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Nervous System (Semester 5) > 2.1 Embryology (Pt 1) > Flashcards

2.1 Embryology (Pt 1) Flashcards

1
Q

What is the process that forms the basic germ layers and when does this occur?

List the 3 layers and what these are collectively known as

A

GASTRULATION: occurs 18 Days following conception

Blastula reaches uterine cavity and implants, Blastula cells differentiate into 3 layers:

  • Endoderm
  • Mesoderm
  • Ectoderm

Collectively known as a Trilaminar disc

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2
Q

Ovum + Sperm forms what?

A

ZYGOTE

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3
Q

What is the timescale that defines an embryo vs a foetus?

A

Embryo = first 8 weeks

Foetus = 8 weeks till birth

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4
Q

Label the image below and state 4 thing each germ layer becomes

A
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5
Q

Following formation of the 3 germ layers, what occurs next?

Briefly explain how this occurs?

A

Neurulation:

1) Thickening of ectoderm: development of neural plate
2) formation of the neural groove: at 20 days
3) formation of neural folds
4) completion of neural Tube

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6
Q

List the 5 phases of brain development

A

1) Neural plate induction
2) Neural proliferation
3) Migration & Aggregation
4) Axon growth & Synapse formation
5) Apoptosis & Synapse rearrangement

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7
Q

What is neurulation and when does it begin?

A

A process of folding and transformation of neural plate into neural tube which begins in 3rd week

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8
Q

How do we get development of the neural plate?

A

The notochord induces the formation of the neural plate in overlying ectoderm (which goes on to form the neural fold)

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9
Q

As both the skin and neural tube develop from the ectoderm what triggers differential development?

A

The ectoderm develops into skin due to exposure to proteins such as BMP-4 (from endoderm & mesoderm)

Primitive node secretes BMP-4 anatagonists (eg. noggin, chordin, follistatin)

This allows a certain region of ectoderm to develop into nerve tissue

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10
Q

What triggers ‘neural plate induction’?

What 4 things are formed after neural plate induction?

A

Triggered by BMP-4 antagonists which allow a certain region of ectoderm to develop into nerve tissue

Results in formation of:

1) Primitive node
2) Notochord
3) Primitive streak
4) NEURAL PLATE

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11
Q

What structure induces neurulation?

A

The Notochord: thickening of mesodermal cells

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12
Q

How does the neural plate develop?

A

The notochord signals the overlying ectoderm to thicken and develop to form the neuroectoderm

This then forms the neural plate

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13
Q

Describe the process of neurulation

A

1) The notochord induces the formation of the neural plate in overlying ectoderm at the cranial pole
2) It forms and the neural groove and neural folds (as it has to accommodate more cell)
3) The groove deepens (becoming the neural trench), and neural crest cells begin to detach (these will go on to form a variety of structures).
4) Eventually the neural folds fuse at the midline to form the neural tube (first fuse in the centre then towards the cranial and caudal ends)

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14
Q

Why is the neural groove wider at the cranial and caudal ends?

A

This is where cranial (anterior) and caudal (posterior) neuropores will form

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15
Q

What process accompanies organisation and closure of the neural tube?

Why is this useful clinically

A

Somitogenesis: mesoderm starts to organise to form somites

Somites help us to identify foetal age

At day 22, there are 4 occipital somites that form a rough guide allowing development to continue craninally and caudally

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16
Q

Once the neural tube structure is formed, how does development continue?

A

The walls thicken to form various parts of brain and spinal cord and

The cells in the walls of the cranial neural tube give rise to neurones and glial cells

The lumen forms ventricular system and central canal

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17
Q

From which part of the neural tube does the brain vs the spinal cord develop?

A

Cranial 2/3rd (up to 4th pair of somites) develops into future brain

Caudal 1/3rd (distal to 4th pair of somites) develops into future spinal cord

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18
Q

When does each neuropore close?

A

Cranial neuropore - day 25

Caudal neuropore - day 27

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19
Q

What happens if the cranial vs caudal neuropores fails to close?

How can this be diagnosed?

A

If Cranial fails to close there will be failure of development of the brain, skull and scalp

If Caudal fails to close there will be failure of development of the spinal cord

Diagnosis: elevated Alpha-fetoprotien in maternal blood

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20
Q

The cephalic end of the neural tube forms 3 primary vesicles, List these and state which part of the adult brain each becomes?

A

1) Prosencephalon = forebrain
2) Mesencephalon = midbrain
3) Rhombencephalon = hindbrain

21
Q

What does the Prosencephalon differentiate into?

What ‘wall’ and ‘cavity’ of the brain does each specially become?

A

Telencephalon

  • wall: cerebral hemispheres
  • cavity: lateral ventricles

Diencephalon

  • wall: thalamus, hypothalamus and epithalamus
  • cavity: third ventricle
22
Q

What does the Rhombencephalon differentiate into?

What ‘wall’ and ‘cavity’ of the brain does each specially become?

A

Metencephalon

  • wall: pons and cerebellum
  • cavity: upper part of 4th ventricle

Myencephalon

  • wall: medulla oblongata
  • cavity: lower part of the 4th ventricle
23
Q

What cavity does the Mesencephalon become?

A

Aqueduct

24
Q

What are the 5 secondary vesicles?

Study image attached

A

Telencephalon

Diencephalon

Mesencephalon

Metencephalon

Myencephalon

25
Q

During the 4th week we get formation of 2 brain flexures, what are these?

