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Hawthorne effect
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Aerial view of the Hawthorne Works, ca. 1925
The Hawthorne effect (also referred to as the observer effect[1]) is a type of reactivity in which individuals modify an aspect of their behavior in response to their awareness of being observed.[2][3] The original research at the Hawthorne Works in Cicero, Illinois, on lighting changes and work structure changes such as working hours and break times was originally interpreted by Elton Mayo and others to mean that paying attention to overall worker needs would improve productivity. Later interpretations such as that done by Landsberger suggested that the novelty of being research subjects and the increased attention from such could lead to temporary increases in workers' productivity. This interpretation was dubbed "the Hawthorne effect".
Contents
[hide]
1 History
1.1 Relay assembly experiments
1.2 Bank wiring room experiments
2 Interpretation and criticism
3 Trial effect
4 Secondary observer effect
5 See also
6 References
7 External links
History[edit]
The term was coined in 1958 by Henry A. Landsberger,[4] when analyzing earlier experiments from 1924–32 at the Hawthorne Works (a Western Electric factory outside Chicago). The Hawthorne Works had commissioned a study to see if their workers would become more productive in higher or lower levels of light. The workers' productivity seemed to improve when changes were made, and slumped when the study ended. It was suggested that the productivity gain occurred as a result of the motivational effect on the workers of the interest being shown in them.
This effect was observed for minute increases in illumination. In these lighting studies, light intensity was altered to examine its effect on worker productivity. Most industrial/occupational psychology and organizational behavior textbooks refer to the illumination studies.[5] Only occasionally are the rest of the studies mentioned.[6]
Although illumination research of workplace lighting formed the basis of the Hawthorne effect, other changes such as maintaining clean work stations, clearing floors of obstacles, and even relocating workstations resulted in increased productivity for short periods. Thus the term is used to identify any type of short-lived increase in productivity.[4][7][8]
Interpretations and views vary. H. McIlvaine Parsons defines the Hawthorne effect as "the confounding that occurs if experimenters fail to realize how the consequences of subjects' performance affect what subjects do" (i.e. performance is affected – possibly unconsciously – by possible positive or negative personal consequences not considered by the experimenter).[9] Elton Mayo describes it in terms of a positive emotional effect due to the perception of a sympathetic or interested observer. Clark and Sugrue say that uncontrolled novelty effects cause on average 30% of a standard deviation (SD) rise (i.e. 50–63% score rise), which decays to small level after eight weeks.[10] Braverman argues that the studies really showed that the workplace was not "a system of bureaucratic formal organisation on the Weberian model, nor a system of informal group relations, as in the interpretation of Mayo and his followers but rather a system of power, of class antagonisms".[11] Studies of the demand effect also suggests that people might take on pleasing the experimenter as a goal.[12]
Evaluation of the Hawthorne effect continues in the present day.[13][14][15]
Relay assembly experiments[edit]
In one of the studies, researchers chose two women as test subjects and asked them to choose four other workers to join the test group. Together the women worked in a separate room over the course of five years (1927–1932) assembling telephone relays.
Output was measured mechanically by counting how many finished relays each worker dropped down a chute. This measuring began in secret two weeks before moving the women to an experiment room and continued throughout the study. In the experiment room they had a supervisor who discussed changes with their productivity. Some of the variables were:
Giving two 5-minute breaks (after a discussion with them on the best length of time), and then changing to two 10-minute breaks (not their preference). Productivity increased, but when they received six 5-minute rests, they disliked it and reduced output.
Providing food during the breaks.
Shortening the day by 30 minutes (output went up); shortening it more (output per hour went up, but overall output decreased); returning to the first condition (where output peaked).
Changing a variable usually increased productivity, even if the variable was just a change back to the original condition. However it is said that this is the natural process of the human being adapting to the environment, without knowing the objective of the experiment occurring. Researchers concluded that the workers worked harder because they thought that they were being monitored individually.
