Quiz1 Flashcards
(209 cards)
1
Q
Surface Ectoderm
A
Forms Epidermis
covering of the embryo is initially a single-cell layer thick.
2
Q
Periderm
A
New layer formed by proliferation of ectoderm after week 4.
Simple squamous epithelium
3
Q
Basal layer
A
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.
4
Q
Intermediate layer
A
Formedin the 11th week by proliferation of the basal layer.
Forerunner of the outer layers of the mature epidermis.
5
Q
Germinative layer
A
stratum germinativum
Layer of stem cells that will continue to replenish the epidermis throughout life.
6
Q
Keratinocytes
A
The cells of the intermediate layer contain theKeratin proteins characteristic of differentiated epidermis
7
Q
Apical vs Basal surface
A
Basal Cells regenerate & apical cells slough off, they are replaced by basal cells
8
Q
function & location of Simple squamouse eithelium
A
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
9
Q
function & location of simple cuboidal epithelium
A
Location: in ducts & secretory portions of small glands & in kidney tubules
Function: secretes & absorbs
10
Q
function & locationof simple columnar epitheliu
A
Location: cilated tissues are in bronchi, uterine tubes & uterus; smooth (nonciliated tissues) are indigestive tract bladder
Function: Absorb, secretes mucous & enzymes
11
Q
function & location of stratified squamous epithelium
A
Location: lines the esophagus, mouth, & vagina
Function: protects against abrasion
12
Q
function & location of stratified cuboidal epithelium
A
Location: sweat glands, salivary glands, & mammary glands
Function: protective tissue
13
Q
function & location of stratified columnar epithelium
A
Location: male urethra & ducts of some glands
Function: secretes & protects
14
Q
function & locatio of ransitional epithelium
A
Location: lines the bladder, uretha & ureters
Function: allows the urinary organs to expand stretch
15
Q
What are the 3 definitive layers of skin?
A
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
16
Q
Where are the cells of the stratum germinativum connected
A
to the basement membrane by hemidesmosomes, which containIntegrins.
17
Q
what cells are formed once they are in the stratum spinosum?
A
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.
18
Q
Envelope proteins
A
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.
19
Q
lamella granules
A
Lipid-containing granules (lamellar granules) are also produced that help seal the skin.
20
Q
Cornification
A
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.
21
Q
What are the 4 specialized cell types of epidermis?
A
- Keratinocytes: Majority of cells; ectodermal origin
- Melanocytes: Pigment cells; neural crest cell origin (roof of neural tube, ectoderm)
- Langerhans cells
- Merkel cells
22
Q
Melanocytes
A
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
23
Q
Langerhan
A
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.
24
Q
Merkel cells
A
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.
25
Dermis
corium
the layer of skin that underlies the epidermis and contains blood vessels, hair follicles, nerve endings, sensory receptors.
Formed by mesoderm
26
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).
27
Dermal papillae
the outer layer of the developing dermis proliferates to form ridge-like that protrude into the overlying epidermis
28
Epidermal ridges
The intervening protrusions of the epidermis into the dermis
29
Papillary layer
Top layer of dermis
30
Reticular layer
thick underlying layer of dense, irregular connective tissue
31
Hypodermis
(subcorium): Subcutaneous fatty connective tissue
32
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.
33
sebaceous glands
produce sebum, an oily substance that protects the skin against friction and dehydration
Sebaceous glands produce the oily sebum that 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
34
sweat glands
heat regulation
35
teeth and salivary glands
mastication
36
lacrimal glands
produce tears
37
mammary gland
in females provides both nutrition and a source of immunity for the breastfeeding infant
38
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.
39
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.
40
Germinal matrix
Ectodermal cells that produce the hair shaft. Add keratin
41
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 the bulge.
42
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.
43
Bulbous hair peg
stratum germinativum
| Layer of stem cells that will continue to replenish the epidermis throughout life.
44
Hair peg
Proliferation that pushes down into the dermis.
45
Hair Bulge
where stem cells reside
| signal to stem cells from dermal papilla to produce TA cells & send them to the matrix
46
Lanugo
First hair of fetus, Shed before birth but sometimes sticks around
47
vellus
Replaces lanugo
| fine non-pigmented hairs
48
Terminal hairs
Pigmented and get thicker at puberty
49
Holocrine cells
replaced by stem cells
50
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
51
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.
