Body reactivity

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The body reactivity is usually understood as its ability to react in a proper way to influence the environment. Resistance of an organism is its stability under the influence of pathogenic factors.The body reactivity can range from homeostasis to a fight or flight response. Ultimately, they are all governed by the nervous system.

Nervous System Divisions[edit]

The central nervous system consists of parts that are encased by the bones of the skull and spinal column: the brain and spinal cord. The peripheral nervous system is found outside those bones and consists of the nerves and most of the sensory organs.[1]

Central Nervous System[edit]

The CNS can be divided into the brain and spinal cord. 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.[2] The brain is responsible for integrating most sensory information and coordinating body function, both consciously and unconsciously.[3]

Peripheral Nervous System[edit]

The PNS can be divided into the autonomic and somatic nervous system. 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.[4]

Structure[5] Sympathetic Stimulation[5] Parasympathetic Stimulation[5]
Iris (Eye Muscle) Pupil Dilation Pupil Constriction
Salivary Glands Saliva Production Reduces Saliva Production Increases
Oral/ Nasal Mucosa Mucus Production Reduced Mucus Production Increases
Heart Heart Rate and Force Increased Heart Rate and Force Decreased
Lung Bronchial Muscle Relaxed Bronchial Muscle Contracted
Stomach Peristalsis Reduced Gastric Juice Secreted, Motility Increased
Small Intestine Motility Reduced Digestion Increased
Large Intestine Motility Reduced Secretion and Motility Increased
Liver Increased Conversion of Glycogen to Glucose
Kidney Decreased Urine Secretion Increased Urine Secretion
Adrenal Medulla Norepinephrine and Epinephrine Secreted
Bladder Wall Relaxed, Sphincter Closed Wall Contracted, Sphincter Relaxed


Fight or Flight[edit]

This 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.[6]

Rest and Digest[edit]

This is governed by the parasympathetic nervous system. 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.[6]

Startle and Orienting Response[edit]

Startle response interrupts and disengages the organism from ongoing activity, directs attention to stimuli, and protects the organism from potential harmful stimuli. Orienting response is an organism’s innate reaction to a novel stimulus, and it is a defensive response.[7] Heart rate increases after the onset of startle stimuli. The heart rate decreases during the orienting response.

Measurement Techniques for Body Reactivity[edit]


The electroencephalogram 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.[6]

Rhythm[6] Typical Frequencies (Hz)[6] Typical Amplitude (µV)[6]
Alpha 8-13 20-200
Beta 13-30 5-10
Delta 20-200 20-200
Theta 10 10


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.[6] 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.[8]


The detection, amplification, and recording of changes in skin voltage produced by underlying skeletal muscle contraction is called electromyography. 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.[6]

Electrodermal Activity[edit]

Electrodermal Activity 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.[6]


  1. ^ Carlson, N. R. (2013). Structure and Functions of Cells of the Nervous System. Physiology of Behavior (Eleventh ed., p. 29). Upper Saddle River: Pearson Education, Inc..
  2. ^ Tortora, G. J., & Derrickson, B. (2012). The Spinal Cord and Spinal Nerves. Principles of Anatomy (p. 492). Hobobken: John Wiley and Sons Inc..
  3. ^ The Central Nervous System. (n.d.). Molecular and Cell Biology Home. Retrieved May 2, 2013, from
  4. ^ Tortora, G. J., & Derrickson, B. (2012). Nervous Tissue. Principles of Anatomy and Physiology (pp. 448,449). Hobobken: John Wiley and Sons Inc..
  5. ^ a b c Chudler, E. (n.d.). Neuroscience For Kids - Explore the nervous system . UW Faculty Web Server. Retrieved May 2, 2013, from
  6. ^ a b c d e f g h i Kremer, J. M., & McMullen, W. (2010). Biopac Student Lab. Goleta: Biopac Systems, Inc..
  7. ^ Phelps, B. (n.d.). Orienting Response. SpringerReference. Retrieved May 2, 2013, from
  8. ^ Associate Degree Nursing Physiology Review. (2008, August 1). Austin Community College - Start Here. Get There.. Retrieved May 2, 2013, from