ANS 123 Exam 3 Nervous Tissue

What is hypertrophy?

• Growth due to an increase in cell size

What is hyperplasia?

• Growth due to an increase in cell number

Can hypertrophy and hyperplasia happen at the same time?

• Yes

What is neurogenesis?

• The formation of neurons

What is a neural progenitor cell?

• A multipotent cell that can produce both neurons and glial cells

What does multipotent mean?

• a cell that can code for cells related for a germ layer

What is a neuron?

• A terminally post-mitotic nervous system cell that receives and transmits electrical signals

What does terminally post-mitotic mean?

• cell that no longer divides

What is a neurite?

• any neuronal process, such as an early axon or dendrite.

What is a ganglion?

• A group of neuronal cell bodies, or soma, in the PNS

What is a nerve?

• A bundle of axons from a ganglion.

What is the basal lamina/basement membrane?

• An extracellular matrix layer that attaches, anchors, and surrounds epithelial tissues and structures

What structure turns into a powerful inductive agent?

• basal lamina

What does it mean that neural progenitors are multipotent?

• They can give rise to both neurons and glial cells

What does the brain progress from during development?

• A 3-part brain to a 5-part brain

What causes the neural tube to thicken?

• Cell division of neural tube ectoderm/neural progenitor cells

What process allows distinct brain regions to form?

• Regional differentiation and proliferation

What are the walls of the developing brain made from?

• ectoderm from neural tube

What structure is present at the end of neurulation?

• A fully formed neural tube

What coats the outer surface of the neural tube?

• Basal lamina

What type of cells make up the early neural tube wall?

• A single layer of multipotent neural progenitor cells

Are early neural progenitors bipolar?

• Yes, they have two processes extending in opposite directions

Where do the processes of a bipolar neural progenitor extend?

• Toward the center of the neural tube/future ventricle

• Toward the outer surface of the neural tube/basal lamina

What is the ventricular zone?

• The inner region near the future ventricle where cytokinesis occurs

What is the marginal zone?

• The outer region near the basal lamina where cells enter the resting phase of mitosis

What is unique about the soma of multipotent neural progenitors?

• the soma migrates back and forth between ventricular and outer surfaces during stages of mitosis

Why does the early neural tube look stratified?

• Due to combination of migrating soma and massive proliferation of neural progenitors

Is the early neural tube actually stratified?

• No, it is pseudostratified

What does pseudostratified mean in the neural tube?

• It looks like multiple layers, but it is actually one layer of cells with one neurite anchored in ventricular zone and another neurite anchored in the marginal zone

Where does cytokinesis occur in neural progenitors?

• Near the ventricular surface/ventricular zone

Where do neural progenitors enter the resting phase of mitosis?

• Near the outer surface/marginal zone

Why is neurogenesis dynamic?

• Neural progenitor soma constantly migrate while also proliferating

What is the key idea of early neurogenesis?

• A single layer of multipotent progenitors produces many cells while appearing pseudostratifie

What are the three phases of neurogenesis?

• Expansion

• neurogenic phase

• late neurogenesis

What type of division happens during the expansion phase?

• symmetric only

What is the purpose of the expansion phase?

• To produce many identical neural progenitor cells and thicken the neural tube

• 3 part to 5 part brain

What type of division happens during the neurogenic phase?

• Both symmetric and asymmetric division occur.

Why is the neurogenic phase considered “true neurogenesis”

• It is the first time we see/produce a cell that is actually considered a neuron

what is the product of symmetric division in neurogenic stage?-

• 2 identical daughter cells

what is the product of asymmetric division in neurogenic stage?

• one neural progenitor cell

• one transiently amplifying neuron (TA neuron)

What is a TA neuron?

• A transiently amplifying neuron; a neuron precursor that does not anchor but starts sending out neurites

What happens during late neurogenesis?

• Symmetric division

• asymmetric division

• direct conversion occur

What type of cells are produced during late neurogenesis?

• Neuroglial cells and glial cell precursors

What is direct conversion?

• A progenitor stops dividing and fully differentiates into a neuroglial cell

What do we see during late neurogenesis when it comes to product of asymmetric divisions?

• introduce neuroglial cells from division of the TA Neuron

How does late neurogenesis contribute to adult nervous tissue diversity?

• It produces different neuroglial cell types via TA neuroglial cells, such as oligodendrocytes and astrocytes, adding to the variety of nervous system cells

What is produced early in neurogenesis?

• more neural progenitor cells via symmetric division

What is produced during the main neurogenic phase?

• TA Neurons

• terminally post-mitotic neurons

What is produced in late neurogenesis?

• nueroprogenitor coding shifts to asymmetrically divide into TA Neuron and Nueroglial cells

as neuroprogenitor cells age, they remove their ability to do what?

• be a true progenitor cell and will divide symmetrically to make unipotent neuroglial cells

What are examples of glial cells?

