Development of PNS Flashcards
During what week do the PNS and CNS develop?
Week 3
Weeks 3-8 are considered what during development?
Critical Period
***Major abnormalities can occur here
T/F. Weeks 9-38 (birth) can have both major and minor abnormalities in development.
False. These weeks only have functional and minor abnormalities occur.
What are the weeks in Neural development that major abnormalities can occur and be detrimental?
Weeks 3-16
***Weeks after that can have minor abnormalities occur, and this development continues until age 22 when CNS myelination is complete
These can be used clinically in an ultrasound to age an embryo.
Somites
***Count the number present on the embryo
At the end of which week would we have a Neural Tube/
Week 4
What is included in the CNS?
Brain
Spinal Cord
What is included in the PNS?
Cranial Nerves Spinal Nerves Ganglia Enteric Plexus Sensory receptors
What is the PNS divided into?
Somatic
Autonomic
(SOMATIC/AUTONOMIC) is voluntary and (SOMATIC/AUTONOMIC) is involuntary and done unconsciously.
Somatic
Autonomic
***Each have a sensory and motor component
What is the Autonomic PNS subdivided into?
Parasympathetic
Sympathetic
T/F. Parasympathetic and Sympathetic groups are sensory.
False. They are motor.
What are the types of matter the spinal cord is made up of?
Gray Matter
White Matter
This is the term for a collection of axons.
Funiculus
This is where cell bodies of neurons are located, and it has a posterior, anterior, and lateral horn.
Gray Matter
This is where axons are located and it is where the posterior, anterior, and lateral funiculus are located. It is myelinated.
White Matter
What is the sensory component of Gray Matter?
Dorsal (posterior) horn
What is the autonomic (sympathetic) component of Gray Matter?
Lateral horn
What is the motor component of Gray Matter?
Ventral (anterior) horn
What component of White Matter is only sensory and which one is sensory AND motor?
Dorsal (posterior) funiculus
Lateral funiculus
What component of the White Matter is primarily motor?
Ventral (anterior) funiculus
The Neural Tube is caudal to what?
Fourth pair of somites
This is what produces sensory neurons that stay in the brain and spinal cord.
Alar Plate
***Sensory neurons that go out into the periphery come from Neural Crest cells!
What type of germ layer is the Alar Plate?
Neuroectoderm
This gives rise to motor neurons (Brachial Plexus, etc.).
Basal Plate
What lies between the Alar Plate and the Basal Plate?
Sulcus limitans
In the formation of the spinal cord, this zone is closest to the central canal.
Ventricular zone (Zone 1)
In the formation of the spinal cord, this zone is what makes up the Gray Matter (cell bodies).
Intermediate zone (Zone 2)
In the formation of the spinal cord, this zone is what makes up the White Matter (axons).
Marginal zone (Zone 3)
What cells are near the Central Canal, and what is their path of development?
Germinal or ventricular cell — Ependymoblast — Ependymal Cell — Choroid Plexus Cell (makes CSF)
What cell always lines the Central Canal?
Ependymoblasts
What cells would be in Zone 2 (Gray Matter)?
Germinal or ventricular cells (in Central Canal) would differentiate into —-
Immature Neurons – become Neurons
Glioblasts – become Astrocytes and Radial Glial Cells (Also become Oligodendrocytes but those are in Zone 3)
What cells would be in Zone 3 (White Matter)?
Oligodendrocytes (from Glioblasts in Zone 2)
***Their function is to myelinate axons, hence their location
Neurons, Astrocytes, Oligodendrocytes, and Ependymal cells are all derived from what germ layer?
Neuroectoderm
***Developed from Neural Tube
These cells in the CNS are made from monocytes in the blood, making them mesodermal.
Mesenchymal cells
In the CNS, what do mesenchymal cells differentiate into?
Microglial cells
At what stage of development is the spinal cord and vertebral column the same length?
Third month in utero
At what position does the spinal cord end for a newborn and adult, respectively?
Newborn = L2 or L3 Adult = L1 or L2
Explain why newborns and adults would have a different needle placement for lumbar puncture.
Newborns spinal cord ends at L2 or L3 and as they grow, their vertebral bones grow too. The spinal cord however, does not grow with the bones. Instead, as the bones grow the neurons move up and only the axons will lengthen (Cauda Equina). This is why adults spinal cord ends at L1 or L2.
Spinal ganglion cells and sensory neurons in the periphery are derived from what germ cell layer?
Neural crest
***Means Ectoderm and Mesoderm together
In the formation of the spinal cord, on the ventral side there is the Notochord and the Floor Plate which both signal _______, and on the dorsal side there is the Roof Plate and Epidermis which signal _______.
SHH
BMP
The release of SHH and BMP create a gradient. Which is greater ventrally and which is greater dorsally?
High SHH levels ventrally (less as it moves dorsal)
High BMP levels dorsally (less as it moves ventrally)
***The varying levels throughout this gradient provide signals for many different things!
***Remember dorsal is sensory and ventral is motor!
High BMP levels activate ______ and ______ which give us our sensory neurons. These sensory neurons will differentiate and give us our _______ _______.
