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>Sympathetic Nervous system (Adrenergic)
>Parasympathetic (Cholinergic)

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-Sympathetic N.S.

Acetylcholine (ACH)-cholinergic

Norepinephrine (NE)-adrenergic

Epinephrine (EPI)-adrenergic

Dopamine (DA)

-Parasympathetic N.S.

Acetycholine (ACH)

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Sympathetic Responses

The sympathetic division of the autonomic nervous system maintains internal organ homeostasis and initiates the stress response.

Learning Objectives

Describe the sympathetic responses of the autonomic nervous system

Key Takeaways

Key Points

The fibers from the sympathetic nervous system (SNS) innervate the tissues in almost every organ system.

The SNS is best known for mediating the neuronal and hormonal response to stress known as the fight-or-flight response, also known as sympatho-adrenal response.

The catecholamine hormones adrenaline and noradrenaline are secreted by the adrenal medulla and facilitate physical activity and mobilize the body to respond to threatening environments.

The primary neurotransmitter of SNS postganglionic fibers is noradrenaline, also called norepinephrine.

Key Terms

sympathetic nervous system (SNS): One of the three parts of the autonomic nervous system, along with the enteric and parasympathetic systems. Its general action is to mobilize the body's nervous system fight-or-flight response; it is also constantly active at a basal level to maintain homeostasis.

sympatho-adrenal response: Also called the fight-or-flight response, this activates the secretion of adrenaline (epinephrine) and, to a lesser extent, noradrenaline (norepinephrine).

stress response: This halts or slows down various processes, such as sexual responses and digestive systems, to focus on the stressor situation; this usually causes negative effects like constipation, anorexia, difficulty urinating, and difficulty maintaining sexual arousal.

Examples

Physiological changes induced by the sympathetic nervous system include accelerating the heart rate, widening bronchial passages, decreasing motility of the large intestine, dilating the pupils, and causing perspiration.

Sympathetic Nervous System Physiology

Alongside the other two components of the autonomic nervous system, the sympathetic nervous system aids in the control of most of the body's internal organs. Stress-as in the hyperarousal of the flight-or-fight response-is thought to counteract the parasympathetic system, which generally works to promote maintenance of the body at rest.

The sympathetic nervous system is responsible for regulating many homeostatic mechanisms in living organisms. Fibers from the SNS innervate tissues in almost every organ system and provide physiological regulation over diverse body processes including pupil diameter, gut motility (movement), and urinary output.

The SNS is perhaps best known for mediating the neuronal and hormonal stress response commonly known as the fight-or-flight response, also known as sympatho-adrenal response of the body. This occurs as the preganglionic sympathetic fibers that end in the adrenal medulla secrete acetylcholine, which activates the secretion of adrenaline (epinephrine), and to a lesser extent noradrenaline (norepinephrine).

Therefore, this response is mediated directly via impulses transmitted through the sympathetic nervous system, and also indirectly via catecholamines that are secreted from the adrenal medulla, and acts primarily on the cardiovascular system.

Messages travel through the SNS in a bidirectional flow. Efferent messages can trigger simultaneous changes in different parts of the body.

For example, the sympathetic nervous system can accelerate heart rate, widen bronchial passages, decrease motility of the large intestine, constrict blood vessels, increase peristalsis in the esophagus, cause pupillary dilation, piloerection (goose bumps) and perspiration (sweating), and raise blood pressure.

Afferent messages carry sensations such as heat, cold, or pain. Some evolutionary theorists suggest that the sympathetic nervous system operated in early organisms to maintain survival since the sympathetic nervous system is responsible for priming the body for action. One example of this priming is in the moments before waking, in which sympathetic outflow spontaneously increases in preparation for activity.

The Fight-or-Flight Response

The fight-or-flight response was first described by Walter Bradford Cannon. His theory states that animals react to threats with a general discharge of the sympathetic nervous system, priming the animal for fighting or fleeing. This response was later recognized as the first stage of a general adaptation syndrome that regulates stress responses among vertebrates and other organisms.

Catecholamine hormones, such as adrenaline or noradrenaline, facilitate the immediate physical reactions associated with a preparation for violent muscular action. These include the following:

Acceleration of heart and lung action.

Paling or flushing, or alternating between both.

