Brain protective structure

The pituitary gland lies deep within the cranial vault, connected to the brain by the infundibular stalk (a downward extension of the floor of the third ventricle) and protected by an indentation of the sphenoid bone called the sella turcica (see Fig. 50-1). The pituitary gland, a small, gray rounded structure, has two parts ... 

An intact CNS is critical to the well-being of a person. Nature has gone to a good deal of trouble to protect the CNS from damage, both external and internal. The brain is protected from external trauma by the bony structure we call the skull. The spine is similarly protected by the bony spinal column. The CNS is also protected by the blood-brain barrier against penetration by molecules that might prove a problem. There are special facilitated transport mechanisms for specific molecules required by the CNS but which cannot penetrate the blood-brain barrier. 

On the left (A) is a profile of the human brain, and on the right, a magnified view (B) of a slice through the brain as indicated by the dotted line. The anatomy of the brain consists of two hemispheres, each covered with multiple layers of important cells known as the cerebral cortex. White matter, which consists of wiring —projections from one cell to another—lies beneath the cerebral cortex, along with some groups of cells that perform various functions. The ventricles are cavities through which runs a substance called cerebrospinal fluid, which helps protect and cushion the delicate structures of the nervous system. 

The structure of alpha-0 is designed to overcome these two restrictions. A methyl group on the oxygen (the O-methyl) removes the polarity restriction. A methyl group next to the amine function (the alpha-methyl) protects the molecule from enzymatic attack. With the two obstacles removed, this compound apparently has easy access directly to the brain. Hence, alpha,O-dimethylserotonin (a,0-DMS) goes directly into the central nervous system and has proved to be one of the most potent tryptamines yet described. And it is active following oral administration, where it is exposed to all of the body s protective machinery. 

The brain is the control center of the body. Although it comprises only 2% of the body mass by weight, it uses 16% of the resting bloods supply requiring ten times the blood flow that the rest of the body needs. Because of its importance to life it is protected from physical trauma by the bony structure of the skull on the outside and from chemical trauma by the highly selective blood-brain barrier from within. 

Because the blood-brain barrier is less well developed in immature brains, children are more susceptible to CNS toxicity from certain toxic substances, such as lead salts, than are adults. The patency of the blood-brain barrier may also become increased under conditions of disease and dehydration. Although the CNS is generally well protected from certain drugs by the blood-brain barrier, the PNS does not have a comparable structure. Therefore, it is possible to have drug effects restricted to peripheral structures only, if their entry into the CNS is excluded. 

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