The autonomic nervous system controls the function of our organs and glands, and can be divided into the sympathetic and parasympathetic divisions. Sympathetic activation prepares us for fight or flight, while parasympathetic activation is associated with normal functioning under relaxed conditions. What are the implications of compromised immune function as a result of exposure to chronic stress? Hopefully, you do not face real physical threats from potential predators on a daily basis.
However, you probably have your fair share of stress. What situations are your most common sources of stress? What can you do to try to minimize the negative consequences of these particular stressors in your life? Chronic stress can lead to increased susceptibility to bacterial and viral infections, and potentially an increased risk of cancer. Ultimately, this could be a vicious cycle with stress leading to increased risk of disease, disease states leading to increased stress and so on.
Glossary autonomic nervous system controls our internal organs and glands central nervous system CNS brain and spinal cord fight or flight response activation of the sympathetic division of the autonomic nervous system, allowing access to energy reserves and heightened sensory capacity so that we might fight off a given threat or run away to safety homeostasis state of equilibrium—biological conditions, such as body temperature, are maintained at optimal levels parasympathetic nervous system associated with routine, day-to-day operations of the body peripheral nervous system PNS connects the brain and spinal cord to the muscles, organs and senses in the periphery of the body somatic nervous system relays sensory and motor information to and from the CNS sympathetic nervous system involved in stress-related activities and functions.
Skip to main content. Module 3: Biopsychology. Search for:. Parts of the Nervous System Learning Objectives By the end of this section, you will be able to: Describe the difference between the central and peripheral nervous systems Explain the difference between the somatic and autonomic nervous systems Differentiate between the sympathetic and parasympathetic divisions of the autonomic nervous system.
Answers 1. On the other hand, if activity decreases in the sympathetic fibers, the vessels will vasodilate. Another example of tonic innervation is the parasympathetic innervation of the heart. Where an autonomic neuron connects with a target, there is a synapse. The electrical signal of the action potential causes the release of a signaling molecule, which will bind to receptor proteins on the target cell. Synapses of the autonomic system are classified as either cholinergic , meaning that acetylcholine ACh is released, or adrenergic , meaning that norepinephrine is released.
The terms cholinergic and adrenergic refer not only to the signaling molecule that is released but also to the class of receptors that each binds. The cholinergic system includes two classes of receptor: the nicotinic receptor and the muscarinic receptor.
Both receptor types bind to ACh and cause changes in the target cell. The nicotinic receptor is a ligand-gated cation channel and the muscarinic receptor is a G protein—coupled receptor. The receptors are named for, and differentiated by, other molecules that bind to them. Whereas nicotine will bind to the nicotinic receptor, and muscarine will bind to the muscarinic receptor, there is no cross-reactivity between the receptors. The situation is similar to locks and keys.
Imagine two locks—one for a classroom and the other for an office—that are opened by two separate keys. The classroom key will not open the office door and the office key will not open the classroom door. This is similar to the specificity of nicotine and muscarine for their receptors. However, a master key can open multiple locks, such as a master key for the Biology Department that opens both the classroom and the office doors.
This is similar to ACh that binds to both types of receptors. The molecules that define these receptors are not crucial—they are simply tools for researchers to use in the laboratory. These molecules are exogenous , meaning that they are made outside of the human body, so a researcher can use them without any confounding endogenous results results caused by the molecules produced in the body.
Unlike cholinergic receptors, these receptor types are not classified by which drugs can bind to them. All of them are G protein—coupled receptors.
An additional aspect of the adrenergic system is that there is a second signaling molecule called epinephrine. The chemical difference between norepinephrine and epinephrine is the addition of a methyl group CH 3 in epinephrine. The term adrenergic should remind you of the word adrenaline, which is associated with the fight-or-flight response described at the beginning of the chapter.
Adrenaline and epinephrine are two names for the same molecule. Though the drug is no longer sold, the convention of referring to this molecule by the two different names persists. Similarly, norepinephrine and noradrenaline are two names for the same molecule.
Having understood the cholinergic and adrenergic systems, their role in the autonomic system is relatively simple to understand. All preganglionic fibers, both sympathetic and parasympathetic, release ACh.
All ganglionic neurons—the targets of these preganglionic fibers—have nicotinic receptors in their cell membranes. The nicotinic receptor is a ligand-gated cation channel that results in depolarization of the postsynaptic membrane. The postganglionic parasympathetic fibers also release ACh, but the receptors on their targets are muscarinic receptors, which are G protein—coupled receptors and do not exclusively cause depolarization of the postsynaptic membrane.