PAX3
PAX7
Alar Plate
High SHH levels activate ______ and ______ which give us our ventral neuron formation. These neurons give us our ______ ______.
NKX2.2
NKX6.1
Basal Plate
Just dorsal there are slightly lower SHH and higher levels of BMP. At this point, ______ and ______ signals are activated which give us our ventral motor neurons. Our ventral motor neurons then make up our _______ _______.
NKX6.1
PAX6
Anterior (ventral) horn
What two germ layers make up the PNS?
Neural Crest
Neuroectoderm
In the development of the PNS, cells that develop from the Neural Tube (neuroectoderm) are…
Motor neurons (in ventral/anterior horn) Pre-ganglionic autonomic neurons (in lateral horn)
In the development of the PNS, cells that develop from the Neural Crest are…
- Neurons of dorsal root ganglia
- Sensory ganglia of cranial nerves
- Schwann cells (myelinate)
- Sympathetic ganglia
- Parasympathetic ganglia
In a typical segmental nerve, the Dorsal (Posterior) Root is (MOTOR/SENSORY) and contains a Spinal ganglion (called Dorsal Root Ganglion).
Sensory
In a typical segmental nerve, the Ventral (Anterior) Root is (MOTOR/SENSORY).
Motor
In a segmental nerve, the Dorsal and Ventral Roots come together to form the ______ ______ which is a mix of sensory and motor.
Spinal Nerve
The Spinal Nerve then branches into what? Are they motor or sensory?
Dorsal (Posterior) Ramus
Ventral (Anterior) Ramus
They are mixed – both sensory and motor
What does motor Dorsal Rami supply? Sensory Dorsal Rami?
Motor is to dorsal muscles
Sensory is to dorsal integument
What does motor Ventral Rami supply? Sensory Ventral Rami?
Motor to limbs, lateral, and ventral body wall
Sensory to integument of the same regions
This is autonomic and provides motor and sensory to viscera.
Ramus communicantes
(AFFERENT/EFFERENT) neurons are motor fibers that are derived of neuroectoderm (basal plate).
Efferent
(SOMATIC/VISCERAL) motor fibers end on skeletal muscle, while (SOMATIC/VISCERAL) motor fibers end on autonomic ganglion cells, which in turn control smooth muscle, cardiac muscle, and glands.
Somatic
Visceral
(AFFERENT/EFFERENT) neurons are sensory fibers. If they are going to the periphery then they are derived from Neural Crest.
Afferent
(SOMATIC/VISCERAL) sensory fibers originate chiefly from the integument and (SOMATIC/VISCERAL) sensory fibers originate from the viscera.
Somatic
Visceral
The ANS (Autonomic Nervous System) is involuntary and innervates the smooth muscle, cardiac muscle, and glands. It consists of two motor pathways, which are…
Sympathetic
Parasympathetic
In the ANS, what is formed by Neural Crest and what is formed by Neuroectoderm?
Neural Crest – formation of ganglia and post-ganglion (post-synaptic) cells
Neuroectoderm – formation of the pre-ganglion cells (pre-synaptic) cells from lateral horn
Sympathetic ANS is located in the spinal cord in the thoracolumbar region from ______ to ______ in the lateral horn.
T1
L2 (maybe L3)
What is the two link chain of the Sympathetic ANS?
Short and myelinated Preganglionic fiber from spinal cord to Sympathetic Ganglia (***Neuroectoderm)
Long and unmyelinated Postganglionic fiber from Ganglia to Viscera (***Neural Crest)
These are sympathetic ganglia that lead to the head and heart.
Superior Cervical Ganglion
Middle Cervical Ganglion
Inferior Cervical Ganglion
These are “Prevertebral Ganglia”, which are all sympathetic ganglia.
Celiac Ganglion
Aortico-renal Ganglion
Superior Mesenteric Ganglion
Inferior Mesenteric Ganglion
Parasympathetic ANS is in the Cranial-sacral region. What Cranial Nerves and Sacral Spinal Nerves carry parasympathetic fibers (preganglionic)?
CN 3, 7, 9, 10
Sacral Nerves 2, 3, 4
What is the two link chain of the Parasympathetic ANS?
Long and myelinated Preganglionic fiber from spinal cord to Parasympathetic Ganglia (***Neuroectoderm)
Short and unmyelinated Postganglionic fiber from Ganglia to viscera (***Neural Crest)
These are Parasympathetic Ganglion that you would see in the walls of the viscera (organs).
Ciliary Ganglion
Pterygopalatine Ganglion
Submandibular Ganglion
Otic Ganglion
The CNS is myelinated by _________ and the PNS is myelinated by ________.
Oligodendrocytes (from Neuroectoderm) Schwann Cells (from Neural Crest)
T/F. CNS myelination starts in the lower brain stem with older tracts starting first and ends with newer tracts. This lasts until age 22.
True
In the PNS, (MOTOR/SENSORY) roots are myelinated before (MOTOR/SENSORY) roots. Occurs during the 4th month.
Motor
Sensory