52
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 of myoepithelial 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.
53
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 of myoepithelial 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.
54
polythelia
Occasionally, one or more supernumerary nipples (polythelia)
55
polymastia
supernumerary breasts(polymastia) form along the line of the mammary ridges. The most common location is just below the normal breast.
56
mammary pit
At birth, the mammary glands consist of 15 to 25 lactiferous ducts, which open onto a small superficial depression called the mammary pit.
57
secondary buds
By the 12th week several secondary buds have formed. These buds lengthen and branch throughout the remainder of gestation
58
primary bud
The remnant of the mammary ridge produces the primary bud of 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.
59
mammary ridges.
In the 4th week, a pair of epidermal thickenings called the mammary ridges.
In humans, these ridges normally disappear except at the site of the breasts.
60
Nail anlagen
first appear as epidermal thickenings at the tips of the digits.
61
Nail field
Migrate proximally on the dorsal surface of the digits and forms a shallow depression
62
Nail folds
surrounds nail field
63
formative root
The stratum germinativum of the proximal nail fold proliferates to become the formative zone (also called the formative root or matrix), that produces the horny nail plate.
64
eponychium
A thin layer of epidermis called the eponychium initially covers the nail plate, but this layer normally degenerates, except at the nail base.
65
Dental lamina
U-shaped ridge of epidermis on upper and lower jaw at 6 weeks.
66
Dental papilla
During the 8th week, instructive influences from the epidermis cause the mesenchymal condensation to invade the base of the dental lamina ingrowth.
67
Dental sac
The mesenchyme surrounding the papilla and its dental lamina cap condenses to form an enclosure
68
Cap stage
Stage of tooth development when the dental lamina invests the top of the papilla like a cap.
69
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.
70
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 the dentin of the teeth.
71
Enamel organ
the dental lamina differentiates the enamel layer of the tooth.
First, the dental lamina becomes a three-layered structure, consisting of an inner enamel epithelium overlying the dental papilla; a central layer, the enamel (otellate) reticulum composed of star-shaped cells dispersed in an extracellular layer; and an outer enamel epithelium.
72
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.
73
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.
74
predentin
In the 7th month, the odontoblasts begin to secrete the non-mineralized matrix of the dentin, called predentin, which later progressively calcifies to form dentin.
75
Primary teeth
(deciduous or milk) teeth. The 20 tooth buds consisting in each half-jaw of two incisors, one canine, and two premolars.
76
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.
77
cementoblasts
The tooth roots are enclosed in extensions of the mesenchymal dental sac. The inner cells of the dental sac differentiate into cementoblasts, which secrete a layer of cementum to cover the dentin of the root.
78
cementoenamel junction
At the neck of the tooth root, the cementum meets the enamel at a cementoenamel junction.
79
alveolus
The outermost cells of the dental sac participate in bone formation as the jaws ossify and also form the periodontal ligament that holds the tooth to its bony socket, or alveolus.
80
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 the epithelial 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.
81
2 Types of Bone Development
Axial (vertebral column and ribs)
| Appendicular (limb) bones of the body, with the exception of part of the clavicle.
82
Endochondral ossification
Developmental process in which a cartilaginous template forms preceding ossification.
83
What are the 3 bone cell types?
Three cell types: chondrocytes, osteoblasts, osteoclasts.
84
Chondrocytes
(cartilage cells)
paraxial mesoderm forms the axial skeleton.
lateral plate mesoderm forms the appendicular skeleton and sternum.
neural crest cells (ectoderm) give rise to the cartilaginous elements in the face and neck.
85
Osteoblasts
(bone-forming cells)
| arise from mesenchymal stem cells.
86
Osteoclasts
(bone-resorbing cells)
| arise from the hematopoietic system.
87
Intramembranous ossification
Developmental process in which ossification directly from the mesenchyme.
88
Dermal (membrane bones)
majority of bones of the face and skull.
Dermal bones develop from neural crest cells (facial bones and the frontal bone of the skull) or unsegmented paraxial (head) mesoderm (e.g., parietal bone of the skull).
In dermal bones, the osteoblasts directly differentiate within the mesenchyme.
89
What are Striated muscles of the trunk and limb developed from?
derived from the segmented paraxial mesoderm (somites).
| Additionally the tongue musculature forms from this mesoderm(occipital somites).
