Embryology III

Question 1

What is neurulation?

Answer 1

Neurulation converts the neural plate into a hollow neural tube covered by surface ectoderm. The neural tube then begins to differentiate into brain and spinal cord.

Question 2

Even before the end of the fourth week, the major regions of the brain become apparent:

Answer 2

1. forebrain
2. midbrain
3. hindbrain

OR

1. prosencephalon
2. mesencephalon
3. rhombencephalon.

Question 3

____ and ____ begin to differentiate from the neuroepithelium of the neural tube. As neurulation occurs, neural crest cells detach from the lateral lips of the neural folds and migrate to numerous locations in the body, where they differentiate to form a wide range of structures and cell types.

Answer 3

Neurons and glia

Question 4

Neural crest cells from the mesencephalon and rhombencephalon (hindbrain) regions also give rise to structures in the developing _________. These structures include:

Answer 4

pharyngeal arches of the head and neck

cartilaginous elements and several bones of the nose, face, middle ear, and neck

Question 5

* Mesencephalon and Rhombencephalon – What do neural crest cells form?

Answer 5

Dermis, smooth muscle, and fat of the face and ventral neck, and the odontoblasts of developing teeth.

Question 6

*Neural crest cells arising from the caudalmost rhombencephalon contribute, along with vagal neural crest cells (covered later) to the ___________.

Answer 6

parafollicular cells of the thyroid.

Question 7

The Rhombencephalic neural crest cells also contribute to some of the _______.

Answer 7

cranial nerve ganglia

Question 8

Specifically, rhombencephalic neural crest cells give rise to some neurons and ALL _____in the sensory ganglia of cranial nerves ___, ___, ____ and ____.

Answer 8

glial cells

V, VII, IX, and X

Question 9

* The special sensory nerves, associated glia, and ganglia (when present) also arise from placodes:

Answer 9

o Cranial Nerve I (olfactory) arises from the olfactory placode.

o Cranial nerve II (optic) arises from the optic cup (the distal end of which thickens as the placode-like rudiment of the neural retina)

o Cranial Nerve VIII (vestibulocochlear nerve) and the vestibulocochlear ganglion arise from the otic (means ear) placode. Know what a placode is!

Question 10

What is a placode?

Answer 10

A neurogenic placode is an area of thickening of the epithelium in the embryonic head ectoderm layer that gives rise to neurons and other structures of the sensory nervous system.

Question 11

* The __________ also give rise to the cranial component of the parasympathetic division of the autonomic nervous system.

Answer 11

rhombencephalic neural crest cells

Question 12

Specifically, rhombencephalic neural crest cells give rise to all _________.

Answer 12

POST-ganglionic neurons

Question 13

Pre-ganglionic neurons arise in the ______.

Answer 13

ventral wall of the neural tube

Question 14

The rhombencephalic neural crest cells also give rise to

glial cells in the parasympathetic ganglia of cranial nerves ___, ___, and ___.

Answer 14

VII, IX, and X

7, 9, and 10

Question 15

In conjunction with neural crest cells derived from the caudal prosencephalon and mesencephalon (that give rise to the parasympathetic ganglia of cranial nerve III), the entire cranial component of the parasympathetic division of the autonomic nervous system is formed from ________. (KNOW THIS!)

Answer 15

cranial neural crest cells

Question 16

* **All of the nervous system is ______derivatives and _______. **

Answer 16

neural crest cells

ectoderm

Question 17

* Cranial neural crest cells give rise to other cell types that populate the head and neck. These include the ______ and ________.

Answer 17

pia mater and arachnoid mater.

Question 18

The dura mater, the outermost layer of the three meninges, arises largely or exclusively from head ________.

Answer 18

(paraxial) mesoderm

Question 19

In addition, some cranial neural crest cells invade the surface ectoderm as they migrate away from the neural tube to form the _______.

Answer 19

melanocytes (pigment cells) of the skin of the head and neck.

Question 20

* Neural cells originating from the vagal region have three major contributions:

Answer 20

o 1) Vagal neural crest cells migrate into the cranial pole of the developing heart, where they contribute to the septum that forms to partition the ** outflow tract of the heart. **

o 2) Vagal neural crest cells migrate more distally into the gut wall mesenchyme to form neurons, constituting the enteric nervous system, that innervate all regions of the gut tube from the esophagus to the rectum

o 3) Vagal neural crest cells migrate with those from the caudal rhombencephalon (covered earlier) to the pharyngeal pouches, where they contribute to the parafollicular cells of the thyroid

Question 21

_* The peripheral nervous system of the neck, trunk, and limbs includes the following four types of peripheral neurons:_

Answer 21

o 1) peripheral sensory neurons

o 2) The cell bodies of which they reside in the dorsal root ganglia

o 3) sympathetic and parasympathetic autonomic peripheral motoneurons

o 4) The cell bodies of which reside, respectively, in the sympathetic and parasympathetic ganglia (and enteric neurons, considered a third subdivision of the autonomic nervous system).

