bundle of His

Examples of bundle of His in the following topics:

• Electrical Events

  • The SA node is a bundle of nerve cells located on the outer layer of the right atria.
  • The SA node stimulates the right atria directly, and stimulates the left atria through the Bachmann's bundle.
  • The AV node is a bundle of conducting tissue (not formally classified as nerve tissue) located at the junction between the atria and ventricles of the heart. 
  • The AV node receives action potentials from the SA node, and transmits them through the bundle of His, the left and right bundle branches, and purkinje fibers, which cause depolarization of ventricular muscle cells, leading to ventricular contraction.
  • Certain types of autonomic nervous stimulation will alter the rate of firing in the AV node.

• The Cardiac Cycle

  • The cardiac cycle is the coordination of the filling and emptying of blood by electrical signals that cause the heart muscles to contract and relax.
  • The pumping of the heart is a function of the cardiac muscle cells, or cardiomyocytes, that comprise the heart muscle.
  • From the AV node, the electrical impulse enters the bundle of His, then to the left and right bundle branches extending through the interventricular septum.
  • This information can be observed as an electrocardiogram (ECG): a recording of the electrical impulses of the cardiac muscle.
  • The beating of the heart is regulated by an electrical impulse that causes the characteristic reading of an ECG.

• Electrocardiogram and Correlation of ECG Waves with Systole

  • An electrocardiogram, or ECG, is a recording of the heart's electrical activity as a graph over a period of time.
  • An electrocardiogram, or ECG or EKG, is a recording of the heart's electrical activity as a graph over a period of time, as detected by electrodes attached to the outer surface of the skin and recorded by a device external to the body.
  • It can also detect enlargement of the heart, decreased blood flow, or the presence of current or past heart attacks.
  • The P wave is the first wave on the ECG because the  action potential for the heart is generated in the sinoatrial node, located on the atria, which sends action potentials directly through the Bachman's bundle to depolarize the atrial muscle cells.
  • The QRS complex represents action potentials moving from the AV node, through the bundle of His and left and right branches and Purkinje fibers into the ventricular muscle tissue.

• Optimization of consumption

  • Optimization of consumption is defined by two factors:
  • A budget constraint represents all the combinations of goods and services that a consumer may purchase given current prices within his or her given income.
  • An indifference curve is a graph showing different bundles of goods between which a consumer is indifferent.
  • That is, at each point on the curve, the consumer has no preference for one bundle over another.
  • Instead of comparing two single goods, you can construct the indifference curve so it compares the utility of one good with the utility of a composite of all other goods.

• Axon Bundles

  • A bundle of axons is called a nerve in the peripheral nervous system and a tract in the central nervous system.
  • Bundles of neurons processes are called tracts in the CNS and nerves in the PNS.  
  • There are twelve pairs of cranial nerves and thirty one pair of spinal nerves.
  • Underlying this layer of flat cells, the perineurium, forms a complete sleeve around a bundle of axons called fascicles.
  • Describe bundles of axons in the central and peripheral nervous systems

• Structure of a Nerve

  • A nerve is the primary structure of the peripheral nervous system and is composed of bundles of axons.
  • A nerve is an enclosed, cable-like bundle of axons (the projections of neurons) in the peripheral nervous system (PNS) .
  • The axons are bundled together into groups called fascicles.
  • The endoneurium consists of an inner sleeve of material called the glycocalyx and a mesh of collagen.
  • Nerves are bundled along with blood vessels, which provide essential nutrients and energy to the enclosed, and metabolically demanding, neurons.

• Stem Anatomy

  • When the stem is viewed in cross section, the vascular bundles of dicot stems are arranged in a ring.
  • In (a) dicot stems, vascular bundles are arranged around the periphery of the ground tissue.
  • The xylem tissue is located toward the interior of the vascular bundle; phloem is located toward the exterior.
  • Sclerenchyma fibers cap the vascular bundles.
  • In (b) monocot stems, vascular bundles composed of xylem and phloem tissues are scattered throughout the ground tissue.

• Classification of Nerves

  • Mixed nerves: contain both afferent and efferent axons, and thus conduct both incoming sensory information and outgoing muscle commands in the same nerve bundle.
  • The lack of myelination in the C group is the primary cause of their slow conduction velocity.
  • C fiber axons are grouped together into what is known as Remak bundles.
  • These occur when an unmyelinated Schwann cell bundles the axons close together by surrounding them.
  • Because of their higher conduction velocity, A-delta fibers are responsible for the sensation of a sharp, initial pain and respond to a weaker intensity of stimulus.

• Brain: Cerebral Cortex and Brain Lobes

  • The brain is the part of the central nervous system that is contained in the cranial cavity of the skull.
  • A thick fiber bundle, the corpus callosum, connects the two hemispheres, allowing information to be passed from one side to the other.
  • For example, the neurons that control movement of the fingers are next to the neurons that control movement of the hand.
  • The role of the hippocampus in memory was partially determined by studying one famous epileptic patient, HM, who had both sides of his hippocampus removed in an attempt to cure his epilepsy.
  • His seizures went away, but he could no longer form new memories (although he could remember some facts from before his surgery and could learn new motor tasks).

• Gammaproteobacteria

  • Gammaproteobacteria is a class of several medically, ecologically and scientifically important groups of bacteria.
  • Members of the Enterobacteriaceae can be trivially referred to as enterobacteria, as several members live in the intestines of animals.
  • Members of Chromatium are photosynthetic and oxidize hydrogen sulfide instead of water, producing sulfur as excrement.
  • In order to get the disease cholera, the bacteria must be able to colonize in the small intestine and a critical factor necessary for this colonization is the toxin-co-regulated pilus(TCP). 0395 is a wild type strain, showing the normal bundling of toxin-co-regulated pilus(TCP).
  • Wild-type pili are clearly visible as 7 nm fibres that form bundles @ 0.2Ð0.3 µm wide and 3Ð6 µm long.