phagocytic cells of the CNS; involved in immune defense

Are microglial stains used routinely in clinical labs?

No, they are mostly used for research purposes.

Where are ependymal cells located and what is their role?

• Line the ventricles and spinal canal

• Form a selective barrier between cerebrospinal fluid (CSF) and nervous tissue

What is myelin composed of?

A white, fatty material containing:

• Protein

• Cholesterol

• Phospholipids

• Cerebrosides

What happens to myelin during routine paraffin processing?

It is largely lost, leaving behind only neurokeratin, a resistant proteolipid

Which cells produce the myelin sheath in the CNS and PNS?

• CNS: Oligodendroglia

• PNS: Schwann cells

Fill in the blank: In response to myelin breakdown, a __________ lipid forms that becomes increasingly __________.

• Simple lipid

• Sudanophilic (stains well with lipid stains)

What are two common staining methods for demonstrating the myelin sheath?

1. Luxol fast blue

2. Iron hematoxylin

What is the shared purpose of both Cresyl Echt Violet Methods I and II?

• Identification of neurons in tissue sections

• Demonstration of loss of Nissl substance (i.e., chromatolysis)

Fill in the blank: Loss of Nissl substance occurs when the __________ are transected, injured, or destroyed.

Axons

True or False: Chromatolysis is a permanent change in neurons following axonal injury.

Explanation: Chromatolysis is reversible. The Nissl substance reappears after the neuron completes the necessary protein synthesis to regenerate a new axon.

Under what condition might a neuron disappear completely following axonal injury?

If the axon is injured very close to the cell body, the neuron may not survive and will disappear.

What makes Nissl substance basophilic and suitable for staining with basic aniline dyes?

RNA content from rough endoplasmic reticulum (RER)

What cellular components are stained with cresyl echt violet methods?

• Nissl substance (RER + RNA)

• Nuclei (especially in Method II, due to acid pH preference)

True or False: Nissl substance can be visualized using acidic dyes because it contains DNA.

False.
Explanation: Nissl substance is basophilic due to RNA, and it is stained with basic dyes, not acidic ones.

How can staining selectivity be adjusted in Cresyl Echt Violet Method I?

By varying the pH and degree of differentiation, you can stain:

• Both Nissl substance and nuclei

• Or only Nissl substance alone

What is the preferred fixative for both Cresyl Echt Violet Methods I and II?

10% Neutral Buffered Formalin (10% NBF)

What is the recommended section thickness for both Cresyl Echt Violet methods?

Cut paraffin sections at 6–8 µm

What is a recommended tissue control for Cresyl Echt Violet Method I?

A section of spinal cord

Fill in the blank: In both Cresyl Echt Violet methods, the Nissl substance and nuclei appear __________ in color.

Blue to purple (or Blue-purple)

What is the color of the background in both Cresyl Echt Violet methods?

Colorless, providing strong contrast

True or False: Cresyl Echt Violet Method II results in background staining that helps localize the neurons.

False.
Explanation: In Method II, the background remains colorless, which enhances the contrast of the Nissl substance and nuclei.

How does Method II differ from Method I in terms of staining selectivity?

• Method II uses acid pH, which restricts staining to DNA- and RNA-containing structures (nuclei and Nissl substance only)

• The contrast with the unstained background is enhanced

What is the main purpose of the Bodian staining method?

To stain nerve fibers, nerve endings, and neurofibrils in tissue sections

What type of neuronal damage is specifically demonstrated using the Bodian method?

Wallerian degeneration, where the axon and myelin sheath distal to a severe or irreversible injury disappear

True or False: Wallerian degeneration affects only the myelin sheath, not the axon.

False.
Explanation: Wallerian degeneration involves the loss of both the axon and its myelin sheath distal to the injury.

What silver-based compound is used for impregnation in the Bodian method?

Protargol S, a brand name for silver proteinate

. Fill in the blank: In the Bodian method, __________ is added to the silver solution to reduce connective tissue staining and improve differentiation.

Copper

What is the proposed mechanism of action for copper in the Bodian method?

• Copper is thought to be more reactive than silver

• It replaces silver in connective tissue fibers, effectively destaining them and enhancing contrast

What reagent is used to reduce silver salts to visible metallic silver?

Hydroquinone

What is the role of gold chloride in the Bodian method?

• Used for toning, similar to reticulum silver methods

• Enhances image clarity and definition by replacing silver with metallic gold

Fill in the blank: __________ may be used to reduce gold chloride, increasing gold deposition and intensifying the stain.

Oxalic acid

What is the purpose of sodium thiosulfate in thBodian method?

To remove any unreduced silver, preventing nonspecific background staining

What is the preferred fixative for the Bodian method?

10% Neutral Buffered Formalin (10% NBF)

What is the recommended section thickness for Bodian staining?

Cut paraffin sections at 6–8 µm

True or False: Spinal cord is the best control tissue for the Bodian method.

False.
Explanation: Spinal cord is not ideal because most nerve fibers appear in cross-section rather than longitudinally. Peripheral nerve or cerebral cortex is preferred.

What precautions should be taken with tools and equipment during the Bodian method?

• Use chemically clean glassware

• Use nonmetallic forceps to avoid unwanted metal contamination or reaction

What cell elements stain with the Bodian method?

• Nerve fibers = Black

• Nuclei = Black

• Background = Light blue or gray

True or False: In the Bodian method, only nerve fibers turn black due to silver reduction.

False.
Explanation: Both nerve fibers and nuclei appear black due to silver deposition.

What is the purpose of the Holmes silver nitrate method?

To demonstrate nerve fibers and neurofibrils in tissue sections.

