11. Peripheral Nervous System Flashcards by Darren Rippee

Where (in terms of somites) does the divison between Brain and Spinal Cord occur?

Brain is 4th Somite and Superior

Spinal Cord is Inferior to the 4th Somite

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What is grey matter mostly made of?

Unmyelinated cell bodies

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What is White Matter mostly made of?

Myelinated Axons

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What region of the spine contains the Lateral Horns?

T1 to L2

(absent in most of the spine)

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What is the dorsal part of the Spinal Cord (grey and white matter) primarily responsible for?

Sensory input

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Before the Epiblast invaginates, is the region of the Alar Plate medial or lateral to the region of the Basal Plate of the future Neural Tube?

Lateral -The Alar Plate will be on top of the Basal Plate in the Neural Tube

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What is found in the Alar Plate of the Neural Tube?

Sensory Neurons that never leave the Central Nervous System

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Where do the Sensory Neurons of the Peripheral Nervous System (First Order Neurons) come from?

The Neural Crest

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What comes from the Basal Plate of the Neural Tube?

Motor Neurons

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What separates the afferent from the efferent nerves in the Neural Tube?

The Sulcus Limitans

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What is the name for the center space in the Neural Tube?

Central Canal

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What does the Intermediate Zone of the early Spinal Cord become?

Gray Matter

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What does the Marginal Zone of the early Spinal Cord become?

White Matter

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What cell type does the Ventricular Zone contain?

What do these cells do within the Ventricular Zone?

Stem Cells

They become Ependymoblasts, which can then either become Ependymal Cells or Choroid Plexus Cells (which make CSF)

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What do Ventricular Zone Stem Cells become in the Intermediate Zone of the Early Spinal Cord?

Neruons, Astrocytes (protoplasmic), Glial Cells

(and others)

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What do Ventricular Zone Stem Cells become in the Marginal Zone of the Early Spinal Cord?

What precursor to these cells is found in the Intermediate Zone?

Oligodendrocytes, Astrocytes (fibrous)

Glioblasts

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What do Schwann Cells do?

What embryological structure do they come from?

They myelinate neurons of the Peripheral Nervous System

Neural Crest

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What do Oligodendrocytes do?

What embryological structure do they come from?

They myelinate neurons of the Central Nervous System

Neuroectoderm

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What germ layer do Microglial Cells come from?

What do they do?

Mesoderm

They come from monocytes, which come from mesoderm

They are phagocytes

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In an early fetus, the Vertebrae and the Spinal Cord are the same length. What causes the Spinal Cord to stop short of the Vertebrae in a newborn?

The Vertebrae grow faster than the Spinal Cord

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Where does Keim say a newborn’s Spinal Cord stops?

Where does Keim say an adult’s Spinal Cord stops?

Why is this clinically relevant?

Newborn: L2-L3

Adult: L1-L2

NICU Spinal Taps are lower.

What embryonic structure gives rise to the Spinal Ganglion Cells

Neural Crest

What signal triggers early Dorsal Nerve differentiation?

What gives off this signal?

What kinds of nerves are these incited to become?

BMP

Roof Plate and Dorsal Surface Ectoderm

Sensory Nerves

What signal triggers early Ventral Nerve differentiation?

What releases this signal?

What kinds of nerves are these incited to become?

Sonic Hedgehog

Floor Plate and Notocordal Process of the Notocord

Motor Neurons

What signal triggers differentiation of the Spinal Cord into the Alar Plate?

BMP

What signal triggers Spinal Cord differentiation into the Basal Plate?

Sonic Hedgehog

What genes do high levels of BMP activate?

PAX₃ and PAX₇ ## Footnote *BatMan's Pouch might be on display at PAX*

What genes do high levels of SHH (Sonic Hedgehog) activate?

NKX_2.2 and NKX_6.1 ## Footnote *"Sonic Hedgehog NKX_2.2" and _6.1 sound like Sega skiing games to me*

In the Peripheral Nervous System, what two structures come from the Neural Tube?