Researchers hypothesized that choosing one's own coworkers, working as a group, being treated as special (as evidenced by working in a separate room), and having a sympathetic supervisor were the real reasons for the productivity increase. One interpretation, mainly due to Elton Mayo,[16] was that "the six individuals became a team and the team gave itself wholeheartedly and spontaneously to cooperation in the experiment." (There was a second relay assembly test room study whose results were not as significant as the first experiment.)
Bank wiring room experiments[edit]
The purpose of the next study was to find out how payment incentives would affect productivity. The surprising result was that productivity actually decreased. Workers apparently had become suspicious that their productivity may have been boosted to justify firing some of the workers later on.[17] The study was conducted by Elton Mayo and W. Lloyd Warner between 1931 and 1932 on a group of fourteen men who put together telephone switching equipment. The researchers found that although the workers were paid according to individual productivity, productivity decreased because the men were afraid that the company would lower the base rate. Detailed observation of the men revealed the existence of informal groups or "cliques" within the formal groups. These cliques developed informal rules of behavior as well as mechanisms to enforce them. The cliques served to control group members and to manage bosses; when bosses asked questions, clique members gave the same responses, even if they were untrue. These results show that workers were more responsive to the social force of their peer groups than to the control and incentives of management.
Interpretation and criticism[edit]
Richard Nisbett has described the Hawthorne effect as "a glorified anecdote", saying that "once you have got the anecdote, you can throw away the data."[18] Other researchers have attempted to explain the effects with various interpretations.
Adair warns of gross factual inaccuracy in most secondary publications on Hawthorne effect and that many studies failed to find it.[19] He argues that it should be viewed as a variant of Orne's (1973) experimental demand effect. So for Adair, the issue is that an experimental effect depends on the participants' interpretation of the situation; this is why manipulation checks are important in social sciences experiments. So he thinks it is not awareness per se, nor special attention per se, but participants' interpretation that must be investigated in order to discover if/how the experimental conditions interact with the participants' goals. This can affect whether participants believe something, if they act on it or do not see it as in their interest, etc.[vague]
Possible explanations for the Hawthorne effect include the impact of feedback and motivation towards the experimenter. Receiving feedback on their performance may improve their skills when an experiment provides this feedback for the first time.[9] Research on the demand effect also suggests that people may be motivated to please the experimenter, at least if it does not conflict with any other motive.[12] They may also be suspicious of the purpose of the experimenter.[9] Therefore, Hawthorne effect may only occur when there is usable feedback or a change in motivation.
Parsons defines the Hawthorne effect as "the confounding that occurs if experimenters fail to realize how the consequences of subjects' performance affect what subjects do" [i.e. learning effects, both permanent skill improvement and feedback-enabled adjustments to suit current goals]. His key argument is that in the studies where workers dropped their finished goods down chutes, the participants had access to the counters of their work rate.[9]
Mayo contended that the effect was due to the workers reacting to the sympathy and interest of the observers. He does say that this experiment is about testing overall effect, not testing factors separately. He also discusses it not really as an experimenter effect but as a management effect: how management can make workers perform differently because they feel differently. A lot to do with feeling free, not feeling supervised but more in control as a group. The experimental manipulations were important in convincing the workers to feel this way: that conditions were really different. The experiment was repeated with similar effects on mica-splitting workers.[16]
Clark and Sugrue in a review of educational research say that uncontrolled novelty effects cause on average 30% of a standard deviation (SD) rise (i.e. 50%–63% score rise), which decays to small level after 8 weeks. In more detail: 50% of a SD for up to 4 weeks; 30% of SD for 5–8 weeks; and 20% of SD for > 8 weeks, (which is < 1% of the variance).[10]:333
