3. Neuroanatomy

Why do my neurons look like food?

At the most basic level, the body is run by neurons. These cells link together to provide sensory information and trigger muscle movements.

Each neuron is a cell with all the regular functions. It’s cell body (soma) has a nucleus, DNA, RNA, mitochondria and all the standard cell components.

Neurons have some additional structure components and a very different functional component. Structurally, neurons typically come with extensions. The dendrites look like ginger covered with spiny bristles. Neurotransmitters bind to the receptors of the dendritic spines, so dendrites are important for inputs.

Neurons are amazing. Functionally, they are living batteries that discharge quickly, recharge and discharge again. There are factories to produce the needed components, tubes to carry products, and pumps and gates to manage its climate.

Pay particular attention to how neurons are formed and how they are aided by glia.

Learning Objectives

By the end of this module, you should be able to:

• Compare and contrast neurons and glia.
• Identify the parts and functions of a neuron
• Describe the properties of a semipermeable membrane.

Readings

Read these posts (if there are links):

• Parts of a neuron
• Founding neurons
• 6 types of glial cells
• How glial cells save the day
• Soma

Videos

 

 

Slides

Links

• Wikipedia: Neural Anatomy
• Neuroscience for Kids: Types of Nerve Cells
• Ducksters: The Nervous System

Terms

• 6 types of glial cells
• astrocytes
• ATP
• axon
• axon hillock
• axon terminals
• bipolar neuron
• chromophil granules
• chromosomes
• dendrites
• dendritic spines
• endoplasmic reticulum (ER)
• extensions (processes)
• extracellular space
• gates
• glial cells
• golgi apparatus
• hippocampus
• interneurons
• membrane
• microglia
• mitochondrion
• motor neurons (efferent)
• multipolar neurons
• mushroom
• myelin
• myelin sheath
• myelinated axon
• neural glue
• neuroglia
• neurolemma
• neurons
• neurotransmitter
• Nissl body
• nodes of Ranvier
• nucleus
• oligodendrocyte
• organelles
• phagocytes
• phagocytosis
• plasma membrane
• plasticity
• processes (extensions)
• protein synthesis
• pseudounipolar neuron
• Purkinje cells
• pyramidal neurons
• radial glial
• repropagation
• ribosome
• saltatory conduction
• satellite cells
• Schwann Cells
• sensory neurons (afferent)
• site of summation
• soma
• star cells
• stubby
• synapses
• terminal buttons
• thin
• unipolar neuron
• winnowing