Inhibition of stomach and upper-intestinal action to the point where digestion slows down or stops.

General effect on the sphincters of the body.

Constriction of blood vessels in many parts of the body.

Liberation of nutrients (particularly fat and glucose) for muscular action.

Dilation of blood vessels for muscles.

Inhibition of the lacrimal gland (responsible for tear production) and salivation.

Dilation of pupil (mydriasis).

Relaxation of bladder.

Inhibition of erection.

Auditory exclusion (loss of hearing).

Tunnel vision (loss of peripheral vision).

Disinhibition of spinal reflexes; and shaking.

In prehistoric times, the human fight-or-flight response manifested fight as aggressive, combative behavior and flight as fleeing potentially threatening situations, such as being confronted by a predator.

In current times, these responses persist, but fight-and-flight responses have assumed a wider range of behaviors. For example, the fight response may be manifested in angry, argumentative behavior, and the flight response may be manifested through social withdrawal, substance abuse, and even television viewing.

Males and females tend to deal with stressful situations differently. Males are more likely to respond to an emergency situation with aggression (fight), while females are more likely to flee (flight), turn to others for help, or attempt to defuse the situation (tend and befriend). During stressful times, a mother is especially likely to show protective responses toward her offspring and affiliate with others for shared social responses to threats.

Parasympathetic Responses

The parasympathetic nervous system regulates organ and gland functions during rest and is considered a slowly activated, dampening system.

Learning Objectives

Describe the parasympathetic responses of the autonomic nervous system

Key Takeaways

Key Points

Body functions stimulated by the parasympathetic nervous system (PSNS) include sexual arousal, salivation, lacrimation, urination, digestion, and defecation.

The PSNS primarily uses acetylcholine as its neurotransmitter.

Peptides (such as cholecystokinin) may also act on the PSNS as neurotransmitters.

Key Terms

acetylcholine: An organic, polyatomic cation (often abbreviated ACh) that acts as a neurotransmitter in both the peripheral nervous system (PNS) and central nervous system (CNS) in many organisms, including humans.

parasympathetic nervous system: One of the divisions of the autonomic nervous system, based between the brain and the spinal cord, that slows the heart and relaxes muscles.

lacrimation: Shedding tears; crying.

The Parasympathetic Nervous System

The parasympathetic nervous system (PSNS, or occasionally PNS) is one of the two main divisions of the autonomic nervous system (ANS). The autonomic nervous system (ANS, or visceral nervous system, or involuntary nervous system) is the part of the peripheral nervous system that acts as a control system, functioning largely below the level of consciousness and controlling visceral functions.

The ANS is responsible for regulating the internal organs and glands, which occurs unconsciously. Its roles include stimulation of rest-and-digest activities that occur when the body is at rest, including sexual arousal, salivation, lacrimation (tears), urination, digestion, and defecation.

Its action is described as being complementary to that of one of the other main branches of the ANS, the sympathetic nervous system, which is responsible for stimulating activities associated with the fight-or-flight response.

The sympathetic and parasympathetic divisions typically function in opposition to each other. This natural opposition is better understood as complementary in nature rather than antagonistic.

The sympathetic nervous system can be considered a quick response, mobilizing system; and the parasympathetic system is a more slowly activated, dampening system.

Parasympathetic Nervous System Functions

A useful acronym to summarize the functions of the parasympathetic nervous system is SLUDD (salivation, lacrimation, urination, digestion, and defecation). The parasympathetic nervous system may also be known as the parasympathetic division.

The parasympathetic nervous system uses chiefly acetylcholine (ACh) as its neurotransmitter, although peptides (such as cholecystokinin) may act on the PSNS as neurotransmitters. The ACh acts on two types of receptors, the muscarinic and nicotinic cholinergic receptors.

Most transmission occurs in two stages. When stimulated, the preganglionic nerve releases ACh at the ganglion, which acts on nicotinic receptors of the postganglionic neurons. The postganglionic nerve then releases ACh to stimulate the muscarinic receptors of the target organ.

Autonomic Interactions

The sympathetic and parasympathetic autonomic nervous systems cooperatively modulate internal physiology to maintain homeostasis.

