Cardiac muscle is one of the three types of muscle found in the human body. It is found exclusively in the heart, where it forms the main component of its middle layer, the myocardium.  

[Myo]=combining form for "muscle"; [-card-]=heart; and [-ium]=layer or membrane. The myocardium is the muscle layer of the heart.

Cardiac muscle has distinct striations and intercalated discs (see accompanying image). The cardiac muscle acts as a functional syncytium. 

The key characteristic of cardiac muscle is its capacity to contract rhythmically in the absence of an external electrical stimulus. The other two types of muscle (smooth and skeletal) lack this characteristic, called automatism or automaticity.

The terms [medial] and [lateral] are opposing anatomical relationship terms that indicate the location of a structure or structures in relation to the midline or median plane. The accompanying image depicts the median plane.

The term "midline" is a bit of a misnomer, as this is a plane and not a line, although if you look at the median plane from the anterior or posterior aspect of an individual in the anatomical position, you would have a line, ergo, midline! Look at this article on the anatomical position to see an explanation and image of this concept.

The term [medial] means "closer to the midline". An example of the use of this term is: "the head of the clavicle is medial to the shoulder joint", that is, the head of the clavicle is closer to the midline than the shoulder joint.

The term [lateral] means "further from the midline". An example of the use of this term is: "the wrist joint is lateral to the elbow joint", that is, the wrist joint is further away from the midline than the elbow joint.

Click on the image for a visual explanation of the concepts of "medial" and "lateral".

Images property of: CAA.Inc. Artist: Victoria G. Ratcliffe

The term [inion] is Greek and originally referred to the posterior aspect of the neck, as mentioned in the Iliad.

The term fell in disuse for hundreds of years, until it was resurrected by Peter Paul Broca (1824-1880) as a craniometric point. The inion is the midline protuberance in the posteroinferior aspect of the external surface of the occipital bone. Today, in most anatomy texts the inion is referred to as the "external occipital protuberance"

The inion is found at the intersection of three bony lines that are easily palpable, the bilaterally situated superior nuchal line, and the median nuchal line (see accompanying image). There is a corresponding internal occipital protuberance in the internal aspect of the occipital bone.

Original image courtesy of Bartleby.com. Click on the image for a larger version. 

The word [sesamoid] means "similar to a sesame". First used by Galen c.180AD, he describes small ovoid bones that are "similar to a sesame seed", referencing the seed of the plant sesamum indicum, the oil of which was used as a laxative at that time. 

Sesamoid bones are found in the tendons of some muscles and are mostly inconstant. Largey and Bonnet proposed a classification for these bones as: accessory, capsuloligamentous, intratendineous, and mixed.

Of special interest to this article are the sesamoid bones found within the two tendons of the flexor hallucis brevis muscle in the base of the foot (see accompanying X-ray image). These bones, especially the medial sesamoid bone, was attributed religious, mystical, and magical powers since ancient times. This is due to the fact that this small bone is highly resistant to natural decomposition. A Hebrew medical text dated 210 BC, attributed to Ushaia presented a small bone he called "luz" as the "depository of the soul". Many other authors, including Vesalius (who called it Albadaran), believed that upon resurrection, the whole body could reform from this "seed" bone.

This belief was later reinforced by religious texts into the early Renaissance which stated that this bone was indestructible and its presence was enough to guarantee resurrection for believers. 

Sources:
1. "Les os se?samo?¨des de l’hallux : du mythe a` la fonction" Largely,A; Bonnel, BE Med Chir Pied 2008 24: 28–38
2. "Tratado de Anatomia Humana" Testut et Latarjet 8 Ed. 1931 Salvat Editores, Spain
3. "De Humani Corporis Fabrica" Vesalius, Andrea. 1543 Oporinus
Thanks to the first year medical students at the University of Cincinnati who inspired this article. Dr. Miranda 

Original image courtesy of
Wesley Norman, Ph.D.

Ignaz Semmelweis, MD (1818- 1865). Born in Budapest as Ign?c F?l?p Semmelweis, he started his university studies as a lawyer, but changed to Medicine and in 1844, at the age of 26, attained his MD degree. in 1847 he was appointed as an assistant in Obstetrics, almost at the same time of the death of a friend (Kolletschka, a pathologist) who died of what appeared to be "puerperal fever", also known as "childbed fever" after being accidentally stabbed by a knife during the autopsy of a female who had died of that disease. Semmelweis reasoned that the disease somehow was transmitted via the wound and started a crusade to have surgeons and students clean their hands with a carbolized solution before examining a healthy pregnant woman.

Although the obstetric wards under his care reduced the rate of this disease to almost nothing, Semmelweis endured criticism from his teachers, colleagues, and peers, and he did not make any friends by calling "murderers" those who did not follow his ideas.  murderers".  An excerpt of a letter to one of this detractors reads: "I denounce you before God and the world as a murderer and the history of puerperal fever will not do you an injustice when for the service of having been the first to oppose my life-saving technique it perpetuates your name as a medical Nero". He did not publish his findings until later in life, and then received even more criticism.

In 1865 was committed to an mental asylum only to die a few days later. He was only 47 years old. The same year he died Joseph Lister performed the first operations using antiseptic technique.

Original image courtesy of
Images from the History of Medicine.

The term [muscle] arises from the Latin word [musculus] which derives from the Latin term [mus] meaning "mouse". We can only guess that, just as today, Roman fathers would show their biceps and forearm muscles to their children and tried to make them believe a mouse had gotten under their skin!. The root term for muscle is [-my-]. The corresponding combining form is [-myo-]. 

There are three types of muscle in the human body:

• Skeletal muscle: it is typical of muscles related to bones (skeletal) and they are voluntary.
• Smooth muscle: found in organs that act without volition (involuntary), such as the digestive system and glands.
• Cardiac muscle: found exclusively in the heart.

Muscles are formed by subunits, each one surrounded by a named membrane. One of the suffixes that means layer or membrane is [-sium]:

• Epimysium: Epi=outer; my=muscle; sium=membrane. The outer or external membrane (layer) of a muscle
• Perimysium: Peri=around; my=muscle; sium=membrane. A membrane around a muscle
• Endomysium: Endo= inner or internal; my=muscle; sium=membrane. The inner or internal membrane of a muscle- 

Original image courtesy of Wikipedia. Click on the image for a larger version.