Development of the Nervous System Flashcards
When does the development of the central nervous system occur?
At the beginning of the third week
Describe the formation of the neural tube
The neural folds continue to elevate, approach each other in the midline, and finally fuse to form the neural tube
Where does fusion of the neural folds begin and how does it proceed onward?
Fusion begins in the cervical region and proceeds in cephalic and caudal directions
What are the open ends of the neural tube called?
Cranial and Caudal Neuropores
When do these neuropores close?
The cranial neuropore closes around the 25th day and the caudal neuropore closes approximately 3 days later
What is Neurulation?
Formation of the neural tube
What are the 3 dilations at the cephalic end of the neural tube?
The Primary Brain Vesicles
1) Prosenchphalon (forebrain)
2) Mesencephalon (midbrain)
3) Rhombencephalon (hindbrain)
Around the 28th day how many flexures are formed? What are they called and where are they located?
Two
1) the cervical flexure at the junction of the hindbrain and spinal cord
2) the cephalic flexure in the midbrain
When the embryo is 5 weeks old what are the two parts of the prosencephalon?
- Telencephalon
- Diencephalon
When the embryo is 5 weeks old what are the two parts of the rhombencephalon?
- Metencephalon
- Myelencephalon
What are neural crest cells?
When the neural folds fuse and elevate, they are the cells found at the lateral or crest of the neuroectoderm that begin to dissociate from their neighbors.
What 7 things do the neural crest cells give rise to?
1) spinal, cranial nerve (V, VII, IX, and X), and autonomic ganglia
2) ensheathing cells of the peripheral nervous system (Schwann cells)
3) pigment cells (melanocytes) of the skin and some muscles in the head and neck
4) some connective tissues
5) some bones of pharyngeal arch origin (pharyngeal arch cartilages)
6) suprarenal medulla
7) conduction tissue in the heart
How is a 3D embryo produced?
Folding in the Longitudinal and Horizontal Planes resulting from rapid growth of the embryo.
Growth along which plane occurs more rapidly?
The growth rate at the sides of the embryonic disc fails to keep pace with the rate of growth in the long axis
Describe folding at the cranial and caudal ends and sides of the embryo
It occurs simultaneously, resulting in a relative constriction at the junction of the embryo and umbilical vesicle (yolk sac)
Describe Head Folding
The developing forebrain grows cranially beyond the oropharyngeal membrane and overhangs the developing heart. At the same time, the septum transversum, primordial heart, pericardial coelom, and oropharyngeal membrane move onto the ventral surface of the embryo.
Describe what happens to the septum transversum after head folding
The septum transversum lies caudal to the heart where it subsequently develops into the central tendon of the diaphragm.
How is the foregut produced during head folding?
Part of the endoderm of the yolk sac is incorporated into the embryo and is called the foregut.
The foregut leads to the ______ membrane, which will breakdown to form what?
Oropharyngeal
the mouth
Describe the order of the diaphragm, heart, and mouth before and after head folding
Before the sequence is diaphragm, heart, and then mouth
After the sequence is mouth, heart, diaphragm
Folding at the caudal end of the embryo results primarily from what?
Growth of the distal part of the neural tube (the primordium of the spinal cord)
As the embryo grows caudally what does the tail region project over?
The colacal membrane, which is the future site of the anus.
During the tail fold what happens to part of the endodermal germ layer?
It is incorporated into the embryo as the hindgut
During the tail fold, the terminal part of the hindgut dilates to form what?
The colaca which will become the urinary bladder and rectum
Describe the order of the primitive streak, cloacal membrane, and allantois before and after tail folding
Before the sequence is primitive streak, cloacal membrane, and then allantois.
After the sequence is allantois, cloacal membrane, primitive streak
What is the allantois?
Vestigial structure that serves as a respiratory and waste storage organ for the embryo.
*It is a diverticulum of the umbilical vesicle
Describe what happens to the connecting stalk and allantois after the tail fold
The connecting stalk is now attached to the ventral surface of the embryo, and the allantois is partially incorporated into the embryo.