Learning Objectives

Describe the interactions between the sympathetic and parasympathetic divisions of the autonomic nervous system

Key Takeaways

Key Points

The sympathetic and parasympathetic divisions typically function in opposition to each other, with one division exciting, triggering, or activating a response that is countered by the alternate system, which serves to relax, decrease, or negatively modulate a process.

The sympathetic division typically functions in actions requiring quick responses. The parasympathetic division functions with actions that do not require immediate reaction. The sympathetic division initiates the fight-or-flight response and the parasympathetic initiates the rest-and-digest or feed-and-breed responses.

The sympathetic and parasympathetic nervous systems are important for modulating many vital functions, including respiration and cardiac contractility. For example, the activities of both the sympathetic and parasympathetic systems maintains adequate blood pressure, vagal tone, and heart rate.

Key Terms

feed-and-breed: The parasympathetic nervous system is often colloquially described as the feed-and-breed or rest-and-digest portion of the autonomic nervous system.

fight or flight: All the coordinated physiological responses that the sympathetic nervous system initiates in response to stress or other emergency situations.

vital function: A measure of various physiological states that life depends on, such as recording body temperature, pulse rate (or heart rate), blood pressure, and respiratory rate.

Examples

Some processes that are modulated by the sympathetic and parasympathetic systems but that are not easily labeled as fight or rest include the maintenance of blood pressure when standing and the maintenance of regular heart rhythms.

Sympathetic and parasympathetic divisions typically function in opposition to each other. However, this opposition is better termed complementary in nature rather than antagonistic. For an analogy, one may think of the sympathetic division as the accelerator and the parasympathetic division as the brake.

The sympathetic division typically functions in actions requiring quick responses. The parasympathetic division functions with actions that do not require immediate reaction. Consider sympathetic as fight or flight and parasympathetic as rest and digest or feed and breed.

However, many instances of sympathetic and parasympathetic activity cannot be ascribed to fight or rest situations. For example, standing up from a reclining or sitting position would entail an unsustainable drop in blood pressure if not for a compensatory increase in the arterial sympathetic tonus.

Another example is the constant, second-to-second modulation of heart rate by sympathetic and parasympathetic influences, as a function of the respiratory cycles. More generally, these two systems should be seen as permanently modulating vital functions, usually in an antagonistic fashion, to achieve homeostasis. Some typical actions of the sympathetic and parasympathetic systems are listed below.

The SNS promotes a fight-or-flight response, corresponds with arousal and energy generation, and performs the following functions:

Inhibits digestion.

Diverts blood flow away from the gastro-intestinal (GI) tract and skin via vasoconstriction.

Blood flow to skeletal muscles and the lungs is enhanced (by as much as 1,200% in the case of skeletal muscles).

Dilates bronchioles of the lung, which allows for greater alveolar oxygen exchange.

Increases heart rate and the contractility of cardiac cells (myocytes), thereby providing a mechanism for the enhanced blood flow to skeletal muscles.

Dilates pupils and relaxes the ciliary muscle to the lens, allowing more light to enter the eye and far vision.

Provides vasodilation for the coronary vessels of the heart.

Constricts all the intestinal sphincters and the urinary sphincter.

Inhibits peristalsis.

Stimulates orgasm.

Conversely, the PSNS promotes a rest-and-digest response, and promotes the following functions:

Dilates blood vessels leading to the GI tract, increasing blood flow.

Constricts the bronchiolar diameter when the need for oxygen has diminished.

Causes constriction of the pupil and contraction of the ciliary muscle to the lens, allowing for closer vision.

Stimulates salivary gland secretion, and accelerates peristalsis.

Stimulates sexual arousal.

Control of Autonomic Nervous System Function

The medulla oblongata, in the lower half of the brainstem, is the control center of the autonomic nervous system.

Learning Objectives

Describe the control of the autonomic nervous system

Key Takeaways

Key Points

The medulla contains the cardiac, respiratory, and vasomotor centers.

The ANS is classically divided into two subdivisions, the sympathetic division and the parasympathetic division.

As a rule, the SNS functions in actions that require quick responses, while the PSNS is initiated in actions that don't require immediate response.

Key Terms

fight or flight: This theory states that animals react to threats with a general discharge of the sympathetic nervous system, priming the animal for fighting or fleeing.

