Lecture 16: Peripheral Nervous System Flashcards
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
What is grey matter mostly made of?
Unmyelinated cell bodies
What is White Matter mostly made of?
Myelinated Axons
What region of the spine contains the Lateral Horns?
T1 to L2
(absent in most of the spine)
What is the dorsal part of the Spinal Cord (grey and white matter) primarily responsible for?
Sensory input
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
What is found in the Alar Plate of the Neural Tube?
Sensory Neurons that never leave the Central Nervous System
Where do the Sensory Neurons of the Peripheral Nervous System (First Order Neurons) come from?
The Neural Crest
What comes from the Basal Plate of the Neural Tube?
Motor Neurons
What separates the afferent from the efferent nerves in the Neural Tube?
The Sulcus Limitans
What is the name for the center space in the Neural Tube?
Central Canal
What does the Intermediate Zone of the early Spinal Cord become?
Gray Matter
What does the Marginal Zone of the early Spinal Cord become?
White Matter
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)
What do Ventricular Zone Stem Cells become in the Intermediate Zone of the Early Spinal Cord?
Neruons, Astrocytes (protoplasmic), Glial Cells
(and others)
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
What do Schwann Cells do?
What embryological structure do they come from?
They myelinate neurons of the Peripheral Nervous System
Neural Crest
What do Oligodendrocytes do?
What embryological structure do they come from?
They myelinate neurons of the Central Nervous System
Neuroectoderm
What germ layer do Microglial Cells come from?
What do they do?
Mesoderm
They come from monocytes, which come from mesoderm
They are phagocytes
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
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
BatMan’s Pouch might be on display at PAX
What genes do high levels of SHH (Sonic Hedgehog) activate?
NKX2.2 and NKX6.1
“Sonic Hedgehog NKX2.2” 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”
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 2nd, 3rd, and 4th 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
