DEVELOPMENT AND PROTECTION OF CNS

 

BIO21013  THE SPINAL CORD AND SPINAL NERVES

BIO21014  THE BRAIN AND CRANIAL NERVES

 

I.                Development of the CNS

a.     Cephalization

                                                    i.     evolution of brain

                                                   ii.     increased # neurons

b.     embryonic development

                                                    i.     ectoderm folds inward to form neural tube

                                                   ii.     differentiation begins

                                                 iii.     primary brain vesicles become secondary brain  vesicles

1.     forebrain

2.     midbrain

3.     hindbrain

                                                 iv.     secondary brain vesicles

1.     telencephalon

2.     diencephalon

3.     mesencephalon

4.     metencephalon

5.     myelencephlon

                                                  v.     adult brain structures develop from secondary

1.     cerebrum from telencephalon.

2.     thalamus, hypothalamus, epithalamus from diencephalons

3.     midbrain from mesencephalon.

4.     pons, cerebellum from metecephalon

5.     medulla oblongata from myelencephlon

c.     Brain Ventricles

                                                    i.     spaces within brain

                                                   ii.     lined with ependymal cells

                                                 iii.     lateral ventricles

1.     into each hemisphere ofcerebrum

2.     close anteriorly and separated by septum                           pellucidum

                                                 iv.     third ventricle

1.     in diencephalons

2.     cerebral aqueduct connects to 4th

                                                  v.     fourth ventricle

1.     two lateral apertures and median aperture connect ventricle to subarachnoid space of meninges

d.     Spinal cord

                                                    i.     passes through foramen magnum and continues to end in lumbar vertebral formamen at conus medullaris

                                                   ii.     central canal

1.     cavity within the spinal cord

2.     lined with ependymal cells

 

II.              Protection of the CNS

a.     Bones

                                                    i.     all cranial bones forming the crainial cavity

                                                   ii.     vertebra

1.     Vertebral canal

a.     formed by stacked vertebral foramen

b.     vertebral ligaments add support

b.      Meninges

                                                    i.     3 connective tissue membranes

                                                   ii.     function

1.     covers and protects CNS

2.     protects blood vessels

3.     contain cerebrospinal fluid

                                                 iii.     Dura mater

1.     tough outer layer

2.     dense connective tissue

3.     epidural space in vertebral canal

                                                 iv.     Arachnoid

1.     delicate collage fibers

2.     subarachnoid space

a.     Cerebrospinal fluid and blood vessels

                                                  v.     pia mater

1.     thin transparent membrane that clings tightly to surface of brain and spinal cord.

2.     contains collagen and elastic fibers

III.            Cerebrospinal Fluid (CSF)

a.     Liquid cushion of brain and spinal cord

                                                    i.     protects from trauma

                                                   ii.     nourishment

                                                 iii.     equivalent to blood plasma

                                                 iv.     made at choroid plexus

1.     capillary network at roof of third and fouth ventricle

                                                  v.     located in ventricles, central canal of spinal cord, and subarachnoid space

                                                 vi.     CSF must be produced and drained at constant rate

                                                vii.     returned to blood (veins) via dural sinuses

         

                   

 

IV.            Blood brain barrier

a.     helps maintain brain environment

b.     certain molecules pass freely, others do not

c.     easy pass by facilated diffusion through endothelial cells of capillaries

                                                    i.     glucose

                                                   ii.     essential amino acids

                                                 iii.     some electrolytes

d.     fat soluble cross freely

                                                    i.     oxygen

                                                   ii.     carbon dioxide

                                                 iii.     fats

                                                 iv.     alcohol

                                                  v.     nicotine

                                                 vi.     anesthetics

e.     drugs

                                                    i.     toxic in newborns due to inefficient BBB

                                                   ii.     to get drugs to crossBBB

                                                 iii.     mannitol changes osmotic pressure of endothelial cells and cells shrink to increase junction and make more permeable

                                                 iv.     antibiotics which cross are reserved to use to treat bacterial mennigitis or encephalitis