Quiz1 Flashcards
Surface Ectoderm
Forms Epidermis
covering of the embryo is initially a single-cell layer thick.
Periderm
New layer formed by proliferation of ectoderm after week 4.
Simple squamous epithelium
Basal layer
The underlying layer of proliferating periderm cells.
Separated from the dermis by the basement membrane containingCollagens, Laminin, andFibronectin.
The cells of the periderm are gradually sloughed into the amniotic fluid. The periderm is normally shed completely by the 21st week.
Intermediate layer
Formedin the 11th week by proliferation of the basal layer.
Forerunner of the outer layers of the mature epidermis.
Germinative layer
stratum germinativum
Layer of stem cells that will continue to replenish the epidermis throughout life.
Keratinocytes
The cells of the intermediate layer contain theKeratin proteins characteristic of differentiated epidermis
Apical vs Basal surface
Basal Cells regenerate & apical cells slough off, they are replaced by basal cells
function & location of Simple squamouse eithelium
Location: Air sacs of lung & the lining of the heart, blood vessels, & lymphatic vessels
Function: allow materials to pass through by diffusion & filtration, & secretes lubricating substance
function & location of simple cuboidal epithelium
Location: in ducts & secretory portions of small glands & in kidney tubules
Function: secretes & absorbs
function & locationof simple columnar epitheliu
Location: cilated tissues are in bronchi, uterine tubes & uterus; smooth (nonciliated tissues) are indigestive tract bladder
Function: Absorb, secretes mucous & enzymes
function & location of stratified squamous epithelium
Location: lines the esophagus, mouth, & vagina
Function: protects against abrasion
function & location of stratified cuboidal epithelium
Location: sweat glands, salivary glands, & mammary glands
Function: protective tissue
function & location of stratified columnar epithelium
Location: male urethra & ducts of some glands
Function: secretes & protects
function & locatio of ransitional epithelium
Location: lines the bladder, uretha & ureters
Function: allows the urinary organs to expand stretch
What are the 3 definitive layers of skin?
Intermediate layer is replaced by the three definitive layers of keratinocytes:
- Stratum spinosum(orspinous layer): inner layer
- Stratum granulosum(orgranular layer): middle layer
- Stratum corneum(orhornyorcornified layer): outer layer
Where are the cells of the stratum germinativum connected
to the basement membrane by hemidesmosomes, which containIntegrins.
what cells are formed once they are in the stratum spinosum?
As the cells in the stratum germinativum move into the overlying stratum spinosum (four to eight cells thick, theK5 and K14 intermediate filaments are replaced by Keratinproteins,K1andK10.
Envelope proteins
Envelope proteinsline the inner surface of the plasma membrane, and the enzymeTransglutaminase, which crosslinks the envelope proteins.
This layer also produces a protein calledFilaggrin, which aggregates with theKeratin.
Filaments to form tight bundles, helping to flatten the cell.
lamella granules
Lipid-containing granules (lamellar granules) are also produced that help seal the skin.
Cornification
Finally, in the process calledcornification, lytic enzymes are released within the cell, metabolic activity ceases, and enucleation occurs, resulting in the loss of cell contents including the nucleus.
Keratinocytes that enter the stratum corneum are flattened, scalelike, and terminally differentiated.
What are the 4 specialized cell types of epidermis?
- Keratinocytes: Majority of cells; ectodermal origin
- Melanocytes: Pigment cells; neural crest cell origin (roof of neural tube, ectoderm)
- Langerhans cells
- Merkel cells
Melanocytes
come from neural crest cells, make melanin
Represent between 5% and 10% of the cells of the epidermis in the adult.
In the 10th week, many melanocytes become associated with developing hair follicles where they function to donate pigment to the hairs.
function as a sunscreen, producing melanin
Langerhan
form bone marrow
Macrophage immune cells of the skin, functioning both in contact sensitivity (allergic skin reactions) and in immune surveillance against invading microorganisms.
They arise in the bone marrow and first appear in the epidermis by the 7th week.
Langerhans cells continue to migrate into the epidermis throughout life.
Merkel cells
pressure detecting
Pressure-detecting mechanoreceptors that lie at the base of the epidermis and are associated with underlying nerve endings in the dermis.
They contain keratin and form desmosomes with adjacent keratinocytes.
They arise from neural crest cells and appear in the 4th to 6th months.
Dermis
corium
the layer of skin that underlies the epidermis and contains blood vessels, hair follicles, nerve endings, sensory receptors.
Formed by mesoderm
Tissue with a triple embryonic origin
Trunk, the majority of the dermis is derived from the somatic layer of the lateral plate mesoderm but part of it is derived from the dermatomal divisions of the somites.
In the head most of the dermis is derived from neural crest cells (ectoderm origin).
