________________
36
Preksha Dhyana :
sensations into perception is complicated. While the sensation varies according to the power of stimuli, perception varies by an infinity of factors, some within the body and the others without. The state of emotion, in particular, may have a profound, and at times, decisive effect.
The R.A.S. action permits one to concentrate on a particular thought or activity, disregarding the background noises and other potential distractions. There is also a limit to the capacity of concentration of the brain in the perception of more than one thing at a time. If, for example, one attempts to hear music and read at the same time, he cancon centrate on one or the other, but not both.
In addition, a continual dialogue between the cerebral cortex and the R.A.S. keeps the higher brain awake and alert.
Protection of the Brain
The brain is the most carefully protected structure in the body. Not ony is it encased in a rigid helmet of bonethe skull-but within the skull it is wrapped in a series of three separate membranes--the medioges. The three membranes are (from the outside inward) the dura mater (hard mother), the arachnoid membrane and the pia mater (tender mother). Extensions of these three membranes similarly encase and protect the spinal cord. Cavities inside the brain--the ventricles, are filled with cerebrospinal fluid which provides a cushioning effect. B. SPINAL CORD
The spinal cord extends from the foraman magnum (opening in the base of the skull) down to the level of the second lumbar vertebral. The cord itself is suspended rather loosely in the vertebral canal. It is approximately 45 cms long and is about the thickness of a little finger. It is well-protected by the bony tube of the vertebral column, as well as the three meninges whose multiple joints provide fiexibility. From the outside the spinal cord looks white, but like the brain it contains both grey and white matier. Unlike the brain, however, the grey matter is concentrated inside.
Jain Education International
For Private & Personal Use Only
www.jainelibrary.org