Harry Braverman points out that the Hawthorne tests were based on industrial psychology and were investigating whether workers' performance could be predicted by pre-hire testing. The Hawthorne study showed "that the performance of workers had little relation to ability and in fact often bore an inverse relation to test scores...".[11] Braverman argues that the studies really showed that the workplace was not "a system of bureaucratic formal organisation on the Weberian model, nor a system of informal group relations, as in the interpretation of Mayo and his followers but rather a system of power, of class antagonisms". This discovery was a blow to those hoping to apply the behavioral sciences to manipulate workers in the interest of management.[citation needed]
The economists Steven Levitt and John A. List long pursued without success a search for the base data of the original illumination experiments, before finding it in a microfilm at the University of Wisconsin in Milwaukee in 2011.[20] Re-analysing it, they found that the variance in productivity could be fully accounted for by the fact that the lighting changes were made on Sundays and therefore followed by Mondays when workers' productivity was refreshed by a day off.[21] This finding supported the analysis of an article by S R G Jones in 1992 examining the relay experiments.[22][23] Despite the absence of evidence for the Hawthorne Effect in the original study, List has said that he remains confident that the effect is genuine.[24]
It is also possible that the illumination experiments can be explained by a longitudinal learning effect. Parsons has declined to analyse the illumination experiments, on the grounds that they have not been properly published and so he cannot get at details, whereas he had extensive personal communication with Roethlisberger and Dickson.[9]
Trial effect[edit]
Various medical scientists have studied possible trial effect (clinical trial effect) in clinical trials.[25][26][27] Some postulate that, beyond just attention and observation, there may be other factors involved, such as slightly better care; slightly better compliance/adherence; and selection bias. The latter may have several mechanisms: (1) Physicians may tend to recruit patients who seem to have better adherence potential and lesser likelihood of future loss to follow-up. (2) The inclusion/exclusion criteria of trials often exclude at least some comorbidities; although this is often necessary to prevent confounding, it also means that trials may tend to work with healthier patient subpopulations.
Secondary observer effect[edit]
Despite the observer effect as popularized in the Hawthorne experiments being perhaps falsely identified (see above discussion), the popularity and plausibility of the observer effect in theory has led researchers to postulate that this effect could take place at a second level. Thus it has been proposed that there is a secondary observer effect where researchers working with secondary data such as survey data or various indicators may impact the results of their scientific research. Rather than having an effect on the subjects (as with the primary observer effect), the researchers likely have their own idiosyncrasies that influence how they handle the data and even what data they obtain from secondary sources. For one, the researchers may choose seemingly innocuous steps in their statistical analyses that end up causing significantly different results using the same data; e.g., weighting strategies, factor analytic techniques, or choice of estimation. In addition, researchers may use different software packages that have different default settings that lead to small but significant fluctuations. Finally, these data that researchers use may not be identical, even though it seems so. For example, the OECD collects and distributes various socio-economic data; however, these data change over time such that a researcher who downloads the Australian GDP data for the year 2000 may have slightly different values than a researcher who downloads the same Australian GDP 2000 data a few years later. The idea of the secondary observer effect was floated by Nate Breznau in a thus far relatively obscure paper.[28] Although little attention has been paid to this phenomenon, the scientific implications are very large[29]. Evidence of this effect may be seen in recent studies that assign a particular problem to a number of researchers or research teams who then work independently using the same data to try and find a solution. This is a process called crowdsourcing data analysis and was used in a groundbreaking study by Silberzahn, Rafael, Eric Uhlmann, Dan Martin and Brian Nosek et al. (2015) about red cards and player race in football (i.e., soccer).[30][31]
See also[edit]
Demand characteristics
John Henry effect
Mass surveillance
Novelty effect
Panopticon
Placebo effect
Pygmalion effect
Quantum Zeno effect
Reflexivity (social theory)
Self-determination theory
Social facilitation
Stereotype threat
Subject-expectancy effect
Watching-Eye Effect
Goodhart's law
References[edit]
Jump up ^ Monahan, Torin; Fisher, Jill A. (June 1, 2010). "Benefits of 'Observer Effects': Lessons from the Field". U.S. National Library of Medicine, National Institutes of Health.