Dermal papillae
the outer layer of the developing dermis proliferates to form ridge-likethat protrude into the overlying epidermis
Epidermal ridges
The intervening protrusions of the epidermis into the dermis
Papillary layer
Top layer of dermis
Reticular layer
thick underlying layer of dense, irregular connective tissue
Hypodermis
(subcorium): Subcutaneous fatty connective tissue
Dermal vasculature
Blood vessels form within the subcutaneous mesenchyme, deep to the developing dermis, in the 4th week.
These branch to form a single layer of vessels in the dermis by the late 6th week and two parallel planes of vessels by the 8th week.
It is estimated that the skin of the neonate contains 20 times more blood vessels than it needs to support its own metabolism. This excess is required for thermoregulation.
Much of the definitive vasculature of the skin develops in the first few weeks after birth.
sebaceous glands
produce sebum, an oily substance that protects the skin against friction and dehydration
Sebaceous glandsproduce the oilysebumthat lubricates the skin and hair.
Form as diverticula of the hair follicle shafts, budding from the side of the root sheath about four weeks after the hair germ begins to elongate
sweat glands
heat regulation
teethand salivary glands
mastication
lacrimal glands
produce tears
mammary gland
in females provides both nutrition and a source of immunity for the breastfeeding infant
Time for hair development
Hair follicles first appear at the end of the 2nd month on the eyebrows, eyelids, upper lip, and chin.
Most hair follicles are present by the 5th month.
Novel hair follicles do not form after birth.
About 5 million hair follicles develop in both males and females. The differences between the two sexes in the distribution of various kinds of hairs are caused by the different concentrations of circulating sex steroid hormones.
Hair germ
The hair follicle first appears as a small concentration of ectodermal cells in the basal layer of the primitive, two-layered epidermis.
Hair germs are thought to be induced by the underlying dermis. The hair germ recruits dermal cells to form a dermal condensate that promotes further differentiation of the hair germ.
Germinal matrix
Ectodermal cells that produce the hair shaft. Add keratin
Arrector pili muscle
functions to erect the hair (making goose bumps). The stem cells of the follicular epithelium that regenerate the follicle periodically during postnatal life are found near the site of the attachment of the arrector pili muscle in thebulge.
Dermal papilla
cells just beneath the tip of the bulb proliferate to form a small hillock/About four weeks after the hair germ begins to grow, the dermal papilla invaginates into the expanded base of the hair bulb.
Bulbous hair peg
stratum germinativum
Layer of stem cells that will continue to replenish the epidermis throughout life.
Hair peg
Proliferationthat pushes down into the dermis.
Hair Bulge
where stem cells reside
signal to stem cells from dermal papilla to produce TA cells & send them to the matrix
Lanugo
First hair of fetus, Shed before birth but sometimes sticks around
vellus
Replaces lanugo
fine non-pigmented hairs
Terminal hairs
Pigmented and get thicker at puberty
Holocrine cells
replaced by stem cells
vernix caseosa
Sebaceous glands of fetus
Waxy or cheese-like white substance found coating the skin of newborn human babies
Waterproof protective coating for the fetus
apocrine glands
Highly coiled, unbranched glands that develop in association with hair follicles.
They initially form over most of the body, but in the later months of fetal development they are lost except in certain areas, such as the axillae, mons pubis, prepuce, scrotum, and labia minora.
They begin to secrete at puberty, producing a complex mix of substances that are modified by bacterial activity into odorous compounds.
These compounds may function mainly in social and sexual communication.
Sweat glands
First appear at about 20 weeks as buds of stratum germinativum that grow down into the underlying dermis to form unbranched, highly coiled glands.
Have an outer layer ofmyoepithelial cells, which are innervated by sympathetic fibers and contract to expel sweat from the gland. The secretory cells secrete fluid directly across the plasma membrane.
Sweat glands
First appear at about 20 weeks as buds of stratum germinativum that grow down into the underlying dermis to form unbranched, highly coiled glands.
Have an outer layer ofmyoepithelial cells, which are innervated by sympathetic fibers and contract to expel sweat from the gland. The secretory cells secrete fluid directly across the plasma membrane.
polythelia
Occasionally, one or more supernumerary nipples(polythelia)
polymastia
supernumerary breasts(polymastia)form along the line of the mammary ridges. The most common location is just below the normal breast.
mammary pit
At birth, the mammary glands consist of 15 to 25lactiferous ducts, which open onto a small superficial depression called themammary pit.
secondary buds
By the 12th week severalsecondary budshave formed. These buds lengthen and branch throughout the remainder of gestation
primary bud
The remnant of the mammary ridge produces the primary budof the mammary gland in the 5th week.
This bud grows down into the underlying dermis towards the presumptive fat pad that will induce the duct to branch.
mammary ridges.
