Unit 3.L1-Development of the Nervous System, Brain & Sense Organs Flashcards
(148 cards)
1
Q
Neurulation: Early Neural Specification
What develops dorsally from the flat sheet of ectoderm (of the trilaminar embryo)?
A
Neural Plate + Neural groove (Neural Plate) develop dorsally from the flat sheet of ectoderm of the Trilaminar embryo
2
Q
Neurulation: Early Neural Specification
What step of Neurulation occurs around Day 17?
A
Day 17: The neural plate and early development of the neural groove and neural folds begins
3
Q
Neurulation: Early Neural Specification
By Day 22, Where do neural folds fuse? Where so they remain spread apart?
A
- Neural folds fuse opposite 4th - 6th somites
- Remain spread apart at both ends:
1. Rostral Neuropore
2. Caudal Neuropore
4
Q
Neurulation: Early Neural Specification
Centrally, what does the neural fold form?
A
Centrally, the neural fold forms neural tube (Closed), which detaches from the surface ectoderm (and neural crest cells)
5
Q
What forms the primitive node?
A
Gastrulation Neuronal progenitors: Midline epiblast near the primitive streak (caudal end), forms the primitive node
6
Q
What does the primative node extend to form?
A
primitive node→extends to form notochordal process
7
Q
What type of cells above the Notochord process (NP) causes it to change to the Notochord?
A
The notochordal process (NP), (mesoderm cells deep-down under the epiblast), flanked above by epidermal neural progenitors transforms the NP into the Notochord
8
Q
The Notochord induces the above ectoderm to become what?
A
Notochord induces the above ectoderm →Neuroectoderm→Neural plate
9
Q
What does the Neural plate form and how?
A
Neural plate (which folds/Involution)→Neural Folds
10
Q
How is the Neural tube formed? And what happens to the Primitive streak?
A
- The Neural fold fuses to form the Neural tube
- Primitive streak degenerates
11
Q
What 2 structures does the Neural tube form and how?
A
The Neural tube (delaminates from the ectoderm) & forms the primordial brain vesicles (cranially) & spinal cord (caudally).
12
Q
What is the Neural Fold flanked by?
A
Neural Fold is flanked by Neural Crest cells
13
Q
Neural Folds fuse and form what two structures?
A
Neural Folds fuse & forms the Neural Tube & Neural canal
14
Q
Neural crest cell via where? migrate to where? to form what? (2)
A
Neural crest cell via epithelial to mesenchymal transition (EMT) migrate into the mesodermal layer, forming:
- The Spinal Ganglia
- Many cell types in multiple organs
15
Q
What occurs when the Neural canal is open?
A
Neural canal is open: Fluid mixes with amniotic fluid
16
Q
When the Neural canal closes what is formed? (2)
A
- The Ventricular System of the Brain
- The Central Canal (neural canal) of the Spinal Cord
17
Q
What is formed by the 4th-6th somite? And what does it initate?
A
Caudal Neural Plate (4-6th somite)→Initiation of Spinal cord
18
Q
By Day 23, the Distinct Neural Canal (central canal) is present. What surrounds it?
Neural canal also called Neurocoel
A
Ventricular Zone (VZ) is (Neuroepithelial)
19
Q
The Ventricular Zone (VZ) proliferate fast and gives rise to what 3 layers?
VZ (proliferating Neuroepithelial Cells (NEC))
A
- Ependymal layer/VZ (inner lining; non-dividing)
- Mantle Layer (middle; Grey matter with Cells)
- Marginal Layer (outer; White matter; cell-fibers run)
20
Q
What shape does the Ventricular Zone (VZ) eventually become? and why?
A
VZ→Diamond shape due to internal specification
Before Neural Canal is circular
21
Q
By 6 weeks, what does the Grey Matter differeniate into?
A
6 weeks: Grey Matter→ Alar Plate cells + Basal plate cells
22
Q
What demarcates the Alar Plate cells and Basal Plate cells?
A
The sulcus limitans demarcates the two plates→ENTIRE CNS
23
Q
What do the Alar Plate cells and Basal Plate cells form?
A
- Alar Plate Cells→ Association cells (interneurons)
- Basal plate→Motor neurons of the VENTRAL HORN
24
Q
What are Neuroepithelial cells (NECs) found and what they differentiate into?
A
Ependymal lining (inner) the Central canal proliferate/differentiate→many type of cells
25
What are the structures around the Central plate diamond? (6)
* **Roof Plate** (Dorsal)
* **Floor Plate** (Ventral)
* **Afferent Fibers**: Sensory –coming in (Alar Plate)
* **Efferent Fibers**: Motor –going out (Basal Plate)
* **Grey matter** (Middle): Neurons & Cell bodies (Soma)
* **White mater** (Outer): Nerve fibers coming out of cells
26
What three neural tube cell types arise from the Neuroepithelium (neuroectoderm)?
