Development Flashcards
1
Q
Conception
A
Penetration of the ovum (egg) by a single sperm
2
Q
Implantation
A
Embryo implants into wall of the uterus
3
Q
Proliferation
A
Multiplication of cells which results in formation of a trilaminar disc
Occurs after conception
4
Q
Trilaminar disc
A
Made up of three layers or lamina of cells Layers are called: Ectoderm Mesoderm Endoderm
5
Q
Ectoderm
A
Outer trilaminar disc layer Made by cells of the trilaminar disc Resulted from cells on outside of embryo Forms the: Epidermis (layer of skin) Neuroectoderm (entire nervous system)
6
Q
Mesoderm
A
Made by cells of trilaminar disc Resulted from cells between endodermal and ectodermal Forms: CT Muscle Some Vascular tissue Blood cells Bone Marrow Meninges Other tissues
7
Q
Endoderm
A
Made by cells of trilaminar disc Resulted from innermost cells on embryo Forms: Serous Membranes Lining of Gastrointestinal tract Portions of some organs, lungs & liver
8
Q
Serous Membranes
A
Produce secretions that moisten some internal surfaces of the body
9
Q
Serous Membranes
A
Produce secretions that moisten some internal surfaces of the body
10
Q
Meninges
A
Coverings of the central nervous system Includes: Pia Mater Arcahnoid Dura Mater
11
Q
Primitive Streak
A
A thickened strip of ectoderm
Occurs before the infolding of the embryo
Appears in trilaminar disc
Composed of ectodermal cells that give rostrocaudal polarity to the embryo
12
Q
Rostrocaudal polarity
A
An orientation that identifies the head end and tail end of the early embryo based on primitive streak
13
Q
Notochord
A
Appears after the primitive streak develops
Aligns in same orientation as streak
Long, narrow group of cells
Located in the mesoderm layer (deep to ectoderm)
Composed of mesodermal cells
14
Q
Neural induction
A
Process of changing ectoderm to neuroectoderm
Occurs in response to chemicals released by the notochord
15
Q
Neural groove
A
or “Rostrocaudal groove”
Formed from neural plate changing shape as neuroectodermal cells continue to proliferate
16
Q
Neural plate
A
After the neuroectodermal cells are formed, they proliferate and form the plate
17
Q
Neural folds
A
Part of the neural plate lateral to the groove on both sides curves dorsally
As it grows, it forms two longitudinally orientated bulges on both sides of the neural groove = “folds”
*think two parallel hills with valley
18
Q
What induces the ectodermal layer to become neuroectoderm?
A
The mesodermal cells of the notochord
19
Q
What is the development of the nervous system dependent on?
A
Presence and normal funding of the notochord
20
Q
Neural tube
A
As more cells proliferate into the neural folds, the fold grows toward midline of embryo until they meet.
This forms a hollow neural tube
Contains ALL the cells that will become part of CNS:
Neurons
Supporting cells (glia)
*two exceptions to this rule
21
Q
CNS
A
Central Nervous system
Contains brain and spinal cord
Has meninges
Formed from ALL the cells in the neural tube *two exceptions
22
Q
Microglia
A
Type of glial cell
Originate in body outside of NS and then migrates to CNS
Involved in removing debris & dead cells from the CNS
23
Q
Mesencephalic nucleus
A
Formed from the primary afferents (sensory neurons) that originate outside the neural tube in the neural crest.
24
Q
Neural crest
A
Small clusters of neuroectoderm cells
Formed when cells of neural folds break away and create small, longitudinally oriented clusters
Reside lateral to the neural tube
Origin for entire PNS*, chromaffin cells, melanocytes
25
What are the two exceptions to the neural tube development rule?
1) Microglia - glial cells that originate in the body outside of the nervous system, then migrate to CNS.
2) Primary afferents - sensory neurons that originate outside tube in the neural crest, & fuses to CNS later. Form the mesencephalic nucleus.
