Download Chapter 02 - Neurons and Glia

Lecture Outline, Chapter 2, Neurons and Glia
INTRODUCTION
1. Introduce the chapter by explaining that all tissues and organs in the body consist of cells.
Explain how the specialized functions of cells determine organ function. (Refer to PowerPoint
slide 02.)
2. Explain the “neurophilosophy” of the book, which is that there is no need to separate mind
and brain. (Refer to PowerPoint slide 02.)
3. Describe the two major cell types that are found in the brain (neurons and glia), including
their distribution and their functions. Emphasize the importance of the neurons for brain
function based on their unique role in information processing. (Refer to PowerPoint slide 02.)
Teaching Suggestion: To explain the distribution of neurons and glia, compare the brain to a
chocolate chip cookie where the chips are the neurons and the dough is the glia.
THE NEURON DOCTRINE
4. Describe the technical advancements leading to the field of histology, and how these
contributed to the growth of neuroscience and overcame obstacles. Describe the Nissl stain,
how it was developed, and its use in neuroscience. (Refer to PowerPoint slide 03.)
Teaching Suggestion: Talk about the jellylike consistency of brain tissue and the difficulty in
making thin slices because of this consistency. Show a microtome to students and
demonstrate its use in slicing brain tissue. Using Figure 2.1, explain how neurons were first
visualized using the Nissl stain. Describe how the Nissl stain has been useful in the study of
cytoarchitecture.
Discussion Point: In an interactive session, discuss the important breakthroughs in the field of
neurohistology.
5. Describe the Golgi stain and how it was developed by Camillo Golgi. In addition, explain the
advantage of the Golgi stain over the Nissl stain. (Refer to PowerPoint slide 04.)
Teaching Suggestion: Using Figure 2.3, point out how Golgi-stained neurons have two
distinguishing parts. Using Figure 2.4, identify the basic parts of a neuron: point out the two
types of neurites: axons and dendrites. Briefly outline the differences between axons and
dendrites. (Refer to PowerPoint slide 05.)
6. Describe the highlights of Ramón y Cajal’s contributions to the field of neuroscience.
Mention how Cajal and Golgi came to different conclusions about how the nervous system is
built from neurons. In addition, explain the neuron doctrine. (Refer to PowerPoint slide 06.)
Teaching Suggestion: Using Figure 2.6, explain Cajal’s view of neurons and also give a brief
outline of cell theory.
Discussion Point: Show students an electron microscope. In an interactive session with
students, using Figure 2.7, discuss how the development of the electron microscope led to the
affirmation of the neuron doctrine.
THE PROTOTYPICAL NEURON
7. Describe the appearance of the neuronal membrane and the physical composition of the soma.
(Refer to PowerPoint slide 08.)
Teaching Suggestion: Using Figure 2.8, create a chart to describe the internal structure of a
neuron. (Refer to PowerPoint slide 10.)
8. Describe the structure of the nucleus. Introduce the terms DNA, chromosomes, gene
expression, and protein synthesis. Explain how protein synthesis takes place in the cytoplasm
and also discuss the role of mRNA in protein synthesis. (Refer to PowerPoint slide 09.)
Teaching Suggestion: Using Figure 2.9a, describe the process of transcription, RNA
processing, and its export from nucleus. Using Figure 2.9b, explain RNA splicing and the
process of translation.
1) Introduce molecular neurobiology as a field and touch on the “central dogma” of
molecular biology.
Discussion Point: Discuss the following case study with students and explain how
differences in gene expression of a normal brain and a diseased brain can be used to identify
the molecular basis of observed symptoms.
Nicolas was diagnosed with a brain disease, and his symptoms were recorded. In order to
understand the root cause of his illness, the research team suggested that checking for
altered gene expression would be useful. Samples of mRNA were collected from Nicolas’s
brain and from a normal brain so that comparisons could be made. mRNAs from the two
brains were labeled green and red, respectively.
1) Why is it useful to test differences in gene expression?
2) What happens when the samples are applied to the microarray?
9. Describe neuronal genes and explain the processes of genetic variation. Describe the uses of
and genetic engineering in neuroscience. (Refer to PowerPoint slide 11.)