## Footnote
1. **Neurons**
2. **Supporting Cells**
3. **Ependymal**
27
What is the precusors for CNS Neurons?
. **Neuroblasts**→CNS neurons (Grey or mantle layer)
* Apolar neuroblast→Bipolar neuroblast→Unipolar neuroblast→Neurons
28
What are the precursors for the Glial cells (supporting cells)? What supporting cells are later formed?
**Glioblasts**→Glial cells (supporting cells)
* Glioblast (spongioblast)
1. Astroblast→(Protoplasmic astrocytes or Fibrous astrocytes)
2. Oligodendroblast→(Oligodendrocyte)
29
What does the Ependymal epithelial cells become?
. Ependymal epithelial cells
* **Line the canal (non-dividing)**
* **Epithelium of Choroid plexus**
30
What other cells type are present in the CNS?
* **Microglia**
* **Neural Crest Cells**
31
Where do the Microglia originate from? What is there role?
* Microglia **(non-neural tube cells)**: These cells migrate into the CNS with the **developing vasculature** (mesenchymal cell→microglia)
* Function: Innate immunity via **phagocytosis**
32
What do Neural Crest Cells form that receive sensory fibers?
NCCs form the **Dorsal Root Ganglia (DRG)**,
or **Spinal Ganglia**
33
What does the Dorsal Root Ganglia (Spinal Ganglia) receive?
receive **Sensory fibers** from Sensory Neurons (afferent fibers) in the periphery
## Footnote
Sensory Neurons are bipolar cells
34
What do the sensory fibers make synapses with? And why?
The sensory fibers make synapses with **association cells (interneurons)** as their exons do not come out of the spinal cord.
35
What will be formed at every somite?
At every Somite there will be a **bilateral ganglia** formed (**~32 ganglia**)
36
What are the 4 parts of the developing spinal cord?
1. Alar plate cells
2. Basal plate cells
3. Dorsal Root Ganglion
4. Ventral Trunk of Spinal Nerves
37
Alar Plate cells are what type of horns? and include what?
Alar plate cells→**Dorsal gray horns** with **afferent nuclei** (no processes)
38
What do Afferent nuclei (from the alar plate cells) synapses with?
synapses with **Dorsal Root Ganglion (DRG; Sensory nerves)**
39
What does the proliferation of the Alar Plate (interneurons) become?
Proliferation of Alar Plates/interneurons→**Dorsal median septum** (Neural Canal→Diamond shaped Central Canal)
40
Basal Plate cells are what type of horns? and include what?
. Basal plate cells→Ventral & lateral gray columns (**Ventral horns**)→ **Axons**→**Ventral roots** of the spinal nerves (**“remi”**)
41
What does the proliferation of the Basal Plate (Motor Neuroblast) become in the developing spinal cord?
Proliferation of Basal Plates/Motor Neuroblasts→ Ventral deep longitudinal groove →**Ventral Median Fissure**
42
What forms the Dorsal Root Ganglion and where do they send processes to?
Formed by **Neural Crest Cells** send processes to **Alar plate interneurons (association cells)**
43
What structures form the Ventral Trunk of Spinal Nerves?
**Ventral Motor Root + Sensory Fibers from DRG**
## Footnote
DRG: Dorsal Root Ganglion
44
Where are the Unipolar neurons in the Spinal ganglia (DRG) derived from? What mechanism creates the unipolar neurons?
* The unipolar neurons in the spinal ganglia (DRG: dorsal root ganglia) are **derived from neural crest cells**
* **Mechanism: Bipolar to T-shaped Cells** (Neural crest cell→bipolar neuroblast→Unipolar afferent neuron)
45
Where does the peripheral processes of the spinal ganglion cells from the DRG pass through? To what locations? and innervate what?
The peripheral processes of spinal ganglion cells from the DRG pass in **the spinal nerves to sensory endings** in **somatic (skin) or visceral (gut, lungs)** structures & innervate tissues having **Neural Crest Cells (NCCs)** with:
1. **Nociceptors**
2. **Mechanoreceptors**
3. **Proprioceptors**
46
What do the receptors listed below sense?
1. **Nociceptors**
2. **Mechanoreceptors**
3. **Proprioceptors**
1. **Nociceptors**
* Pungent/obnoxious/acrid/acidic smells & hot/cold–thermosensing
2. **Mechanoreceptors**
* Tactile touch / level of pressure at foot/fingers.
3. **Proprioceptors**
* Sense movement of muscles, over/under-stretched, energy dispensed
47
Which receptor associated with Sensory Nerves leave the Basal Plate?
Proprioceptors
48
What are all the structures the Neural Crest Cells give rise to? (6)
1. Cranial & Sensory Ganglia & Nerves
2. Medulla of Suprarenal Glands
3. Pigment Cells (Melanocytes everywhere)
4. Pharyngeal Arch Cartilage
5. Head Mesenchyme
6. Cardiac Valves
49
What ganglia comes off the spinal nerve and what types of neurons are present?
