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Overview of brain structure (for tutorial)

See pictures in any textbook (eg. Purves) or in Scientific American September, 1992.

See also:

Frontal, Parietal, Occipital and Temporal lobes

Forebrain = cerebral hemispheres, thalamus and hypothalamus

Midbrain = tectum and tegmentum

Hindbrain = cerebellum, pons and medulla

Brain stem = midbrain, pons and medulla

Spinal chord

Cerebral hemisphere = Cerebral cortex + lateral ventricles + white matter + basal ganglia

Cerebral cortex Top layer of grey matter comprising nerve cells, nerve fibres, blood vessels and the neuroglia (a supporting tissue). The cortex is stratified into layers of nerve cells and nerve fibres. Stratification is easily recognisable in the visual cortex or area striata. Surface area 1.6 sq.m., thickness 2 mm. (acc. Purves) (According to Crick, AH the total surface area of the left and the right sheets of the cerebral cortex ``is a bit more than that of a man's handkerchief.'' with thickness 2-5 mm.)

Of functional importance is the columnar arrangement of cells in the cortex. The columns extend from the cortical surface to the white matter inside.

Cortices of the parietal, temporal and frontal lobes account for approx. 75% of the human brain tissue. They are responsible for cognitive functions like selectively attending to a particular stimulus, recognising and identifying particular stimulus features and planning and experiencing the response. Because these cortices integrate information from other brain regions they are referred to as the association cortices - see sec. [*]. Excluded here are the sensory and motor cortices and the the occipital lobe - the latter is more exclusively concerned with vision.

Inputs to these association cortices include connections from the primary and secondary sensory and motor cortices, the thalamus and the brainstem. The signals coming to the acs via the thalamus represent highly processed sensory and motor information from multiple areas of the cerebral cortex. (In contrast, the primary sensory cortices receive thalamic info that is directly related to the peripheral sense organs while the motor cortex receives thalamic info from the basal ganglia and the cerebellum.) Outputs from the association cortices reach the hippocampus, the basal ganglia and cerebellum, the thalamus and other association cortices.

The thalamus is the main entrance to to the cortex (but not the main exit). It can be divided into about two dozen regions each of which is connected to a particular subdivision of the neocortex. Each thalamic area also receives massive back-connections from its corresponding cortical area; the function of these connections is not yet known.

Hippocampus (part of limbic system, sometimes called the allocortex) lies deep in the temporal lobe, and is concerned with emotion, sex, learning and long-term memory. ``It probably stores, for a few weeks or so, the codes for new, long-term, episodic memories before the information is conveyed to the neocortex.'' (Crick, TAH - see sec. [*])

The paleocotex is mainly concerned with smell.

Directional terms (the last equivalent applies in the brain context):

Rostral/ Anterior Head or front end
Caudal/ Posterior Tail or hind end
Dorsal Back or top side
Ventral Belly or bottom side
Lateral Away from the midline
Medial Toward the midline
Proximal closer
Distal farther away

The dorsal/ventral and anterior/posterior terminology for the human brain makes sense in the ontogeny (embryonic development) and phylogeny (evolution) context. The large cerebral cortex for the human makes the dorsal side grow disproportionately large and in the process it curves around to the top of the brain. The olfactory lobes are actually at the anterior end in the lower life forms but in higher forms they get curved around to the ventral side.

next up previous contents
Next: Brain function (selected early Up: Neuroscience Lecture 1 Previous: The reflex arc debate   Contents