Development of the Peripheral Nervous System Flashcards
gastrulation
is the formation of the three germ layers
cells are going to ingress thorugh the primitive streak and populate into the three different germ layers
neurulation
taking ectoderm specifying it to become neural ectoderm
notochord induces neural plate formation in overlying ectoderm
forms neural folds –> neural tubes
pinches off ectoderm that will form epidermis from the underlying neural tube
CNS
includes brain and spinal cord
arise from the neural tubre
PNS
all components of the nervou system outside of the CNS Cranial nerves and ganglia spinal nerves and ganglia (DRG) autonomic nerves and ganglia enteric nervous system
develops from neural tube
neural crest cells, neuroectoderm, ectodermal placodes
modalities
sensory or motor
sensory comes in from the periphery (therefore afferent)
motor is efferent and goes to the periphery
somatic sensory
sensations of the body - skin
visceral sensory
sensations of internal organs/abdominal viscera
somatic motor
motor innervation of skeletal muscle
visceral motor
involuntary motor - smooth/cardiac muscle and glands
equivalent to ANS
parasympathetic division and sympathetic division
gray matter can be divided into
posterior horn- sensory information
lateral - typically motor but related to autonomics
anterior horn - motor information
white matter of spinal cord
not very many neuron cell bodies- have myelinated axons, using this area as tracts to move up and down spinal cord can divide into: posterior funiculus lateral funiculus anterior funiculus ascending/descending tracts
sulcus limitans
notochord division separating what will become dorsal and ventral regions
neuroblasts from the neuroepithelium become
neurons
glioblasts from the neuroepithelium become
astrocytes
ependymal cells
special types of glial cells that are reponsible for becoming the chori plexus that becomes the CSF
microglial cells are not derived from
neuroepithelium, come from mesenchymal cells - act as macrophage debris eaters
neural tube divisions from inner to outer
ventricular zone (stem cells) Mantle/intermediate zone (migrating cells undergoing differentation - extend axons away from lumen toward outer surface) marginal zone (contains axons that will eventually be myelinated)
mantle reorganizes into
alar (dorsal) columns
basal (ventral) columns
connected by roof plate and floor plate
alar and basal columns run
all the way up and down vertebral column
roof plate and floor plate provide
signals that induce differentiation of alar and basal column cells
floor plate signal
sonic hedge hog - specifies motor neuron identity
ventral = motor
cool
sonic hedge hog induces
motor neuron identity
sonic hedgehog downstream products
NKX2.2 and NKX6.1
roof plate signal
BMP (TGF-Beta family signaling molecule)
counteracts SHH gradient
responsible for induction of dorsal association neurons
BMP4 downstream products
PAX3 and PAX7
intermediolateral cell columns
T1-L3(thoracolumbar and sympathetic) S2-S4 (sacral and parasympathetic)
dorsalmost cells of the basal plate (and therefore are motor)
form the lateral horns (ANS precursors)
cranial PNS derived from
NCC and ectodermal placodes - sensory ganglia of cranial nerves
trunk PNS development
sensory neurons in DRG
Schwann cells (myelinate nerves)
sympathetic ganglia (pockets of neuronal cell bodies that contribute to
enteric nervous system
axons exiting ventral horn pass through the
cranial sclerotome - form the ventral root - joined by lateral root (follows ventral root path)
components of spinal nerves
posterior sensory information
ventral/anterior motor information
lateral autonomic information
spinal nerves are mixed sensory/motor modalities
types of nerves
General somatic efferent (somatic motor)
general visceral efferent (ANS)
special visceral efferent (brachial muscles)
general somatic afferent (sensory in skin)
general visceral afferent (sensory of viscera)
special somatic afferent (hearing,balance,sight)
special visceral afferent (taste and smell)
autonomics contain ___ neurons
2 neuron chain system
synapse in the ganglionic neuron
sympathetic pathway
postgangiolic fibers release norepinephrine
preganglionic utilizes acetylcholine
parasympathetic pathway
pre and postsynaptic (postganglionic) fibers release acetylcholine
Myelinates CNS
oligodendrocytes
glial cells derived from neuroepithelium
begins in lower brain stem, older tracts first
Myelinates PNS
schwann cells
NCC derived
motor roots myelinated before sensory roots