In the 4th week, a pair of epidermal thickenings called themammary ridges.
In humans, these ridges normally disappear except at the site of the breasts.
Nail anlagen
first appear as epidermal thickenings at the tips of the digits.
Nail field
Migrate proximally on the dorsal surface of the digits and forms a shallow depression
Nail folds
surrounds nail field
formative root
The stratum germinativum of the proximal nail fold proliferates to become theformative zone(also called theformative rootormatrix), that produces the hornynail plate.
eponychium
A thin layer of epidermis called theeponychiuminitially covers the nail plate, but this layer normally degenerates, except at the nail base.
Dental lamina
U-shaped ridge of epidermis on upper and lower jaw at 6 weeks.
Dental papilla
During the 8th week, instructive influences from the epidermis cause the mesenchymal condensation to invade the base of the dental lamina ingrowth.
Dental sac
The mesenchyme surrounding the papilla and its dental lamina cap condenses to form an enclosure
Cap stage
Stage of tooth development when the dental lamina invests the top of the papilla like a cap.
Bell stage
By 14 weeks, the dental papilla has deeply invaginated the dental lamina and constitutes the core of the developing tooth.
dental lamina looks like a bell resting over the dental papilla.
Odontoblasts
During the bell stage, the outermost cells of the dental papilla become organized into a layer just adjacent to the inner enamel epithelium.
Will produce thedentinof the teeth.
Enamel organ
the dental lamina differentiates the enamel layerof the tooth.
First, the dental lamina becomes a three-layered structure, consisting of aninner enamel epitheliumoverlying the dental papilla; a central layer, the enamel (otellate) reticulumcomposed of star-shaped cells dispersed in an extracellular layer; and anouter enamel epithelium.
ameloblasts
The inner mesenchyme of the dental papilla becomes the tooth pulp. As soon as dentin is formed, the odontoblasts in turn induce the cells of the inner epithelium to differentiate into enamel-producing ameloblasts, which begin to secrete rod-shaped enamel prisms between themselves and the underlying dentin.
odontoblastic processes
Production of predentin is induced by signals from the inner enamel epithelium and begins at the apex of the tooth and moves downward. As the odontoblasts migrate downwards, they leave long cell processes(odontoblastic processes)that extend through the thickness of the dentin behind them.
predentin
In the 7th month, the odontoblasts begin to secrete the non-mineralized matrix of the dentin, calledpredentin, which later progressively calcifies to formdentin.
Primary teeth
(deciduousormilk) teeth. The 20 tooth buds consisting in each half-jaw of two incisors, one canine, and two premolars.
Secondary teeth
Secondary (permanent) teeth:Early in the cap stage the dental lamina superficial to each tooth bud produces a small diverticulum that migrates to the base of the primary tooth bud and becomes the bud of the tooth that will replace it.
These secondary teeth develop to the bell stage and arrest until about 6 years of age.
Then they start to develop secondarily, destroying the root of the primary tooth in the process. The buds of the permanent molars burrows back into the posterior jaw.
The full human dentition consists of 32 teeth, including three molars, but the third molars (wisdom teeth) often fail to develop or to erupt.
cementoblasts
The tooth roots are enclosed in extensions of the mesenchymal dental sac. The inner cells of the dental sac differentiate intocementoblasts, which secrete a layer of cementumto cover the dentin of the root.
cementoenamel junction
At the neck of the tooth root, the cementum meets the enamel at acementoenamel junction.
alveolus
The outermost cells of the dental sac participate in bone formation as the jaws ossify and also form the periodontal ligamentthat holds the tooth to its bony socket, oralveolus.
epithelial root sheath
The roots of the teeth begin to form in late fetal and early postnatal life. At the junction of the inner and outer enamel epithelia,the cervical loop, the cells proliferate and elongate to form theepithelial root sheath.
The mesenchyme just internal to the epithelial sheath differentiates into odontoblasts, which produce dentin.
Each root contains a narrow canal of dental pulp by which nerves and blood vessels enter the tooth.
2 Types of Bone Development
Axial(vertebral column and ribs)
Appendicular(limb)bonesof the body, with the exception of part of the clavicle.
Endochondral ossification
Developmental process in which a cartilaginous template forms preceding ossification.
What are the 3 bone cell types?
Three cell types:chondrocytes, osteoblasts, osteoclasts.
Chondrocytes
(cartilage cells)
paraxial mesodermforms the axial skeleton.
lateral plate mesodermforms the appendicular skeleton and sternum.
neural crest cells(ectoderm) give rise to the cartilaginous elements in the face and neck.
Osteoblasts
(bone-forming cells)
arise from mesenchymal stem cells.
Osteoclasts
(bone-resorbing cells)
arise from thehematopoieticsystem.
