AE Practical - Neural Histology

From Embryology

Introduction

Adult human brain (lateral view)
Draft Page
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AEB Practical 10 for Monday October 15 and Wednesday October 17.

AEB Practical Virtual Slides

This page provides histology support information for central nervous system structure.

Disclaimers

  • does not form part of the actual practical class based upon the virtual slides.
  • does not cover the pathology content.
Adult brain animation 01.gif

Aims

Historic cortex histology
  1. Obtain an understanding of the normal histological appearance of selected central and peripheral nervous system tissues namely spinal cord, cerebellum and peripheral nerve.
  2. To examine unique microscopic characteristics of each of the nervous tissues.
  3. To introduce the histology and neuropathology associated with cerebral infarction and haemorrhage.

Key concepts

A Neuron - the functional unit of the nervous system

The brain and spinal cord comprise the central nervous system (CNS). The nerves that emerge from the spinal cord and brain to pass to parts of the body are the peripheral nervous tissue (PNS). Nervous tissue, with many interconnections, forms a complex system of neuronal communication within the body and is specialized for detecting stimuli, integrating functions, controlling effectors and higher functions. Nervous tissue consists of cell bodies, cell processes (nerves), and neuroglia (supporting cells).

Neurons

Structural and Functional units of the nervous system.

These cells (around 12 billion) are responsible for the receptive, integrative, and motor functions of the nervous system. They can generate nerve impulses (irritability), and can transmit these impulses along their processes (conductivity). They range in diameter from 5 to 150 μm and contain 3 parts: a cell body, multiple dendrites and a single axon.

  1. Cell body (soma, perikaryon) is the region of the neuron containing a large pale-staining spherical, nucleus with a conspicuous nucleolus and perinuclear cytoplasm.
  2. Dendrites project from the cell body and are specialized for receiving (afferent) stimuli from sensory cells, axons and other neurons which are then transmitted towards the soma.
  3. Axons arise as a single thin process extending longer distances from the cell body than the dendrite. As with dendrites, the terminals of the axon are branching and terminate in end bulbs (terminal boutons), which come close to another cell and form a synapse.


Peripheral Nerve Fibers

Peripheral nerves are bundles (fascicles) of nerve fibers (axons) surrounded by several CT sheaths. Each bundle contains sensory and motor components.

Myelinated Fibers (1-20μm diameter)

Myelin (rich in lipid) is the membrane of the Schwann cell organized into a spiral sheath that is wrapped several times around the axon. Schwann cells are cells whose cytoplasm contains a flattened nucleus, a small Golgi apparatus, and a few mitochondria. Myelinated fibers are capable of rapid transfer of impulses (touch sensory pathways).

Unmyelinated Fibers (less than 2μm in diameter)

Some axons in the PNS are surrounded by Schwann cells but not wrapped with layers of myelin. They arefound in pain and temperature sensory pathways and motor paths to the viscera.

Practical class activities

Spinal Cord

Virtual Slide Box (Spinal cord and Spinal cord smear) and Zurich Virtual Slide database (Spinal cord-Thoracic Segment-Luxol Fast Blue, Neutral Red and Spinal cord-Lumbar Segment-Azan and Meninges-Azan).

Identify gray and white matter, central canal (surrounded by ependymal cells), dorsal and ventral horns, meninges (pia, arachnoid and dura mater), subarachnoid space with dorsal and ventral rootlets, blood vessels, a motor neurone with a cell body (soma), nucleus, nucleolus, Nissl granules, an axon with axon hillock area, dendrites, glial cells (oligodendrocytes, astrocytes).

Spinal cord (Luxol Fast Blue)
Spinal cord histology 01.jpg Spinal cord histology 02.jpg
  • What is the difference between white and gray matter?
  • What is the function of ependymal cells?
  • What do Nissl granules represent?
  • What function do the meninges serve and what type of tissue are the meninges made up of?
  • What is the functional difference between an axon and a dendrite?
  • What is the function of an oligodendrocyte and of an astrocyte?

Cerebellum

Virtual Slide Box (Brain/Cerebellum and Cerebellum silver stain) and Zurich Virtual Slide database (Cerebellum silver stain).

  • Identify the folia (folds), meninges (pia and arachnoid mater), blood vessels, and white and gray matter. The gray matter is subdivided into 3 distinct layers namely outer molecular, inner granular and middle Purkinje cell layer. Note the processes on the Purkinje cells.
  • What does white matter consist of?
  • What is the function of the Purkinje fibers?

Peripheral Nerve

Virtual Slide Box (Peripheral Nerve) and Zurich Virtual Slide database (Nerve; Goldner and Nerve; Haematoxylin and Eosin)

  • Identify fascicles (bundles) of nerves, levels of connective tissue wrappings (epineurium, perineurium, endoneurium), fibroblast nuclei, adipose tissue, blood vessels, myelinated nerve fibers, axons, and Schwann cells.
  • What is the function of a Schwann cell and what effect does myelin have on nerve transmission?
  • Why do 3 levels of connective tissue wrap nerve fibers?

Brain Histology

Developing Brain Histology

Stage 22 image 217.jpg

  • Human embryo developing cortex, Week 8, Carnegie stage 22.
  • Inset (upper right) shows section overview and approximate level of section (red line).
  • Thin layer outer called cortical plate will eventually form the adult brain cortex.
    • Other underlying layers are part of the development process and will continue to supply cells to the cortex through fetal period, these layers will eventually be almost completely lost.
  • Developing cerebrum layer thicknesses are shown in microns.

Spinal Cord Histology

Spinal Cord: Overview 1 | Overview 2 | Overview animation | Grey matter | Grey matter | Grey matter | White matter | Overview unlabeled | Grey matter unlabeled 1 | Grey matter unlabeled 2 | White matter unlabeled 1 | Ependymal cells unlabeled


Terms

  • artifact - changes and distortions introduced to the normal tissue structure by the histological processing. Common artifacts include: folds (gives the tissue a darker appearance), tears (rips in the tissue can be seen in epithelia), shrinkage when tissues loose mainly liquid through histological processing, and cuts often used in tissue preparation.
  • myelin - is the membrane of a glial cell (brain, oligodendrocyte; peripheral nerve, Schwann cell) organized into a spiral sheath that is wrapped many times around the axon.

Glossary Links

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Cite this page: Hill, M.A. (2024, March 28) Embryology AE Practical - Neural Histology. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/AE_Practical_-_Neural_Histology

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© Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G