ECTODERM & NEURAL CREST CELLS DERIVATIVES

Question 1

What forms from epiblast cells at the caudal end during early development?

Answer 1

Primitive streak, which gives rise to all 3 germ layers.

Question 2

Where is the primitive streak first seen?

Answer 2

At the caudal end, progressing cranially.

Question 3

What is the name of the thickening at the cephalic end of the primitive streak?

Answer 3

Henson’s node or Primitive knot

Question 4

Which two membranes lack mesoderm and why?

Answer 4

Buccopharyngeal membrane (cranial)

Cloacal membrane (caudal)
Because ectoderm and endoderm directly fuse without intervening mesoderm.

Question 5

What is the central ectoderm called?

Answer 5

Neuroectoderm (forms the neural plate → CNS)

Question 6

What is at the margin of the neuroectoderm?

Answer 6

Neural crest cells (NCCs) – often called the 4th germ layer

Question 7

Where is placodal ectoderm located and what does it form?

Answer 7

It is peripheral to the neural plate and forms:

Olfactory placode → smell

Otic placode → ear (hearing & balance)

Optic placode → retina/lens

Question 8

What are the 4 regions of ectoderm?

Answer 8

1. Neural plate ectoderm (→ CNS)
2. Neural crest ectoderm (→ PNS + many other structures)
3. Placodal ectoderm (→ sense organs)
4. Surface ectoderm (→ skin, lens, anterior pituitary, etc.)

Question 9

In a transverse section of the embryo, which cavity is located dorsally?

Answer 9

Amniotic cavity (AC)

Question 10

In a transverse section, which cavity lies ventrally?

Answer 10

Yolk sac cavity (YSC)

Question 11

What is the order of germ layers post-gastrulation from dorsal to ventral?

Answer 11

1. Ectoderm (dorsal)
2. Mesoderm (middle)
3. Endoderm (ventral)

Question 12

What is the axial mesoderm called?

Answer 12

Notochord

Question 13

What is the role of the notochord in neural development?

Answer 13

It stimulates overlying ectoderm to become neural ectoderm (→ neural plate → neural tube → CNS)

Question 14

Where is the neural ectoderm located?

Answer 14

Midline central ectoderm (forms neural plate → CNS)

Question 15

Where is the surface ectoderm located?

Answer 15

At the periphery on both sides of the neural ectoderm

Question 16

Where are neural crest cells (NCCs) found?

Answer 16

Between neural ectoderm and surface ectoderm

Question 17

What is the origin of neural crest cells?

Answer 17

Epiblast cells (considered 4th germ layer, earlier thought to be from neuroectoderm)

Question 18

Neural crest cells contribute to the formation of which part of the nervous system?

Answer 18

Peripheral nervous system (PNS) → ganglia, Schwann cells, etc.

Question 19

What does the neuroectoderm form?

Answer 19

Central nervous system (CNS) → brain & spinal cord via neural plate → neural tube

Question 20

What is primary mesenchyme and what forms it?

Answer 20

Formed from mesoderm (mesoblast)
Function: Forms muscles of pharyngeal arches, e.g., masseter

Question 21

What is secondary mesenchyme and what forms it?

Answer 21

Formed from neural crest cells
Function: Forms bones of pharyngeal arches, aorticopulmonary septum

Question 22

What major cardiovascular structure is formed by neural crest cells?

Answer 22

Aorticopulmonary septum (defects → Transposition of Great Arteries)

Question 23

What happens in DiGeorge Syndrome related to neural crest cells?

Answer 23

Failure of NCC migration to head & neck →

Skull & facial defects (e.g., hypognathia)

Pharyngeal arch bone defects

Aorticopulmonary septum defects (MC cause of death)

Question 24

Which ganglia are derived from neural crest cells?

Answer 24

Cranial nerve ganglia

Dorsal root ganglia

Sympathetic chain ganglia

Preaortic (prevertebral) ganglia

Enteric ganglia (Auerbach & Meissner plexuses)

Celiac ganglia

Question 25

What are the enteric ganglia and what is their origin?

Answer 25

Auerbach's (myenteric) and Meissner's (submucosal) ganglia from neural crest cells

Question 26

What causes Hirschsprung disease?

Answer 26

Failure of NCC migration to distal colon, causing aganglionic colon → Megacolon

Question 27

What part of the adrenal gland is derived from neural crest?

Answer 27

Adrenal medulla (sympathetic chromaffin cells)

Question 28

Which head and neck structures are NCC derivatives?

Answer 28

Pharyngeal arch cartilages Craniofacial bones (dermal bones) Dermis of head and neck Odontoblasts (dentin-producing cells of teeth)

Question 29

Neural crest contributes to which components of the eye?

Answer 29

Most mesenchyme of eyeball (secondary mesoderm from NCC) Corneal stroma and endothelium Sclera Choroid

Question 30

What are the eye components formed by surface ectoderm?

Answer 30

Lens Corneal epithelium (1st layer)

Question 31

Which structure separates truncus arteriosus into aorta & pulmonary trunk and what is its origin?

Answer 31

Conotruncal (aorticopulmonary) septum, formed by NCCs

Question 32

Which bones in the skull are formed by neural crest cells?

Answer 32

Anterior-lateral skull bones (via secondary mesoderm) Occipital bone from primary mesoderm, not NCC

Question 33

Name pharyngeal arch bones derived from NCCs.

Answer 33

Malleus Incus Stapes Mandible Hyoid bone

Question 34

Are pharyngeal arch muscles derived from NCCs?

Answer 34

❌ No! → Formed from mesoderm

Question 35

What forms the dentin of the teeth?

Answer 35

Odontoblasts from NCCs

Question 36

What forms enamel of the teeth?

Answer 36

Ameloblasts from surface ectoderm

Question 37

What dermal tissue is derived from neural crest cells?

Answer 37

Dermis of head and neck

Question 38

Surface ectoderm gives rise to which skin structures?

Answer 38

Skin epithelium Sweat glands Sebaceous glands Myoepithelial cells of skin

Question 39

What glands develop from surface ectoderm?

Answer 39

Salivary glands: Parotid, Submandibular, Sublingual Mammary glands

Question 40

What parts of the oral and anal cavity come from surface ectoderm?

Answer 40

Stomodeum (primitive mouth/oral opening) Proctodeum (primitive anal pit)

Question 41

Which part of the pituitary develops from surface ectoderm?

Answer 41

Rathke’s pouch → Anterior Pituitary (Adenohypophysis)

Question 42

Which part of the eye is formed by surface ectoderm?

Answer 42

Lens Corneal epithelium (outermost layer)

Question 43

What are the derivatives of neural plate ectoderm?

Answer 43

CNS (Brain + Spinal Cord) Retina Iris muscles (→ Dilator pupillae & Sphincter pupillae) Neurohypophysis (Posterior Pituitary, an extension of diencephalon)

Question 44

What is the embryological origin of the iris muscles?

Answer 44

Neural plate ectoderm (ONLY skeletal muscles of ectodermal origin!)

Question 45

What part of the brain gives rise to the neurohypophysis?

Answer 45

Diencephalon (as an outgrowth) → Posterior pituitary

Question 46

Q: All are derivatives of ectoderm EXCEPT: A. Epidermis B. Parotid gland C. Neurohypophysis D. Arrector pilorum

Answer 46

✅ Answer: D. Arrector pilorum 🧾 Explanation: A, B = Surface ectoderm C = Neural plate ectoderm D = Mesenchyme (mesoderm) → smooth muscle