Intramembranous ossification
Developmental process in which ossification directly from the mesenchyme.
Dermal(membrane bones)
majority of bones of the face and skull.
Dermal bones develop fromneural crest cells(facial bones and the frontal bone of the skull) or unsegmentedparaxial (head) mesoderm(e.g., parietal bone of the skull).
In dermal bones, the osteoblasts directly differentiate within the mesenchyme.
What are Striated muscles of the trunk and limb developed from?
derived from the segmentedparaxial mesoderm (somites).
Additionally the tongue musculature forms from this mesoderm(occipital somites).
Where do Other craniofacial muscles derive from?
arise from the unsegmentedparaxial mesodermandprechordal plate mesoderm(i.e., head mesoderm).
Myogenic cell differentiation
Long distance migrating myoblasts proliferate but then they exit the cell cycle and terminally differentiate to formmyocytes.
The myocytes express contractile proteins such asActinandMyosinand fuse to form amyofiber, which is a multinucleatedsyncytium(i.e., a mass of cells each containing multiple nuclei) containing the contractilemyofibrils.
What arethe 3 waves of striated muscle formation?
Primary myogenesis, Secondary myogenesis, Postnatal muscle growth
Where does Primary myogenesis occur?
in the embryo
Where doesSecondary myogenesis occur?
in the fetus and gives rise to the bulk of fetal muscle.
Postnatal muscle growth
involvessatellite cells, small quiescent cells underlying the basal lamina of the muscle fiber.
In response to exercise or muscle damage, satellite cells form myocytes, which permit further muscle growth.
Smooth Muscle Formation
Smooth muscle of the gut and cardiac muscle forms fromsplanchnic mesoderm.
Smooth muscle contributing to blood vessels and hair follicles arises locally within the mesoderm.
Smooth muscle can also form from neural crest cells.
The iris and ciliary muscles are derived from cranial neural crest cells, as is the smooth muscle of the dermis of the head and neck.
Somites
are transient segmented structures derived fromparaxial mesoderm.
progenitors of the axial skeleton, trunk musculature and associated tendons, trunk dermis, endothelial cells, and meninges of the spinal cord.
Where do Presomitic paraxial mesoderm begin?
begins to segment into epithelial balls with a central cavity of loose core cells.
Somite subdivison
Each somite subdivides into specific mesodermal components
Sclerotome
Made up of ventromedial part plus core cells; epithelial to mesenchyme transformation.
Differentiates eventually into vertebrae and ribs.
The ventral portion of the sclerotome migrate to surround thenotochord and form the rudiment of thevertebral body;
those in the dorsal portion of the sclerotome surround the neural tube and form the rudiment of thevertebral archand vertebral spine;
More laterally located sclerotome forms thevertebral transverse processandribs.
Dermomyotome
The remainder of the somite consists of a dorsal epithelial layer.
Gives rise to two general cell types, dermal and myogenic (skeletal muscle).
Represents the remaining part of the somite left when the sclerotome migrates.
Splits to form the dermatome and the myotome.
Resegmentation of Sclerotomes
Each sclerotome is organized into cranial versus caudal regions.
The caudal portion of each sclerotome is cell dense, with higher cell proliferation
The cranial portion is less cell dense.
These differences result in segmentation of the neural crest cells and motor axons, which can only migrate towards the cranial portion of the sclerotome, as the caudal portion of the sclerotome is inhibitory for migration.
In later development, the sclerotomes split along this fissure, and the caudal segment of each sclerotome fuses with the cranial segment of the sclerotome caudal to it, with each of the two segments of the sclerotome contributing to a vertebra.
Resegmentation thus produces vertebrae that lieintersegmentally.
Intrasegmental boundary, orvon Ebner’s fissure
The division between the cranial and caudal portions of each sclerotome.
Result of sclerotomal resegmentation
Intersegmental arteries pass over the vertebral body.
Segmental spinal nerves exit between the vertebrae.
Seven cervical vertebrae but there areeightcervical spinal nerves.
Therefore, following resegmentation, the myotome that was initially associated with one sclerotome becomes attached to two adjacent vertebrae and crosses the intervertebral space.
What happens to the 1st spinal nerve after sclerotomal resegmentation?
The 1st spinal nerve exits between the base of the skull and the 1st cervical vertebra (in alignment with the 1st cervical somite), and thus the 8th spinal nerve exits above the 1st thoracic vertebra (in alignment with the 8th cervical somite).
What happens to the other spinal nerve after sclerotomal resegmentation?
Each spinal nerve exits just below the vertebra of the same number. Finally, each sclerotome is associated with an overlying myotome, which contains the developing muscle plate.
Intervertebral discs
Develops at the intra-segmental boundary.
Nucleus pulposus
The original core of each disc is composed of cells of notochordal origin that will die, leaving a gelatinous core.
