1.2.1 Neurohistology

Question 1

What is a multipolar neuron?

Answer 1

Multipolar: Majority of neurons are this type.

They have a single axon and many dendrites. Described as fusiform, stellate, pyramidal, granule, polyhedron, and spherical based on the morphology of the soma and the arrangement of their processes

Question 2

What is this an image of and what is the importance?

Answer 2

Node of Ranvier – small unmyelinated spot of axon, concentrated of Na channels, allows saltatory conduction of APs

Question 3

What is the role of microglia?

Answer 3

Microglia – activated during injury to phagocytose debris

Question 4

What is the importance of the CSF?

Answer 4

removes waste products/drugs, cushions brain, carries hormones and neurotransmitters

Question 5

Describe the endoplasmic reticulums of neurons.

Answer 5

Neurons have elaborate ER containing both smooth and rough ER

Question 6

What are astrocytes and what is their importance?

Answer 6

Astrocytes – CNS, fibrous (white matter tracts, lipid), protoplasmic (grey matter)

Functions – BBB, structural support, insulation of synapses, electrolyte (K+) and pH balance, sequesters neurotransmitters, immune system and phagocytosis

Question 7

What is a pseudo-unipolar neuron?

Answer 7

single process extends from soma, but may give rise to multiple branches function as dendrites or an axon. Pseudounipolar neurons are found in ganglia of cranial nerves and dorsal root ganglia. They originate as bipolar neurons in which axon/dendrite fuse to form a single T-shaped process extending from soma.

Question 8

What is the arrow pointing at and what is the importance?

Answer 8

Nissl Substance or Nissl Bodies

Alanine stains the RER that is often aggregated in large clusters, known as Nissl bodies. The ER is well developed since neurons produce many molecules

Question 9

What are the characteristics of the Pia Mater?

Answer 9

single cell thick, intimate with brain and spinal tissue, denticulate ligaments in the spinal cord

Question 10

What is neuromelanin?

Answer 10

metabolic byproduct that is dark in fresh tissue, located in substantia nigra (tegmentum) and in noradernergic neurons in the locus coeruleus

Question 11

What is a dendritic spine?

Answer 11

Dendritic spines – increases surface area of dendrite, increase then decreases with age

Question 12

What is a neurofilament?

Answer 12

Neurofilaments – intermediate filaments unique to neurons

Question 13

What is a bipolar neuron?

Answer 13

Bipolar – one axon with single axon and single dendrite on the opposite side, many neurons are bipolar before fully differentiating

Question 14

What is the role of microtubules?

Answer 14

Microtubules – maintain cellular structure integrity, axon growth, and vesicle transport

Question 15

What are the characteristics of the arachnoid mater?

Answer 15

thin and web-like, heavy vasculature, subarachnoid space contains the CSF

Question 16

What are the three layers of the meninges?

Answer 16

Most outside: Dura mater

Arachnoid mater

Most inside: Pia Mater

Question 17

What is the role of a schwann cell?

Answer 17

Schwann cells – myelin formation in Peripheral NS, only one internode, neural crest derived

Question 18

What is an internode?

Answer 18

Internode – axon segment under myelin sheath

Question 19

What is the soma of a neuron?

Answer 19

cell body of the neuron

Question 20

What is the role of an ependymal cell?

Answer 20

single layer to separate neural tissue and ventricle cavities, cuboidal with cilia

Question 21

What is the role of an oligodendrocyte?

Answer 21

Oligodendrocytes – myelin formation in CNS, up to 50 internodes

Question 22

What are some characteristics of the blood brain barrier?

Answer 22

Blood-brain barrier: separates the brain tissue from the rest of the body and environment

Specialized endothelial cells with super tight junctions

Outer surface surrounded by end-feet of astrocytes to help maintain the BBB

Question 23

Describe axonal transport and the difference between anterograde vs retrograde transportation.

Answer 23

Transport – proteins synthesized in the soma are sent up and down the axon

• Anterograde* – toward the + end (synapse), uses kinesin
• Retrograde* – toward the – end (soma), dynein

Question 24

What is this an image of and describe the characteristics.

Answer 24

Neuronal nuclei – large and round located in the center of soma, lack of chromatin → looks clear, prominent nucleololus

Question 25

What are the characteristics of the Dura Mater?

Answer 25

attached to skull, tough due to collagen, contains fibroblasts, vessels, lymphatics

Question 26

What is an axon and what is the importance of them?

Answer 26

Axon – transmission of action potential to the next cell, usually covered with myelin sheath

Question 27

What is the Choroid plexus?

Answer 27

cells in lateral ventricle that produce CSF

Question 28

What is a synapse and what is the importance?

Answer 28

Synapses are highly specialized intercellular junctions that allow neurons to communicate with other neurons or effector cells. Action potentials cause the release of chemical neurotransmitters (housed in synaptic vesicles) that diffuse across the synaptic cleft to affect the postsynaptic cell. Synapses on other neurons can be axodendritic, axosomatic, or axoaxonic.

The synapse between motor neurons and muscle are highly specialized synapses and are one of the most intensely studied synapses. Acetylcholine is the neurotransmitter released by motor neurons. Several neuromuscular diseases affect this important synapse.

Question 29

How do these two images compare to each other?

Answer 29

Top - Normal

Bottom - Parkinsons

Depigmentation of the substantia nigra is the main macroscopic neuropath hallmark of Parkinson’s Disease.

Question 30

What is an axon hillock and what is the importance?

Answer 30

Hillock – cone shaped and is faint staining (few organelles), origin of the axon from the soma

This is also the site where the action potential is generated

Question 31

What is a dendrite and how does it relate to cellular activity?

Answer 31

Dendrite – arise from the soma, spines seen, receives synaptic input from other cells, more dendrites = more activity