• Oligodendrocytes

• astrocytes

• microglial cells

• ependymal cells

What happens to one daughter cell after asymmetric division of neurogenic phase?

• One daughter cell is not bipolar and begins migrating toward the marginal zone

How do migrating daughter cells during neurogenic phase move outward?

• They wrap around the process of a neural progenitor cell and climb toward the marginal zone

What were neural progenitors originally misidentified as?

• Radial glial cells/glial cells

What happens as neurons leave the intermediate zone?

• They differentiate and become post-mitotic

Why can TA Neurons undergo divisions as they climb up the neurite?

• because when they hit the subventricular zone they undergo determination and differentiation leading to their division and more crowding

Why do newer neurons migrate farther outward?

• Earlier neurons settle first, so newer neurons must move past them to find open space

What structure forms as newer neurons migrate farther outward?

• Cortical Layers (Layers of the Cortex)

When does the neural tube stop being pseudostratified?

• As neurons migrate outward and form cortical layers, around birth

Is post-natal neurogenesis common in endotherms?

• No its rare

What is the general mammalian pattern for neurogenesis after sexual maturity?

• little evidence of neurogenesis beyond sexual maturity

Where is adult neurogenesis usually restricted in mammals?

• The hippocampus and subventricular zone of the lateral ventricle, with migration to the olfactory bulb.

What are bird exceptions to limited post-natal neurogenesis?

• Birds with seasonal behavioral changes can show dramatic hippocampal neurogenesis

What behaviors are linked to bird hippocampal neurogenesis?

• learn songs/ perform

• migrate

• Caching food

When can rodents show post-natal neurogenesis?

• During olfactory memory formation

Where can rodent post-natal neurogenesis occur?

• Forebrain with migration to the olfactory bulb, and possibly hippocampus throughout life

What causes most post-natal nervous tissue growth?

• Growth of neurites, especially axons

Why do axons need to grow after neurons become post-mitotic?

• The soma are stationary, so axons must extend to reach distant target tissues.

Why is axon growth important as the body grows?

• Body parts move farther from the CNS, so axons must maintain or establish connections

What drives axonal growth before synapse formation?

• The axon growth cone

What happens after an axon synapses with its target?

• Growth shifts from growth-cone-driven growth to stretching/interstitial growth

What signals a neurite to become an axon?

• Contact or signaling from the basal lamina

Which neurite becomes the axon?

• The neurite of a post-mitotic neuron that induced by morphogens related to the outer surface of the neural tube/basal lamina

What happens after one neurite becomes the axon?

• The amoeba like neuron becomes polarized, and other processes become dendrites by default

What does neuronal polarization mean?

• The neuron establishes distinct axon and dendrite identities

What signals axons to exit the neural tube?

• Morphogens as neural tube layers form

Where does the soma stay after the axon exits the neural tube?

• The soma remains within the neural tube/CNS region

What is the axon growth cone?

• The specialized, autonomous tip of a growing axon

Why is the growth cone called autonomous?

• It contains what it needs to make proteins and guide growth without waiting for the soma

What is the “cytoplasmic suitcase”?

• The growth cone’s supply of of ribosomes, mRNA, actin, microtubules, and proteins needed for growth

What does the growth cone need for survival and elongation?

• Cytoplasmic proteins, actin, microtubules, and navigation proteins

What are filopodia?

• Finger-like projections from the growth cone that sense signals and pull the axon forward

How do filopodia help axons grow?

• They pull on the environment and cause the axon to elongate toward attractant morphogens

What determines growth cone behavior?

• the morphogens that filopodia encounter

What do attractant/adhesion molecules tell a growth cone to do?

• advance toward them

What is an example of an adhesion molecule?

• Cell adhesion molecules (CAMs)

What do repellent molecules tell a growth cone to do?

• retreat/grow away

What do physical/mechanical barriers make growth cones do?

• make them go around them

What is an example of a physical barrier?

• Stiff cells, such as cells with collagen

How does a growth cone use concentration gradients?

• It follows increasing attractant/CAM concentrations toward a target

What are pioneer axons?

• The first axons to exit the neural tube or enter a new region

What is special about pioneer axon growth cones?

• They are hyperactive and highly responsive to guidance signals

Whats unique about pioneer axon filopodia ?

• have filopodia that move faster

What do pioneer axons do?

• They follow regional signals and forge a pathway to the correct target tissue

How do pioneer axons help follower axons?

• They produce region-specific CAMs along their membranes that attract and guide follower axons

What are follower axons?

• Later-growing axons that follow the pathway created by pioneer axons

Why do follower axons adhere to pioneer axons?

• Pioneer axons display CAMs that help guide and attach follower axons

Where do PNS neurons come from?

• Neural crest cells

When do neural crest cells form?

• During neural tube formation

Where do neural crest cells originate?

• at ehe margins of closing neural tube, loose ends from neurulation