Module 4: Development of the Nervous System, Musculoskeletal System, and Limbs Flashcards
When does development of brain vesicles begin
-week 5
Where do brain vesicles begin to form
-cranial end of neural tube
3 brain vesicles
-prosencephalon
-mesencephalon
-rhombencephalon
Prosencephalon derivatives
-cerebrum
Mesencephalon derivatives
-midbrain
Rhombencephalon derivatives
-pons, medulla, cerebellum
When does brain flexure begin
-week 5
-same time as development of vesicles
Where does brain flexure begin
-cranial end of neural tube
3 brain flexures
-midbrain flexure
-cervical flexure
-pontine flexure
Midbrain flexure
-first flexure to appear
-in region of mesencephalon
Cervical flexure
-second to appear
-at junction between future spinal cord and rhombencephalon
Pontine flexure
-third to appear
-when neural tube bends anteriorly at cervical and midbrain flexures, but the pontine flexure is directed posteriorly
What is the pituitary gland derived from
-ectoderm that develops from rathkes pouch and infundibulum
Rathkes pouch
-ectodermal out-pocketing of developing mouth
Infundibulum
-downward extension of the hypothalamus
Rathkes pouch derivative
-forms anterior lobe of pituitary gland
Infundibulum derivative
-posterior lobe of pituitary gland
Development of the pituitary gland stages
-outpocketing
-migration
-regression
-detachment
-differentiation
Pituitary gland outpocketing
-infundibulum and rathkes pouch outpocket from hypothalamus and stomodeum
Pituitary gland migration
-infundibulum and rathkes pouch migrate towards eachother
Pituitary gland regression
-connecting stalk between stomodeum and rathkes pouch regresses
Pituitary gland detachment
-rathkes pouch detaches from the stomodeum and becomes associated with the developing posterior pituitary
Pituitary gland differentiation
-rathkes pouch differentiates to form anterior pituitary
-meanwhile distal portion of infundibulum differentiates to form posterior pituitary
Cellular layers of the neural tube
-ventricular layer
-mantle layer
-marginal layer
Ventricular layer
-innermost layer
-lies adjacent to the lumen of neural tube
What kind of cells does ventricular layer contain
-neuroepthelial cells
-which are precursors to cells that comprise CNS
What is the first generation of cells produced by neuroepithelial cells
-neuroblasts
Neuroblasts
-eventually become neurons in the CNS
Mantle layer
-once ventricular layer is formed, neuroblasts migrate away to form this layer
What does mantle layer become
-grey matter in CNS
Marginal layer
-formed from neuronal processes that germinate from neuroblasts
What does marginal layer become
-white matter of the CNS
Spinal cord development
-proliferation of neuroblasts within ventricular layer causes differential thickening of mantle layer creating alar and basal thickenings
Where is alar thickening
-dorsal region
Where is basal thickening
-ventral region
Alar plate
-grey matter of dorsal half
-separated from eachother by roof plate
What kind of neurons does alar plate contain
-sensory
Basal plate
-white matter of ventral half
-separated by floor plate
What kind of neurons does basal plate contain
-motor neurons
Sulcus limitans
-appears in lateral wall of neural tube
-separating it into dorsal and ventral halves throughout future spinal cord and brainstem
Holoprosencephaly
-occurs when prosencephalon fails to develop
-can include neurological deficits, seizures, vision and motor difficulties
-craniofacial malformations, reduction of frontonasal prominence
Which horn do motor nerves emerge from
-ventral horn
Which horn do sensory nerves emerge from
-dorsal horn
-dorsal root ganglion
Which horn do autonomic nerves emerge from
-lateral horns
Formation of motor nerves
-begins with outgrowth of axons from motor neuroblasts located in basal plate
Formation of sensory nerves
-derived from neural crest cells
Formation of sensory nerve dendrites
-grow toward nerve cell body
Formation of sensory nerve axons
-terminate in the alar plate
Formation of autonomic nerves
-similar to sensory nerves, autonomic nerves are also derived from neural crest cells
Ventral pathway development
-some of the cells travelling ventrally stop migrating as soon as they enter the somite
-these cells give rise to dorsal root ganglia
-cells that tale ventral pathway also form autonomic ganglia
Discrete peripheral nerves
-built by channelling neural crest cells through a restricted region of the somite
Hirschsprung’s disease
-results from the absence of nerve cells in some parts of the large intestine
-incomplete innervation of the smooth muscle layers of gastrointestinal tract
Newborn symptoms of hirschsprungs disease
-constipation
-bowel obstruction
Somites derivative
-muscle and bone
Coelom derivative
-body cavities
How many pairs of somites will be formed from the paraxial mesoderm in week 5
-42-44
Somite development stages
-segmentation
-epithelialization
Somite segmentation
-process of somite formation from paraxial mesoderm
Somite epithelialization
-once the paraxial mesoderm becomes segmented to form epithelial somites with somitocele cells inside them
2 somite cell groups
-sclerotome
-dermomyotome
Sclerotomes
-formed from ventral portion of somite
Sclerotomes fate
-will contribute to cartilage and bone of vertebral column and ribs
Dermomyotomes
-formed from dorsal part of somite
Dermomyotomes fate
-gives rise to overlying dermis of back and to the skeletal muscles of the limb
Divisions of dermomyotomes
-myotomes
-dermatomes
Myotomes fate
-will develop into striated muscle
Myotomes divisions
-dorsal myotome
-ventral myotome
Dorsal myotome fate