Jump up ^ McCarney R, Warner J, Iliffe S, van Haselen R, Griffin M, Fisher P; Warner; Iliffe; Van Haselen; Griffin; Fisher (2007). "The Hawthorne Effect: a randomised, controlled trial". BMC Med Res Methodol. 7: 30. PMC 1936999  . PMID 17608932. doi:10.1186/1471-2288-7-30. CS1 maint: Multiple names: authors list (link)
Jump up ^ Fox NS, Brennan JS, Chasen ST; Brennan; Chasen (2008). "Clinical estimation of fetal weight and the Hawthorne effect". Eur. J. Obstet. Gynecol. Reprod. Biol. 141 (2): 111–4. PMID 18771841. doi:10.1016/j.ejogrb.2008.07.023. CS1 maint: Multiple names: authors list (link)
^ Jump up to: a b Henry A. Landsberger, Hawthorne Revisited, Ithaca, 1958.
Jump up ^ The Industrial Organization Psychologist, Volume 41, What We Teach Students About the Hawthorne Studies, Santa Clara University 2004
Jump up ^ What We Teach Students About the Hawthorne Studies: A Review of Content Within a Sample of Introductory I-O and OB Textbooks
Jump up ^ Elton Mayo, Hawthorne and the Western Electric Company, The Social Problems of an Industrial Civilisation, Routledge, 1949.
Jump up ^ Bowey, Dr. Angela M. "MOTIVATION AT WORK: a key issue in remuneration". Archived from the original on 1 July 2007. Retrieved 22 November 2011. CS1 maint: BOT: original-url status unknown (link)
^ Jump up to: a b c d e Parsons, H. M. (1974). "What happened at Hawthorne?: New evidence suggests the Hawthorne effect resulted from operant reinforcement contingencies". Science. 183 (4128): 922–932. PMID 17756742. doi:10.1126/science.183.4128.922.
^ Jump up to: a b Clark, Richard E.; Sugrue, Brenda M. (1991). "30. Research on instructional media, 1978-1988". In G.J.Anglin. Instructional technology: past, present, and future. Englewood, Colorado: Libraries Unlimited. pp. 327–343.
^ Jump up to: a b Braverman, Harry (1974). Labor and Monopoly Capitalism. New York: Monthly Review Press. pp. 144–145. ISBN 0853453403.
^ Jump up to: a b Steele-Johnson, D.; Beauregard, Russell S.; Hoover, Paul B.; Schmidt, Aaron M. (2000). "Goal orientation and task demand effects on motivation, affect, and performance". The Journal of Applied Psychology. 85 (5): 724–738. PMID 11055145. doi:10.1037/0021-9010.85.5.724.
Jump up ^ Kohli E, Ptak J, Smith R, Taylor E, Talbot EA, Kirkland KB; Ptak; Smith; Taylor; Talbot; Kirkland (2009). "Variability in the Hawthorne effect with regard to hand hygiene performance in high- and low-performing inpatient care units". Infect Control Hosp Epidemiol. 30 (3): 222–5. PMID 19199530. doi:10.1086/595692. CS1 maint: Multiple names: authors list (link)
Jump up ^ Cocco G (2009). "Erectile dysfunction after therapy with metoprolol: the hawthorne effect". Cardiology. 112 (3): 174–7. PMID 18654082. doi:10.1159/000147951.
Jump up ^ Leonard KL (2008). "Is patient satisfaction sensitive to changes in the quality of care? An exploitation of the Hawthorne effect". J Health Econ. 27 (2): 444–59. PMID 18192043. doi:10.1016/j.jhealeco.2007.07.004.
^ Jump up to: a b Mayo, Elton (1945) Social Problems of an Industrial Civilization. Boston: Division of Research, Graduate School of Business Administration, Harvard University, p. 72
Jump up ^ Henslin, James M. (2008). Sociology: a down to earth approach (9th ed.). Pearson Education. p. 140. ISBN 978-0-205-57023-2.
Jump up ^ Kolata, G. (December 6, 1998). "Scientific Myths That Are Too Good to Die". New York Times.
Jump up ^ Adair, J.G. (1984). "The Hawthorne Effect: A reconsideration of the methodological artifact" (PDF). Journal of Applied Psychology. 69 (2): 334–345. doi:10.1037/0021-9010.69.2.334.