The autonomic nervous system (ANS) is the part of the peripheral nervous system that controls involuntary functions that are critical for survival. The ANS participates in the regulation of heart rate, digestion, respiratory rate, pupil dilation, and sexual arousal, among other bodily processes.

Within the brain, the ANS is located in the medulla oblongata in the lower brainstem. The medulla's main functions are to control the cardiac, respiratory, and vasomotor centers, to mediate autonomic, involuntary functions, such as breathing, heart rate, and blood pressure, and to regulate reflex actions such as coughing, sneezing, vomiting, and swallowing.

The hypothalamus acts to integrate autonomic functions and receives autonomic regulatory feedback from the limbic system to do so. The ANS is classically divided into two subdivisions, the sympathetic division and the parasympathetic division.

The sympathetic division of the ANS is often referred to as the sympathetic nervous system (SNS). The SNS provides noradrenergic drive to the ANS. It is often referred to as a quick response mobilizing system that initiates the body's fight-or-flight response.

PSNS input to the ANS is responsible for the stimulation of feed-and-breed and rest-and-digest responses, as opposed to the fight-or-flight response initiated by the SNS. The parasympathetic division of the ANS (PSNS) acts to complement and modulate the drive provided by SNS neurotransmission within the ANS.

As a rule, the SNS functions in actions requiring quick responses while the PSNS is initiated in actions that don't require immediate response.

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The sympathetic division of the autonomic nervous system maintains internal organ homeostasis and initiates the stress response. Describe the sympathetic responses of the autonomic nervous system Key Points The fibers from the sympathetic nervous system (SNS) innervate the tissues in almost every organ system.

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WHERE ARE THE NEUROTRANSMITTERS LOCATED?

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WHERE ARE THE NEUROTRANSMITTERS LOCATED?

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-Sympathetic N.S.

ACH- neurotransmitter released at ganglia from presynaptic nerve endings

NE- neurotransmitter released at postganglionic nerve endings; synthesized from dopamine and  released by adrenal medulla and neurons

EPI- acts on adrenergic receptors, produced by adrenal medulla

DA- Produced in the brain, and located in the midbrain and nucleus of hypothalamus.

-Parasympathetic N.S.

ACH- released at ganglia from presynaptic nerve endings

Hitner, H., Nagle, B. T., Kaufman, M. B., Ariel, H. (., & Peimani-Lalehzarzadeh, Y. (2022). Pharmacology: An introduction. New York, NY: McGraw-Hill Education.

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-Sympathetic N.S.

Alpha 1- found on glands, smooth muscles, arteries and veins

Beta 1- located on heart; stimulated by NE and EPI

Beta 2- located on smooth muscle, lungs, uterus, skeletal muscle arteries and coronary arteries; stimulated by EPI only.

-Parasympathetic N.S.

Alpha 2- Located in the brain and in the periphery.

Hitner, H., Nagle, B. T., Kaufman, M. B., Ariel, H. (., & Peimani-Lalehzarzadeh, Y. (2022). Pharmacology: An introduction. New York, NY: McGraw-Hill Education.

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-Sympathetic N.S.

Alpha 1 Adrenergic agonists-  all alpha and beta receptors are stimulated; contraction of smooth muscle  and blood vessels, BP increases.

-SPECIFIC EXAMPLES: ephedrine, phenylephrine (Neo-Synephrine™),
epinephrine (Adrenalin™)

Alpha  1 Adrenergic blocking drugs- binds to alpha 1 receptors and blocks them; relaxation of smooth muscle, vasodilation.
-SPECIFIC EXAMPLES: prazosin (Minipress™), terazosin (Hytrin™), doxazosin (Cardura™)

Beta 2 Adrenergic agonists- Stimulates beta 2 receptors; bronchodilation, relaxation of lungs.

SPECIFIC EXAMPLES: formoterol (Foradil™), albuterol (Proventil™/Ventolin), terbutaline (Brethine™)

Beta 1- Adrenergic blocking drugs- Beta 1 receptor is blocked; decreases force of contraction, BP, HR, and conduction

SPECIFIC EXAMPLES: dobutamine

-Parasympathetic N.S.

Anticholinergics- bind to a cholinergic receptor; increase HR, slows digestion and urination, ats as blocking drug.

SPECIFIC EXAMPLES: atropine, dicyclomine (Bentyl™), ipratropium bromide (Atrovent™).

