Temporal muscle

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A Moment in History

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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Details: Written by: Fernanda Cortes, DDS, MSc; Published: January 17, 2017; Hits: 6508

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The temporal muscle (Lat:Temporalis) is a bilateral muscle located on the side of the head. It belongs to a subgroup of head muscles called Masticatory Muscles, named after their function elevating the mandible to produce the mandible movements (1,2). Masticatory muscles are four per side: Temporalis, Masseter, Pterygoideus medialis and Pterygoideus lateralis (1,2).

The temporalis muscle is a fan-shaped muscle which occupies the temporal fossa from which its fascicles (fibers) converge to the coronoid process of the mandible. Classic description for this muscle recognizes three main muscular bodies (anterior, midle, and posterior) originated from the temporal fossa up to the lower temporalis line and the temporalis fascia, fascicles which descend through the inner part de the zygomatic arch converging to be inserted on the coronoid process of the mandible, its temporalis crest and anterior margin of the mandibular branch through thick tendons (1,2).

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In 1996 Dunn et al. (3) reported the discovery of a so far unknown masticatory muscle called the “sphenomandibularis”, originated from the greater wing of the sphenoid bone medial to the temporalis muscle and descends on an oblique (lateral and slightly posterior) fashion reaching distally the coronoid process of the mandible. This muscular portion has been recognized as the “deep belly of the temporalis muscle” and has been described by several authors since then (4,5,6,8). The importance that has been given to this particular bundle lies on the fact that its medial insertion can reach a close relationship to the foramen rotundum, place of emergency from the cranium of the maxillary nerve, which has been hypothesized, could lead to eventual alteration of this nerve if it got trapped by this part of the muscle (6, 7).

The temporalis muscle receives innervation fundamentally from branches of the mandibular nerve: Deep temporal nerve (N. temporalis profundus)through its anterior middle and posterior branches.

The temporalis muscle is covered by a thick fascia layer: the temporalis fascia.

Article written by: Maria F. Cortés, DDS, MSc.

Images from:
Fig 1. Public domain, by Henry Vandyke Carter, MD - Gray's Anatomy, 1918
Fig 2. Geers C, Nyssen-Behets C, Cosnard G, Lengelé B. The deep belly of the temporalis muscle: an anatomical, histological and MRI study. Surg Radiol Anat. 2005 Aug;27(3):184-91. Epub 2005 Apr 9

Sources:
1. “Anatomía humana” V.2. Latarjet- Ruiz Liard, 4ª ed. 6ª reimp. 2008 Médica Panamericana, Buenos Aires, Argentina.
2. “Anatomía humana: descriptiva, topográfica y funcional. Tomo 1. Cabeza y Cuello, Rouviere H – Delmas A, 11° ed. 2005 MASSON, S.A., Barcelona, Spain.
3. Dunn GF, Hack GD, Robinson WL, Koritzer RT. Anatomical observation of a craniomandibular muscle originating from the skull base: the sphenomandibularis. Cranio. 1996 Apr;14(2):97-103; discussion 104-5.
4. Shimokawa T, Akita K, Soma K, Sato T. Innervation analysis of the small muscle bundles attached to the temporalis: truly new muscles or merely derivatives of the temporalis? Surg Radiol Anat. 1998;20(5):329-34.
5. Akita K, Shimokawa T, Sato T. Aberrant muscle between the temporalis and the lateral pterygoid muscles: M. pterygoideus proprius (Henle). Clin Anat. 2001 Jul;14(4):288-91.
6. Schön Ybarra MA, Bauer B. Medial portion of M. Temporalis and its potential involvement in facial pain. Clin Anat. 2001;14(1):25-30.
7. Fuentes E, Llanos S, Gómez R, Llanos P, Llanos F, Cortés-Sylvester MF, Solaria P, Melian A, Asfura J, Santos M, Zamorano E. Discovery of deep temporalis muscle belly close to maxillary nerve in a patient with trigeminal neuralgia: hypothesis of muscular compression and case report treated by Botox® Onabotulinum toxin tipe-A. Chirurgia 2016 June;29(3):99-102
8. Geers C, Nyssen-Behets C, Cosnard G, Lengelé B. The deep belly of the temporalis muscle: an anatomical, histological and MRI study. Surg Radiol Anat. 2005 Aug;27(3):184-91. Epub 2005 Apr 9.

Temporal muscle

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