What is lateral folding produced by?
The rapidly growing spinal cord and somites.
How does lateral folding affect the amniotic cavity?
It brings the amniotic cavity around to the fron of the embryo
Describe how the embryo gets its cylindrical shape
The primordia of the ventrolateral abdominal wall fold toward the median plane, rolling the edges of the embryonic disc ventrally and forming a roughly cylindrical embryo.
How is the midgut formed?
As the abdominal walls form, part of the endoderm germ layer is incorporated into the embryo as the midgut
What is the midgut a primordium of?
small intestines and part of the colon
What 7 things does the ectoderm give rise to?
- the central and peripheral nervous systems
- sensory epithelia of the eyes, ears, and nose
- epidermis and its appendages (hair and nails)
- mammary glands
- pituitary gland
- subcutaneous glands
- enamel of teeth
Neural Crest cells are derived from what?
Neuroectoderm
What are the two pathways along which crest cells from the trunk region migrate?
1) A dorsal pathway through the dermis where they will enter the ectoderm through holes in the basal lamina to form melanocytes in the skin and hair follicles
2) A ventral pathway through anterior half of each somite to become sensory ganglia, sympathetic and enteric neurons, Schwann cells and cells of adrenal medulla.
What 2 things do the crest cells from the cranial neural folds become?
- Craniofacial skeleton
- Neurons for cranial ganglia, glial cells, melanocytes and other cell types
What 2 things do the crest cells from the bilateral ectodermal thickenings become?
- Otic placodes
- Lens placodes
What 5 things do the crest cells from the Generalized Derivatives of the Ectodermal Germ Layer become?
- Central Nervous System
- Peripheral Nervous System
- Sensory Epithelium of ear, nose and eye
- Epidermis including hair and nails
- Subcutaneous glands, mammary glands, pituitary gland, and enamel of teeth
What 10 things does the paraxial mesoderm give rise to?
- muscles of the head
- skeletal muscle trunk and limbs
- skeleton except cranium
- dermis
- connective tissue
- cartilage
- bone
- striated and smooth muscles
- blood and lymphatic vessels
- probably the spinal meninge
What 4 things does the intermediate mesoderm give rise to?
- kidneys
- ovaries
- testes
- genital ducts
What 6 things does the lateral plate mesoderm give rise to?
- serous membranes lining the body cavities
- heart
- spleen
- connective tissue and muscle of viscera
- some blood and lymphatic cells
- cortex of suprarenal glands.
What things does the endoderm give rise to?
- the epithelial lining of the digestive
- epithelial lining of the respiratory tract
- epithelial lining of the urinary bladder and most of the urethra
What are neuroblasts?
The primitive nerve cells
What do the neuroblasts form?
The mantle layer
What does the mantle layer later form?
The grey matter of the spinal cord
What is the outermost layer of the spinal cord called?
The marginal layer
What does the marginal layer contain?
Nerve fibers emerging from neuroblasts in the mantle layer
What is the marginal layer also known as?
The white matter of the spinal cord
As neuroblasts are continuously added to the mantle layer what forms?
A ventral and dorsal thickening of on each side of the neural tube
What is the basal plate?
The motor area in the ventral portion of the spinal cord
What is the alar plate?
The sensory area in the dorsal region of the spinal cord
What specifically does the alar plate become later on?
the dorsal gray matter of the spinal cord
What does the alar plate develop into?
- the sensory nuclei of cranial nerves V, VII, VIII, IX, and X
- the inferior olivary nucleus
- mesencephalic nucleus of V
- main sensory nucleus of V
- the cerebellum
What is the sulcus limitans?
The longitudinal groove that marks the boundary between the sensory input dorsally (alar plate) and the motor output ventrally (basal plate)
What are interneurons?
They are relay, or associative neurons that carry information between sensory and motor neurons
What are dermatomes?
an area of the skin supplied by a single segment of the spinal cord
What are oligodendrocytes?
They are equivalent to Schwann cells in the central nervous system