Pre-ganglionic Autonomic Neurons (come from the lateral horn - remember this is only present from T1 to L2) Motor Neurons

Where do the Neurons of the Dorsal Root Ganglia come from? What kind of Nerves (in terms of orientation) are they?

Neural Crest Pseudo-Unipolar

Where do the Sympathetic and Parasympathetic Ganglia come from?

Neural Crest Cells

What embryological structures give rise to the nerves of the Ventral and Dorsal Rami?

The Rami are where the Dorsal Roots and Ventral Roots have already come together, so they are both Neural Crest and Neuroectoderm

What does the Ramus Communicantes allow you to do?

"Get into and out of the Autonomic Ganglia"

For the General Somatic Efferent Neurons: Where do they come from? What do they innervate?

Neuroectoderm Muscles that came from Somites (Skeletal Muscles) *This is what you often think of as a "nerve", like the Musculocutaneous Nerve for the Biceps Brachii M.*

For General Visceral Efferent Nerves What do they come from? What do they innervate?

Neuroectoderm Parasympathetic and Sympathetic Neurons

For the Special Visceral Efferent Nerves Where do they come from? What do they innervate?

Neuroectoderm Muscles of the Head and Neck (Muscles from the Pharyngeal Arches)

For General Somatic Afferent Nerves Where do they come from? What do they innervate?

Neural Crest Anything made by **Ectoderm**, or Mesoderm that was adjacent to that Ectoderm (Skin, joint capsules, tendons)

For General Visceral Afferent Nerves What do they come from? What do they innervate?

Neural Crest **Endoderm**, or anything adjacent to Endoderm (Organs)

For Special Somatic Afferent Nerves What two nerves are they?

CN 8 (IIX), and CN 2 (II) (Hearing and Sight) * That body is a 10* * (Soma = Body, 8 + 2 = 10)*

For Special Visceral Afferent Nerves What Cranial Nerves fit this category?

CN 7, 9, and 10 ## Footnote * It's like someone screwed up the joke* * Why was 6 afraid of 7? Because 7, 9 ,10.*

Where are the cell bodies for the Preganglionic Sympathetic Nervous System located? What are they derived from?

In the Spinal Cord (lateral horn) in the _Thoraco Lumbar Region_ (T1-L2) Neuroectoderm

Where are the cell bodies for the Postganglionic Sympathetic Nerves? What do they come from?

Off of the Spinal Cord, at the Synapse of the Preganglionic Nerves Neural Crest Cells

Which fiber of the Sympathetic Nervous system is Short vs Long? Which Fibers are Myelinated?

Short / Myelinated: Preganglionic Long / Unmyelinated: Postganglionic

In what two regions of the spinal cord do we see Parasympathetic Nerves?

Cranial and Sacral

In the Cranial Region, where do the Parasympathetic Nerves travel?

With Cranial Nerves 3, 7, 9, 10

In the Sacral Region, where do the Parasympathetic Nerves travel?

With the 2^nd, 3^rd, and 4^th Sacral Nerves

For the Parasympathetic Nervous System Preganglionic vs Postganglionic Fibers Which ones are Long vs Short, and which ones are Myelinated vs Unmyelinated?

Preganglionic Fibers for the Parasympathetic Nervous System are _long_ and myelinated. Postganglionic Fibers are Short and Unmyelinated

The cell bodies for which link of the Parasympathetic Nervous System are in the Parasympathetic Ganglia, and what are they derived from?

The Postganglionic Nerve Fibers Neural Crest

When does Central Nervous System Myelination begin, and when does it end? What cell does this? What is that cell derived from?

Starts in the 6th month, continues to year 23 or so. Oligodendrocytes Neuroectoderm (stem cells of the Ventricular Zone)

When does Peripheral Nervous System Myelination begin? Which nerves (motor or sensory) are Myelinated first? What cell does this, and where does it come from?

About the 4th Month Motor Schwann Cells / Neural Crest

What might a patient notice happens about the time the Motor Neurons of the Peripheral Nervous System begin to Myelinate in a fetus?

It begins to move and kick