2. General Organization of the Brain


·          neuropil: dendritic trees where most synapses occur

·          left hemisphere: intellectual, rational, verbal, analytical thinking

-           dominant for language (except: prosody, inflection: right)

·          right hemisphere: emotional, non-verbal, intuitive thinking

·          axon collaterals

·          axons of the corticospinal tract decussate in medulla


Divisions of brain

1.         Telencephalon = cerebrum

neocortex: 6 layers

paleocortex, archicortex: 3 layers

basal ganglia, amygdale, claustrum, nucleus basalis of Meynert

White matter

a.         Projection fibers (ascending/descending)

b.         Commisural fibers

c.         Association fibers

2.         Diencephalon

lateral to third ventricle

a.         thalamus

with few exceptions, all pathways destined for the cortex must synapse here

b.         hypothalamus

3.         Mesencephalon = midbrain

parasympathetic divisision of III exits here

fits through tentorial notch

divided by aqueduct of Sylvius into tectum and tegmentum

SC (visual), IC (auditory)

contains nuclei: substantia nigra

4.         Metencephalon

a.         pons

connects cerebellum to brainstem

b.         cerebellum

integrates sensory information à coordinated motor response (timing, coordination, skilled movement, cognitive learning)

5.         Myelencephalon = hindbrain

a.         medulla oblongata = bulb

contains: long pathways, reticular formation (consciousness, heart rate/rhythm, breathing, etc.)

continuous with spinal cord at foramen magnum

corticobulbar pathway: cortexàcranial nerve motor nuclei in medulla



·          Longitudinal cerebral = sagittal fissure

·          Lateral = Sylvian fissure

·          Central sulcus = sulcus of Rolando

·          Parieto-occipital sulcus



·          frontal lobe (Sylvian fissure à central sulcus of Rolando)

o          precentral sulcus

o          precentral gyrus = Area 4: primary motor cortex

o          Broca’s area: 44, 45 (pars triangularis, pars opercularis)

o          Motor planning

§          Area 6: premotor cortex

§          Area 8: frontal eye fields (conjugate eye movements to contralateral side)

o          Prefrontal cortex (mores, complex intellectual functions, imagination; re-organizes in adolescents)

§          prefrontal association area

§          limbic association cortex

o          depression: associated with left frontal lobe lesions

o          mania: associated with right frontal lobe lesions

·          parietal lobe (central sulcus of Rolando à Sylvian fissure à parieto-occipital sulcus)

o          postcentral sulcus

o          postcentral gyrus = Area 3,1,2: primary somatosensory cortex (pain, temperature, touch, pressure, proprioception)

§          4 separate body representations (different submodalities kept separate)

§          pain does not require cortex (thalamus)

o          intraparietal sulcus: divides:

§          superior parietal lobule

·          Area 2,5: somatosensory agnosia

·          Area 5,7: coordinates visual and somatosensory information

§          inferior parietal lobule (agraphia, alexia)

·          Area 40 = supramarginal gyrus

·          Area 39 = angular gyrus

·          occipital lobe

o          calcarine cortex = Area 17

§          cuneus gyrus (above calcarine fissure)

§          lingual gyrus (below calcarine fissure)

o          Area 18,19: visual association areas, visual agnosias

·          temporal lobe (Sylvian fissure à parieto-occipital sulcus)

o          superior/inferior temporal sulci

o          Area 41 (transverse temporal gyri of Heschl): primary auditory cortex

o          Area 22 (Wernicke’s Area): auditory association area