nodes of Ranvier

Examples of nodes of Ranvier in the following topics:

• Nerve Impulse Transmission within a Neuron: Action Potential

  • A node of Ranvier is a natural gap in the myelin sheath along the axon .
  • If nodes of Ranvier were not present along an axon, the action potential would propagate very slowly; Na+ and K+ channels would have to continuously regenerate action potentials at every point along the axon.
  • Nodes of Ranvier also save energy for the neuron since the channels only need to be present at the nodes and not along the entire axon.
  • Nodes of Ranvier are gaps in myelin coverage along axons.
  • Nodes contain voltage-gated K+ and Na+ channels.

• Characteristics of Nervous Tissue

  • Nervous tissue is one of four major classes of tissues.
  • A typical neuron consists of dendrites, cell body and an axon.
  • The medullary sheath is interrupted at intervals by the nodes of Ranvier.
  • Transmission electron micrograph of a myelinated axon.
  • Image illustrates the parts of a neuron.

• Introducing the Neuron

  • The synapse is the chemical junction between the axon terminals of one neuron and the dendrites of the next.
  • Periodic gaps in the myelin sheath are called nodes of Ranvier.
  • At these nodes, the signal is "recharged" as it travels along the axon.
  • This neuron diagram also shows the oligodendrocyte, myelin sheath, and nodes of Ranvier.
  • The above image shows the basic structural components of an average neuron, including the dendrite, cell body, nucleus, Node of Ranvier, myelin sheath, Schwann cell, and axon terminal.

• Stages of the Action Potential

  • As these positive ions rush in, the membrane of the stimulated cell reverses its polarity so that the outside of the membrane is negative relative to the inside.
  • Once the electric gradient has reached the threshold of excitement, the "downswing" of repolarization begins.
  • In myelinated axons (axons covered by a myelin sheath), this process is described as saltatory because voltage-gated channels are only found at the nodes of Ranvier, and the electrical events seem to "jump" from one node to the next.
  • The amplitude of an action potential is independent of the amount of current that produced it.
  • The frequency of action potentials is correlated with the intensity of a stimulus.

• Neurons

  • The ability of neurons to communicate with each other, as well as with other types of cells, underlies all of these behaviors.
  • The myelin sheath is not actually part of the neuron.
  • These gaps, called "nodes of Ranvier," are sites where the signal is "recharged" as it travels along the axon.
  • There are different types of neurons; the functional role of a given neuron is intimately dependent on its structure.
  • There is an amazing diversity of neuron shapes and sizes found in different parts of the nervous system (and across species) .

• Electrical Events

  • The SA node is a bundle of nerve cells located on the outer layer of the right atria.
  • 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 slows the neural impulse from the SA node by a slight amount, which causes a delay between depolarization of the atria and the ventricles.
  • The normal firing rate in the AV node is lower compared to the SA node because it slows the rate of neural impulses.
  • Certain types of autonomic nervous stimulation will alter the rate of firing in the AV node.

• Lymph Nodes

  • Lymph nodes are small oval-shaped balls of lymphatic tissue, distributed widely throughout the body and linked by a vast network of lymphatic vessels.
  • Lymph fluid flows into and out of the lymph nodes via the lymphatic vessels, a network of valved vessels that are similar in structure to cardiovascular veins.
  • Each lymph node has an afferent lymph vessel, which directs lymph into the node, and an efferent lymph vessel, which directs lymph out of the node at the concave side of the node, known as the hilum.
  • The hilium also contains the blood supply of the lymph node.
  • This diagram shows the network of lymph nodes and connecting lymphatic vessels in the human body.

• Lymph Transport

  • The lymph fluid drains into the node just beneath the capsule of the node into the various sinus spaces of the lymph node.
  • The sinuses converge at the hilum of the node, and lymph then leaves the lymph node via an efferent lymphatic vessel towards either a more central lymph node or towards a lymph duct for drainage into one of the subclavian veins.
  • The lymph nodes also contain a large number of B and T lymphocytes, which are transported throughout the node during many components of the adaptive immune response.
  • The lymph flows from the afferent vessels into the sinuses of the lymph node, and then out of the node through the efferent vessels.
  • Describe the location of B cells and T cells in lymph nodes and the path of lymph circulation

• Electric Activity in the Heart

  • The sinoatrial node (also commonly spelled sinuatrial node) is the impulse-generating (pacemaker) tissue located in the right atrium of the heart: i.e., generator of normal sinus rhythm.
  • The sinoatrial node (also commonly spelled sinuatrial node, abbreviated SA node) is the impulse-generating (pacemaker) tissue located in the right atrium of the heart, and thus the generator of normal sinus rhythm.
  • If the AV node also fails, Purkinje fibers are capable of acting as the pacemaker.
  • In contrast, the SA node outside of parasympathetic control can fire a rate of almost 100 beats per minute.
  • High magnification micrograph of sinoatrial node tissue and an adjacent nerve fiber.

• Node attributes

  • Using colors and shapes are useful ways of conveying information about what "type" of actor each node is.
  • But, generally, a k-core is a set of nodes that are more closely connected to one another than they are to nodes in other k-cores.
  • In addition, the size of the nodes in each K-core are proportional to the size of the K-core.
  • Differences of amount: Figure 4.3 also uses the size of the nodes (Properties>nodes>size>attribute-based) to display an index of the number of nodes in each group.
  • This difference of amount among the nodes is best indicated, visually, by assigning the size of the node to values of some attribute.