26
Nucleus
A collection of neuron cell bodies in the CNS
27
Neural crest cells
Origin for the entire PNS
28
PNS Cells
All neurons located in sensory and autonomic ganglia, and glial cells associated
Schwann cells, satellite cells
Originate from neural crest cells
*one exception to the rule
29
Exception to PNS cell development rule
The mesencephalic nucleus is derived from the neural crest, but it is a component of the CNS during development
30
Non-Nervous System derivatives of the Neural Crest
Neural crest also forms chromaffin cells and melanocytes
31
Chromaffin cells
Originate from neural crest
Migrate to the medulla and adrenal glands
Function: as post-ganglionic sympathy nervous system cells, BUT secrete substances directly to blood (hormones).
32
Melanocytes
Originate from neural crest
Function: pigment producing cells that provide skin color
33
Somites
Column of cell clusters that forms on either side of of embryo midline
Each is divided into 3 parts, and each part serves as a origin for specific tissue types
34
Number and orientation of Somites
42-44 in the human embryo
Numbered head to tail
Organized as bilateral columns of clusters from head to tail of the embryo midline (rostrocaudal direction)
35
Sclerotome subdivision
A division of somites
| Primary origin for cartilage and bone cells
36
Myotome subdivision
A division of somites
| Origin for many (not all) striated skeletal muscles
37
Dermatome division
A division of somites
| Origin for dermis (deep layer) of skin
38
3 Divisions of Somites
Sclerotome Subdivison
Myotome Subidivision
Dermatome Divison
39
Branchial arches
Formed by some mesodermal cells
Located in the head region of embryo
Origin for some striated skeletal muscles found in head/neck of human
40
Innervation served from somites
Mostly associated with the spinal cord
| Some tissues also associated with cranial nerves
41
Innervation of tissues from the branchial arches that are innervated by cranial nerves
All innervated by cranial nerves
Originate in the pons and medulla
Served some striated skeletal muscles, but some are still somatic origin
42
Neuropores
The openings at the caudal and costal ends of the neural tube
Eventually fuse and tube becomes a hollow blind-ended tube or neuroectoderm
43
Microencephaly
Occurs when the neural tube and neuropores fail to fuse
Occurs at rostral end
Little to no brain development
44
Anencephaly
Occurs when the neural tube and neuropores fail to fuse
Occurs as rostral end
No significant brain development
Not compatible with life
45
Spina Bifida
Occurs when the neural tube and neuropores fail to fuse
Occurs at caudal end of neural tube
Several forms
Can produce severe sensory and/or motor deficits
Extent of function dependent on extent of defect
46
Neural Tube Organization
```
Has three basic layers
Ventricular layer (innermost)
Mantle layer (middle layer)
Marginal layer (outermost)
```
47
Ventricular layer
Innermost layer of neural tube
| Made up of single layer of ependymal cells
48
Ependymal cells
A single layer of these makes up the ventricular layer
Serve as "parent" cells for continued proliferation of cells that will become neurons or glial cells of CNS
Cells remain through life to line ventricles of the brain and central canal of spinal cord
Some become specialized (create CSF)
49
At what level does fusing process of left and right neural folds begin?
Between somites 4 and 6, continues rostrally and caudally
50
CSF
Cerebrospinal fluid
Are specialized ependymal cells
Fill the ventricles and bathe external surfaces of brain and spinal cord
Provides buoyancy
Protects against injury
Does NOT flow within central canal of adult spinal cord
51
Mantle Layer
Multi-celled layer of cells (mantle)
Intermediate layer of neural tube
Cells here proliferate quickly
Cells here are destined to become neurons or glial cells
Eventually this layer becomes Gray matter of CNS
52
Astrocytes or Ogliodendrocytes
Cells formed in mantle layer of neural tube
Destined to become glial cells that differentiate into the CNS
Specialized glial cells
53
Marginal Layer
Neurons in mantle grow axons (projections)
Axons extend away from mantle and form marginal layer
Glial cells migrate here
Eventually this layer becomes White matter of CNS
54
Sulcus limitans
A small indentation of the inner lining of the neural tube, bilaterally
Can be seen if an imaginary line is drawn right to left between dorsal and central halves of a n. tube cross section
55
Alar plate
Contains structures located dorsal to the sulcus limitans
Neurons here are primarily sensory
Primary afferents terminate on neurons derived from the alar plate
56
Basal plate
Contains structures located ventral to the sulcus limitans
| Neurons here are primarily motor
57
Motor functions
Include both somatic motor and visceral motor (autonomic)
Both major systems originate from the basal plate
Portion associated with visceral motor function is located adjacent and ventral to sulcus limitans
58
Appearance of neural tube in adults
Many changes in shape and orientation
| Alar and basal plate relationship is unclear
59
Horn and plate orientation
```
Dorsal horn = alar plate
Ventral horn (& lateral horn) = basal plate
```
60
Where is origination of the plates maintained best? Worst?
