Body reactivity is usually understood as the body's ability to react in a proper way to influence the environment. Resistance of an

organism In biology, an organism () is any living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are classified by taxonomy into groups such as multicellular animals, plants, and ...

is its stability under the influence of pathogenic factors. The body reactivity can range from

homeostasis In biology, homeostasis (British English, British also homoeostasis) Help:IPA/English, (/hɒmɪə(ʊ)ˈsteɪsɪs/) is the state of steady internal, physics, physical, and chemistry, chemical conditions maintained by organism, living systems. Thi ...

to a

fight or flight response The fight-or-flight or the fight-flight-or-freeze response (also called hyperarousal or the acute stress response) is a physiological reaction that occurs in response to a perceived harmful event, attack, or threat to survival. It was first des ...

. Ultimately, they are all governed by the

nervous system In biology, the nervous system is the highly complex part of an animal that coordinates its actions and sensory information by transmitting signals to and from different parts of its body. The nervous system detects environmental changes th ...

Nervous system divisions

The

central nervous system The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain and spinal cord. The CNS is so named because the brain integrates the received information and coordinates and influences the activity of all par ...

(CNS) consists of parts that are encased by the bones of the skull and spinal column: the brain and spinal cord. The

peripheral nervous system The peripheral nervous system (PNS) is one of two components that make up the nervous system of bilateral animals, with the other part being the central nervous system (CNS). The PNS consists of nerves and ganglia, which lie outside the brain ...

(PNS) is found outside those bones and consists of the nerves and most of the sensory organs.

Central nervous system

The CNS can be divided into the

brain A brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as vision. It is the most complex organ in a v ...

and

spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column (backbone). The backbone encloses the central canal of the spi ...

. The CNS processes many different kinds of incoming sensory information. It is also the source of thoughts, emotions, and memories. Most signals that stimulate muscles to contract and glands to secrete originate in the CNS. The spinal cord and spinal nerves contribute to homeostasis by providing quick reflexive responses to many stimuli. The spinal cord is the pathway for sensory input to the brain and motor output from the brain. The brain is responsible for integrating most sensory information and coordinating body function, both consciously and unconsciously.

Peripheral nervous system

The PNS can be divided into the autonomic and

somatic nervous system The somatic nervous system (SNS), or voluntary nervous system is the part of the peripheral nervous system associated with the voluntary control of body movements via skeletal muscles. The somatic nervous system consists of sensory nerves carryi ...

. The autonomic nervous system can be divided into the parasympathetic, sympathetic, and enteric nervous system. The sympathetic nervous system regulates the “fight or flight” responses. The parasympathetic nervous system regulates the “rest and digest” responses. The enteric nervous system innervates the viscera (gastrointestinal tract, pancreas, and gall bladder). The somatic nervous system consists of peripheral nerve fibers that send sensory information to the central nervous system and motor nerve fibers that project to skeletal muscle. The somatic nervous system engages in voluntary reactions, and the autonomic nervous system engages in involuntary reactions.

Reactions

Fight or flight

Fight or flight is governed by the sympathetic nervous system. The sympathetic division increases automaticity and excitability of the SA node, which increases heart rate. It also increases conductivity of electrical impulses through the atrioventricular conduction system and increases the force of atrioventricular contraction. Sympathetic influence increases during inhalation.Kremer, J. M., & McMullen, W. (2010). Biopac Student Lab. Goleta: Biopac Systems, Inc..

Rest and digest

This governed by the

parasympathetic nervous system The parasympathetic nervous system (PSNS) is one of the three divisions of the autonomic nervous system, the others being the sympathetic nervous system and the enteric nervous system. The enteric nervous system is sometimes considered part of ...

. The parasympathetic division decreases automaticity and excitability, which increases heart rate. It also decreases conductivity of electrical impulses through the atrioventricular conduction system and decreases the force of atrioventricular contraction. Parasympathetic influence increases during exhalation.

Startle and orienting response

Startle response In animals, including humans, the startle response is a largely unconscious defensive response to sudden or threatening stimuli, such as sudden noise or sharp movement, and is associated with negative Affect (psychology), affect.Rammirez-Moreno, D ...

interrupts and disengages the organism from ongoing activity, directs attention to stimuli, and protects the organism from potential harmful stimuli.

Orienting response The orienting response (OR), also called ''orienting reflex'', is an organism's immediate response to a change in its environment, when that change is not sudden enough to elicit the startle response, startle reflex. The phenomenon was first descr ...

is an organism’s innate reaction to a novel stimulus, and it is a defensive response. Heart rate increases after the onset of startle stimuli. The heart rate decreases during the orienting response.

Measurement techniques for body reactivity

Electroencephalography

The

electroencephalogram Electroencephalography (EEG) is a method to record an electrogram of the spontaneous electrical activity of the brain. The biosignals detected by EEG have been shown to represent the postsynaptic potentials of pyramidal neurons in the neocortex ...

records the electrical activity on the surface of the cerebral cortex. Four simple periodic rhythms recorded in the EEG are alpha, beta, delta, and theta, which are distinguished by frequency and amplitude.

Electrocardiography

By placing electrodes on other parts of the body, the echoes of the heart’s electrical activity can be detected. The record of the electrical signal is called an electrocardiogram. The heart’s mechanical activity can be inferred from the ECG. A p wave which signifies atrial depolarization (contraction), a QRS complex which indicates ventricular depolarization, and a T wave which indicates ventricular repolarization (recovery.) Atrial repolarization would take place roughly around the QRS complex, but is hidden due to its small signal, as well as the ventricular contraction's amplitude.Associate Degree Nursing Physiology Review. (2008, August 1). Austin Community College - Start Here. Get There.. Retrieved May 2, 2013, from http://www.austincc.edu/apreview/PhysText/Cardiac.html

Electromyography

The detection, amplification, and recording of changes in skin voltage produced by underlying skeletal muscle contraction is called

electromyography Electromyography (EMG) is a technique for evaluating and recording the electrical activity produced by skeletal muscles. EMG is performed using an instrument called an electromyograph to produce a record called an electromyogram. An electromyog ...

. Motor recruitment and skeletal muscle fatigue can be examined by combining EMG and dynamometry, which measures power. Facial EMG can measure startle response in humans.

Electrodermal activity

Electrodermal activity Electrodermal activity (EDA) is the property of the human body that causes continuous variation in the electrical characteristics of the skin. Historically, EDA has also been known as skin conductance, galvanic skin response (GSR), electrodermal ...

describes changes in the skins ability to conduct electricity. EDA used to be known as the galvanic skin response, which is the combination of the changes in the galvanic skin resistance and galvanic skin potential. The polygraph measures the EDA, respiration and heart rate.

References

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