10. Explain the process of protein synthesis that takes place in ribosomes in the rough
endoplasmic reticulum or ER. (Refer to PowerPoint slide 12.)
Teaching Suggestion: Using Figure 2.10, describe the location and structure of rough ER.
11. Differentiate between free ribosomes and polyribosomes. (Refer to PowerPoint slide 13.)
Teaching Suggestion: Using Figure 2.11, differentiate between protein synthesis on a free
ribosome and on rough ER.
12. Describe the functions of smooth ER and the Golgi apparatus. (Refer to PowerPoint slide
14.)
Teaching Suggestion: Using Figure 2.12, describe how proteins are sorted in Golgi apparatus
and readied for delivery to appropriate locations in the neuron.
13. Describe the location and structure of the mitochondria. Explain what a mitochondrion
“inhales” and “exhales.” (Refer to PowerPoint slide 15.)
Teaching Suggestion: (1) Using Figure 2.13a, identify the parts of a mitochondrion.
(2) Using Figure 2.13b, explain how cellular respiration takes place in mitochondria. Explain
Krebs cycle and give an account of how ATP, the energy currency of the cell, is produced in
mitochondria.
14. State the function of the neuronal membrane and explain how the protein composition of the
membrane varies. (Refer to PowerPoint slide 16.)
15. Discuss the cytoskeleton and its structure. List the primary structures of the cytoskeleton.
(Refer to PowerPoint slide 17.)
Teaching Suggestion: Using Figure 2.14, illustrate the structural components of the
cytoskeleton. Explain the process of polymerization. Illustrate how the tubulin molecule is
arranged in the microtubule and also the arrangement of actin molecule in the microfilament.
Describe the structure of the neurofilament and why it is considered to be stronger than the
other two cytoskeletal components.
Discussion Point: Discuss the following case study in the classroom and explain how the role
of cytoskeletal components in Alzheimer’s disease.
Martha, age 51 years, showed various symptoms of Alzheimer’s disease. She expressed a
strong feeling of jealously toward her husband, had memory impairments, was disoriented
and at times paranoid, and experienced auditory hallucinations. Her condition deteriorated
over the next few years. Postmortem examination of her brain revealed characteristic
neurofibrillary tangles.
1) What is the relationship between the cytoskeletal disruptions and the functioning of the
brain?
2) What happens to the microtubule-associated protein tau in the neurons, and what are the
consequences of this change?
16. Explain the structure of an axon and the soma. (Refer to PowerPoint slide 18.)
Teaching Suggestion: Using Figure 2.15, point out the axon hillock and explain that this is the
region where the axon begins. Define axon collaterals, the branches of the axon. Describe
recurrent collaterals, the branches that curve back and return to the same cell that gave rise to
them. State the relationship between the diameter of the axon and the speed of an electric
signal.
17. List the differences between the cytoplasm of the axon and that of the axon terminal.
Describe the synapse, the site where the axon meets the postsynaptic cell. Describe the
process of synaptic transmission. (Refer to PowerPoint slides 19 and 20.)
Teaching Suggestion: Using Figure 2.16, explain how axon terminals form synapses with the
dendrites or somata of other neurons.
1) Describe terminal arbors and briefly explain innervation.
2) Discuss the terms presynaptic, postsynaptic, and synaptic cleft.
18. Explain that the distal portion of a cut axon degenerates, a process called Wallerian
degeneration. This degeneration occurs because the distal portion is cut off from the parent
cell body. Explain how the process of degeneration led to the discovery of axoplasmic
transport. In addition, describe axoplasmic transport and the concept of the molecular “legs”
that drive it. (Refer to PowerPoint slide 21.)
Teaching Suggestion: Using Figure 2.18, explain anterograde transport and retrograde
transport and describe the roles of kinesin and dynein.
Discussion Point: Discuss the following case study in the classroom and explain how
retrograde transport help when studying brain connections.
A competent research team injected HRP into the brain in order to study the connections of
the cells at the injected site.
1) What happens to the HRP? (It is taken up by the cell bodies and transported anterogradely
to the axon terminals; it is also taken up by axon terminals at the site of injection and
transported retrogradely to the cells that project to the injected site.)
2) How is the HRP visualized? (By use of a chemical reaction.)
