Stress (physiology)
Encyclopedia
Physiological stress represents a wide range of physical responses that occur as a direct effect of a stressor
causing an upset in the homeostasis
of the body. Upon immediate disruption of either psychological or physical equilibrium the body responds by stimulating the nervous
, endocrine, and immune systems. The reaction of these systems causes a number of physical changes that have both short and long term effects on the body.
(PNS) consists of two subsystems: the sensory-somatic nervous system and the autonomic nervous system
. When a physical stressor acts upon the body the sensory-somatic nervous system is triggered through stimulation of the body's sensory nerves
. The signal acts as a nerve impulse and travels through the body in a process of electrical cell-to-cell communication until it reaches the automatic nervous system. Activation of the automatic nervous system immediately triggers a series of involuntary chemical responses throughout the body. Preganglionic neurons release the neurotransmitter acetylcholine(ACh). This stimulates postganglionic neurons which release noradrenaline. The noradrenaline flows directly into the bloodstream ensuring that all cells in the body's nervous and endocrine systems have been activated even in areas which the ganclionic neurons are unable to reach.
(CNS) is made up of the brain and the spinal cord. The brain is equipped to process stress in three main areas: the amygdala
, the hippocampus
, and the prefrontal cortex
. Each of these areas is densely packed with stress corticosteroid receptors which process the intensity of physical and psychological stressors acting upon the body through a process of hormone reception. The mineralocorticoid receptors (MR) make up the majority of stress corticosteroid receptors and have an extremely high affinity for cortisol
. This means that they are at least partially stimulated at all times and therefore are entirely activated almost immediately when a true stressor is disrupting the homeostasis of the body. The second type of receptor, glucocorticoid receptors (GR), have a low affinity for cortisol and only begin to become activated as the sensation of stress reaches its peak intensity on the brain.
Stress dramatically reduces the ability of the blood brain barrier (BBB) to block the transfer of chemicals including hormones from entering the brain from the bloodstream. Therefore when corticosteroids are released into the bloodstream – they are immediately able to penetrate the brain and bind to first the MR and then the GR. As the GR begin to become activated, neurons in the amygdala, hippocampus, and prefrontal cortex become over stimulated. This stimulation of the neurons triggers a fight-or-flight response
which allows the brain to quickly process information and therefore deal with life threatening situations.
If the stress response continues and becomes chronic, the hyperactivity of the neurons begins to physically change the brain and have severe damaging effects on one's mental health. As the neurons begin to become stimulated, calcium is released through channels in their cell membranes. Although initially this allows the cells chemical signals to continue to fire, allowing nerve cells to remain stimulated, if this continues the cells will become overloaded with calcium leading to over-firing of neuron signals. The over-firing of the neurons is seen to the brain as a dangerous malfunction; therefore, triggering the cells to shut down to avoid death due to over stimulation.
Decline in both neuroplasticity
and long term potentiation (LTP) occurs in humans after experiencing levels of high continual stress. To maintain homeostasis the brain is continuously forming new neural connections, reorganizing its neural pathways, and working to fix damages caused by injury and disease. This keeps the brain vital and able to perform cognitive complex thinking. When the brain receives a distress signal it immediately begins to go into overdrive. Neural pathways begin to fire and rewire at hyper-speed to help the brain understand how to handle the task at hand. Often, the brain becomes so intently focused on this one task that it is unable to comprehend, learn, or cognitively understand any other sensory information that is being thrown at it during this time. This over stimulation in specific areas and extreme lack of use in others causes several physiological changes in the brain to take place which overall reduce or even destroy the neuroplasticity of the brain. Dendritic spines found of the dendrite
of neurons begin to disappear and many dendrites become shorter and even less complex in structure. Glia cells begin to atrophy and neurogenesis
often ceases completely. Without neuroplasticity, the brain loses the ability to form new connections and process new sensory information. Connections between neurons become so weak that it becomes nearly impossible for the brain to effectively encode long term memories; therefore, the LTP of the hippocampus declines dramatically.
is triggered by the release of the neurotransmitter, noradreniline, by the automatic nervous system. Noradreniline stimulates the Hypothalamo-Pituitary-Adrenal (HPA) axis which processes the information about the stressor in the hypothalamus
. This quickly signals the pituitary gland
and finally triggers the adrenal cortex
. The adrenal cortex responds by signaling the release of the corticosteroids cortisol
and corticotropin releasing hormone (CRH) directly into the bloodstream.
are T-cells found in the form of T-helper and T-suppressor cells. Cortisol, once released into the bloodstream, immediately begins to cause division of T-Suppressor cells. This rapid cell division increases the number of T-Suppressor cells while at the same time suppressing T-helper cells. This reduces immune protection and leaves the body vulnerable to disease and infection.