Cholinergics- bind to muscarinic receptors; mimics ACH

SPECIFIC EXAMPLES:

acetylcholine, pilocarpine (Pilocar™), neostigmine (Prostigmin™)
Sources: ACC Unit 2 ANS pt. 2 powerpoint.
Hitner, H., Nagle, B. T., Kaufman, M. B., Ariel, H. (., & Peimani-Lalehzarzadeh, Y. (2022). Pharmacology: An introduction. New York, NY: McGraw-Hill Education.

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-Sympathetic N.S.

Heart- increases heart rate and AV conduction; increases contractility

Brain- hypothalamus activates sympathetic responses  by sending signals the adrenal glands. These glands respond by pumping the hormone epinephrine into the bloodstream

lungs- Bronchodilation; increases airflow to the lungs

Bladder- relaxes

Gi Motility- decreased

-Parasympathetic N.S.

Heart- decreases heart rate and contractility

Lungs- Bronchoconstriction

Endocrine and Exocrine glands- stimulates salivation

Bladder- contracts

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What you'll learn to do: describe the role of the nervous system and endocrine systems

In this section, you'll learn about the basics of the central nervous system, which consists of the brain and spinal cord, as well as the peripheral nervous system. The peripheral nervous system is comprised of the somatic and autonomic nervous systems. The somatic nervous system transmits sensory and motor signals to and from the central nervous system. 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. The consists of a series of glands that produce chemical substances known as hormones, which produce widespread effects on the body. Got all that? We'll review each of these systems in the coming pages.

Learning Objectives

Describe the difference between the central and peripheral nervous systems and the somatic and autonomic nervous systems

Differentiate between the sympathetic and parasympathetic divisions of the autonomic nervous system

Describe the endocrine system and explain its primary responsibilities within the body

The Central Nervous System and the Peripheral Nervous System

The nervous system can be divided into two major subdivisions: the central nervous system (CNS) and the peripheral nervous system (PNS) , shown in Figure 1. The CNS is comprised of the brain and spinal cord; the PNS connects the CNS to the rest of the body. In this section, we focus on the peripheral nervous system; later, we look at the brain and spinal cord.

Peripheral Nervous System

The peripheral nervous system is made up of thick bundles of axons, called nerves, carrying messages back and forth between the CNS and the muscles, organs, and senses in the periphery of the body (i.e., everything outside the CNS). The PNS has two major subdivisions: the somatic nervous system and the autonomic nervous system.

The somatic nervous system is associated with activities traditionally thought of as conscious or voluntary. It is involved in the relay of sensory and motor information to and from the CNS; therefore, it consists of motor neurons and sensory neurons. Motor neurons, carrying instructions from the CNS to the muscles, are efferent fibers (efferent means "moving away from"). Sensory neurons, carrying sensory information to the CNS, are afferent fibers (afferent means "moving toward"). Each nerve is basically a two-way superhighway, containing thousands of axons, both efferent and afferent.

The autonomic nervous system controls our internal organs and glands and is generally considered to be outside the realm of voluntary control. It can be further subdivided into the sympathetic and parasympathetic divisions (Figure 2). The sympathetic nervous system is involved in preparing the body for stress-related activities; the parasympathetic nervous system is associated with returning the body to routine, day-to-day operations. The two systems have complementary functions, operating in tandem to maintain the body's homeostasis. Homeostasis is a state of equilibrium, in which biological conditions (such as body temperature) are maintained at optimal levels.

The sympathetic nervous system is activated when we are faced with stressful or high-arousal situations. The activity of this system was adaptive for our ancestors, increasing their chances of survival. Imagine, for example, that one of our early ancestors, out hunting small game, suddenly disturbs a large bear with her cubs. At that moment, his body undergoes a series of changes-a direct function of sympathetic activation-preparing him to face the threat. His pupils dilate, his heart rate and blood pressure increase, his bladder relaxes, his liver releases glucose, and adrenaline surges into his bloodstream. This constellation of physiological changes, known as the fight or flight response , allows the body access to energy reserves and heightened sensory capacity so that it might fight off a threat or run away to safety.

