The body is an interconnected, somewhat overlapping, grouping of systems, each having its own part to play in maintaining optimal function.

Regulatory Functions The first of the functional systems we will look at are those that perform a regulatory role, the nervous and endocrine systems.

Nervous System Neural cells are "excitable," that is, they can pass an electric charge when properly stimulated. They cannot divide or replicate, therefore the neural cells the puppy is born with are the same ones that it later dies with minus the ones lost along the way through trauma and normal aging processes. The nervous system performs three general functions: motor activity (muscle activation, glandular secretion), sensory functions (conscious and unconscious) and association functions (neural activity within the brain).

The loss of sensory function, as the brain ages, correlates directly with the loss of neural cells. As age reduces the brain's effectiveness, reduced sensory perception is inevitable: perception of sight, smell, hearing and taste fades. The brain runs on glucose for fuel--in a study of aging Beagles, the frontal area of the cerebral cortex utilization rate for glucose declines by 50% from three years of age to fourteen years of age.vi Not only does the ability of the central nervous system to receive and handle input decrease over time, but also the sensory organs, themselves, become less capable. We will take a look at progressive degenerative (aging) failure of the sensory organs:

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