Neural Development

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Neural Development
2011-05-04 21:10:16
neural development

Animal Growth and Development
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  1. What is the goal of neural development?
    Creation of a structural and functional mechanism that can respond to changes in the organism's external or internal environment
  2. What are the 3 basic fuctions of neural tissue?
    • Recieve signals from the internal and external environments
    • Integrate the input
    • Respond to stimuli
  3. Memory
    Capability of recalling a thought at least once and usually again and again
  4. Short term memory
    remember, use, forget
  5. Intermediate memory
    reversible chemical changes in the brain
  6. Long term memory
    permanent chemical changes in the brain
  7. Learning
    Capability of the nervous system to integrate and store memories
  8. Central nervous system
    brain and spinal cord
  9. Cranial nerves
    nerves connecting brain to head
  10. Peripheral nerves
    nerves that branch from the spinal cord
  11. Spinal cord
    • cylinder of nerve tissue that runs down the center canal in the spine
    • handles some automatic motor responses to sensory information by itself
  12. Autonomic nervous system
    handles involuntary jobs
  13. Sympathetic system
    stimulates the "fight or flight" response to threating situations
  14. Parasympathetic system
    relaxes the body
  15. Sensory neurons
    • Length of fibers: long dendrites and short axon
    • Location: cell body and dendrites are outside of the spinal cord; the cell body is located in a dorsal root ganglion
    • Function: conduct impulse to the spinal cord
    • moving away from a central organ or point
  16. Motor neurons
    • Length of fibers: short dendrites and long axons
    • Location: dendrites and the cell body are located in the spinal cord; the axon is outside of the spinal cord
    • Function: conduct impulse to an effector (muscle or glad)
    • moving toward a central organ or point
  17. Interneurons
    • aka connector neurons, relay neurons
    • Length of fibers: short dendrites and short or long axon
    • Location: entirely within the spinal cord or CNS
    • Function: interconnect the sensory neuron with appropriate motor neuron
    • smaller cells
    • form complex chains or circuits
  18. Reflex arc flow chart
    stimulus, receptor, sensory neuron, coordinator, motor neuron, effector, response
  19. Neurogenesis
    the formation of new neurons ( can take place in the adult brain, unknown how functional these neurons are)
  20. Infarcts
    areas of necrosis resulting from obstruction of local circulation
  21. Effects of aging on the brain
    • decrease in volume and weight
    • widening of grooves on the surface of the brain
    • enlargement of the ventricles (open spaces)
    • acculation of lipofuscin (pigment in the cells)
    • neurofibrillary tangles
    • senile plaques
    • small infarcts
  22. Purpose of the blood brain barrier
    • separates blood and cerebrospinal fluid (CSF)
    • physical isolation for the CNS (not the PNS)
    • allows glucose, oxygen, vitamins, and some amino acids to pass through
    • causes differential drug sensitivity
  23. What are the 2 components of the BBB?
    general barrier and choroid plexus
  24. General barrier
    the juction beween the endothelial cells lining the capillaries are much tighter in the CNS than in most other areas of the body
  25. Choroid plexus
    leaky capillary endothelium but tight junctions between choroids epithelial cells (found in ventricles of the brain)
  26. Dendrites
    • multiple elongated processes specialized in receiving stimuli
    • usually covered by a large number of throny spines (gemmules) - site of synapses
  27. Cell body
    • aka soma
    • contains cytoplasm and nucleus (mono- or bi- nucleated)
    • can also recieve stimuli
  28. Axon
    single process specialized in generating or conducting nerve impulses to other cells
  29. Classification of neurons
    • based on size and shape
    • Multipolar: 1 axon, multiple dendrites, most common type
    • Bipolar: 1 axon, 1 dendrite
    • Pseudounipolar: 1 process close to the cell body but which divides into 2 branches froming a T shape
  30. Synapses
    • specialized, localized regions of contact between 2 cells
    • typical neuron has between 100-1000 synapses
  31. Synapse function
    • alter membrane potential of neurons by chemical or electrical means
    • Chemical: release neurotransmitters
    • Electrical: via gap junctions
  32. Synapse composition
    • Terminal membrane: presynaptic membrane, i.e. axon terminal buds that contain neurotransmitters
    • Region of extra cellular space: synaptic gap, space between the presynaptic and postsynaptic endings
    • Postsynaptic membrane: membrane of effector organ, contains receptor sites for neurotransmitters
  33. Neuroreceptors
    chemical-gated ion channels in membrane of post-synaptic cell
  34. Synaptic vesicles
    vesicles containing neurotransmitters in pre-synaptic cells
  35. What are the 5 types of synpses?
    • Excitatory ion channel synapses
    • Inhibitory ion channel synapses
    • Non channel synapses
    • Neuromuscular junctions
    • Electrical synapses
  36. Excitatory ion channel synapse
    • sodium channel neuroreceptors
    • when channels open positive ions flow in, causing a local depolarization, making an action potential more likely
  37. Inhibitory ion channel synapse
    • chloride channel neuroreceptors
    • when channels open negitive ions flow in, causing a local hyperpolarisation, making an action potential less likely
    • an impulse in one neuron can inhibit an impulse in the next
  38. Non channel synapse
    • No channels
    • Have membrane-bound enzymes
    • When activated by a neurotransmitter, enzymes catalyse the production of a mesenger chemical inside the cell
  39. Neuromuscular junctions
    • synapses formed between motor neurons and muscle cells
    • always use neurotransmitter acetylcholine
    • always excitatory
  40. Electrical synapse
    • the membranes of the two cells actually touch and share proteins
    • allows for an action potential to be passed directly from one membrane to the next