-back musculature
Ventral myotome fate
-muscle cells of rest of the trunk and limbs
Dermatomes fate
-form the dermis
Development of skeletal muscle stages
-dividing myoblasts
-cell alignment
-myotube formation
-muscle fibre formation
Dividing myoblasts
-they proliferate in early development if there is enough fibroblast growth factor (FGF) present
Cell alignment
-when FGF runs out, myoblasts cease division, and these cells begin to align for myotube formation
Myotube formation
-alignment of myoblasts results in structures called myotubes
Muscle fibre formation
-myotubes fuse to form a multinucleated muscle fibre
Types of ossification
-endochondral ossification
-intramembranous ossification
Endochondral ossification
-process of forming a bone through a cartilage intermediate
What bones form from endochondral ossification
-skull base
-vertebral column
-long bones
-pelvis
Intramembranous ossification
-directly forms bone from mesenchyme
What bones form from intramembranous ossification
-cranial vault
-maxilla/mandible
-clavicle
Endochondral ossification stages
-mesenchymal cells
-chondroblasts
-osteoblasts
-continued growth
Endochondral ossification mesenchymal cells
-differentiate into chondroblasts that form cartilagenous skeletal precursor of bones
Endochondral ossification chondroblasts
-produce hyaline cartilage which resembles future shape of bone
Endochondral ossification osteoblasts
-formed from invasion of blood vessels
-restricts chondrocytes to ends of bones
-chondrocytes in shaft of bone mineralize surrounding matrix
-osteoblasts bind to this matrix and deposit bone matrices to form bone tissue
Endochondral ossification continued growth
-this process repeats while growth plates continue to elongate into adulthood
Intramembranous ossification stages
-osteoblasts
-osteocytes
-spongy bone
-compact bone
Intramembranous ossification osteoblasts
-mesenchymal cells differentiate into osteoblasts and are grouped into ossification centres
Intramembranous ossification osteocytes
-secrete osteiod and binding of calcium to this osteoid results in hardening of matrix and entrapment of osteoblasts
What is osteoid
-unminealized portion of bone matrix that eventually calcifies
Intramembranous ossification spongy bone
-osteoid continues to be secreted by osteoblasts around blood vessels forming trabeculae (spongy bone)
Intramembranous ossification compact bone
-periosteum is formed when calcified spicules become surrounded by compact mesenchymal cells
-this layer forms superficially to spongy bone
Development of spinal cord stages
-migration
-neuronal extension
-division
-resegmentation
Vertebral column migration
-cells of sclerotome begin to migrate toward and around notochord and neural tube creating template of vertebrae
Von ebners fissues
-splits the sclerotome in half
Vertebral column neuronal extension
-neural tube neurons extend to innervate nearby myotomes and dermatomes
Vertebral column division
-nerves pass through von ebners fissures within each sclerotome to pass through mytotome and dermatome
Vertebral column resegmentation
-the bodies of vertebrae form where the sclerotome cells of the caudal part of one somite pair intermingle with the cells of the cranial part of the following pair
Development of intervertebral discs
-notochord persists in the region between the adjacent vertebrae as nucleus pulposus
-together with a circular anulus fibrousus the discs are formed
Ascent of the spinal cord
-vertebral column outgrows the spinal cord and the cord appears to acsend within column
-this is why spinal cord segments for not line up, and how cauda equina is formed
Parts of the skull
-viscerocranium
-membranous neurocranium
-chondrocranium
Viscerocranium
-bones of face
How is viscerocranium formed
-first 2 pharyngeal arches
Membranous neurocranium
-surrounds brain
How is membranous neurocranium formed
-from neural crest cells and paraxial mesoderm
-formed from intramembranous ossification
Chondrocranium divisions
-prechordal chondrocranium
-chordal chondrocranium
How is chondrocranium formed
-separate cartilages that fuse via endochondral ossification
Limb development stages
-limb buds
-apical ectodermal ridge
-handplates and footplates
Limb buds
-outpocketings from body wall, consist of a mesenchyme core covered by ectoderm
Apical ectodermal ridge
-distal end ectoderm thickens to form this
-cells from this further differentiate into cartilage and muscle
Handplates and footplates
-limb buds become flattened to form the handplates and footplates terminally
When do fingers and toes develop on hand and footplates
-when apoptosis in apical ectodermal ridge separates the plates into 5 parts
Syndactyly
-when apical ectodermal ridge does not regress, causes 2 or more fingers to be fused (webbed)
-most often only skin connected but can sometimes be bones as well
-treated surgically
Limb rotation parts
-upper limb
-lower limb
Upper limb rotation
-rotates laterally so that palm of hand faces anteriorly and thumb is on lateral side
Lower limb rotation
-rotates medially so that big toe is on medial side of foot
Epidermal ridges
-ridges of epidermis on palms of hands and soles of feet
-what makes up the fingerprint
Volar pads
-temporary swellings of tissues on ventral surfaces of fingers and toes
When do volar pads regress
-weeks 10-12
Epidermal ridge patterns
-loop
-whorl
-arch
Loop epidermal ridge pattern
-volar pad is intermediate
-results in loop configuration
Whorl epidermal ridge pattern
-volar pad is high and round
-epidermal ridges form a whorl
Arch epidermal ridge pattern
-volar pad is low
-epidermal ridges form an arch