Question 22

* Shortly after somite formation, each somite reorganizes into two subdivisions:

Answer 22

o 1) The epithelial dermamyotome

o 2) Mesenchymal sclerotome

Question 23

* Thus, formation of the sclerotome, like ingression of cells through the primitive streak and formation of neural crest cells, is another example of an _________.

Answer 23

epithelial-to-mesenchymal transformation.

Question 24

* _________will develop into the vertebrae.

Answer 24

Sclerotomes

Question 25

* SKIN: The skin, or integument, consists of two layers:

Answer 25

o 1) The epidermis- surface ectoderm

o 2) The dermis – mesenchyme

Question 26

* The Epidermis is formed mainly by embryonic surface ectoderm, although it is also colonized by ______, which are derived from neural crest cells.

Answer 26

melanocytes (pigment cells)

Question 27

* The dermis of the trunk is a _______. The ventral dermis is derived mainly from the somatic layer of the lateral plate mesoderm, whereas the dorsal dermis is derived from the dermamyotome subdivision of the _____. The dermis of the face is formed from neural crest cells.

Answer 27

mesodermal tissue

somites

Question 28

* Bone development:

o Development of bone and muscle occurs within mesenchymal regions of the embryo after the ______ is established during the fourth week of gestation.

Answer 28

tube-within-a-tube body plan

Question 29

Bone formation occurs in two ways:

Answer 29

* 1) Endochondral ossification: a cartilage model first forms and is eventually replaced with bone. This type of ossification underlies formation of the axial skeleton (vertebral column, ribs, and sternum), cranial base, and appendicular (limb) skeleton, with the exception of part of the clavicles.

* 2) Intramembranous ossification: bone forms directly from mesenchymal cells without the prior formation of cartilage. This type of ossification underlies formation of the cranial vault and most of the bones of the face.

* Note: Babies are so flexible because most of their bone is still cartilage.

Question 30

* Muscle development:

o Shortly after formation of the somatic myotome (somites break down into these/ derivative of muscle), the myotome splits into a _____ and a ______. of these muscles reflects their embryonic origin.

Answer 30

dorsal epimere and a ventral hypomere

Question 31

* Muscle development:

The epimere form the deep _______, which are innervated by the dorsal ramus of the spinal nerve. In contrast, the hypomere (toward the front) forms the ______of the lateral and ventral body wall in the thorax and abdomen, which are innervated by the ventral ramus of the spinal nerve.

o Therefore, like all skeletal muscles, the innervation

Answer 31

epaxial muscles of the back

hypaxial muscles

Question 32

* Central Nervous System:

o Even before neurulation begins, the primordia of the three primary brain vesicles- prosencephalon, mesencephalon, and rhombencephalon – are visible as broadenings of the neural plate. During the fifth week, the prosencephalon subdivides into the ______ and _______, and the rhombencephalon subdivides into the ______ and _________.

Answer 32

telencephalon and diencephalon

metencephalon and myelencephalon

Question 33

Thus, along with the mesencephalon, there are five secondary brain vesicles. During this period, the hindbrain is divided into small repetitive segments called _______. The extension of the neural tube caudal to the rhombomeres constitutes the spinal cord.

Answer 33

rhombomeres

Question 34

* Peripheral Nervous System:

o The nervous system of vertebrates consists of two major functional divisions: a ______ and a _______.

Answer 34

nervous system and a visceral nervous system

Question 35

* Peripheral Nervous System:

The somatic nervous system innervates the ____ and most ____muscles (i.e., it provides both sensory and motor components).

Answer 35

skin and most skeletal muscles

Question 36

* Peripheral Nervous System:

Similarly, the visceral nervous system innervates the _____ and the ______ and ____ in the more peripheral part of the body. The visceral nervous system is also called the ______.

Answer 36

viscera (organs of the body)

smooth muscle and glands in the more peripheral part of the body

autonomic nervous system

Question 37

* Lung development:

o Development of the lungs begins on day 22 (beginning of week 4) with formation of a ventral outpouching of the _______ called the respiratory diverticulum. This bud grows ventrocaudally through the mesenchyme surrounding the foregut, and on days 26 to 28, it undergoes a first bifurcation, splitting into right and left _______. These buds are the rudiments of the two lungs and the right and left primary bronchi, and the proximal end (stem) of the diverticulum forms the ___ and ___.

Answer 37

endodermal foregut

primary bronchial (or lung) buds

trachea and larynx.

Question 38

* Heart development:

o The heart derives from _______.

o The heartbeat is initiated around the ____, and its continual beating is required for normal heart development. Between weeks four and eight, the primary heart tube undergoes a series of events, including looping, remodeling, realignment, and septation, eventually leading to the transformation of a single heart tube into a four-chambered heart, thus laying down the basis for the separation of pulmonary and systemic circulations at birth.

Answer 38

splanchnic mesoderm

day 21

Question 39

• Blood vessel development:
• Starting on day 17, vessels begin to arise in the ______ of the yolk sac wall from aggregations of cells called _____.

