Discuss major changes that occurs on the neurological system associated to age. Include changes on central nervous system and peripheral nervous system.

Answer

1. Introduction

The human nervous system is an extraordinary and sophisticated framework made up of several parts which is responsible for the transmission of signals to, from and within the body. This complex system is responsible for controlling everything from the automatic systems of the body, such as heart rate and digestion, to responding to the external environment through things such as higher brain functioning, and most importantly for the psychology student, how we process and respond to information. Nerve cells or neurons are the “basic building blocks” of the nervous system which comprise a cell body, dendrites and an axon. There are estimated to be 100 billion neurons in the brain alone, and trillions of synaptic connections. The diversity and plasticity of the structure of this system is a reflection of its adaptability and capacity to process information in complex ways. The nervous system is understood to be the most crucial and intricate system of the human body. Age-related changes to the nervous system are often not striking and most will occur without the individual even realizing anything has changed. The changes are also not universal and will vary between individuals due to factors such as genetics and lifestyle, and this will be reflected in the range of different cognitive abilities of elderly people. Cognitive change in the older individual takes place over a number of years and may not be obvious in short periods of time; therefore, changes to the nervous system are deemed to be slow and incremental. These changes to the nervous system are a direct result of the changes that occur to the neurons. Some neurons die and are not replaced, this is most obvious in the substantial loss of neurons that occurs in most parts of the cerebral cortex.

1.1. Overview of the Neurological System

The adult nervous system consists of the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS is composed of the brain and the spinal cord; its purpose is to process information and to direct or coordinate activity within the body according to that information. The PNS is the communication link between the CNS and the rest of the body. It is a highly complex array of sensory and motor neurons. Sensory neurons bring information into the CNS from the various sense organs and receptors throughout the body. These sensory neurons provide the CNS with information about changes in the environment both within and around the body. Motor neurons convey information from the CNS that directs muscle activity and other changes in various organs. Efferent or motor neurons are further divided into somatic and autonomic neurons. Somatic neurons innervate skeletal muscle, and the activity of these neurons is under conscious control. Autonomic neurons innervate smooth and cardiac muscle, as well as various glands. The activity of autonomic neurons is not under conscious control, and they serve to regulate the various organ systems of the body. The relationship between the CNS and PNS is such that the PNS is like a computer terminal which enables one to enter information into the computer (CNS) or to retrieve information from it. This is much like the PNS, which is the pathway for information to and from the CNS. The study of the nervous system is very much a study of information processing. The brain is a highly specialized and integrated information-processing organ, continually being changed by experience. Therefore understanding changes at any level of the nervous system and their effects on information processing in the brain requires an understanding of the normal adult system and how information is processed within it. This understanding must include the neural mechanisms underlying changes in motor and sensory function as well as higher level cognitive function and consciousness. Given the diversity and complexity of neural function as well as the continued integration of information processing, this is a tall order. It is complicated further by the fact that neurological changes and associated decline in function is not an all or none process. Therefore understanding normal age-related changes in the nervous system effects on function and quality of life requires identification of primary versus secondary consequences of these changes. This understanding is also relevant in that it sets the stage for potential interventions to prevent or ameliorate age-related neural decline and associated functional impairments. If age-related changes in the nervous system are to be assessed, it is first necessary to define the sets of changes or the functional outcomes of changes that distinguish normal younger function from function altered by the aging process. It is beyond the scope of this chapter to address changes in neural development, or in neuroendocrine function that affect neural mechanisms. Rather, the focus is on the effects of the aging process on established neural mechanisms. This includes the effects of aging on sensory and motor systems and on neural mechanisms underlying cognition and consciousness. Visual and motor systems are special cases in that they are very much studied by the effects of aging on the function of the peripheral system. Nonetheless, changes in attributes of central neural mechanisms underlie all of these sets of changes in function. The general principles of neural changes associated with age can be put into the context of homeostatic regulation of the internal environment and higher level forms of information processing. This provides a framework for understanding how age-related changes may result in primary versus secondary effects on neural function and the overall quality of life.

1.2. Importance of Age-Related Changes

As the population ages, the healthcare system is faced with increasing numbers of patients with neurological diseases. These are often disabling conditions that have a significant impact on quality of life. The most prevalent neurological diseases in the elderly are strokes and neurodegenerative diseases, of which Parkinson’s Disease and Alzheimer’s are examples. Age is the major risk factor for both ischemic and hemorrhagic stroke. The incidence of stroke approximately doubles for each decade after the age of 55. Measures of health status, such as the ability to carry out activities of daily living, decline significantly in the 1-2 years following a stroke. With respect to Parkinson’s disease, the incidence rises exponentially from 50 years of age and is also associated with a decline in health status. These degenerative diseases contribute to increased morbidity and mortality in the elderly, and given the progressive change in the nervous system that occurs with aging, it is likely that the impact of these diseases will become even more significant in the future.

Although people expect to experience some decline in physical capability with aging, it is not commonly understood that this also applies to the neurological system. There is a natural and progressive change in the nervous system over time. The rate of change and the effects of the change are highly individual. It is important that the factors which drive these age-related changes in neurological function are understood. This will allow prevention and treatment of neurological conditions to be more appropriately tailored to the elderly, who are at highest risk of neurological disorders. It will also assist in understanding the normal effects of aging on neurological function versus the effects of disease processes. This can often be difficult to differentiate in older people.

2. Changes in the Central Nervous System (CNS)

2.1. Decline in Brain Volume

2.2. Decreased Neurotransmitter Production

2.3. Impaired Cognitive Functioning

3. Changes in the Peripheral Nervous System (PNS)

3.1. Decreased Nerve Conduction Velocity

3.2. Reduced Sensory Perception

3.3. Impaired Motor Function

4. Impact of Age-Related Neurological Changes

4.1. Increased Risk of Neurodegenerative Diseases

4.2. Higher Vulnerability to Falls and Injuries

4.3. Effect on Quality of Life

5. Strategies to Maintain Neurological Health with Age

5.1. Regular Physical Exercise

5.2. Healthy Diet and Nutrition

5.3. Mental Stimulation and Cognitive Activities

6. Conclusion