Stressor
Stressor is a chemical or biological agent, environmental condition, an external stimulus or an event that causes stress to an organism. An event that triggers the stress response may include for example:...
causing an upset in the homeostasis
Homeostasis
Homeostasis is the property of a system that regulates its internal environment and tends to maintain a stable, constant condition of properties like temperature or pH...
of the body. Upon immediate disruption of either psychological or physical equilibrium the body responds by stimulating the nervous
Nervous
Nervous may refer to:* The nervous system* "Nervous" , a rockabilly/doo-wop song first recorded by Gene Summers and His Rebels in 1958* Nervous Records, a UK record label* Nervous Records , a US record label-See also:...
, endocrine, and immune systems. The reaction of these systems causes a number of physical changes that have both short and long term effects on the body.
Peripheral nervous system (PNS)
The peripheral nervous systemPeripheral nervous system
The peripheral nervous system consists of the nerves and ganglia outside of the brain and spinal cord. The main function of the PNS is to connect the central nervous system to the limbs and organs. Unlike the CNS, the PNS is not protected by the bone of spine and skull, or by the blood–brain...
(PNS) consists of two subsystems: the sensory-somatic nervous system and the autonomic nervous system
Autonomic nervous system
The autonomic nervous system is the part of the peripheral nervous system that acts as a control system functioning largely below the level of consciousness, and controls visceral functions. The ANS affects heart rate, digestion, respiration rate, salivation, perspiration, diameter of the pupils,...
. When a physical stressor acts upon the body the sensory-somatic nervous system is triggered through stimulation of the body's sensory nerves
Sensory nerves
Sensory nerves are nerves that receive sensory stimuli, such as how something feels and if it is painful, smooth, rough, etc.They are made up of nerve fibers, called sensory fibers .Sensory neurons are neurons that are activated by sensory input Sensory nerves are nerves that receive sensory...
. The signal acts as a nerve impulse and travels through the body in a process of electrical cell-to-cell communication until it reaches the automatic nervous system. Activation of the automatic nervous system immediately triggers a series of involuntary chemical responses throughout the body. Preganglionic neurons release the neurotransmitter acetylcholine(ACh). This stimulates postganglionic neurons which release noradrenaline. The noradrenaline flows directly into the bloodstream ensuring that all cells in the body's nervous and endocrine systems have been activated even in areas which the ganclionic neurons are unable to reach.
Central nervous system (CNS)
The central nervous systemCentral nervous system
The central nervous system is the part of the nervous system that integrates the information that it receives from, and coordinates the activity of, all parts of the bodies of bilaterian animals—that is, all multicellular animals except sponges and radially symmetric animals such as jellyfish...
(CNS) is made up of the brain and the spinal cord. The brain is equipped to process stress in three main areas: the amygdala
Amygdala
The ' are almond-shaped groups of nuclei located deep within the medial temporal lobes of the brain in complex vertebrates, including humans. Shown in research to perform a primary role in the processing and memory of emotional reactions, the amygdalae are considered part of the limbic system.-...
, the hippocampus
Hippocampus
The hippocampus is a major component of the brains of humans and other vertebrates. It belongs to the limbic system and plays important roles in the consolidation of information from short-term memory to long-term memory and spatial navigation. Humans and other mammals have two hippocampi, one in...
, and the prefrontal cortex
Prefrontal cortex
The prefrontal cortex is the anterior part of the frontal lobes of the brain, lying in front of the motor and premotor areas.This brain region has been implicated in planning complex cognitive behaviors, personality expression, decision making and moderating correct social behavior...
. Each of these areas is densely packed with stress corticosteroid receptors which process the intensity of physical and psychological stressors acting upon the body through a process of hormone reception. The mineralocorticoid receptors (MR) make up the majority of stress corticosteroid receptors and have an extremely high affinity for cortisol
Cortisol
Cortisol is a steroid hormone, more specifically a glucocorticoid, produced by the adrenal gland. It is released in response to stress and a low level of blood glucocorticoids. Its primary functions are to increase blood sugar through gluconeogenesis; suppress the immune system; and aid in fat,...
. This means that they are at least partially stimulated at all times and therefore are entirely activated almost immediately when a true stressor is disrupting the homeostasis of the body. The second type of receptor, glucocorticoid receptors (GR), have a low affinity for cortisol and only begin to become activated as the sensation of stress reaches its peak intensity on the brain.
Stress dramatically reduces the ability of the blood brain barrier (BBB) to block the transfer of chemicals including hormones from entering the brain from the bloodstream. Therefore when corticosteroids are released into the bloodstream – they are immediately able to penetrate the brain and bind to first the MR and then the GR. As the GR begin to become activated, neurons in the amygdala, hippocampus, and prefrontal cortex become over stimulated. This stimulation of the neurons triggers a fight-or-flight response
Fight-or-flight response
The fight-or-flight response was first described by Walter Bradford Cannon....
which allows the brain to quickly process information and therefore deal with life threatening situations.