Where is each located and when is this completed?

A

Folding of embryo forms 2 brain flexures in the neuraltube:

1) Cephalic flexure: in mesencephalon region.
2) Cervical flexure: at junction of Rhombencephalon & spinal cord.

Completed by the 5th Week

26
Q

What structure connects the lateral ventricles to the third ventricle?

A

Foreman monro

27
Q

What structure connects 3rd ventricle to the 4th ventricle?

A

Aqueduct of Sylvius

28
Q

If there is If there is a blockage of any cavity within the brain what may occur?

A

CSF will accumulate which can lead to increased intercranial pressure and compression of surrounding structures.

This can lead to hydrocephalus.

29
Q

Label the image of the 2o vessicles and the cavities each forms

A
30
Q

What 2 things occur during the migration and aggregation stage? (stage 3)

What day does each occu?

A

1) Formation of neurons (grey and white matter) and Glial cell: by day 26
2) Development and migration of Neural Crest Cells: during the 3rd week

31
Q

Explain the process of how neuron (grey and white matter) and glial cells are formed?

A

Tube differentiates into two concentric rings by day 26:

  • Mantle layer (grey) unmylinated
  • Marginal layer (white) myelinated

Occurs in 3 waves:

  • 1st wave: neurons that migrate to form mantle layer
  • 2nd wave: glioblasts give rise to oligodendrocytes and astrocytes (oligodendrocytes mylinate marginal layer)
  • 3rd wave: ependymal cells form and remain attached to membrane of tube (line the cavity)
32
Q

What are Neural Crest cells and how do they form?

What NS do these cells give rise to?

A

Neural crest cells are of Neuro-ectodermal origin:

They form at neural folds and dissociate once the tube is formed

They migrate into the pharyngeal arches and facial region

They give rise to cells that form most of PNS and ANS:
(cranial, spinal, and autonomic ganglia)

33
Q

What drives the formation of axons, nerves and synaptogenesis?

What is this known as?

A

As the spinal nerve emerges from the neural tube they extend into the peripheries.

This process is driven by the chemical changes in the surroundings. These are called chemical cues eg neurotrophins

These cause chemotaxis which allows the axon to grow outwards, this is known as ‘the growth cone’.

34
Q

How are axons prevented from growing in the wrong direction?

A

If the nerve grows in the wrong direction, neurotrophins are released causing chemotaxis to occur in the correct direction

35
Q

Give 2 factors that drive apoptosis and synapse elimination?

A

1) Activity at the connections as they develop
* The more active a cell is, the less likely it will be eliminated
2) Axonal competition will drive the elimination of some synapses
* muscles: poly-innervated ➞ mono-innervated

36
Q

Give 3 functions of Neurotrophins

A

1) promote growth and survival
2) guide axons
3) stimulate synaptogenesis

involved in both ‘formation of axons’ and ‘synaps rearrangment’

37
Q

What 2 things cause the neural tube to change in shape? (to better resemble our spinal cord, butterfly shape)

What ‘plate’ does each eventually become?

A

1) BMPs from skin induce expression of BMP’s in roof plate (dorsal side)
* becomes the alar plate
2) chemical substances induce changes in the floor plate (ventral side)
* becomes the basal plate

38
Q

What is the roof plate?

What is the floor plate?

A

Signaling center: secretes BMPs and Wnts

Signaling center: secretes Shh

39
Q

What nerve fibres do the basal and alar plates go on to become?

A

1) Alar plate: cells here send sensory projections to brain (afferent neurons) and form the dorsal (posterior) horn of the spinal cord
2) Basal plate: responsible for motor neuron development (efferent neurons) and form the ventral (anterior) horn of the spinal cord.

40
Q

What structure of the midbrain do the basal and alar plates eventually become?

A

ALAR PLATE (neuroblasts migrate towards roof) forms the:

  • Tectum
  • Superior and Inferior colliculi

BASAL PLATE forms the:

  • Tegmentum
  • Efferent Nuclei
  • Red and Reticular Nuclei
  • Substantia Nigra
  • Crus Cerebri
41
Q

What structure of the hindbrain do the alar plates eventually become?

A
  • 4th Ventricle
  • Pons
  • cerebellum
42
Q

What is the Pons?

A

Passageway for fibres from cerebral and cerebellar cortices to spinal cord

43
Q

Which vessicle does the chorid plexus cells develop from?

A

Telencephalon

44
Q

At what week are the spinal cord and vertebral column the same length?

What subsequently happens?

A

Week 12: Spinal cord and vertebral column same length

Later the vertebral colum will thicken, elongate and exceed length of spinal cord

45
Q

Where does the spinal cord end in adults vs children

A

In adults: L1

In children: L3/L4

46
Q

What structure marks the end of the spinal cord?

What is the gathering of spinal nerves that extend beyond the cord?

A

Conus medularis

Cauda Equina

47
Q

List the 10 structures passed in a lumbar puncture from superficial to deep

Incl the 3 ligaments

A
  1. Skin
  2. Superficial fascia
  3. Thoracolumbar fascia
  4. Supraspinous ligament
  5. Interspinous ligament
  6. Ligamentum Flavum
  7. Epidural fat
  8. Dura mater
  9. Arachnoid mater
  10. Subarachnoid space

ligaments shown on image

48
Q

What gives rise to dorsal route ganglion?

A

Migrating neural crest cells

(these cells associate themselves with the growing spinal nerves)

Nervous System (Semester 5) (21 decks)

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