Embryology and development Flashcards
What are the 3 germ layers?
- ectoderm
- mesoderm
- endoderm
What is formed in the body from the Ectoderm?
Skin
Nervous system
What is formed in the body from the Mesoderm?
Bone Kidney Blood Heart Muscle
What is formed in the body from the Endoderm?
Gut
Liver
Lungs
What is formed first during neural tube formation?
Notochord - cylinder of mesoderm
What is formed as the neural fold moves inwards?
The neural groove which fuses to form the neural tube
What does the overlying surface ectoderm form?
Skin
What is formed from the neural tube?
Brain and spinal cord (CNS)
When does neural tube closure occur during development?
3rd week of embryogenesis
In what direction does neural tube closure progress?
Rostrally and caudally
How many vesicles are present at the start and end of brain development?
start = 3 end = 5
What 3 parts of the brain form from the prosencephalon?
- telencephalon
- diencephalon
- optic cup
What occurs as a result of a caudal neural tube close defect?
Spina bifida - vertebrae are incomplete
What are the 3 layers of the neuroepithelium?
- germinal
- mantle
- marginal
What is the purpose of selective pruning?
All neurons are formed during development, which produces an excess
Pruning reduces the number of neurons and selects for the ones that are needed
What do the mantle and marginal form in the brain?
mantle = grey matter marginal = white matter
Compare where afferent and efferent nerves originate from
Afferent (sensory) - from neural crest, cell bodies in ganglia
Efferent (motor) - from neural tube basal plate, cell bodies in CNS
How does development of the medulla occur?
Alar plates move laterally and the cavity of the neural tube expands dorsally forming the fourth ventricle
How does the development of horses, cows and sheep differ to cats and dogs?
Horses, cows, sheep:
- Have young with good motor function at birth
- well developed cerebellum
Cat and dog:
- young have poor motor function
- poorly developed cerebellum at birth
- thick germinal layer
Where is the forebrain developed from?
Alar plate
How many cranial nerves are there?
12 pairs - each has a dorsal and ventral branch
Name the 12 cranial nerves in order
I Olfactory II Optic III Occulomotor IV Trochlear V Trigeminal VI Abducent VII Facial VIII Vestibulo-cochlear IX Glosso-pharyngeal X Vagus XI Accessory XII Hypo-glossal
How are bodies cavities formed in the trunk?
Belts of mesoderm in the trunk contain spaces where cavitation occurs
Why does cavitation not occur in the head?
Intermediate mesoderm fails to develop
Lateral plate mesoderm remains as solid belt of tissue surrounding gut tube
What do the 7 segments in the head consist of?
- Ectoderm
- Somites
- Endoderm
- Lateral plate mesoderm
- Segmental arteries
- Neuraxis
- Nerves
Is conscious control somatic or autonomic?
Somatic
In what direction does afferent supply?
Towards the brain
What are the lateral indentations that mark the segments externally? Which segment does not have this?
Pharyngeal clefts
1st segment
What is the outer epithelial covering (ectoderm) innervated by?
Somatic afferents
What is the inner epithelial covering (endoderm) innervated by?
Autonomic afferents/efferents
Where is the lateral plate mesoderm located?
Belt of striated skeletal muscle that surrounds pharynx of all segments except segment 1 - referred to as pharyngeal arch
What is the lateral plate mesoderm innervated by?
Special visceral efferents
Which is obliterated as the brain/head continues to develop?
- Somites 4 and 5
- Pharyngeal arch 5
- Arterial arches 1 and 2
- Pharyngeal clefts/pouches 5 and 6
- Ectoderm of segments 6 and 7
Which somites migrate, and where do they migrate to?
6 and 7
to the floor of the mouth
Describe the lining of the mouth
Front part of the mouth is lined with ectoderm, the back is lined with endoderm
What is the tongue innervated by?
Somatic efferents
What develops from the depression in the floor of arches 4 and 6 (laryngo-tracheal groove)?
Trachea and lungs which then become part of the thorax
Which clefts/pouches form the different parts of the ear?
Cleft 1 = external ear
Pouch 1 = middle ear cavity
From which segments does most of the skin of the head come from?
1 and 2
What do somites 1-7 go on to form?
1-3 = extrinsic muscles of the eye
4 and 5 = disappear
6 and 7 = muscles of the tongue
