Introduction to the levels of the Nervous System

-composed of the brain and spinal cord

-composed of nuclei and tracts

-includes cerebrum, cerebellum, brainstem and spinal cord

-lies outside CNS

-composed of Ganglia and Nerves

-can be divided into Autonomic Nervous system and Somatic nervous system

groups of cell bodies

Fibers (thread like)

groups of cell bodies outside CNS

fibers outside the CNS that are in the PNS

-spinal and cranial nerves

regulation of internal body function

-self regulating system; not under our control

enables us to perceive sensory stimuli and carry on volitional motor activity

-cerebrum

---cerebral hemisphere

---Diencephalon

---cerebellum

---brainstem

-Ectoderm (outer layer)

-Mesoderm (middle layer)

-Endoderm (inner layer)

develops into brain and skin

Becomes all the connective tissues in the body, muscles, bones, tendons, etc.

becomes all the inner tubes, hearts, lung, digestive tracts, etc.

The neural plate (flat plate folds in to create fuse)

-Neural plate formed at week 3 of embryonic development

-at the end of week 3, the neural folds begin to fuse, forming the neural tube

-as the neural tube closes, it separates from the ectodermal surface

-during fusion, neural crest cells separate from the neural tube to form the PNS

-the cavity in the neural tube becomes the ventricular system of the brain

Divides into the lateral wall of the neural tube into 2 halves

-Alar plate

-Basal plate

= back

-half forms a alar plate

-sensory neurons

= front

-basal plate

-motor neurons

Prosenecephalon

Mesencephalon

Rhombencephalon

Cephalic flexure

Cervical flexure

forebrain→ cerebrum

Midbrain → mainbrain

Hindbrain → cerebellum

between prosencephalon & mesencephalon

Between rhombencephalon & spinal cord

Telencephalon

Diencephalon

Mesencephalon

Metencephalon

Myelencephalon

cerebral hemispheres

thalamus, hypothalamus

Pons, cerebellum

Medulla

divides the rhombencephalon into two parts

the walls of the neural tube spread apart (flatten out)

-the alar and basal plate come to lie on the floor of the fourth ventricle

the telencephalic tissue overlying the fusion between telencephalon & diencephalon

-becomes hidden from the view later in the development

-thickened lateral parts of the alar plate in the brainstem

-becomes the cerebellum

the cavity of the neural tube becomes the ventricular system/ 4 ventricles and canal

-2 lateral ventricles

-3rd ventricle

-4th ventricle

-central canal

in telencephalon

(=one in each hemisphere)

-in diencephalon

in metencephalon & myelencephalon (=in pons and medulla)

in the spinal cord (in the middle of the cray matter)

complete failure of the neural tube to close

-The CNS appears as an open furrow on the back of the head and body

failure of the caudal neuropore to close

a severe form of spinal bifida, in which the spinal cord and/or nerve roots protrude through the posterior defects

-often accompanied by an Arnold-Chiari malformation

the cerebellum and caudal brainstem are elongated and pushed down into the foramen magnum

often obstruction to the flow of CSF results in hydrocephalus

failure of the rostral neuropore to close

-much of each cerebral hemisphere is absent

partial or complete failure of the prosencephalon to separate into the diencephalon and the paired telencephalic vesicles

-the prosencephalon can develop abnormally even if neural tube closure is complete

Characterized by enlarged ventricles of the brain

can result from:

-increased production of cerebrospinal fluid

-decreased absorption of CSF

-blockage of CSF flow

Shunt procedure may help reverse the symptoms