Node

In general, a node is a localised swelling (a "knot") or a point of intersection (a vertex).

Node may refer to:

In mathematics

In computing and electronics

Khan Academy

Khan Academy is a non-profit educational organization created in 2006 by educator Salman Khan with the aim of providing a free, world-class education for anyone, anywhere. The organization produces short lectures in the form of YouTube videos. In addition to micro lectures, the organization's website features practice exercises and tools for educators. All resources are available for free to anyone around the world. The main language of the website is English, but the content is also available in other languages.

History

The founder of the organization, Salman Khan, was born in New Orleans, Louisiana, United States to immigrant parents from Bangladesh and India. After earning three degrees from the Massachusetts Institute of Technology (a BS in mathematics, a BS in electrical engineering and computer science, and an MEng in electrical engineering and computer science), he pursued an MBA from Harvard Business School.

In late 2004, Khan began tutoring his cousin Nadia who needed help with math using Yahoo!'s Doodle notepad.When other relatives and friends sought similar help, he decided that it would be more practical to distribute the tutorials on YouTube. The videos' popularity and the testimonials of appreciative students prompted Khan to quit his job in finance as a hedge fund analyst at Connective Capital Management in 2009, and focus on the tutorials (then released under the moniker "Khan Academy") full-time.

Sinoatrial node

The sinoatrial node (often abbreviated SA node; also commonly called the sinus node and less commonly the sinuatrial node) is the normal natural pacemaker of the heart and is responsible for the initiation of the heartbeat. It spontaneously generates an electrical impulse, which after conducting throughout the heart, causes the heart to contract. Although the electrical impulses are generated spontaneously, the rate of the impulses (and therefore the heart rate) is set by the nerves innervating the sinoatrial node. The sinoatrial node is located in the myocardial wall near where the sinus venosus joins the right atrium (upper chamber); hence sino- + atrial.

Discovery

It was first discovered by a young medical student, Martin Flack, in the heart of a mole, whilst his mentor, Sir Arthur Keith, was on a bicycle ride with his wife. They made the discovery in a makeshift laboratory set up in a picturesque farmhouse in Kent, England, called Mann's Place. Their discovery was published in 1907.

Bundle of His

The bundle of His or His bundle is a collection of heart muscle cells specialized for electrical conduction. As part of the electrical conduction system of the heart, it transmits the electrical impulses from the AV node (located between the atria and the ventricles) to the point of the apex of the fascicular branches via the bundle branches. The fascicular branches then lead to the Purkinje fibers, which provide electrical conduction to the ventricles, causing the cardiac muscle of the ventricles to contract at a paced interval.

Function

The bundle of His is an important part of the electrical conduction system of the heart, as it transmits impulses from the atrioventricular node, located at the inferior end of the interatrial septum, to the ventricles of the heart. The intrinsic rate of the bundle of His is 20 or less beats per minute. The bundle of His branches into the left and the right bundle branches, which run along the interventricular septum. The left bundle branch further divides into the left anterior and the left posterior fascicles. These bundles and fascicles give rise to thin filaments known as Purkinje fibers. These fibers distribute the impulse to the ventricular muscle. The ventricular conduction system comprises the bundle branches and the Purkinje network. It takes about 0.03–0.04 seconds for the impulse to travel from the bundle of His to the ventricular muscle.

Purkinje fibers

The Purkinje fibers (/pərˈkɪndʒiː/ pər-KIN-jee) (Purkinje tissue or subendocardial branches) are located in the inner ventricular walls of the heart, just beneath the endocardium in a space called the subendocardium. The Purkinje fibers are specialised conducting fibers larger than cardiomyocytes with fewer myofibrils and a large number of mitochondria that are able to conduct cardiac action potentials more quickly and efficiently than any other cells in the heart. Purkinje fibers allow the heart's conduction system to create synchronized contractions of its ventricles, and are, therefore, essential for maintaining a consistent heart rhythm.

Histology

Purkinje fibers are a unique cardiac end-organ. Further histologic examination reveals that these fibers are split in atria and ventricles walls. The electrical origin of atrial Purkinje fibers arrives from the sinoatrial node.

Given no aberrant channels, the atrial and ventricular Purkinje fibers are distinctly shielded from each other by collagen or the cardiac skeleton.