The Central Nervous System (CNS)
The CNS is comprised of the brain (command center of the body, i.e. the body’s central computer) and spinal cord (the transmission pathway for the commands from and to the brain). The PNS has the sensory and motor divisions and contains 43 pairs of nerves: 12 pair of cranial nerves that connect with the brain and 31 pairs of spinal nerves that connect directly with the spinal cord. Spinal nerves directly supply the skeletal muscles.
The Peripheral Nervous System (PNS)
The Sensory Division
The sensory division is responsible for informing the CNS as to what is taking place within and outside the body. The neurons within this system originate in:
- Blood and lymph vessels
- Internal organs
- Special sense organs (olfactory, tactile, auditory, vision, gustatory)
- The skin
- Muscles and tendons
The neurons within this division end either in the spinal cord or brain and provide a continuous update as to the body’s changing status. The sensory division receives information from five primary types of receptors found in the sensory neurons:
Mechanoreceptors which respond to mechanical forces (pressure, touch, vibrations, stretch)
Thermoreceptors which respond to temperature changes
Nocireceptors respond to pain
Photoreceptors respond to electromagnetic radiation (light) for vision
Chemoreceptors respond to chemical stimuli (food, odors, and changes in blood concentrations of oxygen, carbon dioxide, and electrolytes).
A number of these receptors are valuable in exercise, sport, and activities of daily living performances. Examples are free nerve endings detecting:
- crude touch
- pressure
- pain
- heat and cold
These nerve endings are valuable for preventing injury during any type of performance.
Additionally, there are numerous specialized muscle and joint nerve endings which are each sensitive to a specific stimulus. These are:
Joint kinesthetic receptors located in joint capsules which are sensitive to joint angles and rates of change in these angles (these receptors sense position and any movement in the joint being monitored)
Muscle spindles – sense of muscle lengthening (stretch)
Golgi Tendon Organ – senses pressure within the tendon when the muscles contracts (force production/strength of contraction)
The Motor Division
The motor (efferent) division of your PNS is responsible for sending information from the CNS to the various parts of the body in response to the signals coming in from the sensory division. Once your CNS has processed the afferent (incoming) information it receives from the sensory division, it decides how the body should respond to a particular input. This information, from the brain and spinal cord, is sent via the intricate networks of neurons to all parts of the body, providing detailed instructions to the specified/target areas, i.e. the various muscles for a particular system. The motor division consists of two sections: the autonomic nervous system and the somatic nervous system (Willmore and Costill, 2004).
Autonomic Nervous System (ANS)
The autonomic nervous system controls the body’s involuntary internal functions. Those internal functions in this system that are important in physical activity are:
- Blood pressure
- Blood distribution
- Respiration
The ANS has two major divisions: the sympathetic nervous system and the parasympathetic nervous system. Each originates from different sections of the spinal cord and base of the brain. While the functions of each are often antagonistic, both systems always function simultaneously.
The Sympathetic Nervous System (SNS)
Called the “fight or flight” system, it prepares your body to face any crisis. The effects of this system for any performance include:
- Heart rate and strength of cardiac contractions
- Coronary vessel dilation (increased blood flow to heart to meet increased demands)
- Peripheral vasodilation (blood flow increase to muscles)
- Vasoconstriction (blood flow decreased to most other tissues to meet increased blood demand in working muscles)
- Increased blood pressure (increased perfusion of muscles and improved return of venous blood to heart)
- Bronchodilation (increased gas exchange)
- Increased metabolic rate (increase capacity to perform work, i.e. energy output to meet the increased demands of physical activity)
- Increased glucose release from liver into blood (increased energy source)
- Energy conservation in functions not directly needed in particular activity (e.g. renal and digestive functions
- Increased mental activity (concentration, sensory stimuli)
All these basic alterations in bodily functions facilitates/improves motor response demonstrating the importance of the ANS during increased stressful situations (both emotional and physically demanding events).
The Parasympathetic Nervous System
This nervous system branch is considered the body’s housekeeping system with its primary role of carrying out such functions as digestion, urination, glandular secretion, and conservation of energy. This system is primarily active during rest and when a person is in a calm or relaxed state. The effects of the PNS tend to oppose those of the sympathetic system i.e. decreased heart rate, constriction of blood vessels, and bronchoconstriction.
