node of Ranvier

Examples of node 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.

• 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) .

• Functions of Stems

  • Plant stems, whether above or below ground, are characterized by the presence of nodes and internodes .
  • Nodes are points of attachment for leaves, aerial roots, and flowers.
  • The stem region between two nodes is called an internode.
  • An internode is the stem region between two nodes.
  • The leaves just above the nodes arise from axillary buds.

• Cytotoxic T Lymphocytes and Mucosal Surfaces

  • The lymphatic system houses large populations of immune cells which are released upon detection of a pathogen.
  • Although the immune system is characterized by circulating cells throughout the body, the regulation, maturation, and intercommunication of immune factors occur at specific sites that are known as lymph nodes.
  • Lymph nodes scattered throughout the body house large populations of T and B cells, dendritic cells, and macrophages .
  • The liquid passes through (b) lymph nodes that filter the lymph that enters the node through afferent vessels, leaving through efferent vessels.
  • Lymph nodes are filled with lymphocytes that purge infecting cells.

• The Cardiac Cycle

  • The internal pacemaker starts at the sinoatrial (SA) node, which is located near the wall of the right atrium.
  • Electrical charges spontaneously pulse from the SA node, causing the two atria to contract in unison.
  • The pulse reaches a second node, the atrioventricular (AV) node, between the right atrium and right ventricle, where it pauses for approximately 0.1 seconds before spreading to the walls of the ventricles.
  • 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.
  • Summarize the caridac cycle and explain the role of the SA node and the AV node in regulating the its rhythm

• Leaf Structure and Arrangment

  • Most leaves have a midrib, which travels the length of the leaf and branches to each side to produce veins of vascular tissue.
  • The edge of the leaf is called the margin .
  • Monocots and dicots differ in their patterns of venation .
  • Plants that have only one leaf per node have leaves that are said to be either alternate or spiral.
  • If there are three or more leaves connected at a node, the leaf arrangement is classified as whorled.

• Stem Modifications

  • A rhizome is a modified stem that grows horizontally underground; it has nodes and internodes.
  • Stolons are stems that run almost parallel to the ground, or just below the surface, and can give rise to new plants at the nodes.
  • Runners are a type of stolon that runs above the ground and produces new clone plants at nodes at varying intervals: strawberries are an example.
  • A bulb, which functions as an underground storage unit, is a modification of a stem that has the appearance of enlarged fleshy leaves emerging from the stem or surrounding the base of the stem, as seen in the iris .
  • Cladodes are green branches of limited growth (usually one internode long) which have taken up the functions of photosynthesis.

• Charales

  • A representative species of Charales is Chara, which is often called muskgrass or skunkweed because of its unpleasant smell .
  • In Charales, large cells form the thallus: the main stem of the alga.
  • Branches arising from the nodes are made of smaller cells.
  • Male and female reproductive structures are found on the nodes; the sperm have flagella.
  • Clearly, plant biologists have yet to solve the mystery of the origin of land plants.

• The Diversity of Life

  • The source of this diversity is evolution, the process of gradual change during which new species arise from older species.
  • A phylogenetic tree is composed of nodes and branches.
  • The internal nodes represent ancestors and are points in evolution when, based on scientific evidence, an ancestor is thought to have diverged to form two new species.
  • The length of each branch is proportional to the time elapsed since the split.
  • The comparison of homologous DNA and RNA sequences provided Woese with a sensitive device that revealed the extensive variability of prokaryotes, and which justified the separation of the prokaryotes into two domains: bacteria and archaea.

• Bone and Joint Disorders

  • The most common bone and joint disorder are types of arthritis.
  • Arthritis is a common disorder of synovial joints that involves inflammation of the joint.
  • There are more than 100 different forms of arthritis.
  • Gout is a form of arthritis that results from the deposit of uric acid crystals within a body joint.
  • The formation of hard nobs at the middle finger joints (known as Bouchard's nodes) and at the farther away finger joint (known as Heberden's node) are a common feature of Osteoarthritis in the hands.