Morphology and embryology Flashcards
(26 cards)
Midbrain represented by:
- Crura cerebri or cerebral peduncles
- Crura are separated by the interpeduncular fossa
What does the pit gland lie ventral to?
Hypothalamus and right behind the chiasm
First step of development:
- Embryonic disk stage- elongated thickening (neural plate) of the ectoderm that overlies the notochord and paraxial mesoderm
Second step of development:
- Lateral parts of neural plate are raised above surrounding surface by growth of underlying mesoderm and form the bilateral neural folds that slope toward an axial crease- neural groove
Third step of development:
- Edges of the folds become increasingly prominent and then bend inward toward each other, meet and fuse and then becomes a neural tube
What happens to the neural tube?
- Sinks ventral to and is separated from the overlying non-neural ectoderm that fuses dorsal to the neural tube to produce a continuous ectodermal layer
- Cells at the crest of the neural folds at junction of nonneural ectoder, separate from fold s to form continous cords, the neural crests
What happens to neural crest cells?
- Those that remain adjacent to neural tube eventually develop into neurons which populate peripheral ganglia
- Those that migrate away from neural tube produce neurons of the enteric nervous system, medullary parts of adrenal glands, glia, skin melanocytes and craniofacial CT
How does closure of the neural tube happen?
- Initially occurs in the presumptive occipital region
- Fusion happens rostral and caudal so have two neuropores
Which neuropore closes first?
- Rostral
- Caudal one will remain open so the tube can lengthen at is caudal extremity by extension and subsequent infolding of the neural plate
Anencephaly
Failure at the rostral extremity leads to malformation of forebrain and midbrain accompanying anomalies of skull
Spina bifida
Failure of caudal extremity and associated with defective closure of the vert arches
Three primary brain vesicles:
- Prosencephalon
- Mesencephalon
- Rhombencephalon
What are the layers?
- Innermost layer- neuroepi cells - ependyma
- Middle - mantle - becomes gray matter
- Outer - marginal - becomes white matter
What happens with the mantle layer?
Dorsal (alar plate) and ventral columns (basal plate)
Dorsal - alar plate:
Dorsal column of gray matter- neurons are receiving synaptic input from sensory neurons
Ventral - basal plate:
Ventral column of gray matter - has cell bodies of motor neurons
What is the order of neurons?
- Somatic afferent
- Visceral afferent
- Visceral efferent
- Somatic efferent
What are commissures?
Roof and floor plates provide passages for nerve fibers that pass from one side of cord to other
What divides the spinal cord?
- Dorsal median sulcus
- Ventral median fissure
Dorsal roots
- Develop as sensory
- Axons extend medially into the cord to reach and penetrate the outer marginal layer
- Branches of the axons can extend over several segments before entering mantle layer to terminate on neurons in dorsal columns
- Some branches do not synapse with SC but turn cranially and extend within marginal layer to reach brain
Ventral roots
- Develop as motor
- Axons extend laterally through the marginal layer to emerge on surface of cord
What do the dorsal and ventral roots help form?
- Divides the white matter into dorsal, lateral and ventral funiculi
What are the three flexures?
- Caudal ventral
- Rostral ventral
- Dorsal
Prosencephalon:
- Telencephalon: cerebral cortex, basal nuclei, limbic system
- Diencephalon: Epithalamus, thalamus, hypothalamus