**Ganglia of Sympathetic Trunk**
* Multipolar neuron (sympathetic ganglion cell)
50
What does the Ganglia of Sympathetic Trunk innervate?
Constitutive innervation to **Visceral Organs**→ **Constitutive functions**: Digestion, respiration, secretion, peristalsis, renal filtration
51
What are the directions of Afferent and Efferent Neurons?
* Afferent Neurons (NCCs)-**Bidirectional**
* Efferent Neurons-**Uni-directional**
52
Where does the spinal cord and vertebral column run?
* For 8 week Fetus
* Adulthood
**8 Week Fetus**:
* Spinal cord & vertebral column (same length) run **parallel till the end**
**Adulthood**
* Spinal cord only reaches: **L1/ L2 vertebrae**
* Reason: **Faster growth of the vertebral column** relative to the spinal cord
53
From 24 wks to Adult, where does the Conus medullaris (cone of medulla) lie?
24 Wks→Adult: **Conus medullaris (Cone of medulla)** lie progressively at higher vertebral level adjacent to **Sacral S1 (24 Wks)→ L3 (neonate)→L1 vertebrae (adult)**
54
What is the Filum terminale? What is its length? Where is it derived from? Where does it continue and end at? What is its function?
**Filum terminale: Fragile strand of fibrous tissue**
* ~20 cm in length
* Derivative of **pia mater**
* Continues down via the apex of the conus medullaris
* **End at Co1** (coccygeal vertebra)
* **Function**: Provides longitudinal support to the spinal cord
55
What is the Meninges? Where does it originate from and what does it form?
* Meninges: **3 layers of connective tissue** surrounding the CNS (Brain + spinal cord)
* Originates as a **mesodermal derivative** & forms **connective/fibrous** tissue
56
What are the 3 layers of Meninges?
1. **Pia mater** (inner layer)
2. **Arachnoid mater** (subarachnoid space) (middle layer)
3. **Dura mater** (outer layer)
57
What layer of the meninges is the Pia mater? Where does it end? What is critical for? What does its fibrous threads form?
* Pia mater: **Inner layer;vascularized**
* End at Co1 vertebra
* Critical to brain development (**nourishment**)
* Fibrous thread forms **filum terminale**
58
What layer of the meninges is the Arachnoid mater? What is it space for? Where does it end?
* Arachnoid mater **(subarachnoid space) for CSF (middle layer)**
* End at S2 vertebra
59
What layer of the meninges is the Dura mater? What is it space for? What does it make? Where does it end?
* Dura mater :**Thickest outer layer**
* **Blood islands, vascularized for circulation**
* Makes Cerebrospinal fluid (CSF)
* End at S2 vertebra
60
When does the Cerebrospinal fluid (CSF) begins to form?
Week 5
61
Where are Oligodendrocyte cells located? What is there function? What is the origin?
Oligodendrocytes: **(CNS; Central Nervous System)**
* Function: **Insulate axons in multiple layers** forming the **Myelin Sheath**
* Origin: **Neural Tube cells** (supporting cells)
62
How many axons can a single oligodendrocyte wrap around? How many axons can myelin sheath wrap around?
* The **“feet”** of a single oligodendrocyte **enwraps ~50 axons**
* A **thick ~1 μm of myelin sheath** around each axon
63
Where are Schwann Cells present? What is there function? What is the origin?
* **Present in PNS**
* Function: **Insulates Axons in PNS→One axon/cell**
* Origin: **Neural Crest Cells**
64
What are the two types of Schwann Cells and what are their functions?
1. **Myelinating (lipid layer around Single Axon): Insulation**
2. **Non-myelinating (Multiple Axons encased in one Schwann cell cytoplasm)→Protects newly formed short axons**
65
# Spinal Cord or Neural Tube Defects (NTDs)
What is **Spina bifida occulta**? Where is defect? What is sign of this defect?
* **Unfused neural arch**: Arches of a child's vertebrae remain open, usually in the **lumbar region** (Symptomless)
* **Defect of the vertebral development**
* Sign: **Tuft of hair in the lumber region (lower back)**
66
# Spinal Cord or Neural Tube Defects (NTDs)
What is the feature of **Spina bifida Cystica**? List the 3 types?
* **Have Cysts or open Cyst→Need surgical repair**
1. **Spina bifida with Meningocele**
2. **Spina bifida with meningomyelocele**
3. **Spina bifida with myeloschisis**
67
# Spina bifida Cystica
What is **Spina bifida with Meningocele**? Are spinal cord/nerves present? What is the state of lumbar region? Is repair possible, if so how?
* **CSF-filled sac** of the spinal canal with **dura mater intact**; no spinal cord/nerves in it; **closed lesion in lumber region**
* Repair Possible: **Sealed by simple obliteration of the sac**
68
# Spina bifida Cystica
What is **Spina bifida with Meningomyelocele**? Are spinal cord/nerves present? What is the clinical manifestion?
