Ectodermal Differentiation

Ectoderm

1. Ectoderm covers the surface of the embryo and will form:

   1. Nervous system

   2. Major sense organs (nose, eyes, taste buds, ears, lateral line, electrosensory systems)

   3. Integument

1. Nervous system

1. After the neural folds close, the following develop:

   1. Prosencephalon (forebrain)

   2. Mesencephalon (Midbrain)

   3. Rhombencephalon (Hindbrain)

   4. Early Spinal Cord

   5. Cerebrospinal fluid (CSF) fills the cavities (provides nutrients, takes away wastes, etc.)

1. Prosencephalon

1. Divisions of the Prosencephalon

   1. Telencephalon

      1. Olfactory Nerves (cranial nerve I)

      2. Olfactory Bulbs

      3. Cerebral Hemispheres (higher thought)

      4. Left & Right Lateral Ventricles (cavities)

   2. Diencephalon

      1. Optic Nerves (cranial nerve II)

      2. Optic Structures (cover later)

      3. Epithalamus - [from the roof] (produces CSF)

      4. Thalamus (relay station)

      5. Hypothalamus (forms infundibulum and portion of pituitary

      6. Third Ventricle (cavity)

1. Mesencephalon

1. 1. Oculomotor Nerve (cranial nerve III)

   2. Trochlear Nerve (cranial nerve IV)

   3. Optic Lobes

   4. Aqueduct of Sylvius 

   5. Corpora Quadrigemina (centers for optic and auditory reflexes)

1. Rhombencephalon

1. Divisions of the Rhombencephalon

   1. Metencephalon

      1. Cerebellum (balance)

   2. Myelencephalon

      1. Cranial Nerves (V-X) - shark

      2. Cranial Nerves (V-XII) - higher vertebrates

      3. Medulla Oblongata - (breathing and heartbeat)

      4. Fourth Ventricle (cavity)

      5. Posterior Choroid Plexus - Produces cerebrospinal fluid

      6. Fourth Ventricle (Rhombocoel) coel = cavity

Placode

thickened disc of ectoderm that gives rise to some sense organs and nerves

Early eye development

1. Optic Vesicle - Outpocketing of Diencephalon

2. Optic Cup - Optic Vesicle inpockets and forms two layers of the retina: 

   1. Inner neural area of retina (rods and cones)

   2. Outer pigmented area of retina

3. Optic Stalk - Connects eye to brain

Lens Placode

1. Lens Placode invaginates and becomes the Lens Cup

2. Lens Cup pinches away from ectoderm and becomes the Lens Vesicle

3. Space within the Lens Vesicle (Lenticoel) develops

Nasal Placode

1. Nasal (Olfactory) Placode - Anterior to part of the telencephalon, an area of the ectoderm thickens to form the placode

2. Nasal Pit - Invagination of nasal placode

3. Beginning of sensory nasal area

1. Otic (Ear) Vesicle

1. Otic Placode - In the rhombencephalon, an area of the ectoderm thickens to form the placode

2. Otic Vesicle - Invagination of the otic placode

3. Otic Vesicle then pinches off

4. Otocoel - Space inside Otic Vesicle

1. Visceral Arches

1. Visceral Arch - Pieces of cartilages or bones that support the pharyngeal region (throat and neck) of vertebrates. They also help attach the jaws to the skull

2. Numbered 1-7

   1. Mandibular Arch (1st) - lower jaw

   2. Hyoid Arch (2nd) - important for base of tongue

   3. Branchial Arches (3rd-7th) - gills

1. Primitive and Early Blood Vessels

1. One Atrium and one Ventricle in Heart

2. Sinus Venosus - Leads into Atrium

3. Ventral Aorta - Leads away from Ventricle

4. Aortic Arches - Link Ventral to Dorsal aorta (numbers 1-6)

5. Dorsal Aorta runs anteriorly and posteriorly

Caudal Artery - In tail; continues from Dorsal Aorta

1. Cardinal Veins

1. Anterior Cardinal Vein comes from the head to join the Posterior Cardinal Vein

2. Duct of Cuvier - Joining of Anterior and Posterior Cardinal Veins (also called the Common Cardinal Vein)

3. Caudal Vein - In the tail region; Leads into the Posterior Cardinal Vein

1. Stomodeum Development

1. Development of the Stomodeum (developing mouth):

   1. Endodermal evagination

   2. Ectodermal invagination

   3. Oral plate is a meeting of endoderm and ectoderm (made of two layers)

1. Stomodeum Development

1. Rathke’s Pouch

   1. Found above the stomodeum and under the prosencephalon

   2. Ectoderm invaginates to form a pocket and becomes anterior lobe of the pituitary (adenohypophysis)

Proctodeum Development

1. Development of the Proctodeum (developing cloaca) in the hindgut:

   1. Endodermal evagination

   2. Ectodermal invagination

   3. Meeting of endoderm and ectoderm

   4. Cloacal membrane, which separates Proctodeum from archenteron (early gut) disintegrates, forming the cloaca