Download Embryonic develoment of nervous system

Embryonic Development of
the Human Neurological
System
Chapter 4
Embryonic Development of the Human Neurological System
(pp. 66-76 in W&A)
OVERVIEW
• Neural plate, which is part of the ectoderm, folds in on itself
(neural fold, neural groove), to form the neural tube (Fig 3-25)
with the neural crest dorsal to it
• Neural crest (dorsal to neural tube) splits laterally to form
ganglia of the PNS, e.g. dorsal root ganglia (Figs 3-28 and 3-34)
• Lateral walls of the neural tube thicken to form:
– alar plate (dorsal, sensory) and basal plate (ventral, motor)
• Alar and basal plates (together) develop into
– central gray matter of spinal cord (Fig 3-29-A)
– Nuclei of brainstem (Fig 3-29-B)
• Neural tube flexes (bends) as the brain develops
– Sections separated by flexures develop into different brain
structures
Embryo, and its early stages of
development
• Embryo: Beginning of third week after conception to end of
eighth week after conception
– Beginning of 3rd week: 3 germ cell layers form
• Ectoderm (outer)
• Endoderm (inner)
• Mesoderm (between the other two)
– Later: Germ cell layers expand and develop to give rise to:
• Epidermis (of skin) and nervous system (ectoderm)
• Linings of digestive and respiratory system (endoderm)
• Everything else, ie.., muscles, bone, blood vessels,
connective tissue, etc. (mesoderm)
We’ll focus on ECTODERM
Ectoderm, Mesoderm,Endoderm (18 days):
Focus on ECTODERM and formation of
NEURAL PLATE
Neural plate develops in midline portions of ectoderm (neurulation)
(Signals that start neurulation come from notocord)
Neural plate FOLDS IN ON ITSELF to begin
formation of the neural tube
Note neural groove with neural folds along each side, and
neural crest dorsally
Neural folds move together and begin to fuse to form neural tube
Fusion occurs first in the middle, then progresses
cranially and caudally
Neural plate FOLDS IN ON ITSELF to form
neural tube
Fusion occurs first in the middle, then progresses cranially and
caudally
Neural tube and the dorsal neural crest separate from the
surface ectoderm.
Central canal gives rise to ventricular system of brain, and the
central canal of the spinal cord. Somites become muscle, bone.
Neural plate FOLDS IN ON ITSELF to form
neural tube
Fusion occurs first in the middle, then progresses cranially and
caudally. Neural tube fully closed at both ends by end of fourth
week. (NOTE: spinal bifida and anencehpaly….)
Neural crest separates laterally to form sensory ganglia of PNS,
which will later send out axonal processes to connect to CNS
Lateral walls of the neural tube thicken to form
alar plate and basal plate.
alar plate (dorsal,
sensory)
basal plate (ventral,
motor)
Note again how neural crest has split to form future (sensory)
ganglia of PNS.
The ganglia send axonal processes to the CNS, and the ventral
CNS sends axons to the muscles
Alar and basal plates (alar sensory, basal motor) will develop into
– central gray matter of spinal cord (Fig 3-29-A)
– nuclei of brainstem (Fig 3-29-B)
• Neural tube flexes (bends) and expands as the brain develops
– At the rostral end of the tube, sections separated by
flexures develop into different brain structures
PRIMARY BRAIN
VESICLES (5th week)
SECONDARY BRAIN
VESICLES (7th week)
MATURE BRAIN
Rhombencephalon
(hindbrain)
Myelencephalon
Medulla oblongata
Metencephalon
Pons and cerebellum
Mesencephalon
(midbrain)
Mesencephalon
Midbrain
Prosencephalon
(forebrain)
Diencephalon
Thalamus, epithalamus,
hypothalamus,
subthalamus
Telencephalon
Cerebral hemispheres,
including olfactory system;
cortex; basal ganglia
Embryonic Development of the Human Neurological System
(pp. 66-76 in W&A)
OVERVIEW
• Neural plate, which is part of the ectoderm, folds in on itself
(neural fold, neural groove), to form the neural tube (Fig 3-25)
with the neural crest dorsal to it
• Neural crest (dorsal to neural tube) splits laterally to form
ganglia of the PNS, e.g. dorsal root ganglia (Figs 3-28 and 3-34)
• Lateral walls of the neural tube thicken to form:
– alar plate (dorsal, sensory) and basal plate (ventral, motor)
• Alar and basal plates (together) develop into
– central gray matter of spinal cord (Fig 3-29-A)
– Nuclei of brainstem (Fig 3-29-B)
• Neural tube flexes (bends) as the brain develops
– Sections separated by flexures develop into different brain
structures