Module 4: Development of the Nervous System, Musculoskeletal System, and Limbs Flashcards
When does development of the brain begin?
formation of the notochord in week 3
When do brain vesicles start forming?
week 5
Where do brain vesicles and flexures start to form?
cranial end of the neural tube
What are the 3 primary vesicles and what do they differentiate into?
prosencephalon -> cerebrum
mesencephalon -> midbrain
rhombencephalon -> pons, cerebellum, medulla
What are the 3 major brain flexures?
midbrain flexure, cervical flexure, pontine flexure
Where does the ectoderm that forms the pituitary gland come from?
Rathke’s pouch and the infundibulum
What is Rathke’s pouch and what pituitary lobe does it form?
ectodermal out-pocketing of the developing mouth; forms the anterior lobe
What is infundibulum and what pituitary lobe does it form?
downward extension of the hypothalamus; forms the posterior lobe
What are the steps to pituitary gland development?
out pocketing - infundibulum Rathke’s pouch outpocket from the hypothalamus and stomodeum, respectively
migration - migrate towards each other
regression - connecting stalk between stomodeum and Rathke’s pouch regresses
detachment - Rathke’s pouch detaches from the stomodeum and becomes part of the posterior lobe
differentiation - Rathke’s pouch becomes the anterior lobe and infundibulum becomes the posterior lobe
What are the 3 ectoderm layers of the neural tube?
ventricular, mantle, marginal
What is the ventricular ectoderm layer?
innermost layer that contains neuroepithelial cells; produces neuroblasts; eventually become neurons in the CNS
What is the mantle ectoderm layer?
middle layer; eventually becomes the grey matter of the CNS
What is the marginal ectoderm layer?
outer layer; eventually becomes the white matter of the CNS
How does the spinal cord development?
proliferation of neuroblasts in the ventricular layer thickens the mantle layer
What are dorsal thickenings of the mantle layer called?
alar plates
What are ventral thickenings of the mantle layer called?
basal plates
What separates the alar and basal plates throughout the spinal cord?
sulcus limitans
What do the alar plates contain?
sensory neurons
What do the basal plates contain?
motor neurons
What is the peripheral nervous system divided into?
autonomic and somatic nervous systems
What does the ANS do?
involuntary functions of the body
What are the divisions of the ANS?
sympathetic and parasympathetic
What does the SNS do?
voluntary control of body movements
What are the divisions of the SNS?
motor and sensory
What do peripheral nerves carry?
motor an sensory nerves from the SNS and autonomic nerves
Where do motor nerves emerge from?
ventral horn of the spinal cord
Where do sensory nerves emerge from?
dorsal horn of the spinal cord
Where do autonomic nerves emerge from?
lateral horns of the spinal cord
What does the peripheral nervous system develop from?
neural crest cells from the motor, sensory, and autonomic components
How do neural crest cells migrate?
migrate from the neural tube along dorsolateral and ventral pathways through somites
What happens when neural crest cells pass through somites?
imposes a segmental pattern on the cells; cells that stop migrating after entering a somite give rise to dorsal root and autonomic ganglia
What are somites precursors for?
muscles and bones
What do somites form from?
paraxial mesoderm
How do somite form?
epithelialization - occurs on both sides of the neural tube
segmentation - presomitic paraxial mesoderm forms epithelial somites with somitocele cells inside them
differentiation - somites differentiate into sclerotome and dermomyotome
What are sclerotomes?
formed from the ventral portion of the somite and contribute to the cartilage and bone of the vertebral column and ribs
What are dermomyotomes?
formed from the dorsal portion of the somite and contribute to the overlying dermis of the back and skeletal muscles of limbs
How do dermomyotomes further divide?
into myotomes and dermatomes
What does the dorsal myotome contribute to?
back musculature
What does the ventral myotome contribute to?
trunk and limb muscles
What happens to the dermatome?
re-acquire their mesenchymal phenotype and mix with the somatic layer of the lateral plate mesoderm to form the dermis
What is skeletal muscle derived from?
paraxial mesoderm (somites and somitomers)
What is smooth muscle derived from?
splanchnic mesoderm
What is cardiac muscle derived from?