Annulus fibrosus
develops from sclerotomal cells that are left in the region of the resegmentating sclerotome as its cranial and caudal halves split apart.
Development of Ribs and Sternum
Concomitantly, transverse processes grow laterally along the dorsal side of each costal process.
In the cervical vertebrae, the costal and transverse processes give rise to the lateral and medial boundaries of theforamina transversaria(ortransverse foramen) that transmit the vertebral arteries.
In the lumbar region, the costal processes do not project distally and contribute to the transverse processes. The costal processes of the first two or three sacral vertebrae contribute to the development of the lateral sacral mass, orala, of thesacrum.
Costal processes
Small lateral mesenchymal condensations develop in association with the vertebral arches of all the developing neck and trunk vertebrae.
Rib formation
Ribs form from the distal tips of the costal processes; lengthen to form in the thoracic region.
The ribs begin to form and lengthen on day 35.
The first seven ribs connect ventrally to the sternum viacostal cartilagesby day 45 and are called thetrue ribs.
The five lower ribs do not articulate directly with the sternum and are called thefalse ribs.
The ribs develop as cartilaginous precursors that later ossify by endochondral ossification.
Sternum formation
As the most cranial ribs make contact with them in the 7th week, the sternal bars meet along the midline and begin to fuse.
Fusion commences at the cranial end of the sternal bars and progresses caudally, finishing with the formation of the xiphoid process in the 9th week.
Like the ribs, the sternal bones ossify from cartilaginous precursors. The sternal bars ossify in cranio-caudal succession from the 5th month until shortly after birth.
Produce the definitive bones of thesternum: themanubrium, body of the sternum, andxiphoid process.
Sternal bars
A pair of longitudinal mesenchymal condensations.
Dermomyotome
dorsal part of the somite remains epithelial; structure quickly separates into two structures, dermatome and myotome
Dermatome
Contribute to the dermis (including fat and connective tissue) of the neck and the back.
Note that most dermis comes from lateral plate mesoderm and head dermis from neural crest cells.
What are 2 structures the myotome splits into?
a dorsalepimereand a ventralhypomere.
Myotome
Differentiate into myogenic (muscle-producing) cells.
Epimeres
give rise to the deepepaxial musclesof the back.
Epaxial muscles: Dorsal muscles associated with the vertebrae, ribs, and base of the skull.
These are innervated by the dorsal ramus of the spinal nerve.
Hypaxial muscles
Include some vertebral muscles, the diaphragm, the abdominal muscles, and all limb muscles.
Hypomeres
form thehypaxial musclesof the lateral and ventral body wall in the thorax and abdomen.
In the occipital region, hypaxial myoblasts migrate to form theintrinsicand extrinsic tongue musculature.
These are innervated by the ventral ramus of the spinal nerve.
In addition to the musculature, the tendons in the body wall also arise from somites.
Appendicular skeleton
bones of the limbs and girdle.
Form byendochondral ossification.
Note, part of the clavicle, in contrast, is amembrane bone.
Their development begins as mesenchymal cells condense.
In response to growth factors,chondrocytesdifferentiate within this mesenchyme and begin to secrete molecules characteristic of the extracellular matrix of cartilage, such as Collagen type IIandProteoglycans.
Epiphyses
ends of forming bones where chondrocytes are resting, the progenitor cells for cartilage growth.
Diaphysis
central area of the long bone, is a proliferating layer of chondrocytes
Prehypertrophiczone
in which the chondrocytes have enlarged.
Hypertrophic zone
chondrocytes are surrounded by calcified matrix. Hypertrophic chondrocytes expressCollagen type X.
Primary ossification center
at the center of the long bone.
Ossification
Ossification begins when the developing bone is invaded by multiple blood vessels that branch from the limb vasculature.
One of these vessels eventually becomes dominant and gives rise to thenutrient arterythat nourishes the bone.
The establishment of the vasculature brings in the pre-osteoblastic cells that differentiate into osteoblasts and replace the hypertrophic chondrocytes.
The osteoblasts lay downCollagen type Iand mineralized matrix.
Ossification spreads from the primary ossification center toward the epiphyses of the anlage to form a loose trabecular networkof bone.
Epiphyseal cartilage plate (growth plateorphysis)
Persists between the epiphysis and the growing end of the diaphysis(metaphysis).
In the epiphyseal cartilage plate, distinct zones of chondrocytes are present, and because growth is predominantly along the long axis of the bones, the chondrocytes are arranged in columns allows the diaphysis to lengthen.
Growth of the body is complete at about 20 years of age; the epiphyseal growth plate completely ossifies.
secondary ossification
After birthsecondary ossification centersdevelop in the epiphyses, which gradually ossify.
diaphyses
At birth, thediaphyses—or shafts of the limb bones (consisting of a bone collar and trabecular core)—are completely ossified, whereas the ends of the bones, called the epiphyses, are still cartilaginous.