If the stress response continues and becomes chronic, the hyperactivity of the neurons begins to physically change the brain and have severe damaging effects on one's mental health. As the neurons begin to become stimulated, calcium is released through channels in their cell membranes. Although initially this allows the cells chemical signals to continue to fire, allowing nerve cells to remain stimulated, if this continues the cells will become overloaded with calcium leading to over-firing of neuron signals. The over-firing of the neurons is seen to the brain as a dangerous malfunction; therefore, triggering the cells to shut down to avoid death due to over stimulation.
Decline in both neuroplasticity
Neuroplasticity
Neuroplasticity is a non-specific neuroscience term referring to the ability of the brain and nervous system in all species to change structurally and functionally as a result of input from the environment. Plasticity occurs on a variety of levels, ranging from cellular changes involved in...
and long term potentiation (LTP) occurs in humans after experiencing levels of high continual stress. To maintain homeostasis the brain is continuously forming new neural connections, reorganizing its neural pathways, and working to fix damages caused by injury and disease. This keeps the brain vital and able to perform cognitive complex thinking. When the brain receives a distress signal it immediately begins to go into overdrive. Neural pathways begin to fire and rewire at hyper-speed to help the brain understand how to handle the task at hand. Often, the brain becomes so intently focused on this one task that it is unable to comprehend, learn, or cognitively understand any other sensory information that is being thrown at it during this time. This over stimulation in specific areas and extreme lack of use in others causes several physiological changes in the brain to take place which overall reduce or even destroy the neuroplasticity of the brain. Dendritic spines found of the dendrite
Dendrite
Dendrites are the branched projections of a neuron that act to conduct the electrochemical stimulation received from other neural cells to the cell body, or soma, of the neuron from which the dendrites project...
of neurons begin to disappear and many dendrites become shorter and even less complex in structure. Glia cells begin to atrophy and neurogenesis
Neurogenesis
Neurogenesis is the process by which neurons are generated from neural stem and progenitor cells. Most active during pre-natal development, neurogenesis is responsible for populating the growing brain with neurons. Recently neurogenesis was shown to continue in several small parts of the brain of...
often ceases completely. Without neuroplasticity, the brain loses the ability to form new connections and process new sensory information. Connections between neurons become so weak that it becomes nearly impossible for the brain to effectively encode long term memories; therefore, the LTP of the hippocampus declines dramatically.
Endocrine system
When a stressor acts upon the body, the endocrine systemEndocrine system
In physiology, the endocrine system is a system of glands, each of which secretes a type of hormone directly into the bloodstream to regulate the body. The endocrine system is in contrast to the exocrine system, which secretes its chemicals using ducts. It derives from the Greek words "endo"...
is triggered by the release of the neurotransmitter, noradreniline, by the automatic nervous system. Noradreniline stimulates the Hypothalamo-Pituitary-Adrenal (HPA) axis which processes the information about the stressor in the hypothalamus
Hypothalamus
The Hypothalamus is a portion of the brain that contains a number of small nuclei with a variety of functions...
. This quickly signals the pituitary gland
Pituitary gland
In vertebrate anatomy the pituitary gland, or hypophysis, is an endocrine gland about the size of a pea and weighing 0.5 g , in humans. It is a protrusion off the bottom of the hypothalamus at the base of the brain, and rests in a small, bony cavity covered by a dural fold...
and finally triggers the adrenal cortex
Adrenal cortex
Situated along the perimeter of the adrenal gland, the adrenal cortex mediates the stress response through the production of mineralocorticoids and glucocorticoids, including aldosterone and cortisol respectively. It is also a secondary site of androgen synthesis.-Layers:Notably, the reticularis in...
. The adrenal cortex responds by signaling the release of the corticosteroids cortisol
Cortisol
Cortisol is a steroid hormone, more specifically a glucocorticoid, produced by the adrenal gland. It is released in response to stress and a low level of blood glucocorticoids. Its primary functions are to increase blood sugar through gluconeogenesis; suppress the immune system; and aid in fat,...
and corticotropin releasing hormone (CRH) directly into the bloodstream.
Immune system
The most important aspect of the immune systemImmune system
An immune system is a system of biological structures and processes within an organism that protects against disease by identifying and killing pathogens and tumor cells. It detects a wide variety of agents, from viruses to parasitic worms, and needs to distinguish them from the organism's own...
are T-cells found in the form of T-helper and T-suppressor cells. Cortisol, once released into the bloodstream, immediately begins to cause division of T-Suppressor cells. This rapid cell division increases the number of T-Suppressor cells while at the same time suppressing T-helper cells. This reduces immune protection and leaves the body vulnerable to disease and infection.