3) How do the herpes virus or rabies virus use retrograde transport to their advantage?
19. Briefly describe the dendritic tree and the function of dendrites. Discuss the role of receptors
as detectors of neurotransmitters. (Refer to PowerPoint slide 22.)
Teaching Suggestion: 1) Using Figure 2.19, describe how dendrites receive synaptic inputs
from axon terminals.
2) Using Figure 2.20, describe how some neurons are covered with specialized protrusions
known as dendritic spines. Explain how the cytoplasm of the dendrite and that of the axon is
similar because both contain cytoskeleton elements and mitochondria. Explain the difference
between the two (polyribosomes are seen in dendrites, as discovered by Oswald Steward).
Discussion Point: Discuss the following case study and explain how the dendritic spines of
mentally retarded children resemble that of a normal human fetus.
Sam was found to be intellectually disabled because of an impoverished environment during
the critical period of his childhood. This can lead to profound changes in the circuits of the
brain. After his death, tissue from his cortex was stained with the Golgi stain and the dendritic
spines on cortical neurons were examined.
1) What changes would you expect to see in the dendritic spines?
2) What is a general feature of dendritic spines in intellectually disabled individuals?
CLASSIFYING NEURONS
20. Explain that neuroscientists have devised various schemes for the classification of neurons.
Discuss the advantages of classifying neurons. In addition, explain the classification that is
based on the number of neurites. (Refer to PowerPoint slide 23.)
Teaching Suggestion: Using Figure 2.22, distinguish among unipolar, bipolar, and multipolar
neurons. This classification is based on the number of neurites on the cell soma.
21. Explain the classification of neurons based on dendritic tree structure. Point out that such
classification is often unique to a particular region of the brain. Give examples of variations in
the shape of dendritic trees. (Refer to PowerPoint slide 24.)
Teaching Suggestion: Using Figure 2.23, distinguish between the stellate cell and the
pyramidal cell, two types of neurons found in the cerebral cortex. Mention a simple way of
classifying neurons, based on whether or not their dendrites have spines. Explain how these
classifications of dendrites often overlap.
22. Explain the classification of neurons based on their connections. Define primary sensory
neurons, motor neurons, and interneurons. Describe the classification of neurons based on
axon length. Differentiate between Golgi type I and Golgi type II neurons. (Refer to
PowerPoint slide 25.)
23. Explain the classification of neurons based on gene expression and type of neurotransmitter.
Mention how neurons are classified based on their chemistry. Provide an example of
cholinergic cells, explaining that motor neurons release the neurotransmitter acetylcholine at
their synapses. (Refer to PowerPoint slide 26.)
GLIA
24. Explain how glia contribute to brain function by supporting neuronal function. Describe
astrocytes and their role in the brain. (Refer to PowerPoint slide 27.)
Teaching Suggestion: Using Figure 2.24, describe how astrocytes fill spaces between neurons
in the brain and how they may influence the growth and retraction of a neurite. In addition,
explain the role of astrocytes in regulating the chemical content of the extracellular space.
25. Describe myelinating glia and explain the primary function of oligodendroglial and Schwann
cells as providing layers of membrane to insulate axons. Describe the function of microglia as
phagocytes. (Refer to PowerPoint slides 28 and 29.)
Teaching Suggestion:
1) Using Figure 2.26, explain how Boston University anatomist Alan Peters showed that
myelin spirals around the axons in the brain.
2) Using Figure 2.27, identify the node of Ranvier as a region where the axonal
membrane is exposed. In addition, differentiate between oligodendroglia and Schwann cells
on the basis of their locations and their mode of contributing myelin to axons.
26. Describe other types of non-neuronal cells. (Refer to PowerPoint slide 30.)
CONCLUDING REMARKS
27. Describe how the structural characteristics of a neuron provide insights to neurons and how
the different parts function. (Refer to PowerPoint slide 31.)
Teaching Suggestion: Ask students to review the structural characteristics of a neuron.
Explain how an important feature of neurons is the presence of rough ER, which is a site for
protein synthesis.
Discussion Point: Ask students to provide rationales for the following:
1) The absence of ribosomes in the axon
2) The large number of mitochondria in the axon terminal
3) The elaborate structure of the dendritic tree