Jump up ^ BBC Radio 4 programme More Or Less, "The Hawthorne Effect", broadcast 12 October 2013, presented by Tim Harford with contributions by John List
Jump up ^ Levitt, Steven D. & List, John A. (2011). "Was There Really a Hawthorne Effect at the Hawthorne Plant? An Analysis of the Original Illumination Experiments". American Economic Journal: Applied Economics. 3 (1): 224–238. doi:10.1257/app.3.1.224.
Jump up ^ "Light work". The Economist. June 6, 2009: 80.
Jump up ^ Jones, Stephen R. G. (1992). "Was there a Hawthorne effect?". American Journal of Sociology. 98 (3): 451–468. JSTOR 2781455. doi:10.1086/230046.
Jump up ^ Podcast, More or Less 12 October 2013, from 6m 15 sec in
Jump up ^ Menezes P, Miller WC, Wohl DA, Adimora AA, Leone PA, Eron JJ; Miller; Wohl; Adimora; Leone; Miller; Eron (2011), "Does HAART efficacy translate to effectiveness? Evidence for a trial effect", Plos One, 6 (7): e21824, doi:10.1371/journal.pone.0021824. CS1 maint: Multiple names: authors list (link)
Jump up ^ Braunholtz DA, Edwards SJ, Lilford RJ.; Edwards; Lilford (2001), "Are randomized clinical trials good for us (in the short term)? Evidence for a "trial effect"", J Clin Epidemiol, 54 (3): 217–224, PMID 11223318, doi:10.1016/s0895-4356(00)00305-x. CS1 maint: Multiple names: authors list (link)
Jump up ^ McCarney R, Warner J, Iliffe S, van Haselen R, Griffin M, Fisher P; Warner; Iliffe; Van Haselen; Griffin; Fisher (2007), "The Hawthorne Effect: a randomised, controlled trial", BMC Medical Research Methodology, 7: 30, PMC 1936999  , PMID 17608932, doi:10.1186/1471-2288-7-30. CS1 maint: Multiple names: authors list (link)
Jump up ^ Breznau, Nate (2016-05-03). "Secondary observer effects: idiosyncratic errors in small-N secondary data analysis". International Journal of Social Research Methodology. 19 (3): 301–318. ISSN 1364-5579. doi:10.1080/13645579.2014.1001221.
Jump up ^ Shi, Yuan; Sorenson, Olav; Waguespack, David (2017-01-30). "Temporal Issues in Replication: The Stability of Centrality-Based Advantage". Sociological Science. 4: 107–122. ISSN 2330-6696. doi:10.15195/v4.a5.
Jump up ^ "OSF | Crowdsourcing Analytics - Final Manuscript.pdf". osf.io. Retrieved 2016-12-07.
Jump up ^ "Crowdsourcing Data to Improve Macro-Comparative Research". Policy and Politics Journal. 2015-03-26. Retrieved 2016-12-07.
External links[edit]
Evan Davis on the Hawthorne Effect, OpenLearn from The Open University
The Hawthorne, Pygmalion, placebo and other expectancy effects: some notes, by Stephen W. Draper, Department of Psychology, University of Glasgow.
BBC Radio 4: Mind Changers: The Hawthorne Effect
Harvard Business School and the Hawthorne Experiments (1924–1933), Harvard Business School.
How lack of attention decreases productivity?, by Marcin Kazaryn, Mateusz Klupczyński, Jagoda Piotrowska, Lab1 insights.
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Subclavian artery
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Subclavian artery
Schematic of the proximal aorta and its branches. The left subclavian artery is the fifth branch of the aorta and the third branch from the arch of the aorta. The right subclavian artery arises from the brachiocephalic artery (labeled 'innominate' on diagram).
The aortic arch, and its branches. (Rt. subclavian is at upper left, and lft. subclavian is at upper right.)