* CSF filled **closed** or **open (leaking)** (10%) swelling containing **spinal cord and/or spinal nerves** in **thoracolumbar, lumbar, or lumbosacral** regions.
* **Irreversible paralysis of the lower body**
69
# Spina bifida Cystica
What is **Spina bifida with Myeloschisis**? Are spinal cord/nerves present? What is the defect?
* (Spina bifida aperta): **The severest form**
* The nerve tissue is **fully exposed** with **no dermal/meningeal covering**
* Closure of the neural folds fails
70
What is **Meroencephaly?** What is the defect present? How can it be diagnosed?
* Partial absense of the brain
* Defective **Rostral neuropore closure**
* Diagnosis: High level of **alpha fetoprotein (AFP) in the amniotic fluid**
71
What is the defect that causes Meningomyelocele? What clinical manifestation may arise?
* Defective **Caudal Neuropore Closure**
* +/- clubfoot
72
What is the defect that causes Meningoencephalocele? What other condition may appear?
* Fontanelle not closed properly. **Both rostral and caudal neuropore are open**
* +/- Hydrocephalus
73
By Day 27, the head -fold has undergone a longitudinal folding in what direction and what is formed (specified)?
Day 27: The head-fold has undergone a longitudinal folding in a **ventro-rostral** direction & **specified 3 regions of the brain**
74
# Definition/demarcation of the brain
What structures make up the brain? What two things are present in the brain?
**Neural tube cranial to 4th somite** is the **“Brain”**, with **vesicles (cells) & ventricles** (cavity with **CSF**).
75
At 4 weeks what are the three primary vesicles of the brain? What structures to they become?
1. **Forebrain** (prosencephalon)→**Cerebrum**
2. **Midbrain**(mesencephalon)
3. **Hindbrain** (rhombencephalon)→**Cerebellum & Brainstem**
76
What do the neural tube cells become in the brain? What does the Ventricular space form?
* Neural tube cells→**Brain cells**
* Ventricular Space→**CSF**
77
By Week 5, how many vesicles & ventricles are present?
* **5 Secondary Vesicles** (from the 3 primary vesicles)
* **4 Ventricles** (2 Lateral + 3 Longitudinal)
78
What are the 2° vesicles formed by the forebrain, midbrain & hindbrain?
1. **Forebrain(prosencephalon)**
* **Telencephalon**
* **Diencephalon**
2. **Midbrain (mesencephalon)**
3. **Hindbrain (rhombencephalon)**
* **Metencephalon**
* **Myelencephalon**
79
What are the adult derivatives (walls & cavities) of the 5 Secondary Vesicles?
1. Telecephalon
* Walls: Cerebral hemisphere
* Cavities: Lateral ventricles
2. Diencephalon
* Walls: Thalami. etc (glands/nuclei)
* Cavities: Third Ventricle
3. Mesencephalon
* Walls: Midbrain
* Cavities: Aqueduct
4. Metecephalon
* Walls: Pons (anterior), Cerebellum (posterior)
* Cavities: Upper part of 4th ventricle
5. Myelencephalon
* Walls: Medulla, Spinal Cord
* Cavities: Lower part of 4th ventricle
80
By Week 5, What folding occurs and what 3 flexures arise?
Week 5: **Ventro-rostral head folding (Neuraxis bend)**
* **1st Flexure: Midbrain flexure** (Cephalic/mesencephalon)
* **2nd Flexure: Cervical flexure** (Junction of hindbrain-spinal cord)
* **3rd Flexure: Pontine flexure (opposite direction; anticlockwise)**
## Footnote
1st & 2nd Flexure: Clockwise bending
81
The Pontine flexure divides the hindbrain into two what?
1. **Metencephalon**
2. **Myelencephalon**
82
Opposite bending of the flexure causes what?
**Thinned 4th Ventricle roof**
83
Where does the Kinking of the Brain Tube occur?
**Myelencephalon & the 4th ventricle**
84
What occurs only at Pointline Flexure?
At Pontine Flexure the **Walls of the Neural Canal (Ependyma)** are **spread apart at the roof**
85
What comes to the floor of the 4th ventricle? What occurs to the roof?
So **both sulcus limitans** come to the floor of the ventricle; **roof thins**
86
At the brainstem, the Sensory (Alar plate) move from where to where? And the Motor (Basal plate) move from where to where?
| Myelencephalon & the 4th ventricle (@ Pontine Flexure)
* **Sensory neurons (Alar plate; AP)** turn **Dorsal to Lateral**
* **Motor neurons (Basal plate; BP)** turn **Ventral to Medial**
87
* Cranial Nerve Ganglion becomes what?
* Dorsal Root Ganglion becomes what?