Best: in spinal cord
Worst: cerebral hemispheres
61
Meninges
Formed by tissues that originate in the mesoderm
CNS coverings
Three layers:
Dura mater, arachnoid, pia mater
62
Pia mater
```
Internal layer
"Delicate mother"
Thin
Delicate network of tissue
Adheres to outside of CNS
Extends into folds and crevices
Surrounds blood vessels on surface of CNS
```
63
Arachnoid
```
Middle layer
Spider web appearance
Thin
Fibrous tissue
CSF found in subarachnoid space between Pia mater and arachnoid
```
64
Dura mater
```
Outermost layer of meninges
"tough mother"
Made of two layers
Strong, dense CT
Outer layer adheres to skull bone
Inner layer adheres to arachnoid
```
65
Subarachnoid space
Potential space between pia mater and arachnoid
| CSF flows here
66
Dilations of the Neural Tube
```
Also considered swellings
Follow the fusing of neurospores
Three dilations, from rostral to caudal:
Prosencephalon
Mesencephalon
Rhombencephalon
```
67
Prosencephalon
```
Most rostral dilation of neural tube
Later can alter shape and form two dilations
Becomes:
Telencephalon &
Diencephalon
```
68
Mesencephalon
Middle dilation of neural tube
| Does not later form other dilations
69
Rhombencephalon
Most caudal dilation of neural tube
Later can alter shape and form two dilations:
Metencephalon &
Myelencephalon
70
Telencephalon
Forms majority of cerebral hemispheres, including:
Cerebral cortex
Subcortical white matter
Subcortical gray matter (nuclei)
71
Diencephalon
```
Becomes the forebrain
Forms:
Thalamus
Hypothalamus
Epithalamus
```
72
Mesencephalon
Becomes the adult midbrain
73
Myelencephalon
Becomes the medulla in adults
74
Metencephalon
Becomes the cerebellum and pons
75
Medulla
Most caudal portion of the brain
| Continuous with the spinal cord
76
Ventricles & Central Canal of Brain
| Development
Formed by the interior hollow of the neural tube
| Ventricles and canal are just a series of lumen in the CNS
77
Lumen
Cavities or spaces
78
Lateral Ventricles
| Development
Two lumen in the telencephalon
"Paired"
Lumen forming these are large and have complex shape
79
3rd Ventricle
| Development
Lumen of the narrow space between median walls of the right and left half of thalamus and hypothalamus
Continuous with the cerebral aqueduct
80
Cerebral aqueduct
Continuous with 3rd ventricle
Also called aqueduct of Sylvius
Lumen or space in core of midbrain (MES) and rostral pons (MET)
Continuous with 4th ventricle
81
4th ventricle
Continuous with cerebral aqueduct
Lumen of the caudal pons & rostral medulla
Continuous with central canal
82
Central canal
Lumen of caudal medulla and spinal cord
Canal is blocked or closed in adults
Gradually becomes obliterated between birth and adult
83
Flexures
Bends or fold in the neural tube as development progresses
Bending occurs in two phases
These explain differences in orientation of spinal cord and brain structure
84
Phases of flexures bending
Initial - two ventral concavities form
one in prosencephalon
one in rhombocephalon
Second - one dorsal concavity forms (in pons - MET)
85
What has the greatest cell proliferation during development?