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brachiocephalic (right)
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vertebral artery
internal thoracic artery
thyrocervical trunk
costocervical trunk
dorsal scapular artery (mostly)
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subclavian vein
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arteria subclavia
MeSH
A07.231.114.839
Dorlands
/Elsevier
a_61/12156042
TA
A12.2.08.001
FMA
3951
Anatomical terminology
[edit on Wikidata]
In human anatomy, the subclavian arteries are paired major arteries of the upper thorax, below the clavicle. They receive blood from the aortic arch. The left subclavian artery supplies blood to the left arm and the right subclavian artery supplies blood to the right arm, with some branches supplying the head and thorax. On the left side of the body, the subclavian comes directly off the aortic arch, while on the right side it arises from the relatively short brachiocephalic artery when it bifurcates into the subclavian and the right common carotid artery.
The usual branches of the subclavian on both sides of the body are the vertebral artery, the internal thoracic artery, the thyrocervical trunk, the costocervical trunk and the dorsal scapular artery, which may branch off the transverse cervical artery which is a branch of the thyrocervical trunk. The subclavian becomes the axillary artery at the lateral border of the first rib.
Contents
[hide]
1 Structure
1.1 First part
1.1.1 Right subclavian artery
1.1.2 Left subclavian artery
1.2 Second part
1.3 Third part
1.4 Branches
1.5 Development
1.6 Variation
2 Additional images
3 See also
4 References
5 External links
Structure[edit]
From its origin, the subclavian artery travels laterally, passing between anterior and middle scalene muscles, with the anterior scalene (scalenus anterior) on its anterior side and the middle scalene (scalenus medius) on its posterior. This is in contrast to the subclavian vein, which travels anterior to the scalenus anterior. As the subclavian artery crosses the lateral border of the first rib, it becomes the axillary artery.
On the right side the subclavian artery arises from the brachiocephalic (innominate) artery behind the right sternoclavicular articulation; on the left side it springs from the arch of the aorta. The two vessels, therefore, in the first part of their course, differ in length, direction, and relation with neighboring structures.
In order to facilitate the description, each subclavian artery is divided into three parts:
The first portion extends from the origin of the vessel to the medial border of the Scalenus anterior.
The second lies behind this muscle.
The third extends from the lateral margin of the muscle to the outer border of the first rib, where it becomes the axillary artery.
The first portions of the two vessels require separate descriptions; the second and third parts of the two arteries are practically alike.
First part[edit]
Right subclavian artery[edit]
The first part of the right subclavian artery arises from the brachiocephalic trunk, behind the upper part of the right sternoclavicular articulation, and passes upward and lateralward to the medial margin of the Scalenus anterior. It ascends a little above the clavicle, the extent to which it does so varying in different cases.
It is covered, in front, by the integument, superficial fascia, the Platysma (platysma) muscle, deep fascia, the clavicular origin of the Sternocleidomastoideus (sternocleidomastoid) muscle, the Sternohyoideus (sternohyoid) muscle, and the Sternothyreoideus (sternothyroid) muscle, and another layer of the deep fascia. It is crossed by the internal jugular vein and the vertebral vein, by the vagus nerve and the cardiac branches of the vagus and sympathetic, and by the subclavian loop of the sympathetic trunk which forms a ring around the vessel. The anterior jugular vein is directed laterally in front of the artery, but is separated from it by the Sternohyoideus and Sternothyreoideus. Below and behind the artery is the pleura, which separates it from the apex of the lung; behind is the sympathetic trunk, the Longus collie and the first thoracic vertebra (T1). The right recurrent nerve winds around the lower and back part of the vessel.
Left subclavian artery[edit]
The first part of the left subclavian artery arises from the arch of the aorta, behind the left common carotid, and at the level of the fourth thoracic vertebra; it ascends in the superior mediastinal cavity to the root of the neck and then arches lateralward to the medial border of the Scalenus anterior.
