glial cell

Examples of glial cell in the following topics:

• Glia

  • While glia (or glial cells) are often thought of as the supporting cast of the nervous system, the number of glial cells in the brain actually outnumbers the number of neurons by a factor of ten.
  • Neurons would be unable to function without the vital roles that are fulfilled by these glial cells.
  • Glial cells support neurons and maintain their environment.
  • Glial cells of the (a) central nervous system include oligodendrocytes, astrocytes, ependymal cells, and microglial cells.
  • (a) Astrocytes and (b) oligodendrocytes are glial cells of the central nervous system.

• Muscle Tissues and Nervous Tissues

  • A nerve consists of a neuron and glial cells.
  • Glial cells support the neurons.
  • Other glial cells support the nutritional and waste requirements of the neuron.
  • Some of the glial cells are phagocytic, removing debris or damaged cells from the tissue.
  • Also shown are two types of glial cells: astrocytes to regulate the chemical environment of the nerve cell, and oligodendrocytes to insulate the axon so the electrical nerve impulse is transferred more efficiently.

• Neurons and Glial Cells

  • Instead, they have a system of separate-but-connected nerve cells (neurons) called a "nerve net."
  • Echinoderms, such as sea stars, have nerve cells that are bundled into fibers called nerves.
  • Although glial cells support neurons, recent evidence suggests they also assume some of the signaling functions of neurons.
  • (a) In cnidarians, nerve cells form a decentralized nerve net.
  • (b) In echinoderms, nerve cells are bundled into fibers called nerves.

• Spinal Cord

  • Myelinated axons (the part of neurons that send signals) compose the "white matter," while neuron and glial cell bodies (neuronal "support" cells) compose the "grey matter."
  • Axons and cell bodies in the dorsal (facing the back of the animal) spinal cord convey mostly sensory information from the body to the brain.
  • Axons and cell bodies in the ventral (facing the front of the animal) spinal cord primarily transmit signals controlling movement from the brain to the body.
  • Spinal cord injuries are notoriously difficult to treat because spinal nerves do not regenerate, although ongoing research suggests that stem cell transplants may be able to act as a bridge to reconnect severed nerves.
  • A cross-section of the spinal cord shows grey matter (containing cell bodies and interneurons) and white matter (containing axons).

• Neurons

  • Myelin is produced by glial cells.
  • An example of a bipolar neuron is a retinal bipolar cell, which receives signals from photoreceptor cells that are sensitive to light and transmits these signals to ganglion cells that carry the signal to the brain.
  • Pseudounipolar cells share characteristics with both unipolar and bipolar cells.
  • A pseudounipolar cell has a single structure that extends from the soma (like a unipolar cell), which later branches into two distinct structures (like a bipolar cell).
  • Examples include (a) a pyramidal cell from the cerebral cortex, (b) a Purkinje cell from the cerebellar cortex, and (c) olfactory cells from the olfactory epithelium and olfactory bulb.

• Cellular Differentiation

  • Three basic categories of cells make up the mammalian body: germ cells, somatic cells, and stem cells.
  • Pluripotent stem cells undergo further specialization into multipotent progenitor cells that then give rise to functional cells.
  • Hematopoietic stem cells (adult stem cells) from the bone marrow that give rise to red blood cells, white blood cells, and platelets
  • Mesenchymal stem cells (adult stem cells) from the bone marrow that give rise to stromal cells, fat cells, and types of bone cells;
  • Epithelial stem cells (progenitor cells) that give rise to the various types of skin cells

• Gene Expression in Stem Cells

  • In mammals, there are two broad types of stem cells: embryonic stem cells, which are isolated from the inner cell mass of blastocysts, and adult stem cells, which are found in various tissues.
  • Stem cells can now be artificially grown and differentiated into specialized cell types with characteristics consistent with muscle or nerve cells through cell culture.
  • In one, the daughter cells are initially equivalent but a difference is induced by signaling between the cells, from surrounding cells, or from the precursor cell.
  • Stem cells are indicated by (A), progenitor cells by (B), and differentiated cells by (C).
  • Pluripotent, embryonic stem cells originate as inner cell mass (ICM) cells within a blastocyst.

• Cell Theory

  • Cell theory states: living things are composed of one or more cells; the cell is the basic unit of life; cells arise from existing cells.
  • The unified cell theory states that: all living things are composed of one or more cells; the cell is the basic unit of life; and new cells arise from existing cells.
  • "All cells only arise from pre-existing cells.
  • Cells carry genetic material passed to daughter cells during cellular division
  • The cell is the basic unit of life and the study of the cell led to the development of the cell theory.

• The Role of the Cell Cycle

  • In other words, that original single cell is the ancestor of every other cell in the body.
  • Single-celled organisms use cell division as their method of reproduction.
  • While there are a few cells in the body that do not undergo cell division, most somatic cells divide regularly.
  • A somatic cell is a general term for a body cell: all human cells, except for the cells that produce eggs and sperm (which are referred to as germ cells), are somatic cells.
  • The cell cycle is an ordered series of events involving cell growth and cell division that produces two new daughter cells.

• Natural Killer Cells

  • After a pathogen enters the body, infected cells are identified and destroyed by natural killer (NK) cells, which are a type of lymphocyte that can kill cells infected with viruses or tumor cells (abnormal cells that uncontrollably divide and invade other tissue).
  • As such, NK cells offer a complementary check for unhealthy cells, relative to T cells.
  • NK cells are always active; an interaction with normal, intact MHC I molecules on a healthy cell disables the killing sequence, causing the NK cell to move on.
  • After the NK cell detects an infected or tumor cell, its cytoplasm secretes granules comprised of perforin: a destructive protein that creates a pore in the target cell.
  • Phagocytic cells then digest the cell debris left behind.