True or False: The Holmes method is used to demonstrate myelin sheaths.

False.
Explanation: The Holmes method specifically stains nerve fibers and neurofibrils, not myelin.

How did Holmes modify the Bodian method to improve consistency?

• Holmes introduced a buffered impregnation solution containing pyridine, a mild alkali, to improve silver impregnation.

• He believed this altered the electrostatic condition of the tissue for more consistent results.

Fill in the blank: Holmes improved staining consistency by ensuring the silver solution had sufficient __________.

Alkalinity

What type of silver staining technique is the Holmes method classified as?

Argyrophil silver method
Explanation: Argyrophil techniques require chemical reduction (not just physical deposition) to visualize silver deposits.

What is the function of gold chloride, oxalic acid, and sodium thiosulfate in the Holmes method?

• Gold chloride: Toning agent; enhances contrast by replacing silver with gold

• Oxalic acid: Reduces gold, increasing deposition of metallic gold

• Sodium thiosulfate: Removes unreduced silver, preventing nonspecific staining
  (These roles are the same as in the Bodian method)

What fixative is recommended for the Holmes silver nitrate method?

10% Neutral Buffered Formalin (10% NBF)

What is the optimal section thickness for the Holmes method?

10–15 µm paraffin sections

Fill in the blank: Sections for Holmes staining must be handled with __________ glassware and __________ forceps.

• Chemically clean glassware

• Nonmetallic forceps

What is the best control tissue for the Holmes method?

Cerebral cortex

True or False: Spinal cord is a good control tissue for the Holmes method.

False.
Explanation: In spinal cord tissue, most axons are in cross-section, which does not provide optimal visualization of nerve fibers and neurofibrils.

What and how do elements stain in the Holmes method?

• Axons and nerve fibers = Black

• Neurofibrils = Black

True or False: In the Holmes method, the background is intensely stained to enhance nerve visibility.

False.
Explanation: The background remains lightly stained or colorless, allowing black-stained nerve fibers and neurofibrils to stand out clearly.

Compare the Bodian and Holmes methods in terms of silver solution properties.

• Bodian: Uses Protargol (silver proteinate) without a strong alkaline component; results can be inconsistent

• Holmes: Uses a buffered alkaline silver nitrate solution with pyridine to improve consistency and clarity

What is the primary purpose of the Bielschowsky-PAS stain?

To demonstrate:

• Nerve fibers

• Neurofibrillary tangles

• Senile plaques, particularly in Alzheimer disease

True or False: Neurofibrillary tangles are only seen in Alzheimer disease.

False.
Explanation: Although numerous tangles are characteristic of Alzheimer disease, aging alone can cause some neurofibril alteration, including clumping and twisting in a limited number of neurons.

Fill in the blank: In Alzheimer disease, tremendous numbers of __________ develop.

Neurofibrillary tangles

What staining techniques are combined in the Bielschowsky-PAS method?

• Silver impregnation (for nerve structures)

• Periodic acid-Schiff (PAS) (for basement membranes and amyloid)

What reagent is used to impregnate the tissue and deposit silver on neurofibrils and axons?

Ammoniacal silver solution

What reduces the silver to visible metallic silver in Bielschowsky-PAS stain?

Formaldehyde in the developer

What is the role of gold chloride in the Bielschowsky-PAS stain?

• Toning agent: Removes yellow background

• Enhances contrast and definition of black structures

What is the purpose of sodium thiosulfate in Bielschowsky-PAS stain?

To remove unreduced silver, preventing nonspecific staining

What does the PAS component of the stain specifically demonstrate?

• Basement membranes

• Amyloid, particularly in the plaque cores and vessel walls

True or False: The PAS reaction in Bielschowsky-PAS stain is used to enhance silver staining.

False.
Explanation: The PAS reaction targets different structures, notably amyloid and basement membranes, not silver-impregnated nerve fibers.

What is the recommended fixative for the Bielschowsky-PAS stain?

10% Neutral Buffered Formalin (10% NBF)

What is the ideal section thickness for the Bielschowsky-PAS stain?

10% Neutral Buffered Formalin (10% NBF)

What is the most appropriate tissue for quality control in the Bielschowsky-PAS stain?

• Central nervous system (CNS) tissue

• Ideally containing neurofibrillary tangles and senile plaques

True or False: CNS tissue that lacks plaques and tangles is a reliable quality control for the Bielschowsky-PAS stain?

False.
Explanation: The tissue should ideally contain tangles and plaques to confirm proper staining.

What are the tissue components stained in Bielschowsky-PAS method?

• Neurofibrillary tangles & peripheral neurites = Dark black

• Axons = Black

• Amyloid = Magenta

• Lipofuscin = Magenta

Fill in the blank: Both amyloid and lipofuscin stain __________ with the PAS component.

Magenta

True or False: Neurofibrillary tangles and amyloid plaques both appear black with the Bielschowsky-PAS stain.

False.
Explanation:

• Neurofibrillary tangles = Black (silver stain)

• Amyloid = Magenta (PAS stain)

Why might lipofuscin be magenta in the Bielschowsky-PAS stain?

Because it contains carbohydrate-rich components that react with PAS, similar to amyloid

What is the purpose of the microwave modification of the Bielschowsky method?

To demonstrate:

• Nerve fibers

• Neurofibrillary tangles

• Senile plaques
  Especially in the diagnosis of Alzheimer disease

True or False: The microwave modification of the Bielschowsky method is only useful in patients with Alzheimer disease.

False.
Explanation: While Alzheimer disease shows extensive neurofibrillary tangles, normal aging may also cause some neurofibril alteration, including clumping and twisting.