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Concepts in Human Factors Engineering (Part 4 of 11)

Concepts in Human Factors Engineering (4): The Message Delivery System

by Dennis R Andrews PhD, PSP, CECD

By Dennis R Andrews PhD, PSP, CECD (ExpertPages member profile page)

The delivery system can also be called the central nervous system, which controls and regulates the human body to complete chosen tasks. Pathways are known as neurons, which transmit the body's messages. This system is required to maintain the status quo while various efforts requiring energy is used toward work. There are actually two systems one hormonal and the other is nerves. The autonomic nervous system generates the motion and regulates involuntary movement, such as breathing and blood flow. The somatic nervous system deals with mental, and skeletal muscle activities in an awareness state. The brain consists of the cerebral, anterior or frontal section, the cerebellum, the under portion of the posterior section. The brain stem (medulla) is the main highway for the transmission to and from the functioning brain. The ganglia or center brain controls semi voluntary activities such as walking. The spinal cord is the main junction box of the bundle of nerves, which branch out to their respective endings. If the spine is injured the nerves pathway will be interrupted and either a lack of function or pain sensation will occur. Internal sensors monitor information concerning the level of strength of the muscles and respond accordingly by increasing or decreasing movement of the muscle or joint. External receptors relay information system, which monitors the environment outside of the body such as sound, vision, smell, temperature and touch. The spine, which consists of the cervical, thoracic, lumbar and sacral sections of the spine, has nerves, which monitor specific parts of the body. A typical neuron consists of a soma, axon, snyapses and dendrites. The soma is the central body of the neuron the long extension is the axon and the branching from the soma is the dendrite. The neuron has up to several hundred dendrites, which receive signals from axons. Snyapses are similar to bulbs or clubs, which contained a substance, which transmit signals. The velocity of the nerve impulses is a constant for each nerve fiber and ranges from .5 m/s to about 150 m/s. Velocity is faster in a thick fiber than in a thin one.

Concepts in Human Factors Engineering is a series containing eleven articles:
  1. An Overview of Anthropomorphic Data Gathering
  2. The Fragile Skeletal System
  3. The Energy Force of Our Frame
  4. The Message Delivery System
  5. The Body as a Machine
  6. The Oxygen Machine
  7. The Body’s Transportation System
  8. Human Body Energy
  9. A Hot Workplace
  10. The Rhythm of Working
  11. The Bionic Worker of the Future
The spinal cord is where certain actions mainly relating to the limbs are centered and coordinated. The reflex usually begins with a stimulation of a sensor receptor such as touch. A reaction of the muscle can be executed in a few milliseconds after the stimulus was received, since no time consuming higher brain function is necessary. This understanding is crucial when attempting to determine perception and reaction times for various hazardous reactions. Some muscle movements, which require a higher brain involvement, will require much more reaction time. Reactions which require more information during the perception phase are considered discriminatory perception and can greatly increase the time from first identifying a hazard to completing the appropriate reaction. This function is extremely important pertaining to motor vehicle operation and dangerous machinery. If the nerve is damaged or temporarily impaired reaction time could be considerably different. If the nerve transmits a signal to innervate the muscle the reaction may be performed after the reason of the intervation is reached. It is crucial that sensory nerves are not impaired since immediate danger and injury can occur. If the sensory nerves of touch are impaired, the reaction of moving one's hand from a hot surface could be seriously delayed and be a secondary cause of a severe burn. Whiplash syndrome is a serious problem in the United States, which causes nerve damage or radiculopathy. To date the exact mechanism on whiplash injury is still unknown flexion and extension is considered the leading cause but the threshold force of injury are still in question. Carpal tunnel syndrome or CTS has become well known with the increased usage of computers. The problem is at a point where the carpal media nerve is pinched due to the constant use of the computer keyboard. Within the last few years computer keyboards have been more ergonomic friendly than in the past. CTS occur with any constant or static movement within the hand/wrist complex. Proper alignment of the body part and joint section is necessary to help eliminate CTS. Surprisingly restraint systems such as seatbelts and airbags have been known to contribute to increase the severity of whiplash.

In summary the body controls muscle function through various sensors. The sensors are crucial to guard against injury and to perform selected tasks properly and safely. Feedback through the central nervous system is of paramount importance when considering perception and reaction times and movements. Feedback and feedforward signals are transmitted along the nervous system through neurons, which act as a message center. Signal strength is also of importance when life-threatening hazards are possible.

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