Nerve and development Flashcards
nervous tissue
- ectoderm
- detect and analyze sensory input, coordinate body activities, store and recal experiences
- parts=PNS and CNS
somatotopic organiztion
- different brain areas dedicated to different body parts or different modes of info
- gyri=bumps on outer portion
- sulci=groves on outer cortical portion of brain
- primary motor cortex=precentral gyrus, anterior to central sulcus
- primary sensory cortex=postcentral gyrus posterior to central sulcus
spinal chord
- ascending tracts carry sensory info to brain, located dorsally
- descending tracts send motor information, located ventrally
peripheral nervous system
=all nerves except brain and spinal chord, mixed motor and sensory
afferent sensory nerves enter spinal chord via dorsal roots
efferent motor nerves exit via ventral nerve roots
somatic portion of PNS
- carry consciously percieved info like voluntary mm contraction
- consists of single neuron connections
autonomic/visceral portion of PNS
-unconscious info like proprioception and contraction of involuntary or cardiac muscle, gland secretion
-multiple nerve connections and lots of integration
divided into parasympathetic (nerves origionating in midbrain, cervical, and sacral regions) and sympathetic (thoracic and lumbar region nerves)
nervous tissue cell types
- neurons-excitable
- neuroglial cells-non-excitable but enhance transmission
- support cells (from mesoderm) includes blood vessel cells like endothelium and fibroblasts and microglia (CNS immune cells)
neurons
soma has nucleus, cytoplasm with cytoskeleton, nissal bodies (ribosome rich RER)
dendrites has mitochondria, SER, microtubules and neurofilaments but no golgi
axon has mitochondria and SER but few/no ribosomes and many microtubules
axon terminal
axonal transport
anterograde=from soma to axon terminal
retrograde from terminal to soma
ganglion
PNS-cluster of nerve cell bodies where many synapses occur
nucleus
CNS-cluster of cell bodies where many synapses occur
six steps of synaptic transmission
- vesicle transport 2. vesicle loading 3. depolarization 4. exocytosis 5. binding of neurotransmitter and 6. further depolarization
glia
different cell types that contribute to neurotransmission
-help speed up impulses my forming myelin sheath around axons in CNS
schwann cells
myelinate axons in PNS
1 schwann cell/1-2mm of axon
can swallow axons (10) but not myelinate them-they can communicate w/extracellular space still
oligodendrocytes (CNS)
myelinate CNS neurons
protoplasmic and fiberous astrocytes (CNS)
- send out processes that contact blood vessels and maintain blood flow, scavange ions and maintain homeostasis
- facillitate transport accross BBB
- protoplasmic in grey matter, fiberous in white
microglia (CNS)
-immune phagocytic cells, extend and retract processes and attracted to damaged neurons
ependymal cells (CNS)
- form simple epithelium
- line surface of brain beneath pia matter, inner surface of ventricles, and inner surface of central canal of spinal chord
- synthesize, secrete, and exchange CSF
- blood-CSF barrier maintained by tight junctions
PNS connective tissue
all derived from mesoderm
epineurium-dense irregular CT around nerves
perineurium-dense irregular CT around fasicles
endoneurium-loose irregular connective tissue
meninges
dura matter outermost and dense irregular connective tissue,
arachnoid mater dense irregular w/ some elastic fibers
pia mater b/t dense and loose connective tissue
subarachnoid space contains blood vessels that supply and drain brain and spinal chord and is where CSF is outside ventricular system
BBB
- formed by epithelium that lines blood vessels of brain (capillary endothelium)
- many tight junctions to prevent diffusion
- lipid substances can pass and macromolecules can be actively transported across
ventricular system
CSF=liquid cushion, nutrient suport, neurotransmitters, waste material
choroid plexus transports things from capillaries into ventricles to make CSF
CSF flows into subarachnoid spaces where it is returned to venous blood via aracnoid villi, which pierce dura matter
periods of pre-natal development
- pre-embryonic-first 2 weeks
- embryonic-weeks 3-9
- fetal-week 9-birth
fertalization to blastocyst formation
- fertalization occurs in the uterine tube
- receptor mediated process leads to membrane fusion of sperm and egg that generates a totipotent single cell zygote
