Development of the Nervous System, Dermatomes & myotomes Flashcards
CNS & motor neurons
develop from the neural tube
Sensory & autonomic ganglia
develop from the neural crest cells.
The musculoskeletal system and dermis
develops from segments of mesoderm.
The nervous system
is somatotopically organised.
0 to 8 weeks
embryo:
initial development of each organ system
3-8wks period of greatest sensitivity
9-38 weeks
fetus:
period of functional maturation
week 3
- trilaminar germ disc
- craniocaudal axis
- bilateral symmetry
Trilaminar germ disc
superficial > deep
ectoderm - forms NS - is the outer surface
mesoderm - connective and muscle tissues
endoderm
Neurulation
Development of the neural tube & neural crest cells
somites
segments of mesoderm
- the mesodermally derived somites, adjacent to the neural tube, go on to form most of the vertebral column, as well as segmental structures such as skeletal muscle and dermis corresponding to spinal cord segments
Neurulation timeline
The neural plate and beginning neural groove at about 18 days of development > 2 days later development of neural groove > Neural tube closure during the fourth week > Neural folds begin to fuse at the cervical level of the future spinal cord at about day 21 > By about day 24, the rostral end of the neural tube has closed; the caudal end will close 2 to 3 days later
notochord
forerunner of the skeletal axis, helping to form the vertebral column
- comes from mesoderm; important in inducing development of neural tube
Neurulation timeline simple
Notochord forms from mesoderm (inductive)
Neural plate > Neural groove > Neural tube > Neural tube
…. CNS (brain/spinal cord)
Rostral neural tube develops into the brain - 3 weeks
3 primary vesicles: encephalon = brain 1. Prosencephalon 2. Mesencephalon 3. Rhombencephalon
Rostral neural tube develops into the brain - 5 weeks
5 secondary vesicles: Prosencephalon: 1.telencephalon 2.diencephalon 3. Mesencephalon Rhombencephalon: 4.metencephalon 5.myelencephalon
neural tube tissue
tissue in wall of neural tube becomes brain tissue and Remaining neural tube develops into the spinal cord
1.Telencephalon
cerebrum (cerebral lobes & basal nuclei)
2.Diencephalon
thalamus, hypothalamus, epithalamus & subthalamus
3.Mesencephalon
midbrain
4.Metencephalon
pons & cerebellum
5.Myelencephalon
medulla oblongata
Neural tube lumen
- develops into the ventricular system of the brain & the central canal of the spinal cord
- neural tube distorts along with the development of the brain
- filled with CSF
Ventricular system
1 lateral ventricle in each cerebral hemisphere (with anterior, posterior & inferior horns)
• interventricular foramen
• 3rd ventricle (in midline between L & R diencephalon)
• cerebral aqueduct in midbrain
• 4th ventricle between pons & medulla oblongata anteriorly & cerebellum posteriorly
• central canal of spinal cord
CSF movement
flows from 4th ventricle into subarachnoid space > superior sagittal sinus
Neural tube walls
develop into the CNS neurons & glial cells
Neural tube cavity
becomes the ventricular system of the brain
Neural crest cells develop into:
- pia & arachnoid mater
- sensory ganglion cells (CN V, VII, VIII, IX & X & DRG) -autonomic ganglion cells (CN III, VII, IX, X & spinal) -Schwann cells
- adrenal medulla
Dorsal-ventral organisation within the spinal cord
4th week: Neural tube > 6th week: Embryonic spinal cord > Adult spinal cord.
spinal ganglion (SG = DRG) cells, derived from the neural crest, send their central processes into the spinal cord to terminate mainly on alar plate (AP) cells
many basal plate (BP) cells become motor neurons, whose axons exit in the anterior roots
Medial–lateral organisation within the brainstem
with development of the 4th ventricle the walls of the neural tube spread out
- Lateral alar plate
- Medial basal plate
Lateral alar plate
sensory neurons located laterally
Medial basal plate
motor neurons located medially
4th ventricle
opens out like a book because of peduncles and cerebellum
Mesoderm gives rise to the musculoskeletal system
most of the axial skeleton • appendicular skeleton • skeletal muscles of the neck, trunk & limbs • tendons & ligaments • dermis on the back & limbs
