External Surface Features
The surface of the cerebrum displays a series of convolutions; the ridges are called gyri (gyrus) and the grooves are called fissures or sulci (sulcus). The surface of the cerebellum also displays a series of convolutions, but the ridges or folds are called folia. The purpose of these gyri/fissures is to increase surface area of the brain. Fissures tend to be deeper and act to separate lobes and hemispheres. For example, the cerebrum and cerebellum are separated by the transverse fissure and the longitudinal fissure acts to separate the 2 cerebral hemispheres. In situ the longitudinal and transverse fissures contain folds of the tough dura mater; this functions to stabilize the brain.
Brain Blood Flow
Blood flow to the brain is mainly supplied via the Internal Carotid and Vertebral Arteries . Venous return from the head to the heart is from the Internal Jugular vein . The brain consumes ~ 20% of the O2 and glucose used even at rest. Neurons synthesize ATP almost exclusively from glucose reactions that use O2. No glucose is stored in the brain and thus must be continuously supplied . Low blood glucose to the brain results in mental confusion, dizziness, convulsions, and loss of consciousness in some cases. Increased activity of neurons and neuroglia increases blood flow to that area of the brain. An interruption in blood flow for 1-2 minutes impairs neurological function and no blood flow for ~ 4 minutes results in permanent injury.
Blood-Brain Barrier (BBB)
This barrier protects the brain cells from harmful substances and pathogens by preventing passage of many substances from blood to brain tissue. The BBB consists of tight junctions that seal together the endothelial (layer of simple squamous epithelium that lines the cavities of the heart, blood vessels, and lymphatic vessels) cells of the brain capillaries. The processes of astrocytes press up against the capillaries and secrete chemicals that maintain the permeability characteristics of the tight junctions. Trauma, certain toxins, and inflammation can cause a break- down of the BBB.
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