90
Where do Other craniofacial muscles derive from?
arise from the unsegmented paraxial mesoderm and prechordal plate mesoderm (i.e., head mesoderm).
91
Myogenic cell differentiation
Long distance migrating myoblasts proliferate but then they exit the cell cycle and terminally differentiate to form myocytes.
The myocytes express contractile proteins such as Actin and Myosin and fuse to form a myofiber, which is a multinucleated syncytium (i.e., a mass of cells each containing multiple nuclei) containing the contractile myofibrils.
92
What arethe 3 waves of striated muscle formation?
Primary myogenesis, Secondary myogenesis, Postnatal muscle growth
93
Where does Primary myogenesis occur?
in the embryo
94
Where doesSecondary myogenesis occur?
in the fetus and gives rise to the bulk of fetal muscle.
95
Postnatal muscle growth
involves satellite 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.
96
Smooth Muscle Formation
Smooth muscle of the gut and cardiac muscle forms from splanchnic 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.
97
Somites
are transient segmented structures derived from paraxial mesoderm.
progenitors of the axial skeleton, trunk musculature and associated tendons, trunk dermis, endothelial cells, and meninges of the spinal cord.
98
Where do Presomitic paraxial mesoderm begin?
begins to segment into epithelial balls with a central cavity of loose core cells.
99
Somite subdivison
Each somite subdivides into specific mesodermal components
100
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 the notochord and form the rudiment of the vertebral body;
those in the dorsal portion of the sclerotome surround the neural tube and form the rudiment of the vertebral arch and vertebral spine;
More laterally located sclerotome forms the vertebral transverse process and ribs.
101
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.
102
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 lie intersegmentally.
103
Intrasegmental boundary, or von Ebner’s fissure
The division between the cranial and caudal portions of each sclerotome.
104
Result of sclerotomal resegmentation
Intersegmental arteries pass over the vertebral body.
Segmental spinal nerves exit between the vertebrae.
Seven cervical vertebrae but there are eight cervical 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.
105
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).
106
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.
107
Intervertebral discs
Develops at the intra-segmental boundary.
108
Nucleus pulposus
The original core of each disc is composed of cells of notochordal origin that will die, leaving a gelatinous core.
109
Annulus fibrosus
develops from sclerotomal cells that are left in the region of the resegmentating sclerotome as its cranial and caudal halves split apart.
110
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 the foramina transversaria (or transverse 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, or ala, of the sacrum.
111
Costal processes
Small lateral mesenchymal condensations develop in association with the vertebral arches of all the developing neck and trunk vertebrae.
112
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 via costal cartilages by day 45 and are called the true ribs.
The five lower ribs do not articulate directly with the sternum and are called the false ribs.
The ribs develop as cartilaginous precursors that later ossify by endochondral ossification.
113
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 the sternum: the manubrium, body of the sternum, and xiphoid process.
114
Sternal bars
A pair of longitudinal mesenchymal condensations.
115
Dermomyotome
dorsal part of the somite remains epithelial; structure quickly separates into two structures, dermatome and myotome
116
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.
117
What are 2 structures the myotome splits into?
a dorsal epimere and a ventral hypomere.
118
Myotome
Differentiate into myogenic (muscle-producing) cells.
119
Epimeres
give rise to the deep epaxial muscles of 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.
120
Hypaxial muscles
Include some vertebral muscles, the diaphragm, the abdominal muscles, and all limb muscles.
121
Hypomeres
form the hypaxial muscles of the lateral and ventral body wall in the thorax and abdomen.
In the occipital region, hypaxial myoblasts migrate to form the intrinsic and 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.
122
Appendicular skeleton
bones of the limbs and girdle.
Form by endochondral ossification.
Note, part of the clavicle, in contrast, is a membrane bone.
Their development begins as mesenchymal cells condense.
In response to growth factors, chondrocytes differentiate within this mesenchyme and begin to secrete molecules characteristic of the extracellular matrix of cartilage, such as Collagen type II and Proteoglycans.
123
Epiphyses
ends of forming bones where chondrocytes are resting, the progenitor cells for cartilage growth.
124
Diaphysis
central area of the long bone, is a proliferating layer of chondrocytes
125
Prehypertrophic zone
in which the chondrocytes have enlarged.