Primary bone collar
The region surrounding the diaphysis around the circumference of the bone.
This primary bone collar thickens as osteoblasts differentiate in progressively more peripheral layers of the perichondrium to formcortical bone.
Osteoclasts
Break down previously formed bone. These are important for remodeling of the growing bone. Bone is continually remodeled throughout development and adult life.
Osteoblasts
Terminally differentiated cells that form bone by mineralization
Diarthrodial (synovial) joints
limb bone connections.
Articular cartilage
a cartilage layer at either end of the future joint
Formation of synovial joints
First, the mesenchyme of the interzones between the chondrifying bone primordia differentiates intofibroblastic tissue(undifferentiated connective tissue).
Also area with the adjacent bone primordia and a central region of dense connective tissue.
The connective tissue of this central region gives rise to the internal elements of the joint.
Cartilage condenses to form thesynovial tissuethat will line the future joint cavity.
Its central zone gives rise to themenisciandenclosed joint ligaments, such as the cruciate ligaments of the knee. Vacuoles form within connective tissue and coalesce to form the synovial cavity.
Thejoint capsulearises from the mesenchymal sheath surrounding the entire interzone.
Development of Limb Muscles
Both axial muscles of the trunk and muscles of limb develop similarly, with both groups of muscles arising from somitic myotomes and migrating ventrally—along the dorsolateral body wall into the ventral body wall in the case of axial muscles, and ventrally into the limb buds in the case of limb muscles.
Both groups of muscles are innervated by spinal nerves bordering their level of origin (by dorsal and ventral rami in the case of axial muscles, and by ventral rami only in the case of limb muscles).
The muscle of the diaphragm also arises from somitic myotomes.
When & where does the migration of the myogenic precurosors occur?
Migration of the myogenic precursors into the limb buds starts during the 5th week of development.
The invading myoblasts form two large condensations in the dorsal and ventral limb bud.
The dorsal muscle mass gives rise in general to theextensorsandsupinatorsof the upper limb and to the extensorsandabductorsof the lower limb.
Ventral muscle mass gives rise to theflexorsandpronatorsof the upper limb and to theflexorsandadductorsof the lower limb.
In contrast to limb muscles, which arise from the somitic myotomes, the limb tendons arise from the lateral plate mesoderm.
What are the 2 major divisions of the Nervous system?
Central nervous system (CNS)
Peripheral nervous system (PNS)
Central nervous system (CNS)
brain and spinal cord
Peripheral nervous system (PNS)
all components of the nervous system outside of the CNS cranial nerves and ganglia, spinal nerves and ganglia, autonomic nerves and ganglia, enteric nervous system
Somatic nervous system
Innervates the skin and most skeletal muscles (both sensory and motor components).
Visceral nervous system
Innervates the viscera (organs of the body) and smooth muscle and glands in the more peripheral part of the body.
Also called theautonomic nervous system
sympathetic divisionand theparasympathetic division
What are the two-neuron pathways Visceral (autonomic) system consist of ?
Preganglionic fibers: axons originate in the central neurons.
Postganglionic fibers: axons originate in the peripheral neurons.
What are the three brain divisions?
are marked by expansions of the neural tube:
prosencephalon (forebrain),
mesencephalon (midbrain),
rhombencephalon (hindbrain)
Where do eyes develop from & what closes on day 22 & day 24?
The future eyes appear as outpouchings from the forebrain neural folds by day 22.
Bending of the neural plate begins on day 22, and the cranial neuropore closes on day 24.
What are the primary brain vesicles?
Prosecephalon (forebrain)
Mesencephalon (midbrain)
Rhombencephalon (hindbrain)
What are the secondary brain vesicles
Telencephalon Diencephalon Mesenephalon Metencephalon Myelencephalon
What is adult brain structure of the telencephalon?
Cerebrum: cerebral hemispheres (cortex, white matter, basal nuclei)
What is adult brain structure of the Diencephalon??
Diencephalon (thalamus, hypothalamus, epithalamus), etina
What is adult brain structure of the Mesencephalon?
Brain stem: midbrain
What is adult brain structure of the Metencephalon?
Brain stem: pons & Cerebellum
What is adult brain structure of the Myelencephalon?
Brain stem: medulla oblongata
Neuromeres
morphologically or molecularly definedtransient segments (swellings) of the early developingbrain (day 21).
Prominent in the hindbrain, where seven rhombomerespartition the neural tube into approximately equal-sized segments.
During embryonic development, neural crest cells from each neuromere prompt the development of the nerves and arteries, helping to support the development of craniofacial tissues.
Abnormal development leads to cleft palate.