It is in relation, in front, with the vagus, cardiac, and phrenic nerves, which lie parallel with it, the left common carotid artery, left internal jugular and vertebral veins, and the commencement of the left innominate vein, and is covered by the Sternothyroideus, Sternohyoideus, and Sternocleidomastoideus; behind, it is in relation with the esophagus, thoracic duct, left recurrent laryngeal nerve, inferior cervical ganglion of the sympathetic trunk, and Longus colli; higher up, however, the esophagus and thoracic duct lie to its right side; the latter ultimately arching over the vessel to join the angle of union between the subclavian and internal jugular veins. Medial to it are the esophagus, trachea, thoracic duct, and left recurrent laryngeal nerve; lateral to it, the left pleura and lung.
Second part[edit]
The second portion of the subclavian artery lies behind the Scalenus anterior (anterior scalene) muscle; it is very short, and forms the highest part of the arch described by the vessel.
It is covered, in front, by the skin, the superficial fascia, the Platysma muscle, the deep cervical fascia, the Sternocleidomastoideus, and Scalenus anterior. On the right side of the neck the phrenic nerve is separated from the second part of the artery by the Scalenus anterior, while on the left side it crosses the first part of the artery close to the medial (middle) edge of the muscle. Behind the vessel are the pleura and the Scalenus medius (medial, or middle, scalene) muscle; above, the brachial plexus of nerves; below, the pleura. The subclavian vein lies below and in front of the artery, separated from it by the Scalenus anterior.
Third part[edit]
The third portion of the subclavian artery runs downward and lateralward from the lateral margin of the Scalenus anterior to the outer border of the first rib, where it becomes the axillary artery. This is the most superficial portion of the vessel, and is contained in the subclavian triangle.
It is covered, in front, by the skin, the superficial fascia, the Platysma, the supraclavicular nerves, and the deep cervical fascia. The external jugular vein crosses its medial part and receives the transverse scapular, transverse cervical, and anterior jugular veins, which frequently form a plexus in front of the artery. Behind the veins, the nerve to the Subclavius descends in front of the artery. The terminal part of the artery lies behind the clavicle and the Subclavius and is crossed by the transverse scapular vessels. The subclavian vein is in front of and at a slightly lower level than the artery. Behind, it lies on the lowest trunk of the brachial plexus, which intervenes between it and the Scalenus medius. Above and to its lateral side are the upper trunks of the brachial plexus and the Omohyoideus. Below, it rests on the upper surface of the first rib.
Branches[edit]
Superficial dissection of the right side of the neck, showing the carotid and subclavian arteries. Branch of vertebral artery and thyrocervical trunk is labeled. Internal thoracic artery branches from same segment, but inferiorily, and is therefore not visible.
Part
Branches
Course
First part
From its origin to the medial border of scalenus anterior
Vertebral artery Runs cranially in the transverse foramina of the cervical vertebrae, joins the vertebral artery on the contralateral side, forming the basilar artery and joins the circle of Willis.
Internal thoracic artery Runs caudally behind the ribs, giving off anterior intercostal branches, perforating vessels to the breast and terminating in the superior epigastric artery and the musculophrenic artery
Thyrocervical trunk Very short. Divides into inferior thyroid artery, suprascapular artery and transverse cervical artery (also called cervicodorsal trunk)[1]
Second part
Lying behind scalenus anterior
Costocervical trunk Splits into superior intercostal artery and deep cervical artery.
Third part
Between the lateral border of scalenus anterior and the outer border of the first rib
Dorsal scapular artery From either second or third part. Passes backwards to supply levator scapulae and rhomboids.
Development[edit]
Embryologically, the left subclavian simply arises from the left 7th intersegmental artery,[2] while the right subclavian arises, proximal to distal:
right 4th aortic arch
right dorsal aorta
right 7th intersegmental artery
Essentially, the 4th aortic arch and dorsal aorta form the aortic arch on the left, but since the right dorsal aorta regresses distal to the right 7th intersegmental artery, on the left they form the proximal portion of the subclavian artery. Since the left subclavian is then a tributary of the left common carotid, they can be thought of as arising from the brachiocephalic trunk.
Variation[edit]
The subclavian arteries vary in their origin, their course, and the height to which they rise in the neck.