- the zygote proliferates w/out differentiated until a mass (morula) of cells is formed, morula moves to uterus proper
- morula pumps fluid into its center to form a cavity called blastocyst
- differentiation occurs to form embryoplast cells that form embryo proper
- embryo proper=embryonic stem cells and trophoblasts
implantation
- day 6 is when trophoblasts dive into epithelium and split into two layers that differentiate into cytotrophoblasts which proliferate and outer syncytiotrophoblasts that send finger-like projections into uterine wall and break down ECM in mother’s connective tissue
- trophoblasts surround structure
- syncytiotrophoblasts also release human chorionic gonadotrophin, which maintains the corpus luteum in the over that produces progesterone which prevents menstration
- embryoblast cells split into two layers and differentiate to epiblast (totipotent stem cells and amniotic cells) and hypoblasts (which beome yolk sac lining)
formation of extraembryonic membranes
- epiblast splits and amniotic cavity forms within it, layer of epiblast cells on the roof become amnioblasts and eventually form amniotic membrane
- epiblasts also give rise to extraembryonic mesoderm, which contributes to linings of the chorionic, amnionic, and yolk sac linings and the placenta and blood vessels and germ cells
- hypoblasts generate heuser’s membrane which defines margins of the yolk sac
placenta
- mother’s/uterine component=decidua basalis
- maternal arteries and veins which supply and drain trophoblastic lacunae
- later, trophoblastic lacunae expand and fuse to form intervillous spaces filled w/maternal blood - embryonic/fetal component=chorionic villi
- fingers that connect with trophoblastic lacunae
- made up of syncytiotrophoblasts and cytotrophoblasts and a core of extraembryonic mesoderm
amnion development
epiblast splits into amnioblasts and epiblasts and fluid accumulates in the cavity where embryogenesis happens
yolk sac
hypoblasts generates Heuser’s membrane cells that migrate along cytotrophoblasts–>primary yolk sac
- yolk sac buckles and half degenerates
- produces blood cells until liver forms and is the initial site of germ cells
placental barrier
=syncytiotrophoblasts, cytotrophoblasts, ECM, and endothelium of blood vessels
gastrulation
conversion of bilaminar (epiblast and hypoblast) into 3 primary germ layered embryo of ectoderm, mesoderm, endoderm
gastrulation begins
- primitive streak starts to form in epiblast and the lateral edges push upward while cells in the center ingress
- primitive node=anterior portion, gradually moves toward what will form the cranial/head end
- as cells ingress they start to express sets of genes (ie differentiate)
formation of endoderm
first wave of mesenchymal stem cells that were initially epiblast cells displaces hypoblast cells and becomes the endoderm
becomes much of GI tissue, respiratory and urinary tracts
formation of mesoderm
second wave of ingressing cells push b/t epiblast and hypoblast cells and gives rise to tissue like mm, bone, cartilage, connective tissue, blood, blood vessels)
- paraxial region gives rise to somites
- contains organizer regions like the notochord
ectoderm
cells that remain in the top layer (don’t enter primitive streak) form the ectoderm, which gives rise to outer covering tissue (skin) and nervous tissue
notochord
last mesenchymal cells move through primitive streak and form tubular chord of mesodermal cells, just below ectoderm
prechordal plate mesoderm induces formation of brain and head
neurulation
formation of the neural tube due to induction (notochord releases neural inducers that induce CNS formation by signalling ectoderm above it to form neural plate)
neuroectodermal cells in neural plate fold and form neural groove and change their adhesion molecule to N cadherin, which allows for separation of ectoderm and neural cells
-some cells pinch off-neural crest-and form PNS eventually
-neural folds fuse dorsally and seal the tube
-neural plate buckles inward as regions of the mesoderm become obvious
patterning of neural tube
- notochord secretes sonic hedgehog and signals neural tube to form floor plate on ventral side (motor info)
- ectodermal cells secrete bone morphogentic protein dorsally and induces formation of roof plate, which produces more BMP
- -these gradiants provide ventral/dorsal spatial patterning info that induces different transcription factors at different regions (ie dorsal/sensory and ventral/motor)