126
Hypertrophic zone
chondrocytes are surrounded by calcified matrix. Hypertrophic chondrocytes express Collagen type X.
127
Primary ossification center
at the center of the long bone.
128
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 the nutrient artery that 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 down Collagen type I and mineralized matrix.
Ossification spreads from the primary ossification center toward the epiphyses of the anlage to form a loose trabecular network of bone.
129
Epiphyseal cartilage plate (growth plate or physis)
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.
130
secondary ossification
After birth secondary ossification centers develop in the epiphyses, which gradually ossify.
131
diaphyses
At birth, the diaphyses—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.
132
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 form cortical bone.
133
Osteoclasts
Break down previously formed bone. These are important for remodeling of the growing bone. Bone is continually remodeled throughout development and adult life.
134
Osteoblasts
Terminally differentiated cells that form bone by mineralization
135
Diarthrodial (synovial) joints
limb bone connections.
136
Articular cartilage
a cartilage layer at either end of the future joint
137
Formation of synovial joints
First, the mesenchyme of the interzones between the chondrifying bone primordia differentiates into fibroblastic 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 the synovial tissue that will line the future joint cavity.
Its central zone gives rise to the menisci and enclosed joint ligaments, such as the cruciate ligaments of the knee. Vacuoles form within connective tissue and coalesce to form the synovial cavity.
The joint capsule arises from the mesenchymal sheath surrounding the entire interzone.
138
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.
139
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 the extensors and supinators of the upper limb and to the extensors and abductors of the lower limb.
Ventral muscle mass gives rise to the flexors and pronators of the upper limb and to the flexors and adductors of the lower limb.
In contrast to limb muscles, which arise from the somitic myotomes, the limb tendons arise from the lateral plate mesoderm.
140
What are the 2 major divisions of the Nervous system?
Central nervous system (CNS)
| Peripheral nervous system (PNS)
141
Central nervous system (CNS)
brain and spinal cord
142
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
```
143
Somatic nervous system
Innervates the skin and most skeletal muscles (both sensory and motor components).
144
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 the autonomic nervous system
sympathetic division and the parasympathetic division
145
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.
146
What are the three brain divisions?
are marked by expansions of the neural tube:
prosencephalon (forebrain),
mesencephalon (midbrain),
rhombencephalon (hindbrain)
147
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.
148
What are the primary brain vesicles?
Prosecephalon (forebrain)
Mesencephalon (midbrain)
Rhombencephalon (hindbrain)
149
What are the secondary brain vesicles
```
Telencephalon
Diencephalon
Mesenephalon
Metencephalon
Myelencephalon
```
150
What is adult brain structure of the telencephalon?
Cerebrum: cerebral hemispheres (cortex, white matter, basal nuclei)
151
What is adult brain structure of the Diencephalon??
Diencephalon (thalamus, hypothalamus, epithalamus), etina
152
What is adult brain structure of the Mesencephalon?
Brain stem: midbrain
153
What is adult brain structure of the Metencephalon?
Brain stem: pons & Cerebellum
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What is adult brain structure of the Myelencephalon?
Brain stem: medulla oblongata
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Neuromeres
morphologically or molecularly defined transient segments (swellings) of the early developing brain (day 21).
Prominent in the hindbrain, where seven rhombomeres partition 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.
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When are Secondary brain vesicles develop?
During the 5th week, the mesencephalon enlarges and the prosencephalon and rhombencephalon each subdivide into two portions.
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What does Prosencephalon divides into?
Telencephalon (“end-brain”), a cranial region
| Diencephalon (“between-brain”), a caudal region
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What does Rhombencephalon divides into?
Metencephalon (“behind-brain,”), cranial region
| Myelencephalon (“medulla-brain,”), more caudal region
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Primitive ventricles
Within each of the brain vesicles, the neural canal is expanded into a cavity.
Become the definitive ventricles of the mature brain.
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What does The rhombencephalon cavity?
becomes the fourth ventricle.
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What does The mesencephalon cavity?
becomes the cerebral aqueduct of Sylvius.
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What does The diencephalon cavity?
becomes the third ventricle.
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What does The telencephalon cavity ?
becomes the paired lateral ventricles of the cerebral hemispheres.
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Cerebrospinal fluid
a specialized dialysate of blood plasma.
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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
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Wha are the 3 cell layers Neuronal differentiation leads ?