The origin of the right subclavian from the innominate takes place, in some cases, above the sternoclavicular articulation, and occasionally, but less frequently, below that joint. The artery may arise as a separate trunk from the arch of the aorta, and in such cases it may be either the first, second, third, or even the last branch derived from that vessel; in the majority, however, it is the first or last, rarely the second or third. When it is the first branch, it occupies the ordinary position of the innominate artery; when the second or third, it gains its usual position by passing behind the right carotid; and when the last branch, it arises from the left extremity of the arch, and passes obliquely toward the right side, usually behind the trachea, esophagus, and right carotid, sometimes between the esophagus and trachea, to the upper border of the first rib, whence it follows its ordinary course. In very rare instances, this vessel arises from the thoracic aorta, as low down as the fourth thoracic vertebra. Occasionally, it perforates the Scalenus anterior; more rarely it passes in front of that muscle. Sometimes the subclavian vein passes with the artery behind the Scalenus anterior. The artery may ascend as high as 4 cm. above the clavicle, or any intermediate point between this and the upper border of the bone, the right subclavian usually ascending higher than the left.
The left subclavian is occasionally joined at its origin with the left
The left subclavian artery is more deeply placed than the right in the first part of its course, and, as a rule, does not reach quite as high a level in the neck. The posterior border of the Sternocleidomastoideus corresponds pretty closely to the lateral border of the Scalenus anterior, so that the third portion of the artery, the part most accessible for operation, lies immediately lateral to the posterior border of the Sternocleidomastoideus.
Some authors describe the subclavian artery as arising from the 7th intersegmental artery.
Additional images[edit]
Side of neck, showing chief surface markings.
Magnetic Resonance Angiography
Right subclavian artery
Brachial plexus and subclavian artery
See also[edit]
This article uses anatomical terminology; for an overview, see Anatomical terminology.
Aberrant subclavian artery
Subclavian steal syndrome
Thoracic outlet syndrome
References[edit]
This article incorporates text in the public domain from the 20th edition of Gray's Anatomy (1918)
Jump up ^ http://quizlet.com/3156676/neck-flash-cards/
Jump up ^ "Aortic arches". www.embryology.ch. Retrieved 12 July 2016.
External links[edit]
Wikimedia Commons has media related to Subclavian artery.
Subclavian_artery at the Duke University Health System's Orthopedics program
Anatomy figure: 21:06-03 at Human Anatomy Online, SUNY Downstate Medical Center
Diagram of branches at informatics.jax.org
MedEd at Loyola Radio/curriculum/Vascular/subclavian_artery.htm
[show]
v
t
e
Arteries of the head and neck
CC
EC
sup. thyroid
superior laryngeal
sternocleidomastoid branch
infrahyoid branch
cricothyroid branch
glandular branches
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posterior meningeal
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inferior tympanic
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accessory meningeal
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to muscles of mastication (deep temporal, pterygoid, masseteric)
buccal
3rd part / pterygopalatine
posterior superior alveolar
infraorbital (anterior superior alveolar)
descending palatine (greater palatine, lesser palatine)
artery of the pterygoid canal
sphenopalatine (posterior septal branches, posterior lateral nasal)
pharyngeal
IC
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petrous
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ophthalmic
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ocular group: central retinal
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hypophysial (superior, inferior)
brain
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ACA (anterior communicating, medial striate, Orbitofrontal artery)
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posterior communicating
anterior choroidal
SC
vertebral artery
meningeal
spinal (posterior, anterior)
basilar: pontine
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cerebellar (AICA, SCA, PICA)
cerebral (PCA)
thyrocervical trunk
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inferior laryngeal
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acromial branch
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costocervical trunk
deep cervical
Supreme Intercostal artery
[show]
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Internal thoracic: Anterior intercostal
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Costocervical trunk: Highest intercostal (Posterior intercostal 1–2)
Deep cervical
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aorta
visceral: Bronchial
Esophageal
Mediastinal
parietal: Posterior intercostal 3–11
Subcostal
Superior phrenic
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