Postganglionic sympathetic fibers release norepinephrine, except for fibers that project to sweat glands and to blood vessels associated with skeletal muscles, which release ACh Table What are referred to here as synapses may not fit the strictest definition of synapse. Some sources will refer to the connection between a postganglionic fiber and a target effector as neuroeffector junctions; neurotransmitters, as defined above, would be called neuromodulators.
The structure of postganglionic connections are not the typical synaptic end bulb that is found at the neuromuscular junction, but rather are chains of swellings along the length of a postganglionic fiber called a varicosity Figure When students learn about the sympathetic system and the fight-or-flight response, they often stop and wonder about other responses.
If you were faced with a lioness running toward you as pictured at the beginning of this chapter, would you run or would you stand your ground? Some people would say that they would freeze and not know what to do. What about fear and paralysis in the face of a threat?
The sympathetic system is responsible for the physiological responses to emotional states. Watch this video to learn more about the nervous system. As described in this video, the nervous system has a way to deal with threats and stress that is separate from the conscious control of the somatic nervous system.
The system comes from a time when threats were about survival, but in the modern age, these responses become part of stress and anxiety. This video describes how the autonomic system is only part of the response to threats, or stressors.
What other organ system gets involved, and what part of the brain coordinates the two systems for the entire response, including epinephrine adrenaline and cortisol?
Skip to main content. Module The Autonomic Nervous System. Search for:. Compare and contrast the somatic and autonomic divisions of the PNS Describe the components of the autonomic nervous system Differentiate between the structures of the sympathetic and parasympathetic divisions in the autonomic nervous system Name the components of a visceral reflex specific to the autonomic division to which it belongs Predict the response of a target effector to autonomic input on the basis of the released signaling molecule Describe how the central nervous system coordinates and contributes to autonomic functions.
Divisions of the Autonomic Nervous System. Learning Objectives Name the components that generate the sympathetic and parasympathetic responses of the autonomic nervous system Explain the differences in output connections within the two divisions of the autonomic nervous system Describe the signaling molecules and receptor proteins involved in communication within the two divisions of the autonomic nervous system.
Interactive Link Watch this video to learn more about adrenaline and the fight-or-flight response. Sympathetic Division of the Autonomic Nervous System.
Parasympathetic Division of the Autonomic Nervous System. Dual Innervation Most effector targets of the ANS receive innervation from both the sympathetic and parasympathetic nervous systems.
Chemical Signaling in the Autonomic Nervous System. Signaling molecules can belong to two broad groups. Neurotransmitters are released at synapses, whereas hormones are released into the bloodstream. These are simplistic definitions, but they can help to clarify this point.
Acetylcholine can be considered a neurotransmitter because it is released by axons at synapses. The adrenergic system, however, presents a challenge. Postganglionic sympathetic fibers release norepinephrine, which can be considered a neurotransmitter. But the adrenal medulla releases epinephrine and norepinephrine into circulation, so they should be considered hormones.
This work by Cenveo is licensed under a Creative Commons Attribution 3. Everyday Connections: Fight or Flight? What About Fright and Freeze? The concept of homeostasis and the functioning of the sympathetic system had been introduced in France in the previous century. Cannon expanded the idea, and introduced the idea that an animal responds to a threat by preparing to stand and fight or run away. The nature of this response was thoroughly explained in a book on the physiology of pain, hunger, fear, and rage.
The functions of the ANS are involuntary and reflexive, e. The parasympathetic and sympathetic nervous systems, along with the enteric nervous system make up the ANS.
The parasympathetic nervous system is part of the autonomic nervous system. It originates in the spinal cord and the medulla and controls homeostasis, or the maintenance of the body's systems.
The parasympathetic nervous system controls the "rest and digest" functions of the body. The sympathetic nervous system, also part of the autonomic nervous system, originates in the spinal cord; specifically in the thoracic and lumbar regions. It controls the body's "fight or flight" responses, or how the body reacts to perceived danger. With sympathetic nervous responses , the body speeds up, tenses up and becomes more alert.
Functions that are not essential for survival are shut down. Following are the specific reactions of sympathetic nervous system:. The parasympathetic nervous system counterbalances the sympathetic nervous system. It restores the body to a state of calm. The specific responses are:. The parasympathetic nervous system is a slower system and moves along longer pathways. Preganglionic fibers from the medulla or spinal cord project ganglia close to the target organ.
They create a synapse, which eventually creates the desired response.
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