* CNG (Brain): Cranial Nerve Ganglion→ **Cranial Nerve**
* DRG (Spinal Cord): Dorsal Root Ganglion→ **Spinal Nerve**
88
What does the Cervical Flexure demarcates?
Cervical Flexure demarcates the **Hindbrain + Spinal cord**
89
The Pontine Flexure divides the hindbrain into what?
1. **Metencephalon→[Pons + Cerebellum]**
2. **Myelencephalon→Medulla Oblongata→caudally spinal cord**
90
1. Metencephalon→
2. Myelencephalon→
| Hindbrain
1. Metencephalon → **[Pons + Cerebellum]**
2. Myelencephalon→**Medulla Oblongata→caudally spinal cord**
91
The Myelencephalon neuroblasts in the alar plate become?
| Hindbrain
**Alar Plate: Neuroblast→Marginal Zone**
* **Gracile Nuclei** (medially)
* **Cuneate Nuclei** (laterally)
92
The Alar plate move ventrally and become what?
| HIndbrain: Myelencephalon
Ventrally→neurons in the **Olivary Nuclei**
93
What connections arise at the Myelencephalon & Inferior 4th Ventricle (Hindbrain)?
* **General connections**: Brain connects to **somites (General rami)** just like spinal cord
* **Special Connections**: Brain→**special connections** to **additional skeletal muscles (branchial arches)**
94
List the different General connections. Where are the impulses (afferents) and nerves (efferents)?
1. General **Somatic Afferents (GSA)**: impulses from the surface of the head
2. General **Visceral Afferents (GVA)**: impulses from the viscera
3. General **Somatic Efferents (GSE)**: neurons of the hypoglossal nerve
4. General **Visceral Efferents (GVE)**: vagus and glossopharyngeal nerves
## Footnote
Afferent (Alar Plate)
Efferent (Basal Plate)
95
List the different Special connection. Where do each special connecttion affect?
5. Special **Somatic Afferents (SSA)**: auditory & vestibular
6. Special **Visceral Afferents (SVA)**: taste & smell
7. Special **Visceral Efferents (SVE)**: Muscles of the jaw, face & larynx
96
Where are the cranial nerves for Vision and Olfaction?
Vision & Olfaction (unique): Cranial nerves of **diencephalon & cerebral hemispheres**
97
What does the **Ependymal roof** (4th ventricle + **pia mater** of mesenchymal origin) form?
Ependymal roof (4th ventricle + pia mater of mesenchymal origin→ **Tela choroidea**
98
Tela choroidea proliferates, infolds, & differentiates into?
Tela choroidea proliferates, infolds & differentiates into **“choroidal arteries of the Pia→Choroidal Plexus**
99
What does the Choroidal Plexus secrete? what does it form?
Choroidal Plexus→Secrete **Ventricular Fluid**→Forming **Cerebrospinal Fluid (CSF)**
100
Where are the pons & cerebellum located?
Metencephalon: **Pons (Bottom; ventrally)** & **Cerebellum (Top; dorsally)**
| Hindbrain: Metencephalon & Superior 4th Ventricle
101
What does the Basal plate Neuroblasts become?
| Hindbrain: Metencephalon & Superior 4th Ventricle
Basal plate Neuroblasts→**3 motor nuclei**→3 columns
102
What does Metecephalon Alar plate become?
| Hindbrain: Metencephalon & Superior 4th Ventricle
1. Thickens, swells in the **4th ventricle**→ **Cerebellum**
2. **Dentate, Pontine, Cochlear, Vestibular & Sensory nuclei**
103
What are the 3 parts of the Cerebellum? And what function does each part play?
1. **Archicerebellum** (*flocculo-nodular lobe*)→Connects **Vestibule of the ear**
2. **Paleocerebellum** (*anterior lobe*)→**Sensory** signals from the limbs
3. **Neocerebellum** (*posterior lobe*) →Selective **Fine-Motor** control of limb movements
## Footnote
Cerebellum is divided by evolutionary function
104
By the 16 weeks, what is formed that drains the CSF from the brain? Where does it drain into?
* **Foramen of Luschka** (lateral)
* **Foramen of Magendie (mainly)** (Medial aperture)
* Drains CSF into **Subarachnoid space**
105
# Midbrain: Mesencephalon Development
What occurs when the neural canal narrows?
Forms the **Cerebral aqueduct** which **connects 3rd & 4th Ventricles**
106
# Midbrain: Mesencephalon Development
By Week 11, the Alar plate Neuroblasts migrate to form?
* **Inferior Colliculi →Auditory reflexes**
* **Superior Colliculi→Visual reflexes**
## Footnote
Sensory nerves receives signals
107
# Midbrain: Mesencephalon Development
By Week 11, the Basal plate Neuroblasts form what?
* Red nuclei, reticular nuclei
* Nuclei of 3rd & 4th CNs.