splanchnic mesoderm
How do skeletal muscles develop?
progenitor cells in the myotome of somites differentiate into myoblasts to form muscle cells; myoblasts fuse together to form skeletal muscle fibres
How do skeletal muscle form?
dividing myoblasts - myoblasts proliferate if there is fibroblast growth factor (FGF) present
cell alignment - myoblast proliferation ends when FGF runs out and cell begin to align for myotube formation
myotube formation - alignment of myoblasts
muscle fibre formation - myotubes fuse to form muscle fibres
What are the 2 types of ossification?
endochondral and intramembranous
What does endochondral ossification give rise to?
skull base, vertebral column, long bones, pelvis
What is endochondral ossification?
process of forming bone through cartilage
What are the steps of endochondral ossification?
mesenchymal cells differentiation - into chondroblasts that form cartilaginous skeletal precursor
hyaline cartilage production - chondroblasts produce hyaline cartilage that resemble the shape of future bone
osteoblasts - blood vessel invasion produces osteoblasts pushing the chondrocytes to the ends of the bone; chondrocytes mineralize the surrounding matrix and osteoblasts bind to the matrices to deposit bone matrices
continued growth - cartilage model will grow in length by proliferation of chondrocytes and secretion of bone matices
What does intramembranous ossification give rise to?
cranial vault, maxilla, mandible, clavicle
What is intramembranous ossification?
process of forming bone directly from mesenchyme
What are the steps of intramembranous ossification?
mesenchymal cells differentiation - osteoblasts group into ossification centres and secrete osteiod
osteocytes - binding of calcium to osteoid calcifies the matrix trapping osteoblasts creating osteocytes
spongy bone - osteoid continues to be secreted around blood vessels
compact bone - calcified spicules become surrounded by mesenchymal cells that form periosteum
What portion of the somite develops into the vertebral column, intervertebral discs, and ribs?
sclerotome
What are the steps to vertebral column formation?
migration - sclerotome cells migrate toward the notochord and neural tube and is split by von Ebner’s fissures
neuronal extension - neural tube neurons extend through the fissures to innervate the myo/dermatomes
division - sclerotome is separated into cranial and caudal area by the fissures and peripheral nerves
resegmentation - vertebrae bodies form where a caudal portion and the following cranial portion intermingle
How do intervertebral discs form?
the notochord persists as the nucleus pulposus which is surrounded by a circular annulus fibrosus
How are the spinal nerves and vertebral canal arranged during the start of development?
lie adjacent to each other
What happens the spinal nerves as the vertebral column grows?
outstrips the growth of the spinal cord; loss of physical concordance between spinal nerve and vertebral segments
What does the outstrip in growth cause?
development of the cauda equina
What 2 regions does the skull consist of?
neurocranium and viscerocranium
How is the neurocranium further subdivided?
membranous and cartilaginous neurocranium
How is the membranous neurocranium formed?
through intramembranous ossification
How is the cartilaginous neurocranium formed?
through endochondral ossification
What does the viscerocranium give rise to?
the bones of the face
When does limb development begin?
at the end of week 4
What are limb buds?
visible out pocketings from the body wall
What do limb buds consist of?
mesenchyme core derived from lateral plate mesoderm covered by ectoderm
What is an apical ectodermal ridge?
thickening of the ectoderm at the end of the limb
What is the purpose of the apical ectodermal ridge?
act as a signaling center to ensure proper development
What are hand and foot plates?
flattened limb buds
How do fingers and toes develop?
develop on the hand and foot plates when apoptosis in the apical ectodermal ridge separates the plates into 5 parts
What are volar pads?
temporary swellings of the tissues on the ventral surface of fingers and toes
What does volar pad formation lead to?
epidermal ridge formation
When do volar pads start to regress?
week 10-12
What are epidermal ridges?
epidermis ridges on the palms of hands and soles of feet
What do epidermal ridges make up?
our fingerprints
When do epidermal ridges form?
week 11-17
What are the 3 epidermal ridge patterns?
loop, whorl, arch
What does a loop pattern mean?
intermediate height volar pads
What does a whorl pattern mean?
high and round volar pads
What does an arch pattern mean?
low volar pads
