OVERVIEW OF THENERVOUS SYSTEM


Brief Overview of Neuroembryology


The neural tube (and thus the central nervous system) forms entirely from ectoderm. (Recall that the three layers of the developing embryo are ectoderm, mesoderm, and endoderm.)

A longitudinal neural groove forms in the ectoderm, which gets deeper and deeper.

The edges of the groove fuse and the resulting neural tube detaches: this is the separation of neural ectoderm from surface ectoderm. (The former is now deep to the latter.)

The telencephalon gives rise to the 2 cerebral hemispheres, which are comprised of:

Recall grey vs. white matter:

The diencephalon gives rise to:

The mesencephalon (midbrain) gives rise to:

The metencephalon gives rise to:

The myelencephalon gives rise to the medulla (full name: medulla oblongata.)

General CNS Anatomy


Deep to the cerebrum is the brainstem, which consists of:

Four important landmarks of the cerebral hemispheres that allow us to divide the cerebral hemisphere into lobes:

  1. lateral sulcus (sulcus = trench, often discontinuous)
  2. central sulcus
  3. preoccipital notch, a depression more visible from the medial aspect than the lateral aspect
  4. parieto-occipital sulcus, best visible from the medial aspect of the hemisphere

BRAIN FACTS

The lobes are named according to what bone of the skull they lie under and are bounded by the above landmarks:

More landmarks of the cerebrum:

Other aspects of the frontal lobe:

Other aspects of the temporal lobe:

Collectively, these two gyri are called the inferior parietal lobule:

Important Brodmann's areas:

Origin of the cranial nerves -- they come off in numerical order, front to back, and VI-XII form a kind of circle.

  1. olfactory -- passes through the olfactory tract to the olfactory bulb, and terminates in the olfactory epithelium
  2. optic -- passes through the optic tract to the optic chiasm, where some of the fibers cross to the contralateral side, then continues to the retina
  3. oculomotor -- originates from the mesencephalon
  4. trochlear -- originates from the dorsal mesencephalon
  5. trigeminal -- originates at mid-pontine level
  6. abducens -- originates at the junction of the pons and medulla
  7. facial -- originates at the cerebellopontine angle
  8. vestibulocochlear -- originates just caudal to VII
  9. glossopharyngeal -- originates in the medulla, just caudal to VIII
  10. vagus -- originates just caudal to IX
  11. accessory -- originates from the medulla and spinal cord just caudal to X
  12. hypoglossal -- originates from the medulla in a series of rootlets, between the medullary pyramid (medial) and the inferior olive (lateral.)

BRAIN FACTS