* Substantia Nigra & Crus cerebri
108
At Week 5, during Forebrain: **Dicencephalon** development:
1. What closes?
2. What appear cranio-laterally in the Diencephalon?
3. What nerves began to form?
4. Which vesicles appear?
5. What grows laterally?
6. What expands?
7. What is covered by the cerebral hemispheres?
1. **Rostral neuropore** closes
2. **Optic Vesicles** appear cranio-laterally in the Diencephalon
3. **Retinal + Optic Nerves** begin to form.
4. **Telencephalon vesicles** appear.
5. **Cerebral hemispheres** grow laterally
6. **Lateral Ventricles** expands
7. Cerebral hemispheres cover the **[Diencephalon + 3rd-Ventricle]**
109
At Week 7-8, during Forebrain: **Dicencephalon** development:
1. What occurs to the Wall of 3rd Ventricle (Dicencephalon)? What structures does form?
2. Where does a pair of nuclei (mammillary bodies) grow?
3. What is the Infundibulum?
4. Where is the pineal gland located?
5. What is the origin of the pituitary gland? What is it's structure?
1. Wall of 3rd Ventricle (Diencephalon)→**Lateral Wall thickenings**→**Thalamus, Hypothalamus, and Epithalamus**
2. A pair of nuclei (mammillary bodies)→grow on the **Ventral Surface** of the **hypothalamus**
3. **Infundibulum: A Stalk connecting Hypothalamus & Pituitary** develops.
4. **Pineal gland (melatonin)**: **Caudal roof of the diencephalon**
5. **Pituitary gland (hypophysis): Unique Ectoderm origin** with **3 lobes**
* Anterior, Intermediate, and Posterior lobes.
110
At Week 10, during Forebrain: **Telencephalon** development:
1. Lateral Diverticula becomes what?
2. Cerebral hemispheres grow and covers what?
3. What are the 2 parts of the Forebrain (Cerebrum)?
4. What connects the cerebral ventricles to the 3rd ventricle?
5. Medially the Choroid fissure turns into what?
6. What is revealed when telencephalon is cut at the Interventricular foramina?
1. 10 wks: Lateral Diverticula →**Cerebral Vesicles**
2. Cerebral Vesicles & Hemispheres grow→covers: **diencephalon, midbrain, & hindbrain**
3. Forebrain (Cerebrum): **1) Frontal & 2) Parietal lobes**
4. Cerebral Ventricles connect the 3rd Ventricle by a **canal →“Interventricular foramina"**
5. Medially→Choroid fissure→**Choroid plexus**
6. Cut at Interventricular foramina reveals: **Thalamus, Hypothalamus & Corpus Striatum** at 10 wks.
111
# Forebrain: **Telencephalon** development
At Week 10, what is the Lamina terminalis and Anterior commisure?
* Lamina terminalis: Where the Telencephalon opens into the Diencephalon, all the CSF comes out
* Anterior Commisure: Nerve fibers that attach the two cerebral hemisphere
112
# Forebrain: **Telencephalon** development
At Week 11, what do projections fibers of the internal capsule splits?
11 weeks: Projection fibers of the internal capsule splits→**Corpus Striatum**→ **Caudate + Lentiform nuclei**
113
Growth of the brain:
1. What structures of the brain grow?
2. What develops in the cerebral cortex?
3. What narrows during brain development?
4. What is buried in the cerebral cortex?
5. The surface of the cerebral hemispheres grow fast giving rise to?
1. **Cerebral hemisphere, diencephalon, & brainstem** grow
2. Development of the **sulci (grooves)** & **gyri (convolutions)** in the cerebral cortex.
3. **Narrowing of the lateral sulcus** during brain development
4. **Burying of the insula** of cerebral cortex.
5. The surface of the cerebral hemispheres grows fast giving rise to→ **multiple Gyri & Sulci**
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# Congential Brain Defects
What is Encephalocele? Where does it commonly occur? What causes it? (2)
* Encephalocele: **Herniation** of intracranial contents (**common in occipital region**) called **cranium bifidum**
* **Cause**:
1. Defects in **posterior fontanelle**
2. Defect near the **foramen magnum**
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# Congential Brain Defects
Explain the severity of the defects lised below:
* Meningocele
* Meningoencephalocele
* Meningohydroencephalocele
* **Meningocele: Herniated Meninges**
* **Meningoencephalocele: (Meninges + part of brain)**
* **Meningohydroencephalocele: (Meninges + part of brain + Ventricles)**
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What is Microcephaly? How common is it? What are the causes?
* **Microcephaly**: Due to reduction in brain growth.
* **25,000 infants/annum** in US alone
* **Causes**:
1. **Genetic in origin**
2. **Ionizing radiation**
3. **Infectious agents**
* Cytomegalovirus
* Rubella virus
* Toxoplasma gondii
* Zika Virus
## Footnote
Different from Meroencephaly (little or no brain formed)
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What is the periheral nervous system (PNS)? When does it develop? What does it connect? What is included in the PNS?
