Unit 2-embryology and histology of nervous system Flashcards
What structures are apparent at week 4 of embryological development?
Neural crest and tube
What do the neural crest and tube become?
The spinal cord and 3 primary brain vesicles (which has two flexures: cervical and cephalic)
What are the 3 primary brain vesicles?
The prosencephalon (forebrain), mesencephalon (midbrain), and rhombencephalon (hindbrain)
these 3 vesicles are primary vesicles
During weeks 5-6 what does the prosencephalon develop into?
the telencephalon and diencephalon
secondary vesicles
what structures come from the telencephalon?
cerebral cortex, basal ganglia, and lateral ventricles
secondary vesicles
what structures come from the diencephalon?
thalamus, hypothalamus, pineal gland, and 3rd ventricle
secondary vesicles
During weeks 5-6 what does the mesencephalon develop into?
corpora quadrigemina (tectum), cerebral peduncles, and cerebral aqueduct
secondary vesicles
during weeks 5-6 what does the rhombencephalon develop into?
the metencephalon and myelencephalon
secondary vesicles
what structures come from the metencephalon?
cerebellum, pons, and 4th ventricle
secondary vesicles
what structures come from the myelencephalon?
M.O., and 4th ventricle which is continuous with the spinal cord
The brain at birth equals what percentage of body weight and uses how much O2?
10% and uses 50-60% of O2
As an adult the brain equals what percentage of body weight and uses how much O2?
2-5% and uses 20% of O2
Within 1st year how much in size does the brain grow?
it doubles it size and more then 1/2 of brain growth occurs during this time period
The CNS arises from what structure in general?
the neural tube
The PNS arises from what structs in general?
the neural crest cells
Neuroepithelial cells give rise to what structes?
Neuroblasts, ependymal cells, and glioblasts
Neuroblasts give rise to what?
neurons
Glioblasts give rise to what?
astrocytes and oligodendrocytes
Gliobasts are synonymous with what and can undergo what?
nerve glue
they can undergo mitosis
What are some functions of glioblasts?
their derivations are the FUNCTIONAL connective tissue of the CNS and help guide neurons to their positions in early development
there are 5-10x as many glioblast derivatives as there are neurons
Astrocytes characterisitcs
most numerous cell in adult nervous sytem’
have mobility potential
little evidence to suggest they divided in mature brain
Protoplasmic astrocytes are found where?
in gray matter
Fibrous astrocytes are found where?
in white matter
Functions of astrocytes
structural support cells
found between blood vessel capillaries and neuron cell bodies as part of the BBB
stores what little glucose can be stored in the nervous system
forms “scar-like” tissue in CNS after injury
neurotransmitters like dopamine, glutamate, and serotonin may be influenced by astrocytes at synatpic gaps
Oligodendrocyte characteristics
fewer in number than astrocytes and mainly forms myelin sheaths
Perineuronal satellites (type of oligodendrocyte)
found in gray matter and has possible nutritional role
Interfasicular (type of oligodendrocyte)
found in white matter and forms myelin in CNS
Characteristics of ependymal cells
line the central canal and ventricles
serve as leaky barrier between CSF and CNS parenchyma
classified as simple cuboidal but some are adapted taller cells and with microvilli and are present in ventricles
secretes CSF from choroid plexus in each ventricle
found in 3rd ventricle and transports CSF to hypophyseal portal system
tanycytes
most common primary brain tumor
astrocytoma
most lethal brain tumor and is more likely to occur as one is older
glioblastoma
derived from ependymal cells and dysfunctions CSF which accumulates CSF in brain
ependyoma
Microglio characteristics
Mesodermally derived and arise from fetal macrophages which sequester into blood stream during development
while resting they have numerous tiny processes
they become activated after neural tissue is injured and become phagocytic, clearing damaged or dead tissue
mediates CNS immune responses
only neural cells affected by HIV
Neuralblast chracterictics
neuroepithelial origins near neural tube
show little mitotic ability
depend glial cells to guide them as they move through CNS
radiation or alcohol exposure during development may cause them over/under shoot their destination
(pseudo)unipolar neuron
most common; found in DRG or spinal ganglion
really two neurons wrapped together to look like one
primarily used for sensory function and found in PNS as afferent neuron
bipolar neuron
found dominately in special sense organs such as retina, inner ear, and nasal cavity
multipolar neuron
has only one axon but many dendrites and branches
is the vast majority of neurons in CNS and is most numerous
carries motor information
Golgi type I (multipolar)
has a long axon maybe 1M or longer
Golgi type II (multipolar)
short axons and more numerous than golgi type I
sensory neruon
afferent
runs from PNS to CNS
neural crest derivative
motor neruon
efferent
runs from CNS to PNS
neural tube derivative
Internuncial neuron
only in CNS
messengers or connectors between incoming sensory info and outgoing motor
associative or interneuron are interchangeable with internuncial
commissural neuron
neuron that runs between equal structures on opposite sides of CNS
Ex. Lt. central gyrus to Rt. central gyrus
Projection neuron
type of internuncial that runs from one structure in the CNS and ends in another struture
Ex. Rt. cerebrum to Lt. midbrain
Ipsilateral
runs on the same side
Contralateral
runs on opposite side
Intra segmental
begins and ends in the same cord level
inter segmental
begins in one cord level and ends in another
Cell body (some, or perikaryon)
contains the nucleus of a neuron
Axon hillock
gradually boundary between the axon and cell body
this is where nerve or action potentials are initiated
Axolemma
outer plasma membrane of neuron
Typical diameter of a perikaryon?
