Purkinje fibers

Examples of Purkinje fibers in the following topics:

• Electric Activity in the Heart

  • If the AV node also fails, Purkinje fibers are capable of acting as the pacemaker.
  • The Purkinje fibers are located in the inner ventricular walls of 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.
  • During the ventricular contraction portion of the cardiac cycle, the Purkinje fibers carry the contraction impulse from both the left and right bundle branch to the myocardium of the ventricles.
  • Purkinje fibers also have the ability of automatically firing at a rate of 15-40 beats per minute if left to their own devices.

• Electrocardiogram and Correlation of ECG Waves with Systole

  • 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.
  • Following the T wave is the U wave, which represents repolarization of the Purkinje fibers.

• Anatomy of the Heart

  • The sinoatrial (SA) and atrioventricular (AV) nodes are bundles of nerve fibers that form this conduction system.
  • They are located in the left atrial wall of the heart and send nerve impulses to a large, highly specialized set of nerves called the Purkinje fibers, which in turn send those nerve impulses to the cardiac muscle tissue.

• Electrical Events

  • 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.

• Layers of the Heart Walls

  • The Purkinje fibers are located just beneath the endocardium and send nervous impulses from the SA and AV nodes outside of the heart into the myocardial tissues.

• Functions of the Cerebellum in Integrating Movements

  • In the human cerebellum, information from 200 million mossy fiber inputs is expanded to 40 billion granule cells, whose parallel fiber outputs then converge onto 15 million Purkinje cells.
  • Because of the way that they are lined up longitudinally, the 1,000 or so Purkinje cells belonging to a microzone may receive input from as many as 100 million parallel fibers and focus their own output down to a group of less than 50 deep nuclear cells.
  • Different modules share input from mossy fibers and parallel fibers, but in other respects they appear to function independently.
  • The synapses between parallel fibers and Purkinje cells, and the synapses between mossy fibers and deep nuclear cells, are both susceptible to modification of their strength.
  • As the illustration on the right shows, Purkinje cell dendritic trees are flattened in a way that aligns with the microzone length, and parallel fibers cross the microzones at right angles.

• Modulation of Movement by the Cerebellum

  • It receives input from thousands of parallel fibers, each individually very weak.
  • However, each cerebellar Purkinje cell also gets input from one single climbing fiber, which is so strong that a single climbing fiber action potential will reliably cause a target Purkinje cell to fire a burst of action potentials.
  • Divergence and convergence: The 1000 or so Purkinje cells belonging to a microzone may receive input from as many as 100 million parallel fibers, and focus their own output down to a group of less than 50 deep nuclear cells.
  • Plasticity: The synapses between parallel fibers and Purkinje cells, and the synapses between mossy fibers and deep nuclear cells, are both susceptible to modification of their strength.
  • The influence of each parallel fiber on nuclear cells is adjustable.

• Functions of the Cerebellum

  • Divergence and convergence: In the human cerebellum, information from 200 million mossy fiber inputs is expanded to 40 billion granule cells.
  • This neural divergence is followed by parallel fiber outputs that converge onto 15 million Purkinje cells.
  • Due to their longitudinal alignment, the approximately 1000 Purkinje cells belonging to a microzone may receive input via neural convergence from as many as 100 million parallel fibers.
  • Plasticity: The synapses between parallel fibers and Purkinje cells and between mossy fibers and deep nuclear cells are both susceptible to modification of their strength.
  • In a single cerebellar module, input from as many as a billion parallel fibers converge onto a group of less than 50 deep nuclear cells, and the influence of each parallel fiber on those nuclear cells is adjustable.

• Parts of the Cerebellum

  • This thin layer contains several types of neurons with a highly regular arrangement, most importantly Purkinje cells and granule cells .
  • It sends fibers to deep cerebellar nuclei that in turn project to both the cerebral cortex and the brain stem, thus providing modulation of descending motor systems.

• Dietary Fiber

  • Lignin, a major dietary insoluble fiber source, may alter the fate and metabolism of soluble fibers.
  • The term "fiber" is something of a misnomer since many types of so-called dietary fiber are not actually fibrous.
  • Dietary fiber is found in plants.
  • Fiber-rich plants can be eaten directly.
  • The plum's skin is a source of insoluble fiber while soluble fiber is in the pulp.