* PNS is the nervous system **outside** the **brain & spinal cord**
* PNS develops in **tandem** with the **brain & spinal cord**
* It **connects the CNS** to **structures of the body** as they form
* PNS includes: **[Spinal nerves + Cranial nerves +Autonomic nervous system (ANS)]**
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What is the PNS comprised of? (4)
1. Cranial Nerves
2. Spinal nerves & Plexuses
3. Neurons outside the CNS
4. All peripheral ganglia connecting brain & spinal cord (DRG & CRG).
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Humans have how many pairs of spinal nerves? List them all out.
| "Cats Take Large Shits Constantly"
Humans have **31 pairs of spinal nerves** and they are named after the section of the spine they come out of:
* 8 pairs of **cervical nerves**(C1-C8)
* 12 pairs of **thoracic nerves** (T1 – T12)
* 5 pairs of **lumbar nerves** (L1-L5)
* 5 pairs of **sacral nerves** (S1-S5)
* 1 pair of **coccygeal nerves** (Co1)
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What is the Autonomic Nervous System (ANS)?
It controls bodily **functions not consciously directed**, i.e. **autonomously** (breathing, heartbeat, digestive process, smooth muscle contractions, controls the action of all internal organs, secretion of epinephrine/norepinephrine from the medulaa of the adrenal gland)
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What are the 2 major divisions of the ANS? What do they both consist of?
* **Sympathetic system** (Emergency System)
* **Parasympathetic System** (Constitutive System)
* **Both consist of CNS + PNS neurons that innervate:**
1. Smooth muscle
2. Cardiac muscle
3. Glandular epithelium
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What are the four tissues the eyes are derived from?
1. **Neuroectoderm** of the forebrain
2. **Surface ectoderm** of the head
3. **Mesoderm** between Neuro- & Surface-ectoderm
4. **Neural crest cells**
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By Day 22, what forms the Optic Groove, which becomes the Optic Vesicle?
Day 22: **Bilateral diverticulum invaginations** of the **Neuroectoderm** from the **Diencephalon** forms **Optic Grooves** which become **Optic Vesicle**
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By Day 28, Optic vesicles contact the overlying Surface ectoderm triggering the initiation of what?
Optic vesicles contact the overlying **Surface ectoderm** triggering the initiation of the **Lens Placode (a thickening of ectoderm)** by D28.
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Developing Optic Cup & opposing Lens Vesicle: Reciprocal induction
1. Optic vesicle invaginates and forms what?
2. What are the two layers of Optic cup?
3. The ectodermal Lens Placecode invaginates and forms?
4. What dissociates from the ectoderm?
5. What becomes prominent & is attached to the wall of the brain?
6. What do epithelial cells on the posterior wall of the lens vesicle form?
7. How are the primary lens fibers formed?
1. Optic vesicle invaginates & forms a **double-walled structure →Optic Cup**
2. Optic cup→**Outer pigment layer + inner neural layer**
3. Ectodermal Lens Placode invaginates→**Lens Vesicle**
4. **Lens Vesicle once surrounded by the optic cup,** dissociates from ectoderm.
5. **Optic stalk** becomes prominent & is attached to the wall of the brain.
6. Epithelial cells on the posterior wall of the lens vesicle **lengthen anteriorly to form fibers.**
7. In **2-Weeks** the fibers **reach the anterior wall** of the vesicle→**Primary Lens Fibers**
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What is the fate of the 4 cell-types that from the eye:
1. Neuroectoderm
2. Surface ectoderm
3. Mesoderm
4. Neural crest cells
1. Neuroectoderm→**Retina, posterior layers of iris, & optic nerve**
2. Surface ectoderm→**Lens & corneal epithelium**
3. Mesoderm→**Fibrous and Vascular coats of the eye**
4. Neural crest cells migrate into the mesenchyme: **Choroid, Sclera, & Corneal Endothelium**
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What is the fate of the structures listed below:
1. Optic Cup
2. Optic Stalk
3. Ectoderm + Mesoderm
4. Mesoderm
1. Optic Cup→ **Retina (inner & outer-pigmented layers)**
2. Optic Stalk→**Optic Nerve→Brain**
3. Ectoderm + Mesoderm→**Lens + Cornea**
4. Mesoderm→ **Vessels (Hyaloid artery/vein) within optic stalk)**
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Where does vessels of the eye get contained?
Vessels get contained within the **optic stalk**
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What two layers of the retina do the Optic cup form?
Optic cup
* **Outer layer (Pigmented Retina layer)**
* **Inner layer (Neural Retina layer)**
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Lens induce the inner neuroepithelium to form what?
Lens induces the inner neuroepithelium→ **Light Sensitive Neural Layer**
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What forms the Neuronal Cell Bodies of the inner layer?
