Anatomy of Neurons

• External Features of Neuron

  • Cell Membrane: the semipermeable membrane that encloses the neuron

  • Cell Body: the metabolic center of the neuron; aka soma

  • Dendrites: the short processes emanating from the cell body, which receive most of the synaptic contacts from other neurons

  • Axon Hillock: the cone-shaped region at the junction between the axon and cell body

    • always singular

  • Axon: the long, narrow process that projects from the cell body

    • an axon always starts at the axon hillock

  • Myelin: the fatty insulation around many axons

    • insulation, protection; speeds up transmission or transfer of impulses (most important feature)

  • Nodes of Ranvier: gaps between sections of myelin

  • Terminal Buttons or Buttons: the buttonlike endings of the axon branches, which release chemicals into synapses

  • Synapses or Synaptic Gap or Cleft: the gaps between adjacent neurons across which chemical signals are transmitted

• Internal Features of a Neuron

  • Mitochondria: sites of aerobic (oxygen-consuming) energy release; powerhouse

  • Nucleus: the spherical DNA-containing structure of the cell body

  • Endoplasmic Reticulum: a system of folded membranes in the cell body; rough portions (those with ribosomes) play a role in the synthesis of proteins; smooth portions (those without ribosomes) playa a role in the synthesis of fats

  • Cytoplasm: the clear internal fluid of the cell

  • Ribosomes: internal cellular structures on which proteins are synthesized; they are located on the endoplasmic reticulum

  • Golgi Complex: a connected system of membranes that packages molecules in vesicles

    • Endoplasmic Reticulum vs Golgi Complex:

      • Endoplasmic Reticulum: synthesize protein

      • Golgi Complex: smooth; packaging

  • Microtubules: tubules responsible for the rapid transport of material throughout neurons

    • transport of substances and nutrients happen

    • Synaptic Vesicles: spherical membrane packages that store neurotransmitter molecules ready for release near synapses

    • Neurotransmitters: molecules that are released from active neurons and influence the activity of other cells

• Cell Membrane

  • The cell membrane is a lipid bilayer with signal proteins and channel proteins embedded in it

  • Lipid Bilayer: 2 layers of fat molecules

    • embedded are numerous protein molecules that are the basis of many of the cell membranes functional properties

  • Channel Proteins: through which certain molecules can pass

  • Signal Proteins: transfer a signal to the inside of the neuron when particular molecules bind to them on the outside of the membrane

• Classes of Neurons

  • Unipolar Neuron: a neuron with one process extending from its cell body

    • cell body is smooth

  • Bipolar Neuron: a neuron with 2 processes extending from its cell body

  • Multipolar Neuron: a neuron with more than 2 processes extending from its cell body

    • one axon multiple dendrites; can receive or send out efferent axon away; away from axon (going out the neuron); motor or afferent to the neuron; sensory = accept; sensory

  • Multipolar Interneuron: neurons with a short axon or no axon at all

    • function is to integrate neural activity within a single brain structure, not to conduct signals from one structure to another

    • in between 2 other neurons; serves to conduct impulses through another neuron without the use of axon

  • Neurons and Neuroanatomical Structure

    • Nuclei (singular = nucleus): clusters of cell bodies in the central nervous system

    • Ganglia (singular = ganglion): clusters of cell bodies in the peripheral nervous system

    • Tracts: bundles of axons in the central nervous system

    • Nerves: bundles of axons in the peripheral nervous system

Glia: The Forgotten Cells

• Glia: most common type of cells in the nervous system

• Major Types of Glia

  • Oligodendrocytes: glial cells with extensions that around the axons of some neurons of the central nervous system

    • extensions are rich in myelin, a fatty insulating substance, and the myelin sheaths they form increase the speed and efficiency of axonal conduction

    • “cake roll”

  • Schwann Cells: similar function as oligodendrocytes in the peripheral nervous system

    • only Schwann cells can guide axonal regeneration (regrowth) after damage

    • “sandwich”

• Major Types of Glia

  • Microglia: smaller than other glial cells

    • respond to injury or disease by multiplying, engulfing cellular debris or even entire cells, and triggering inflammatory responses

    • have immune system-like responsibilities in the brain, and they play a role in the regulating of cell death, synapse formation, and synapse elimination

    • rehabs the cell until cells are fully functional

  • Astroglia: largest of the glial cells; support and provide nourishment for neurons and form part of the blood-brain barrier

    • have the ability to contract or relax blood vessels throughout the brain

    • establish and maintain connections between neurons