Medical Terminology Daily - Est. 2012

Medical Terminology Daily (MTD) is a blog sponsored by Clinical Anatomy Associates, Inc. as a service to the medical community. We post anatomical, medical or surgical terms, their meaning and usage, as well as biographical notes on anatomists, surgeons, and researchers through the ages. Be warned that some of the images used depict human anatomical specimens.

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A Moment in History

Jean George Bachman

Jean George Bachmann
(1877 – 1959)

French physician–physiologist whose experimental work in the early twentieth century provided the first clear functional description of a preferential interatrial conduction pathway. This structure, eponymically named “Bachmann’s bundle”, plays a central role in normal atrial activation and in the pathophysiology of interatrial block and atrial arrhythmias.

As a young man, Bachmann served as a merchant sailor, crossing the Atlantic multiple times. He emigrated to the United States in 1902 and earned his medical degree at the top of his class from Jefferson Medical College in Philadelphia in 1907. He stayed at this Medical College as a demonstrator and physiologist. In 1910, he joined Emory University in Atlanta. Between 1917 -1918 he served as a medical officer in the US Army. He retired from Emory in 1947 and continued his private medical practice until his death in 1959.

On the personal side, Bachmann was a man of many talents: a polyglot, he was fluent in German, French, Spanish and English. He was a chef in his own right and occasionally worked as a chef in international hotels. In fact, he paid his tuition at Jefferson Medical College, working both as a chef and as a language tutor.

The intrinsic cardiac conduction system was a major focus of cardiovascular research in the late nineteenth and early twentieth centuries. The atrioventricular (AV) node was discovered and described by Sunao Tawara and Karl Albert Aschoff in 1906, and the sinoatrial node by Arthur Keith and Martin Flack in 1907.

While the connections that distribute the electrical impulse from the AV node to the ventricles were known through the works of Wilhelm His Jr, in 1893 and Jan Evangelista Purkinje in 1839, the mechanism by which electrical impulses spread between the atria remained uncertain.

In 1916 Bachmann published a paper titled “The Inter-Auricular Time Interval” in the American Journal of Physiology. Bachmann measured activation times between the right and left atria and demonstrated that interruption of a distinct anterior interatrial muscular band resulted in delayed left atrial activation. He concluded that this band constituted the principal route for rapid interatrial conduction.

Subsequent anatomical and electrophysiological studies confirmed the importance of the structure described by Bachmann, which came to bear his name. Bachmann’s bundle is now recognized as a key determinant of atrial activation patterns, and its dysfunction is associated with interatrial block, atrial fibrillation, and abnormal P-wave morphology. His work remains foundational in both basic cardiac anatomy and clinical electrophysiology.

Sources and references
1. Bachmann G. “The inter-auricular time interval”. Am J Physiol. 1916;41:309–320.
2. Hurst JW. “Profiles in Cardiology: Jean George Bachmann (1877–1959)”. Clin Cardiol. 1987;10:185–187.
3. Lemery R, Guiraudon G, Veinot JP. “Anatomic description of Bachmann’s bundle and its relation to the atrial septum”. Am J Cardiol. 2003;91:148–152.
4. "Remembering the canonical discoverers of the core components of the mammalian cardiac conduction system: Keith and Flack, Aschoff and Tawara, His, and Purkinje" Icilio Cavero and Henry Holzgrefe Advances in Physiology Education 2022 46:4, 549-579.
5. Knol WG, de Vos CB, Crijns HJGM, et al. “The Bachmann bundle and interatrial conduction” Heart Rhythm. 2019;16:127–133.
6. “Iatrogenic biatrial flutter. The role of the Bachmann’s bundle” Constán E.; García F., Linde, A.. Complejo Hospitalario de Jaén, Jaén. Spain
7. Keith A, Flack M. The form and nature of the muscular connections between the primary divisions of the vertebrate heart. J Anat Physiol 41: 172–189, 1907.


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Brachialis muscle - Image modified from the original. Public domain
Brachialis muscle.
Click on the image for a larger depiction

UPDATED: The brachialis muscle is a skeletal muscle attached proximally to the anterior surface of the humerus and distally to the coronoid process and tuberosity of the ulna. It is one of the three muscles in the anterior compartment of the arm (flexor compartment), the other two being the biceps brachii and the coracobrachialis.

It is a strong flexor of the elbow found deep to the biceps brachii. Because it does not attach to the radius, the brachialis muscle does not participate in the pronation and supination of the forearm.

The brachialis is supplied by branches of the brachial artery and by the recurrent radial artery.

The innervation of the brachialis muscle is a point to be discussed. Most modern books of anatomy state that this muscle is innervated by the musculocutaneous nerve (C5, C6, and C7). Older and more detailed books state that this muscle has a dual innervation. A 2011 research paper published in Spanish (see Sources #6) describes this dual innervation. The proximal portion of the muscles is indeed innervated by the musculocutaneous nerve, but the distal portion (in 90% of the cases) is innervated by muscular branches that arise off the radial nerve. The radial nerve (C5, C6, C7, C8 & T1) is a branch of the brachial plexus.

Following is an excerpt from the "Trail Guide to the Body" by Andrew Biel: "Ironically, (because it is deep to the biceps) the brachialis girth only helps the biceps brachii to bulge further from the arm, making the brachialis the biceps' "best friend"

Personal note: The research paper that describes the double innervation of the brachialis muscle was done at my alma mater, the University of Chile, and the authors' listing includes two of the contributors to this blog, Professors Claudio Molina and Cristian Uribe. Dr. Miranda

Sources:
1. “Gray’s Anatomy” Henry Gray, 1918
2. "Tratado de Anatomia Humana" Testut et Latarjet 8th Ed. 1931 Salvat Editores, Spain
3. "Gray's Anatomy" 42nd British Ed. Churchill Livingstone 2021
4. “An Illustrated Atlas of the Skeletal Muscles” Bowden, B. 4th Ed. Morton Publishing. 2015
5. "Trail Guide to The Body" 4th. Ed. Biel, A. Books of Discovery. 2010
6. "Doble Innervacion del Musculo Brachial en la Poblacion Chilena" Claudio Molina; Cristián Uribe; Álvaro Heras; Cristián Astorga;Jorge Lemus & Alberto Rodríguez. Int. J. Morphol, 2011. 29(4):1207-1211. A PDF copy of this paper is available here.

Note: The side image modified from the original by Anatomography, CC BY-SA 2.1 JP <https://creativecommons.org/licenses/by-sa/2.1/jp/deed.en>, via Wikimedia Commons following Creative Commons attributes.