**Bipolar & Ganglion cells**
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By Week 7, Eye Development:
1. What is the eye primordium embedded in?
2. What converges into the optic nerve?
3. What is the Optic Nerve part of and what are the 3 layers?
1. The eye primordium is embedded in **undifferentiated mesenchyme** (not transparent)
2. **Fibers of the Neural Retina converge** into the optic nerve (produce crystalline to make lens glasslike)
3. The **Optic Nerve** is part of the brain with **3 layers:**
* **Thick Outer Dural Sheath** blends & forms the **sclera**
* **The Intermediate Sheath (Arachnoid mater)** is thin.
* **Inner Sheath (Pia mater)** is **vascular & nourishes** the **Optic Nerve fibers** up to the **Optic Disc** (end of eye ball)
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What do lens induce to form the Cornea?
Cornea: Lens induces the **Surface Ectoderm** to form the **Cornea**
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What are the 3 cell sources that the Cornea is made from?
1. External **corneal epithelium**, derived from **surface ectoderm**
2. **Developing sclera (Mesenchymal Dura mater)**
3. **Neural crest cells** (with varying pigmentation/melanin)
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How are Eyelids formed?
Eyelids form as **outgrowths** of the **surface ectoderm**
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What supplies the vitreous body & lens? What degenerates to permit light to retina?
Vitreous body & lens are supplied by the **hyaloid arteries** which **degenerate to permit** light to the retina
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How is the Iris formed?
**Rostro-anterior rim** of the **optic cup** with **mesenchyme** between optic cup & surface epithelium
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What is induced to form the Sphincter & Dilator Pupillae muscles of the iris?
Rostro-anterior rim of the optic cup with mesenchyme between optic cup & surface epithelium **induces** the **underlying ectoderm** of the **optic cup** to **form Sphincter and Dilator Pupillae muscles**
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By week 15, what structures are present in the morphologically well-developed Eye?
1. Anterior/posterior chambers
2. Iridopupillary membrane (goes away after birth)
3. Inner and Outer Vascular Layers, Choroid, Sclera, Vitreous Body, Optic Nerve
4. Cornea, Iris, Ciliary body, Conjunctival sac, Suspensory Ligament
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What is the Ciliary body? Where is the origin of the ciliary muscles?
* (formed by ciliary process) A wedge-shaped **choroid extension** towards the lens; made of **outer pigmented retina & inner neural layer (non-visual retina)**
* **Ciliary muscles origin: Neural Crest cells** in ciliary body mesenchyme for ciliary muscles
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What are the functions of the Ciliary Body? (4)
1. It releases a **clear liquid in the eye**; the aqueous humor.
2. It has **ciliary muscles** that **change the shape of the lens for focus**.
3. It **delivers oxygen** and **nutrients** to the eye tissues.
4. It **attaches** to the **fibrous suspensory ligaments**, that **suspends the lens**.
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What suspends the lens and is attached to the ciliary body?
**Fibrous suspensory ligaments**
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# Congenital Malformations of the Eye
What is Coloboma iridis? What causes it?
* Coloboma iridis: (Pupil has a keyhole appearance)
* Cause: If the **choroid/retinal fissure** does not close by **week 7, a cleft in the iris** occurs that may **extend into the ciliary body, retina, choroid, or optic nerve**
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# Congenital Malformations of the Eye
What is Palpebral coloboma? What causes it? What type of condition is it?
* Palpebral coloboma: **a notch in the eyelid**
* Cause: Results from a defect in the **developing eyelid**
* **Benign condition**, surgically rectified.
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# Congenital Malformations of the Eye
What is Congenital cataracts? What is the cause?
* Congenital cataracts: **Bilateral lens opacities**
* Due to **rubella virus infection, toxoplasmosis, congenital syphilis, Down syndrome or Galactosemia**
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# Congenital Malformations of the Eye
What Congential glaucoma (buphthalmos)?What is the cause?
* Congenital glaucoma (buphthalmos): **Increased intraocular pressure**
* Due to abnormal drainage of aqueous humor during development. Mostly genetic but seen in **maternal rubella infection**
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# Congenital Malformations of the Eye
What is Congential Retinal Detachment? What defects occur? Where can this be seen?
* Outer and inner layers of the optic cup **fail to fuse, causing retinal tear**
* **Inter-retinal space filled (Vitreous fluid)** & the **neural communication is lost**
* Seen in **Down syndrome & Marfan syndrome (Fibrin-1 deficiency)**
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# Congenital Malformations of the Eye
What happens in the defects listed below:
* Cyclopia
* Micropthalmia
* Anophthalmia
* **Cyclopia**: **Eyes** are partially/completely **fused** →single **median eye in one central orbit**. Proboscis visible.
* **Microphthalmia** is a small eye, due to intrauterine infections (Toxoplasma, rubella, cytomegalovirus, and **herpes simplex virus**)
* **Anophthalmia** is absence of the eye. Optic vesicle fails to form.