When are Secondary brain vesicles develop?
During the 5th week, the mesencephalon enlarges and the prosencephalon and rhombencephalon each subdivide into two portions.
What does Prosencephalon divides into?
Telencephalon(“end-brain”), a cranialregion
Diencephalon(“between-brain”), a caudal region
What does Rhombencephalon divides into?
Metencephalon(“behind-brain,”), cranial region
Myelencephalon(“medulla-brain,”), more caudal region
Primitive ventricles
Within each of the brain vesicles, the neural canal is expanded into a cavity.
Become the definitive ventricles of the mature brain.
What does The rhombencephalon cavity?
becomes thefourth ventricle.
What does The mesencephalon cavity?
becomes thecerebral aqueduct of Sylvius.
What does The diencephalon cavity?
becomes thethird ventricle.
What does The telencephalon cavity ?
becomes the pairedlateral ventriclesof the cerebral hemispheres.
Cerebrospinal fluid
a specialized dialysate of blood plasma.
Where does Cyto-differentiation of Neural Tube occur?
Proliferation in the layer of neuroepithelial cells that immediately surrounds the neural canal leads to precursors of the cell types of the future central nervous system.
neurons
some types of glial cells
ependymal cells that line the central canal of the spinal cord and the ventricles
Wha are the 3 cell layers Neuronal differentiation leads ?
Ventricular layer, Mantle layer, Marginal layer
Ventricular layer
Ventricular layerof the differentiating neural tube.- Young neurons, which migrate peripherally to establish a second layer containing cell bodies.
Mantle layer
external to the ventricular layer.
Develops into thegray matterof the central nervous system.
Marginal layer
the neuronal processes (axons) sprout from the mantle layer neurons grow peripherally to establish this layer which contains no neuronal cell bodies.
Becomes thewhite matterof the central nervous system. Color imparted by the fatty myelin sheaths formed by oligodendrocytes.
Glioblast cells
Produced by the ventricular layer
These cells differentiate into the gliaof the CNS
Astrocytes
Oligodendrocytes
Glia provide metabolic and structural support to the neurons of the central nervous system
Ependymal cells
Line the brain ventricles and central canal of the spinal cord.
Produce cerebrospinal fluid (CSF), which fills the brain ventricles, central canal of the spinal cord, and subarachnoid space that surrounds the CNS.
The CSF is under pressure and thus provides a fluid jacket that protects and supports the brain.
Whendoes Differentiation of Spinal Cord occur?
Starting at the end of the 4th week, the neurons in the mantle layer of the spinal cord become organized into four plates that run the length of the cord
Ventralor basal plates (columns)pair
Become thesomatic motoneuronsof the spinal cord
Innervate somatic motor structures such as the voluntary (striated) muscles of the body wall and extremities.
Outgoing efferent motor neuron fibers exit.
Dorsaloralar plates (columns)pair
Develop intoassociation neurons (interneurons)
These neurons synapse withafferent(incoming) fibers from the sensory neurons of the dorsal root ganglia.
In addition, the axon of an association neuron may synapse with motoneurons on the same (ipsilateral) or opposite (contralateral) side of the cord, forming a reflex arc—or it may ascend to the brain.
What are the 2 parts the brain divides into?
Brain stem & Higher centers
Brain stem
which represents the cranial continuation of the spinal cord and is similar to it in organization.
consists of the myelencephalon, the metencephalon derivative called thepons, and the mesencephalon.
The fundamental pattern of alar columns, basal columns, dorsal sensory roots, and ventral motor roots occur in the brain stem.
This pattern is altered during development as some groups of neurons migrate away from their site of origin to establish a nucleus elsewhere.
Organized into a ventricular zone, mantle zone, and marginal zone.
Higher centers
which are extremely specialized and retain little trace of a spinal cord–like organization.
consist of the cerebellum (derived from the metencephalon) and the forebrain.
Formation of cerebrum and other structures.
The roof plate, floor plate, and ependyma of the diencephalon give rise to several specialized structures through mechanisms that are relatively unique.
These structures include thechoroid plexusand circumventricular organs, posterior lobe of the pituitary gland (neurohypophysis), and optic vesicles.
Medulla oblongata
formed from the myelencephalon.
Relay center between spinal cord and higher brain centers.
Regulates respiration, heartbeat, reflexes
Pons
relay signals between cerebral cortex, spinal cord, and cerebellum.
Cerebellum
balance and position control
The cerebellum is derived from both the alar plates of the metencephalon and rhombic lips.
Mesencephalon (Midbrain)
Involved in vision, hearing, motor control, sleep, temperature regulation.
Mesencephalic trigeminal nucleus
afferent nuclei receiving jaw and sensory information.
Superiorandinferior colliculi
are visible as four prominent swellings on the dorsal surface of the midbrain.