Notes

• Neurons
  • Receive & transmit to other cells
  • Many last your whole life
  • Other cells die and are replaced
  • Most aren’t replaced
    • Hippocampus neurons CAN re-grow
    • In General
  • have less neurons as get older
• Neuron Development
  • Create twice as many as need
  • Winnowing
    • just before and after birth
  • 50,000 cells each second
    • for most of intrauterine life
• Soma
  • maintains cell life
  • contains nucleus
  • support structures
  • only one per neuron
  • cell body
  • Looks spotty
    • (Nissl substance)
      • Chromophil granules
      • In soma & dendrites
      • Not in axons
      • Synthesize proteins & regulate metabolism
• Dendrites
  • Thicker than axon
  • Look like tree roots or ginger
  • Attached to the soma
  • Receives info from other neurons
  • Control which gates open
  • Control how quickly gates open
  • Control how long stay open
  • Control rate thru gate
• Dendritic Spines
  • Spiny outgrowths
  • Adults have fewer, children more
  • Synapse plasticity
    • Involved how?
    • Not in most brain neurons
  • Types
    • Stubby
    • Mushroom
    • Thin
      • Usually: spine head with long skinny neck
• Ribosomes
  • Rough texture
  • An organelle
    • specialized function
  • Protein factory for local use
• Axon Hillock
  • In larger neurons
  • Expanded region at initial end of axon
  • Connects cell body to the axon
  • Site of summation
  • Collection of incoming information
  • Electric charge adds up
  • More than threshold causes discharge (action potential)
• Axon
  • Vary in length
    • .1 mm to 1 meter
    • Longer than dendrite
  • Vary in width
    • Thin; about 1 micrometer
    • Thinner than dendrite
  • Can branch at end
  • Usually only 1
  • Output
    • Branch at end (not near cell)
  • Smooth surface
    • No ribosomones
  • Can have myelin
    • Myelin
    • Insulation
    • Fatty layers that coats some axons
• Myelin sheath
  • wraps axon
  • type of glial cell
  • Prevents activation of adjacent axons
  • 14th week of fetal development
  • Two Types
    • 1. In Brain & Spinal Cord: Oligodendrocyte
      • 80% lipid
      • 20% protein
      • Can cover 50 axons
    • 2. Peripheral System: Schwann Cells
      • myelinating & nonmyelinating
      • 1 axon only
      • Help keep neurons alive
      • Insulate 100 micrometres of axon
        • Each cell 100 micrometers long
        • 10k per meter
      • Regularly spaced
      • Gaps = Nodes of Ranvier
      • Schwann Cells
        • Spiral around axon
        • 100+ revolutions
        • Looks like log or rolled-up paper
        • Inner layers are myelin
        • Mostly lipid
        • Outer layers = neurolemma
        • Plasma membrane
      • Saltatory Conduction
        • Slows down as distance increases
        • Repropagation
        • Node to node
          • 10x faster
        • Exposes neuron to extracell. fluid & ion flow
          • “naked” section of myelinated axon
• Axon Terminals
  • Branches at end of axons
  • Presynaptic
• Terminal Buttons
  • Secrete neurotransmitter
• Organelles = specialty units
  • Mitochondrion
    • Cellular power plants
    • Generate ATP
    • Power chemical changes
  • Nucleus
    • contains chromosomes
    • covered by membrane
  • Nissl Bodies
    • groups of ribosomes
    • protein synthesis
  • Endoplasmic reticulum (ER)
    • system of tubes
    • transport materials within cytoplasm
    • rough (ribosomes)
    • smooth (no ribosomes)
  • Golgi Apparatus
    • Stuff peptides & proteins into vesicles (sack-like cavities)
  • Microfilaments/Neurotubules
    • transport system within a neuron
    • also used for structural support
• Types of Neurons
  • Location
    • Peripheral nervous system
      • Sensory neuron
        • detects changes in world
        • detects internal changes
        • sends info to CNS
          • Central nervous system
      • Motor neuron
        • controls contraction of a muscle
        • controls secretion of a gland
        • Interneuron = connects other neurons
  • Number of Extensions
    • Bipolar
      • 1 dendrite, 1 axon
      • Retina and smell
      • 2 processes (extensions)
    • Pseudounipolar
      • Biploar who lose 1 process
      • No dedrites
      • Becoming a unipolar neuron
    • Unipolar
      • Sensory Neuron
    • Multipolar
      • 99% of neurons
      • many processes (extensions)
      • only one axon
      • Spinal motor neurons
    • Pyramidal neurons
      • Purkinje cells
      • can have over 1000 dendrites
      • connect to 10-20k cells
      • some of largest neurons in brain
      • stacked one in front of the other
      • look like dominos
  • Direction They Send Info
    • Sensory neurons (afferent)
      • from sensory receptors
      • skin, eyes, nose, tongue, ears
      • to central nervous system
    • Motor neurons (efferent)
      • from central nervous system
      • to muscles or glands
      • get info from interneurons
      • directly from sensory neurons
      • in some reflexes
    • Interneurons
      • Between sensory & motor neurons
      • No other neurons around them
      • Don’t need dendrites to receive input
      • Connect to each other
      • Intrinsic, association, relay, or local circuit (local) neuron
• Glial Cells
  • Supporting cells
    • called neuroglia or “neural glue”
    • supporting cells of CNS
  • 6 Types of Glial Cells
  • 1. radial glial
    • Help generate neurons & astrocytes
    • Cables neurons use to find home
  • 2. astrocytes
    • Surround synapses
    • Provide nutrients & raw material
    • Limit neurotransmitters
    • Engulf dead cells & form scar tissue = phagocytosis
    • Regulate chemical composition of extracellular fluid
    • Star cells
    • Help neurons:
      • 1) transport nutrients to neurons
      • 2) regulates extracellular space
      • 3) digest parts of dead neurons
      • 4) clean up brain “debris“
      • 5) hold neurons in place
  • 3. oligodendrocytes
    • produce mylein sheath in CNS
  • 4. Schwann cells
    • produce myelin sheath in PNS
  • 5. microglia
    • smallest glial cells
    • act as if they were phagocytes
      • (Bacterial eating white blood cells)
    • protect brain from invading microorganisms
  • 6. satellite cells
    • physical support to PNS neurons

 Quiz

• 1. The cell body is called a:
  • a.           terminal button
  • b.           mushroom
  • c.           dendrite
  • d.           soma
• 2. Dendrites are:
  • a.           myelinated
  • b.           rough
  • c.           thin
  • d.           all of the above
• 3. Nodes of Ranvier are:
  • a.           protein-producing factories
  • b.           bumps that cover dendrites
  • c.           gaps in myelinated axons
  • d.           neural slime
• 4. Sensory neurons are:
  • a.           mutipolar
  • b.           diapolar
  • c.           unipolar
  • d.           all of the above
• 5. The process of getting rid of excess neurons just before and just after birth is called:
  • a.           systematic desensitization
  • b.           winnowing
  • c.           chucking
  • d.           pons

For the answers: Click Here

Discussion

What surprised you about neural anatomy?

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