4-130 microns, the bigger the perikaryon the faster a nerve impulse travels
The shapes of a perikaryon?
stellate, fusiform, oval, round, and pyramidal
how long can a process be?
from just a few microns up to 40 inches
Axoaxonic
least common form of a synapse
the end of an axon from one neuron synapses onto the axon of another neuron
axodendritic
most common form of a synapse
the axon of one neuron synapses onto the dendrite of another neuron
axosomatic
the axon of one neuron synapses onto the cell body of another neuron
organelle that is considered the powerhouse is most concentrated where in the cell and produces what compound?
the mitochondria and is concentrated in the cell body and telodendria due to high levels of activity
the mtiochondria produces ATP
the golgi apparatus houses what processes?
retispersion and chromatolysis
retispersion is the process of what?
fragmentation of the golgi apparatus
chromatolysis is the process of what?
Nissl bodies are dispersed after neuronal injury
what are nissl bodies and what other name do they go by?
clumps of RER and free ribosomes plus iron deposits
they are also called tigroid bodies
nissl bodies only appear in large neurons and are only found in the cell body and dendrites of neurons
centrosome organelle
likely the remnants of when it was capable of mitosis
Are neurofibrils real?
yes they are
List the three types of microfibrils
microtubules
microfilaments
neurofilaments
What is the function of microtubules and their size?
They help maintain cell shape and are 20-30nm in diameter
What is the function of microfilaments and their size?
they run longitudinally and circumferentially and associate with axolemma. theyre 3-5nm is diameter
How big are neurofilaments?
9-10 nm in diameter
Describe axoplasmic transport
it is the movement of raw materials within a cell
Describe slow transport in a cell
its the movement of materials like protein for neurofibrils and mitochondira within a cell
moves about .1-3 mm/day in the anterograde direction
speed of flow depends on axon length; the longer the faster; also needs little energy
Describe fast transport
is the movement of synaptic vessicles,lysosomes, and enzymes
moves 100-400 mm/day anterograde or retrograde
speed of transport not dependent on axon length but needs energy
What is the myelin covering in the CNS?
intrafasicular oligodendrocytes
What is the composition of myelin?
phospholipid/cholesterol and neurokeratin
Is myelin made by the neuron?
No its made by a surrounding cell
What forms the myelin in the PNS?
Schwaan cells
What part of the neuron does myelin only cover?
the long axon process
How long must a neuron fiber be for myelin to form on it?
at least one micron in length
If the neuron fiber is thicker, in general whats the diameter of the myelin?
its thicker as well
Is a nerve impulse faster if the myelin is thicker or thinner?
if the myelin is thicker
What two things determine conduction velocity?
fiber diameter and myelin
What would be an example of a PNS nerve fiber that has a schaan cell but is not myelinated?
post ganglion sympathetic neurons
What is it called when one schwaan cell in the PNS meets another schwaan cell?
node of ranvier
What is an internode?
the length of a schwaan cell covering
How long can an internode be?
50-750 microns
Do all nerve fibers have a neurilemma?
yes
Describe endoneurium
highly vascular, fibrous and cellular matrix covering neurilemma. continues onto telodendritic branches
Describe perineurium
it wraps around groups of fibers
it is the most elastic of coverings
its continuous with the pia and arachnoid as it gets close to CNS structures
Describe epineurium
outer coat of a nerve
inelastic, gives protection, strength and support to fibers.
is continuous with dura as it gets close to CNS structures
Are nodes of ranvier in the CNS?
yes but are oligodendrocytes instead
How many cells can an oligodendrocyte cover?
up to 40
