lecture 4 Flashcards
Development of the nervous system
What is the most complicated object that we know of in the universe?
the mature nervous system (probably a wrong statement, but impossible to prove that it is wrong)
What is the nervous system grossly divided into?
- the central nervous system: brain and spinal chord
- the peripheral nervous system
What is the trilaminar embryo?
- flat three-layered disc of cells between amniotic cavity and the yolk sac
- ectoderm (from where the NS arises), mesoderm, endoderm
- occurs at around week 2
Where do we see the first signs of the nervous system?
- during the trilaminar embryo
- a patch of tissue on top of the ectoderm, termed the neural plate, starts to specialise and becomes neuroepithelium
What does the origin of the nervous system reflect?
Being from the ectoderm, it reflects that the skin used to be the main interface/sensory place - the connection between the inside and the rest of the world
What do we start to see at the 2-3 week stage?
- structures that could be recognised as organs
- formation of the neural tube
- invagination of neural plate: overlying ectoderm starts to fold downwards into the mesoderm and endoderm
- downward fold forms a groove and then walls of this groove fold over and touch forming a tube
- this ectodermally derived tube breaks free from the ectoderm and floats between mesoderm and endoderm
- this tube forms the central nervous system
How thick is the neural tube initially?
one cell thick
Is the tube hollow or filled?
hollow
Is there a gradient in the formation of the nervous system?
Yes.
There is a rostral to caudal gradient in the formation of the nervous system.
The rostral is older.
What conditions occur when neural fold closure fails?
- failure to zipper shut section 2 on the crown of the head results in anencephaly
- failure to close stage 5 properly (at the base of the spine) results in spina bifida
infants with spina bifida often have disturbed motor neuron function, e.g. in lower in limbs
What is segmentation of the neural tube?
- rostral end of neural tube starts to swell
- forms 3 distinct vesicles
- prosencephalon (forebrain)
- mesencephalon (midbrain)
- rhombencephalon (hindbrain)
- what’s left over becomes the spinal cord
What further segmentation of the neural tube occurs?
- prosencephalon splits: telencephalon (cortex) and diencephalon (deep in the cortex)
- rhombencephalon - 7 segments
- rest is spinal cord
- rhombencephalon splits into metencephalon and myelencephalon (pons and medulla)
- retinae form as optic vesicles from diencephalon
At this early stage, what is the brain?
- a series of thin-walled bubbles
What is the neural crest?
- cells at top of neural tube form neural crest
- migrate away from neural tube to form a wide range of structures
- appear to very primitive
What are the neural crest derivatives?
Peripheral nervous system
- dorsal root ganglia
- sympathetic and parasympathetic ganglia
- enteric ganglia
- schwann cells
Melanocytes
Muscle cartilage and bone of skull, jaws, face and pharynx
Dentine