While it is clear that such a response would be critical for survival for our ancestors, who lived in a world full of real physical threats, many of the high-arousal situations we face in the modern world are more psychological in nature. For example, think about how you feel when you have to stand up and give a presentation in front of a roomful of people, or right before taking a big test. You are in no real physical danger in those situations, and yet you have evolved to respond to any perceived threat with the fight or flight response. This kind of response is not nearly as adaptive in the modern world; in fact, we suffer negative health consequences when faced constantly with psychological threats that we can neither fight nor flee. Recent research suggests that an increase in susceptibility to heart disease (Chandola, Brunner, & Marmot, 2006) and impaired function of the immune system (Glaser & Kiecolt-Glaser, 2005) are among the many negative consequences of persistent and repeated exposure to stressful situations.

Once the threat has been resolved, the parasympathetic nervous system takes over and returns bodily functions to a relaxed state. Our hunter's heart rate and blood pressure return to normal, his pupils constrict, he regains control of his bladder, and the liver begins to store glucose in the form of glycogen for future use. These processes are associated with activation of the parasympathetic nervous system.

Think It Over

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?

The Endocrine System

The endocrine system consists of a series of glands that produce chemical substances known as hormones (Figure 3). Like neurotransmitters, hormones are chemical messengers that must bind to a receptor in order to send their signal. However, unlike neurotransmitters, which are released in close proximity to cells with their receptors, hormones are secreted into the bloodstream and travel throughout the body, affecting any cells that contain receptors for them. Thus, whereas neurotransmitters' effects are localized, the effects of hormones are widespread. Also, hormones are slower to take effect, and tend to be longer lasting.

The study of psychology and the endocrine system is called behavioral endocrinology, which is the scientific study of the interaction between hormones and behavior. This interaction is bidirectional: hormones can influence behavior, and behavior can sometimes influence hormone concentrations. Hormones regulate behaviors such as aggression, mating, and parenting of individuals. Hormones are involved in regulating all sorts of bodily functions, and they are ultimately controlled through interactions between the hypothalamus (in the central nervous system) and the pituitary gland (in the endocrine system). Imbalances in hormones are related to a number of disorders. This section explores some of the major glands that make up the endocrine system and the hormones secreted by these glands.

Major Glands

The pituitary gland descends from the hypothalamus at the base of the brain, and acts in close association with it. The pituitary is often referred to as the "master gland" because its messenger hormones control all the other glands in the endocrine system, although it mostly carries out instructions from the hypothalamus. In addition to messenger hormones, the pituitary also secretes growth hormone, endorphins for pain relief, and a number of key hormones that regulate fluid levels in the body.

Located in the neck, the thyroid gland releases hormones that regulate growth, metabolism, and appetite. In hyperthyroidism, or Grave's disease, the thyroid secretes too much of the hormone thyroxine, causing agitation, bulging eyes, and weight loss. In hypothyroidism, reduced hormone levels cause sufferers to experience tiredness, and they often complain of feeling cold. Fortunately, thyroid disorders are often treatable with medications that help reestablish a balance in the hormones secreted by the thyroid.

The adrenal glands sit atop our kidneys and secrete hormones involved in the stress response, such as epinephrine (adrenaline) and norepinephrine (noradrenaline). The pancreas is an internal organ that secretes hormones that regulate blood sugar levels: insulin and glucagon. These pancreatic hormones are essential for maintaining stable levels of blood sugar throughout the day by lowering blood glucose levels (insulin) or raising them (glucagon). People who suffer from diabetes do not produce enough insulin; therefore, they must take medications that stimulate or replace insulin production, and they must closely control the amount of sugars and carbohydrates they consume.

The gonads secrete sexual hormones, which are important in reproduction, and mediate both sexual motivation and behavior. The female gonads are the ovaries; the male gonads are the testis. Ovaries secrete estrogens and progesterone, and the testes secrete androgens, such as testosterone.

Dig Deeper: Athletes and Anabolic Steroids

Although it is against most laws to do so, many professional athletes and body builders use anabolic steroid drugs to improve their athletic performance and physique. Anabolic steroid drugs mimic the effects of the body's own steroid hormones, like testosterone and its derivatives. These drugs have the potential to provide a competitive edge by increasing muscle mass, strength, and endurance, although not all users may experience these results. Moreover, use of performance-enhancing drugs (PEDs) does not come without risks. Anabolic steroid use has been linked with a wide variety of potentially negative outcomes, ranging in severity from largely cosmetic (acne) to life threatening (heart attack). Furthermore, use of these substances can result in profound changes in mood and can increase aggressive behavior (National Institute on Drug Abuse, 2001).