Telencephalon - results in overgrowth = diencephalon
86
What also has great cell proliferation during development?
Cerebellum - grows very large
87
Spinal cord
```
Retains features similar to during development
Gray matter (internal) resembles Butterly
White matter (external) surrounds gray matter
```
88
Dorsal horn
Portion of gray matter located dorsally
| Primarily sensory function
89
Ventral horn
Portion of gray matter located ventrally
| Primarily motor function
90
Lateral horn
A small portion of gray matter that extends laterally in the thoracic spinal cord
"Interomediolateral column"
Location of sympathetic motor neurons
Thus, preganglionic autonomic neurons
91
Interomediolateral column
Also called lateral horn
92
Hindbrain
Contains:
Medulla (MYE)
Cerebellum and Pons (MET)
93
Medulla (MYE)
Continuous with spina cord, rostrally
Composed of nuclei and white matter tracts
Contains ascending and descending fibers
94
Motor function axons
Either somatic motor or autonomic motor exit the spinal cord in the ventral root
Cell bodies originate either:
lateral (visceral) or
ventral (somatic) horns
95
Ascending fibers
Contain axons traveling to structures at higher levels of CNS
96
Descending fibers
Contains axons traveling to structures at lower levels of CNS
97
Tracts
bundles of axons with similar functions and terminations
98
Cranial nerves associated with the medulla
```
CN IX - XII:
Glossopharangeal
Vagus
Accessory
Hypoglossal
```
99
Cerebellum and Pons
MET
100
Cerebellum
Cortex of three fairly thin coverings of gray matter on surface
Develops near surface because mantle layer neurons migrate through marginal layer to reach cerebellum
Has several nuclei within it's white matter
101
Pons
Composed of nuclei
Scattered throughout ventral portion = pontine nuclei
Also nuclei in dorsal portion
Has ascending and descending white matter tracts
Have four associated cranial nerves
102
Midbrain
MES
Located between pons and diencephalon
Contains many nuclei
Contains ascending and descending white matter tracts
103
Cerebral Peduncles
A very large white matter tract
Located on ventral midbrain
Composed of descending axons that connect cerebral hemispheres to lower brain and spinal cord
104
What brain division most closely resembles the neural tube?
Midbrain
105
What cranial nerves are associated with the midbrain?
CN III - IV
Occulomotor
Trochlear
106
Forebrain
Part of the CNS
Has two regions that are part of cerebral hemispheres:
Telencephalon
Diencephalon
107
Telencephalon
Most rostral of the CNS structures
Includes:
White matter tracts
Cerebral cortex
Several subcortical nuclei
108
Diencephalon
```
Composed of nuclei:
Subnuclei of thalamus
Hypothalamus
Subthalamus
Epithalamus
```
Includes:
Neural portion of retina which forms an extension of the optic cup
109
Cranial nerve associated with diencephalon?
CN II:
| Optic
110
Cranial nerve associated with telencephalon?
CN I:
| Olfactory
111
Cerebral cortex
Part of telencephalon
| Relatively thin 6-layered gray matter structure located on surface of telencephalon
112
Subcortical nuclei
Part of telencephalon
Embedded within white matter
```
Includes:
Hippocampus
Amygdala
Basal ganglia
Claustrum
```
113
Subcortical nuclei
Part of telencephalon
Embedded within white matter
```
Includes:
Hippocampus
Amygdala
Basal ganglia
Claustrum
```
114
Crossovers of neural pathways
Axons cross the midline in many locations
115
Lamina terminalis
Area where the nuerospore located at rostral end of the neurotube fuses
Provides a location for axons from one side of neural tube to cross over to other
Remnant of this is found in the adult brain.
Gives rise to major cross over points for axons to access opposite sides of the brain
116
Commissures or decussations
White matter tracts where axons cross the midline
117
Anterior commissure
Major cross over point in the telencephalon
| Derived from lamina terminalis
118
Corpus callosum
Major cross over point in the telencephalon
| Derived from lamina terminalis
119
Cell differentiation
The question of what makes an individual cell become a certain type of other cell?
