3 Notes: Neuroanatomy – biologicalpsych.com

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

Leave a Reply Cancel reply