AE Practical - Neural Histology

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Introduction

Adult human brain (lateral view)

Adult brain animation 01.gif

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AEB Practical 10 for Monday and Wednesday in October.

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.
Practical Audio
Mark Hill.jpg
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These are a live unedited recording from the neural histology practical and may contain errors in either descriptions or content. Sound quality was affected by building works.

These recordings are designed for University level students and may not be suitable for younger students. No reproduction or publication without permission. For educational purposes only.

Want Embryology on your iPhone?

Hint - Open the "listen" link as a new tab in your browser, then open AEB Practical Virtual Slides in another tab. You can then listen to the audio as you look at the virtual slide being described.

Dr Mark Hill Wednesday October 17 3pm WW G2/4

Medicine Audio


Links: Histology Stains | Terms | Textbooks | Audio | Neural System Development

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.

Structure of myelinated axons 01.jpg
Structure of central and peripheral myelinated axons[1]


a - Myelinating glial cells, oligodendrocytes in the central nervous system (CNS) or Schwann cells in the peripheral nervous system (PNS).


  • Form the myelin sheath by enwrapping their membrane several times around the axon.
  • Myelin covers the axon at intervals (internodes), leaving bare gaps (nodes of Ranvier).
  • Oligodendrocytes can myelinate different axons and several internodes per axon.
  • Schwann cells myelinate a single internode in a single axon.

(text modified from original figure legend)

Practical class activities

Transverse section of the spinal cord in the mid-thoracic region
Fig. 675. A spinal nerve with its anterior and posterior roots

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?
Spinal cord - Grey and white matter
Spinal cord histology 03.jpg Spinal cord histology 04.jpg
Spinal cord - Grey matter
Spinal cord histology 11.jpg

Grey matter (HE)

Spinal cord histology 12.jpg

Grey matter (silver)

  • What do Nissl granules represent?
  • What is the functional difference between an axon and a dendrite?
Spinal cord histology 10.jpg
Mouse ependymal cilia 01-icon.jpg
 ‎‎Ependymal cilia
Page | Play

Spinal Cord ependymal cells

  • What is the function of ependymal cells?
  • What function do the meninges serve and what type of tissue are the meninges made up of?
  • What is the function of an oligodendrocyte and of an astrocyte?

Histology Images

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


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 neuron?


Cerebellum Images: Anatomical position | Upper surface | Projection fibres | Sagittal section | Transverse section folium | Cerebellum Development
Gray0706.jpg

Cerebellum - historic drawing

Cortex

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?
Myelination animation.gif

Simplified animation shown how an axon develops a myelin sheath consisting of layers of either oligodendrocyte (CNS) or Schwann (PNS) cell membrane.

Peripheral nerve histology 04.jpg

neurovascular bundle osmium

Peripheral nerve histology 05.jpg

overview osmium

Peripheral nerve histology 01.jpg

neural connective tissue HE

Peripheral nerve histology 02.jpg

nerve longitudinal HE

Peripheral nerve histology 03.jpg

myelin sheath HE

Nerve Images: neurovascular bundle osmium | overview osmium | neural connective tissue HE | nerve longitudinal HE | myelin sheath HE | Medicine Practical

Sensory and Autonomic Ganglia

Dorsal root ganglion histology 01.jpg Autonomic ganglion histology 01.jpg

Virtual Slide Box (Sensory Trigeminal Ganglion, cat., Luxol Fast Blue and H&E).

  • Identify the pseudounipolar somata, with central nuclei and satellite cells.
  • Identify the axons, axon hillock, neurokeratin and Schmidt-Lanterman cleft.
  • What is the function of the sensory ganglion?

Development

The following information is not part of the current class, but for students interested in issues of normal and abnormal neural development.


Neural Links: Introduction | Ventricular System | Stage 22 | Gliogenesis | Fetal | Lecture - Early Neural | Lecture - Neural Crest | Lab - Early Neural | Neural Crest | Sensory | Abnormalities | Folic Acid | Iodine Deficiency | Fetal Alcohol Syndrome | Postnatal | Postnatal - Neural Examination | Histology | Historic Neural | Category:Neural
Neural Parts: Introduction | Prosencephalon | Telencephalon | Amygdala | Hippocampus | Basal Ganglia | lateral ventricles | Diencephalon | Epithalamus | Thalamus | Hypothalamus | Pituitary | Pineal | third ventricle | Mesencephalon | Mesencephalon | Tectum | cerebral aqueduct | Rhombencephalon | Metencephalon | Pons | Cerebellum | Myelencephalon | Medulla Oblongata | Spinal Cord | Vascular | Meninges | Category:Neural

Developing Cortex

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.
  • Meninges - shown to the left of the section. Note the presence of many blood vessels in this region.
  • Ventricles - shown to the right of the section.
  • Developing cerebrum layer thicknesses are shown in microns.
Stage 22 image 217.jpg

Neural System - Abnormalities

Developing Spinal Cord

Stage 22 - Spinal Cord (rotated)

Human Stage22 spinal cord03.jpg

 ‎‎Mobile | Desktop | Original

Stage 22 | Embryo Slides
These listed features link to zoomed views of the virtual slide with the named feature generally in the centre of the view.

Use the (-) at the top left of the screen to see where this feature is located.

