NERVOUS SYSTEM 2

I.  MYELINATION OF AXONS

-- Myelination = process of wrapping an axon with myelin

-- myelination procedure in PNS:

1.  Neurolemmocyte wraps around a portion of an axon successively

2.  cytoplasm and nucleus of neurolemmocyte gets “squeezed” to the outside

3.  inner successive layers of cell membrane make up the myelin sheath

 

 

 

 

-- Neurolemmocytes separated by neurofibril nodes (nodes of Ranvier)

–  In CNS, one oligodendrocyte myelinates portions of many axons

II.   DEMYELINATION DISORDERS
–  a group of different disorders that destroy myelin

–  some demyelination disorders:

1. heavy metal poisoning

2. diptheria

3. multiple sclerosis

III.  NERVOUS SYSTEM DEVELOPMENT
-- beginning of 3rd week: cells differente:

develop into disc w/ 3 primary germ layers:

1.  Ectoderm:

 

 

2.  Mesoderm:

 

 

3.  Endoderm:

 

 

* primary germ layers: earliest structures from which all tissues develop

 

-- nervous system formed from ectoderm

-- 3rd week:

* neural plate

 

 

 

* neural groove

 

 

 

* neural folds

-- end of 3rd week - 4th week: neural folds fuse, forming a neural tube

Neural Tube Defects (NTDs):

1. Spina bifida

2. anencephaly

-- as neural tube is forming, some ectodermal cells detach
* neural crest cells

IV.  DEVELOPMENT OF BRAIN
--  4th week: cranial part of neural tube develops into 3 primary vesicles (you don’t need to know the names of these primary vesicles)

--  5th week: 3 primary vesicles differentiate into 5 secondary vesicles:

1.  Telencephalon: cerebrum

2.  Diencephalon: thalamus, hypothalamus, epithalamus

3.  mesencephalon: midbrain

4.  Metencephalon: cerebellum & pons

5.  Myelencephalon: medulla oblongata

-- space inside neural tube becomes:
* ventricles
* cerebral aqueduct
* central canal

V.   SPINAL CORD DEVELOPMENT

-- caudal part of the neural tube gives rise to the spinal cord

--  posterior bulging parts of neural tube form the alar plates
-- anterior bulging parts of neural tube form the basal plates

-- basal plates —> anterior (ventral) horns, lateral horns, and anterior ½ of gray commissure

 

* horns contain cell bodies of motor neurons

-- alar plates —> posterior (dorsal) horns and posterior ½ of gray commissure

* axons of sensory neurons in posterior horns
* cell bodies of interneurons

This secondary vesicle will form the medulla oblongata:

a. Telencephalon

b. Diencephalon 

c. Mesencephalon

d. Metencephalon 

e. Myelencephalon

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