Baseball player Alex Rodriguez (A-Rod) has been at the center of a media storm regarding his use of illegal PEDs. Rodriguez's performance on the field was unparalleled while using the drugs; his success played a large role in negotiating a contract that made him the highest paid player in professional baseball. Although Rodriguez maintains that he has not used PEDs for the several years, he received a substantial suspension in 2013 that, if upheld, will cost him more than 20 million dollars in earnings (Gaines, 2013). What are your thoughts on athletes and doping? Why or why not should the use of PEDs be banned? What advice would you give an athlete who was considering using PEDs?

Hormones and Behavior

How might behaviors affect hormones? Extensive studies on male zebra finches and their singing (only males finches sing) demonstrate that the hormones testosterone and estradiol affect their singing, but the reciprocal relation also occurs; that is, behavior can affect hormone concentrations. For example, the sight of a territorial intruder may elevate blood testosterone concentrations in resident male birds and thereby stimulate singing or fighting behavior. Similarly, male mice or rhesus monkeys that lose a fight decrease circulating testosterone concentrations for several days or even weeks afterward. Comparable results have also been reported in humans. Testosterone concentrations are affected not only in humans involved in physical combat, but also in those involved in simulated battles. For example, testosterone concentrations were elevated in winners and reduced in losers of regional chess tournaments.

People do not have to be directly involved in a contest to have their hormones affected by the outcome of the contest. Male fans of both the Brazilian and Italian teams were recruited to provide saliva samples to be assayed for testosterone before and after the final game of the World Cup soccer match in 1994. Brazil and Italy were tied going into the final game, but Brazil won on a penalty kick at the last possible moment. The Brazilian fans were elated and the Italian fans were crestfallen. When the samples were assayed, 11 of 12 Brazilian fans who were sampled had increased testosterone concentrations, and 9 of 9 Italian fans had decreased testosterone concentrations, compared with pre-game baseline values (Dabbs, 2000).

In some cases, hormones can be affected by anticipation of behavior. For example, testosterone concentrations also influence sexual motivation and behavior in women. In one study, the interaction between sexual intercourse and testosterone was compared with other activities (cuddling or exercise) in women (van Anders, Hamilton, Schmidt, & Watson, 2007). On three separate occasions, women provided a pre-activity, post-activity, and next-morning saliva sample. After analysis, the women's testosterone was determined to be elevated prior to intercourse as compared to other times. Thus, an anticipatory relationship exists between sexual behavior and testosterone. Testosterone values were higher post-intercourse compared to exercise, suggesting that engaging in sexual behavior may also influence hormone concentrations in women.

Link to Learning

Learn more about endocrinology from The Noba Psychology article, " Hormones and Behavior."

Think It Over

Given the negative health consequences associated with the use of anabolic steroids, what kinds of considerations might be involved in a person's decision to use them?

Glossary

adrenal gland: sits atop our kidneys and secretes hormones involved in the stress response

autonomic nervous system: controls our internal organs and glands

central nervous system (CNS): brain and spinal cord

diabetes: disease related to insufficient insulin production

endocrine system: series of glands that produce chemical substances known as hormones

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

gonad: secretes sexual hormones, which are important for successful reproduction, and mediate both sexual motivation and behavior

homeostasis: state of equilibrium-biological conditions, such as body temperature, are maintained at optimal levels

hormone: chemical messenger released by endocrine glands

pancreas: secretes hormones that regulate blood sugar

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

pituitary gland: secretes a number of key hormones, which regulate fluid levels in the body, and a number of messenger hormones, which direct the activity of other glands in the endocrine system

thyroid: secretes hormones that regulate growth, metabolism, and appetite

somatic nervous system: relays sensory and motor information to and from the CNS

sympathetic nervous system: involved in stress-related activities and functions

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In this section, you'll learn about the basics of the central nervous system, which consists of the brain and spinal cord, as well as the peripheral nervous system. The peripheral nervous system is comprised of the somatic and autonomic nervous systems. The somatic nervous system transmits sensory and motor signals to and from the central nervous system.