The superior colliculi receive axons from the retinae and mediate ocular reflexes.
The inferior colliculi form part of the perceptual pathway by which information from the cochlea is relayed to the auditory areas of the cerebral hemispheres
Forebrain
Dorsal telencephalon(pallium)gives rise to:
Cerebral hemispheresand to the commissures and other structures that join them.
Olfactory bulbsand olfactory tracts, rhinencephalon(“nose-brain”).
Ventral telencephalon (subpallium) gives rise to:
Basal ganglia
What are the 3 Regions of the Diencephalon gives rise to ?
Three prosomeres
P1: Prethalamus rostral
P2: Hypothalamus, Thalamus,
Epithalamus mid
P3: Pretectum caudalWhat is the Functions of the diencephalon subregion: Thalamus ?
Acts mainly as the relay center for the cerebral cortex: it receives all the information projecting to the cortex from subcortical structures, processes it as necessary, and relays it to the appropriate cortical area(s).
Lateral geniculate nucleus: sense of sight.
Medial geniculate nucleus: sense of hearing.
What is the Functions of the diencephalon subregion: Hypothalamus ?
Regulates the endocrine activity of the pituitary as well as many autonomic responses.
Part of the limbic system, which controls emotion and coordinates emotional state with the appropriate visceral responses.
Controls the level of arousal of the brain (sleep and waking).
What is the Functions of the diencephalon subregion: Epithalamus?
Controls limbic system.
Pineal gland: Secretion of melatonin, sleep/wake.
Optic chiasm and diencephalon
Retinal fibers from the optic cups project to the lateral geniculate nuclei.
The axons from the retinal ganglion cells grow back through the optic nerves to the diencephalon.
Just before they enter the brain, axons growing from both eyes meet to form theoptic chiasm, a joint midline structure in which the axons from the inner (nasal) side of each eye cross over to the other side of the brain (decussate), whereas those of the outer (temporal) side of each eye remains on the same side.
Axons relaying information from the left half of the visual field of both eyes project to the right side of the brain and vice versa.
Rathke’s pouch
diverticulum which grows dorsally toward the infundibulum.
Differentiates to form the adenohypophysisof the pituitary.
Anterior lobeof pituitary gland.
Infundibulum
develops in the floor of the third ventricle and grows ventrally toward the stromodeum.
Stomodeum
(an ectodermal lined space; precursor of the mouth and the anterior lobe of the pituitary gland.
neurohypophysis
Posterior lobe of pituitary gland (neurohypophysis) comes from infundibulum.
Telencephalon
The cerebral hemispheres first appear on day 32 as a pair of bubble-like outgrowths of the telencephalon.
By 16 weeks, the rapidly growing hemispheres are oval and have expanded back to cover the diencephalon.
Each hemisphere represent the futurecerebral cortex.
Internal capsule
The diencephalon and telencephlon are crossed by a massive axon bundle called theinternal capsule, which passes through the corpus striatum (giving it its striated appearance) and carries axons from the thalamus to the cerebral cortex (and vice versa) as well as from the cerebral cortex to lower regions of the brain and spinal cord.
Cerebral lobe formation
The cerebral hemispheres are initially smooth surfaced. However, like the cerebellar cortex, the cerebral cortex folds into an increasingly complex pattern of gyri (ridges) and sulci (grooves) as the hemispheres grow.
Lateral cerebral fossa
First major indentation in the lateral wall of each hemisphere.
lateral cerebral sulcus (fissure)
Creates the temporal lobeof the cerebral hemisphere and converting the fossa into a deep cleft
Central sulcus
separates the frontal and parietal lobes.
Occipital sulcus
demarcates the occipital lobe.
Lateral ventricle
Each cerebral hemisphere contains a ventricle developed from the central canal of the neural tube.
Choroid fissure
Longitudinal groove in the ventricle. A choroid plexus develops along the choroid fissure.
neocortex.
Maturation of cortex produced is unique.
The cerebral cortex is made up of several cell layers (or laminae) including the dominant neocortex.
Nasal formation
Nasal placodes form at the end of the 4th week.
Very early, some cells in the nasal placode differentiate to form theprimary neurosensory cellsof the future olfactory epithelium.
At the end of the 5th week, these cells sprout axons that cross the short distance to penetrate the most cranial end of the telencephalon.
Olfactory nerve
Made up of olfactory tracts (mitral cells) that synapse with sensory neurons.
Commissure formation
The commissures that connect the right and left cerebral hemispheres form from a thickening at the cranial end of the telencephalon
Anterior commissure
forms during the 7th week and interconnects the olfactory bulbs and olfactory centers of the two hemispheres.
Hippocampal commissure
forms between the right and left hippocampus.
Corpus callosum
links together the right and left neocortices along their entire length.