A topic of debate
Two theories
120
Differential cytoplasmic partitioning
First theory of cell differentiation
Idea that with cell division, not all cytoplasmic or nuclear proteins are divided equally.
Thus, two daughter cells are not identical and are destined to become different types.
Determines morphology of cell types
Not the most common theory
121
Cell differentiation - chemical signals
Second theory cell differentiation
Chemicals are produced by cells in same locality
The chemicals can be secreted by cells in surrounding tissue or may be molecules on surfaces
Chemicals cause immature cells to change proteins and be synthesized intracellularly - determining what they are destined
122
Chemical secretion by cells
Chemicals secreted by cells or located on their cell surface can also have attractive influence on specific cells causing them to migrate along certain pathways
123
Cell migration
Occurs primarily after it has undergone its final cell division
The "birthday" of each neuron determines the eventual location and some of the properties of the cells
124
The "birthday"
Refers tot he time when a given neuron undergoes its last cell division
125
CNS structures that are laminated
geniculate nucleus
cerebellar cortex
hippocampus
126
Cerebral cortex lamination
Composed of six layers (layer one surface, six is deep)
Neuron cell shape and size depends on layer where it resides
Functional connections depends on where it resides
"Birthday" of neuron determines where it will ULTIMATELY reside
Experiements: tritated thymidine
127
Tritated thymidine
| Features and Usage in Divisions
Radioactively labeled amino acid
Taken up and incorporated into DNA of cells when administered systemically
When the DNA cells divide, they then carry radioactive substance with them
The more divisions that occur, the less that is present in the neurons.
128
Cell migration
| Layering patterns
Neurons are arranged sequentially across six layers according to age
Oldest cells in deepest layer six, most intensely labeled
Youngest cells in surface layer one, lightly labeled
"Inside Out" pattern
Young cells have to make their way past old cells to reach the outer layers of cortex and permanently reside
129
Radial Glia
Specialized glial cells that the migrating neurons climb along to reach their final destination
130
What factors determine the "birthday" of a neuron?
```
Size
Shape
Type
Chemical environment
Layer it resides in
```
131
Neural connections
Neurons must make connections with the right targets
Targets may be other neurons, peripheral structures, muscles, glands, etc.
132
Growth cone
Occurs just before or after migration is complete
| A process from the cell body of a neuron that grows and elongates over time at its tip
133
Filopodia
A specialized structure with a swollen appearance on the growth cone
Large fingerlike projections
Highly motile
Continually extend and retract
Extends to find specific molecules, when it doesn't find them it retracts and extends another direction to try again
134
Lamellipodia
A thin web like membrane between each of the filopodia
135
Termination of the axon
Filopodia serach for guiding molecules
Molecules assist axon to grow in that direction
Axon follows along diffusion gradient
Growth cone helps establish termination
Axon gets to neighborhood of termination
Terminal branches of each axon try different locations
Neuron makes connection
>
Sometimes connections are left shortly after made
Can be vacated before final connections are permanent
This is said to be "tentative" connections
>
Critical period takes place
>
Final connections must be made
136
Critical period
The period of time when most connections between neurons are still tentative and subject to reorganization
Window of opportunity
137
Congenital
Present at birth
138
Use it or lose it
Appropriate neural activity has to be maintained for cells connections to be kept
If neurons are not stimulated properly then they can lose their initial connections
139
Example of appropriate stimulation in developing NS
Neurons in retina of cats
Axons terminated at LGN (thalamic nucleus)
Vision of kittens restricted at birth for a couple weeks
Left them with poor vision later on
140
Take away
Neural stimulation is critical
Allows for synapses to take place during development
Many connections are hardwired after development
Some connections are also made throughout life
The more we are exposed to novel situations, the more our neural networks continue to change and develop!
141
Plasticity of CNS
CNS is plastic in children and adults
CNS continues to make connections
Changes anatomically and continually in response to events and conditions
Allows for us to learn and function in a complex society
Also allows for overcoming of neural insults/injuries