Spinal Cord Features Other Features

Terms

  • arachnoid mater - (Greek, arachne = spider + -oeides = form) A meshwork (spider web-like) connective tissue covering of the central nervous system, forms part of the meningial layers. Lies between tough outer dura mater layer and the inner fine pia mater layer. These three connective tissue layers have different embryonic origins: dura is from mesoderm, pia and arachnoid layers are neural crest in origin. The space underlying the arachnoid mater (subarachnoid space) is filled with cerebrospinal fluid.
  • 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.
  • axon hillock - point of axon beginning or initiation from the neuron cell body (soma). (hillock, is a small hill)
  • blood-brain barrier - (BBB) formed by endothelial cells of brain capillaries, differing in junctions, transport and glial association from those found in peripheral capillaries. Damage to this layer can occur following injuries involving ischemia and reperfusion. Note a similar vascular "barrier" can be found in the testis.
  • cell body - (soma, perikaryon) is the region of the neuron containing a large pale-staining spherical, nucleus with a conspicuous nucleolus and perinuclear cytoplasm.
  • dura mater - (Latin, dura mater = hard mother) The outer tough connective tissue meningial coat of the 3 layers that cover the central nervous system of 3 layers (overlays the arachnoid mater middle layer and pia mater inner layer). These three connective tissue layers have different embryonic origins: dura is from mesoderm, pia mater and arachnoid layers are neural crest in origin.Duramater at the level of the spinal cord is separated from the periosteum of the vertebral canal by an epidural space.
  • leptomeninges - (thin meninges) Term referring to just the pia mater and arachnoid mater layers of the meninges.
  • Luxol fast blue - stain for myelin sheath of nerve fibres. (More? Histology Stains)
  • meninges - (singular meninx; Greek, meninx = membrane) Anatomical term describing the three connective tissue layers that surround the entire central nervous system (brain and spinal cord). The 3 layers from the central nervous outward are: pia mater, arachnoid mater, and the dura mater. These layers also have differing embryonic origins; dura mater is mesoderm, pia mater and arachnoid are neural crest. The space under the arachnoid layer (subarachnoid space) is filled with cerebrospinal fluid. (More? Image - Meninges cartoon)
  • meningococcal disease - (meningitis) Term describing the bacterial infection of cerebrospinal fluid of the spinal cord and brain. Note meningitis can also be caused by a viral or other organism infection. Treatment and outcomes differ for either viral (less severe, resolves without specific treatment) or bacterial (severe, may result in brain damage, hearing loss, or learning disability) infections. (More? Bacterial Infection | Postnatal Development | CDC - meningococcal disease | Medline Plus - Meningitis)
  • myelin - (myelin sheath) 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.
  • neuropil - (neuropile) is the region of nerve fibres (axons and dendrites) with numerous synapses and also glia, with few neural cell bodies. (Historic term, located in grey matter and does not refer to white matter.)
  • neurokeratin - Term describing the protein network remaining after the myelin has been removed from the myelin sheath of nerves and seen in the histological sections. (Historically used by Ewald and Kuhnefirst in 1877 to describe "the substance contained in medullated nerves and in the central nerve organs which is insoluble in alcohol and ether".)
  • Nissl body - Term describing the chromatophilic granules in the neuronal soma formed by the rough endoplasmic reticulum, very apparent in spinal cord motor neuron histology. (Named after Franz Nissl (1860 - 1919) a German neurologist.)
  • node of Ranvier - Distinct myelinated axon region where two adjacent segments of myelin are separated an short unmyelinated region. Physiological site for action potential saltatory conduction jumping. (Named after their discoverer Louis Antoine Ranvier (1835 – 1922), a German anatomist.)
  • perineurium - A lamellated sheath of connective tissue and cells around a nerve fascicle. (3 CT layers: epineurium-perineurium-endoneurium)
  • pia mater - A fine connective tissue covering of the central nervous system, forms innermost part of the meningial layers. Lies beneath the arachnoid mater and then tough outer dura mater layer. These three connective tissue layers have different embryonic origins: pia mater and arachnoid layers are neural crest in origin, dura is from mesoderm. The space overlying the pia mater (subarachnoid space) is filled with cerebrospinal fluid. The pia mater has close contact with the spinal cord and brain, in the brain it follows down into the sulci and fissures of the cortex. This layer also fuses with the membranous lining of the ventricles (ependyma) forming the choroid plexus.
  • Purkinje (Purkyne), Johannes Evangelista, Ritter von. (1787 - 1869) Breslau pathologist, Prague physiologist; famous microscopist; early use of microtome; P. cells = largest cerebellar neurones with extensive dendrites (1837); P. cells = conducting heart cells (1845); P. phenomenon = casting shadows of retinal blood vessels.
  • satellite cells - (satellite glial cells) Glial cells that surround each neuron in peripheral ganglia (sensory, sympathetic). (Note these should not be confused with entirely different "satellite cells" found in skeletal muscle.)
  • Schmidt-Lanterman cleft - (Schmidt-Lanterman incisure) remnants of Schwann cell cytoplasm forming funnel-shaped circumferential discontinuities distributed irregularly (10 to 100 micron intervals) throughout the internodal myelin. May have a role in peripheral nerve stretch, these incisures are not usually present in the CNS. (More? Schmidt-Lanterman cleft cartoon | Figure 4-9)
  • soma - see cell body.
  • substantia gelatinosa - (substantia gelatinosa of Rolando) Distinct region of spinal cord grey matter in dorsal horn containing both small neurons and neuroglia, appears pale due to presence of very few myelinated fibers.

References

  1. Sebastian Poliak, Elior Peles The local differentiation of myelinated axons at nodes of Ranvier. Nat. Rev. Neurosci.: 2003, 4(12);968-80 PubMed 14682359 | Nat Rev Neurosci.


Textbook

Neuroscience 2nd edition. Purves D, Augustine GJ, Fitzpatrick D, et al., editors. Sunderland (MA): Sinauer Associates; 2001.

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Cite this page: Hill, M.A. 2017 Embryology AE Practical - Neural Histology. Retrieved May 1, 2017, from https://embryology.med.unsw.edu.au/embryology/index.php/AE_Practical_-_Neural_Histology

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© Dr Mark Hill 2017, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G