Ventricular layer, Mantle layer, Marginal layer
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Ventricular layer
Ventricular layer of the differentiating neural tube.- Young neurons, which migrate peripherally to establish a second layer containing cell bodies.
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Mantle layer
external to the ventricular layer.
| Develops into the gray matter of the central nervous system.
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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 the white matter of the central nervous system. Color imparted by the fatty myelin sheaths formed by oligodendrocytes.
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Glioblast cells
Produced by the ventricular layer
These cells differentiate into the glia of the CNS
Astrocytes
Oligodendrocytes
Glia provide metabolic and structural support to the neurons of the central nervous system
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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.
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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
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Ventral or basal plates (columns) pair
Become the somatic motoneurons of 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.
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Dorsal or alar plates (columns) pair
Develop into association neurons (interneurons)
These neurons synapse with afferent (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.
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What are the 2 parts the brain divides into?
Brain stem & Higher centers
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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 the pons, 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.
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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 the choroid plexus and circumventricular organs, posterior lobe of the pituitary gland (neurohypophysis), and optic vesicles.
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Medulla oblongata
formed from the myelencephalon.
Relay center between spinal cord and higher brain centers.
Regulates respiration, heartbeat, reflexes
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Pons
relay signals between cerebral cortex, spinal cord, and cerebellum.
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Cerebellum
balance and position control
| The cerebellum is derived from both the alar plates of the metencephalon and rhombic lips.
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Mesencephalon (Midbrain)
Involved in vision, hearing, motor control, sleep, temperature regulation.
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Mesencephalic trigeminal nucleus
afferent nuclei receiving jaw and sensory information.
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Superior and inferior 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
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Forebrain
Dorsal telencephalon (pallium) gives rise to:
Cerebral hemispheres and to the commissures and other structures that join them.
Olfactory bulbs and olfactory tracts, rhinencephalon (“nose-brain”).
Ventral telencephalon (subpallium) gives rise to:
Basal ganglia
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What are the 3 Regions of the Diencephalon gives rise to ?
```
Three prosomeres
P1: Prethalamus rostral
P2: Hypothalamus, Thalamus,
Epithalamus mid
P3: Pretectum caudal
```
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What 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.
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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).
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What is the Functions of the diencephalon subregion: Epithalamus?
Controls limbic system.
| Pineal gland: Secretion of melatonin, sleep/wake.
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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 the optic 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.
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Rathke’s pouch
diverticulum which grows dorsally toward the infundibulum.
Differentiates to form the adenohypophysis of the pituitary.
Anterior lobe of pituitary gland.
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Infundibulum
develops in the floor of the third ventricle and grows ventrally toward the stromodeum.
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Stomodeum
(an ectodermal lined space; precursor of the mouth and the anterior lobe of the pituitary gland.
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neurohypophysis
Posterior lobe of pituitary gland (neurohypophysis) comes from infundibulum.
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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 future cerebral cortex.
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Internal capsule
The diencephalon and telencephlon are crossed by a massive axon bundle called the internal 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.
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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.
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Lateral cerebral fossa
First major indentation in the lateral wall of each hemisphere.
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lateral cerebral sulcus (fissure)
Creates the temporal lobe of the cerebral hemisphere and converting the fossa into a deep cleft
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Central sulcus
separates the frontal and parietal lobes.
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Occipital sulcus
demarcates the occipital lobe.
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Lateral ventricle
Each cerebral hemisphere contains a ventricle developed from the central canal of the neural tube.
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Choroid fissure
Longitudinal groove in the ventricle. A choroid plexus develops along the choroid fissure.
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neocortex.
Maturation of cortex produced is unique.
| The cerebral cortex is made up of several cell layers (or laminae) including the dominant neocortex.
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Nasal formation
Nasal placodes form at the end of the 4th week.
Very early, some cells in the nasal placode differentiate to form the primary neurosensory cells of 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.
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Olfactory nerve
Made up of olfactory tracts (mitral cells) that synapse with sensory neurons.
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Commissure formation
The commissures that connect the right and left cerebral hemispheres form from a thickening at the cranial end of the telencephalon
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Anterior commissure
forms during the 7th week and interconnects the olfactory bulbs and olfactory centers of the two hemispheres.
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Hippocampal commissure
forms between the right and left hippocampus.
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Corpus callosum
links together the right and left neocortices along their entire length.
