1c: Neurohistology

Question 1

Describe (1) Golgi type 1 neurons, and (2) Golgi type 2 neurons, and give examples (what and where).

Answer 1

1. ) Golgi Type I: Long axons; projection neurons = axons that connect disparate sites, e.g. pyramidal cells (cerebral cortex), purkinje cells (cerebellar cortex), α motor neurons (anterior horn).
2. ) Golgi Type II: Short axons; local circuit neurons, i.e. INTERNEURONS. Axons branch within the vicinity of the dendritic fields, e.g. Stellate cells (cerebral and cerebellar cortices), granular cells (dentate gyrus and cerebellar cortex).

Question 2

What are the components of gray matter (6)?

Answer 2

1.) Neuronal cell bodies
2.) Initial portion of axons
3.) Dendrites
4.) Astrocytes
5.) Synapses
6.) Microglial cells
#70

Question 3

What cytoskeletal element is used as a maker for neural tumors?

Answer 3

Intermediate fibers (within a class of neurofilaments) exclusive to neurons and their precursors. 
#7

Question 4

What structures are present in the presynaptic element (4) vs the post-synaptic element (2).

Answer 4

1.) Presynaptic element: Axonal bouton, mitochondria, vesicles with neurotransmitter, and active zones.
2.) Post-synaptic element: Thicker and darker due to actin filaments accumulating in close relation to the plasma membrane. Mitochondria.
#41

Question 5

What does the axon lack that influences its staining properties?

Answer 5

Lacks polyribosomes and RER (emphasizing its dependence on the perikaryon for maintenance). Thus, it does not stain with Nissl stain.
Junq

Question 6

What are the three main differences between axons and dendrites (in terms of one has it, and one doesn’t)?

Answer 6

1.) Spines: Present in dendrites, absent in axons.
2.) Myelin: Present in dendrites, variable in axons.
3.) Nissl substance: Present in dendrites, absent in axons.
#20

Question 7

Which neurotransmitters are biogenic amines (3)

Answer 7

ACh, dopamine, norepinephrine.

Question 8

How does the cell body stain?

Answer 8

Basophilic; i.e. Nissl positive due to large masses of free polysomes and RER (indicates high levels of active protein synthesis) called “Nissl substance.”
Junq

Question 9

Which neurotransmitters are neuropeptides (3)

Answer 9

Substance P, CCK, somatostatin.

Question 10

What are ependymal cells, where are they found, and what is an exceptional structural feature they bear?

Answer 10

Line ventricles and central canal of spinal cord –They are choroid epithelial cells with choroid plexus.
-Simple cuboidal epithelium with microvilli and cilia.
NO BASAL LAMINA, but have intervening desmosomes
#60

Question 11

What do schwann cells make that oligodendrocytes do not?

Answer 11

Schwann cells make BASAL LAMINA, which is not found in CNS (i.e. not made by oligodendrocytes). 
#61

Question 12

What are the components of white matter (3)?

Answer 12

1.) Myelinated axons
2.) Oligodendrocytes
3.) Microglial cells
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Question 13

1. ) What are the CNS glia and what is their origin?

2. ) PNS?

Answer 13

1.) Astrocytes, oligodendrocytes, ependymal cells – NEURAL TUBE. Exception —> Microglia from MONOCYTES.
2.) Schwann cells and satellite cells –NEURAL CREST.
#53

Question 14

Describe the differences between types I and II synapses in terms of symmetry, connection type(s), excitatory or inhibitory, neurotransmitter type(s), and vesicle morphology.

Answer 14

Type I: Asymmetric, mostly axodendritic (spine), excitatory, NTs = ACh, glutamate, Vesicles = Round, large w/ clear centers.

Type II: Symmetric, axosomatic, axoaxonal, axodendritic (nonspinous), inhibitory, NT = GABA, glycine, vesicles = variable. 
#45, pp.21-22 text

Question 15

What are tanycytes?

Answer 15

Specialized tight junction cells in the 3rd ventricle – Type of ependyma. 
#60

Question 16

Describe the difference between axons and dendrites in terms of Nissl staining.

Answer 16

Nissl stains dendrites due to their ribosomes/polysomes and RER.
Axons have no ribosomes or RER in the hillock and, thus, do not stain with Nissl.
p.81 BRS

Question 17

Which neurotransmitters are amino acids (2)

Answer 17

Glutamate, GABA.

Question 18

Which neurotransmitters are gases (2)

Answer 18

NO, CO

Question 19

What is the function of satellite cells (PNS)?

Answer 19

PNS glia; surround sensory and autonomic ganglia for structural and functional support. 
#68

Question 20

What is the easiest way to differentiate axons from dendrites histologically?

Answer 20

Axons have no RIBOSOMES or RER in the hillock.
Dendrites have ribosomes and RER in their proximal parts.
#16

Question 21

1. ) List the excitatory neurotransmitters (3) and how they depolarize the membranes.
2. ) Inhibitory (2)?

Answer 21

1.) ACh, glutamate, serotonin (5-HT).
-Causes Na+ mediated membrane depolarization.
2.) γ-aminonutyric acid (GABA), and glycine.
-Causes Cl- mediated membrane hyperpolarization.
#42