Answer 39

splanchnic mesoderm

hemangioblasts

Question 40

• From hemangeoblasts, two cell lineages arise: ________ and _______.

Answer 40

primitive hematopoietic progenitor cells and endothelial precursor cells.

Question 41

Vasculogenesis commences in the _____ of the embryonic disc and continues later in the _______. In the embryonic disc, endothelial cell precursors differentiate into endothelial cells and organize into networks of small vessels that coalesce, grow, and invade other tissues to form the primary embryonic vasculature.

• **KNOW the difference between splanchnic and paraxial mesoderm!**

Answer 41

splanchnic mesoderm

paraxial mesoderm

Question 42

********Know that blood vessels arise from à ___________

Answer 42

splanchnic mesoderm.

Question 43

* Gastrointestinal Tract development:

o The endodermal gut tube created by body folding during the fourth week consists of a blind-ended cranial ____, a blind-ended caudal _____, and a _____ open to the yolk sac through the vitelline duct.

Answer 43

foregut

hindgut

midgut

Question 44

GI Tract Development

o By the 5th week, the thoracic and abdominal portion of the foregut is visibly divided into the _____, _____, _____, and ________.

Answer 44

pharynx, esophagus, stomach, and proximal duodenum

Question 45

GI Tract Development

o The midgut forms the distal duodenum, jejunum, ileum, cecum, ascending colon, and proximal 2/3 of the transverse colon.

Answer 45

1. distal duodenum
2. jejunum
3. ileum
4. cecum
5. scending colon
6. proximal 2/3 of the transverse colon.

Question 46

GI Tract Development

o The hindgut forms the distal third of the:

Answer 46

1. transverse colon
2. the descending and sigmoid colon
3. and the upper 2/3 of the anorectal canal.

Question 47

* Kidney Development:

o The intermediate mesoderm on either side of the dorsal body wall gives rise to three _________ of increasingly advanced design.

Answer 47

successive nephric structures

Question 48

Kidney Development:

o The intermediate mesoderm, also known as the ______, forms a segmental series of epithelial buds called _________.

Answer 48

nephrotome

pronephroi

Question 49

* Kidney Development:

As these cranial pronephroi regress in the 4th week, a pair of elongated _______ succeeds them, developing in the thoracic and lumbar regions.

o The ________ become the first kidneys to function in the embryo, having complete, although simple, nephrons.

Answer 49

mesonephroi

Question 50

* Reproductive System Development:

o In addition to the _nephric structures, _________on both sides of the dorsal body wall gives rise to a _______.

Answer 50

the intermediate mesoderm

gonadal ridge

Question 51

**********Reproductive System:

By the sixth week, the germ cells migrating from the yolk sac begin to arrive in the mesenchyme of the dorsal body wall.

o Know that the reproductive system forms during the _____ and is derived from ___________!

Answer 51

6th week

intermediate mesoderm

Question 52

* Development of the Face:

o The skeleton of the head and pharynx is made up of the ________: the bones that support and protect the brain and sensory organs (olfactory organs, eyes, and inner ears), and the ___________: the bones of the face and pharyngeal arches.

Answer 52

neurocranium

viscerocranium

Question 53

* Development of the Face:

The neurocranium can be subdivided into _______ (the bones underlying the brain), __________ (the bones covering the brain), and ________ (the bones encapsulating the sensory organs).

Answer 53

cranial base

cranial vault

sensory capsules

Question 54

*******IMPORTANT!!!!!!

Development of the Face:

o Many of the skeletal structures in the head are unusual in that they are formed from _______ rather than from mesoderm, as they are in the rest of the body.

o The frontal bone is derived from _________.

Answer 54

neural crest cells

ectoderm

Question 55

* Development of the Ear:

o The ear is a composite structure with multiple embryonic origins.

o The external and middle ears arise from the ___________ and the ______________

Answer 55

first and second pharyngeal arches

intervening pharyngeal cleft, membrane, and pouch

Question 56

Development of the Ear

o The inner ear, in contrast, develops from an ectodermal _________that appears on either side of the neural tube at the level of the future caudal hindbrain.

Answer 56

otic placode

Question 57

* Development of the Eye:

o The eyes first appear early in the 4th week in the form of a pair of lateral grooves, the optic sulci, which evaginate from the forebrain neural groove to form the __________.

Answer 57

optic vesicles

Question 58

Development of the Eye:

o As soon as the distal tip of the optic vesicle reaches the surface ectoderm, it invaginates, transforming the optic vesicle into a goblet-shaped ______ that is attached to the forebrain by a narrower, hollow ____. The simultaneously thickens to form a lens placode, which invaginates and pinches off to become a hollow ______.

Answer 58

optic cup

optic stalk

lens vesicle

Question 59

Development of the Eye

o The inner wall of the _____ gives rise to the ______ whereas the outer wall gives rise to the ______________.

Answer 59

optic cup

neural retina

thin, melanin-containing pigmented epithelium

Question 60

Development of the Eye

o Placode initiates change, and begins to invaginate until it closes itself off.

o Before they’re optic ____, they are placodes.

Answer 60

sulci