    • found only in the heart and eye
  41. Why are there synapses?
    • Make sure that impulses only flow in one direction
    • Allow for integration to occur
    • Allow for summation to occur
    • Allow for the filtering out of continual unnecessary or unimportant background stimuli
  42. Spatial summation
    several pre-synaptic neurons converge at a synapse with a single post-synaptic neuron
  43. Temporal summation
    one pre- and post-synaptic neuron but the frequency of impulses reaching the synapse differs
  44. Nerve fibers
    dendrites and axons
  45. What are the three types of connective tissue assoiciated with nerves?
    • epineurius
    • perineurium
    • endoneurium
  46. Ganglia
    aggregation of nerve cell bodies in the PNS
  47. Nucleus
    aggregation of nerve cell bodies in the CNS
  48. Myelinated fibers
    many layers of modified glial cell membrane wrapped around axons (white matter)
  49. Unmyelinated fibers
    enveloped within glial cell clefts or not at all (grey matter)
  50. Myelin
    • united layers of the membranes of the sheath cell forming a lipoprotein complex
    • consists of many layers of modified cell membranes
    • made up of 70-80% lipid and 20-30% protein
  51. Mesaxon
    Formed by the edges of glial cell groove coming together over a developing axon
  52. When does myelination occur?
    • begins at 16-20 weeks of gestation
    • continueing into early twenties
    • demyelination of adult nerve fibers seriously imparis impulse conduction
  53. Nodes of Ranvier
    • spaces inbetween adjacent glial cells along the length of the axon
    • allows ions to flow with ease between the extracellular fluid and the axon
    • electrical impulses spread from node to node
  54. What is the charge on the inside and outside of a neuron?
    • Outside: positive charge (more Na, less K)
    • Inside: negative charge (more K, less Na)
  55. Grand postsynaptic potential (GPP)
    • output through the axon
    • sum of all the excitatory and inhibitory potentials from all that cell's synapses
  56. Action potential
    • temporary reversal of the electrical potential along the membrane
    • sequence of changes in polarity of the membrane
    • results from the propagation of the nerve impulse along the membrane
  57. What factors elicit an action potential?
    • electrical stimulation of the membrane
    • chemicals in contact with the membrane
    • mechanicle damage to the membrane
    • heat and cold
  58. What are the 2 steps of an action potential?
    • depolarization
    • repolarization
  59. What are the steps of an action potential?
    • At rest the outside of the membrane is more positive than the inside
    • Depolarization: cell becomes permiable toNa, positive ions flow into the inside of the cell
    • Repolarization: cell once again becomes impermeable to Na, cell returns to normal charges
    • action potential spreads through membrane (can't move backward)
  60. How fast do action potentials move?
    .1-100 m/s
  61. Speed of action potentials is affected by what 3 factors?
    • Temperature: higher temperature = faster speed
    • Axon diameter: larger diameter = faster speed
    • Myelin sheath: increases speed
  62. Saltatory conduction
    • action potential jumping from node of ranvier to node of raniver
    • makes action potential propagate faster
  63. Neuroplasticity
    new neurons interact with existing brain cells to recreate the function of damaged brain cells
  64. Neuroglia or glial cells
    • ectodermal origin
    • provide passive support
    • help maintain neurons
    • regulate neurite extention and patterning
    • form myelin sheath
    • 10 glial cells per neuron
  65. Astrocytes
    • start shaped
    • cleand up brain debris
    • transport nutrients to neurons
    • hold neurons in place
    • digest parts of dead neurons
    • regulate content of extracellular space
    • control blood flow to neurons
  66. Oligodendrocytes
    provide insulation (myelin) to neurons in CNS
  67. Microglia cells
    digest parts of dead neurons
  68. Ependymal cells
    lines canal of spine and brain
  69. Schwann cells
    provide insulation (myelin) to neurons in the PNS
  70. Satellite cells
    physical support to neurons in the PNS
  71. Brain formation from conception through senescence
    • Waves of cellular proliferation: 1. neuron proliferation 2. glial proliferation
    • Rate of birth mass acretion maximum at birth
    • Brain approximatelly 1/3 to 1/2 of adult size by 1 month post-partum
    • Brain weight plateau by 18 months of age
    • Decrease in brain volume and weight after age 50: 1. loss of neurons 2. shrinkage of neurons 3. changes in dendrites and synapses
    • With advancing age: 1. accumulation of lipofuscin 2. neurofibrillary tangles 3. senile plaques 4. small infarcts
  72. Development of the vertebrate nervous system
    • Major pathways: DNA
    • Minor pathways: environmental ques
  73. What are the early stages of development?
    • Mesoderm forms the notochord which triggers neural induction via chemicals
    • Ectoderm (above the mesoderm) forms the neural plate
    • Neural plate folds to form a tube, neural tube first closes in the center, moving outward in both directions; anterior portion forms 3 outpouchings which will become the brain
    • Neural crest then moves outward forming the PNS
  74. Anencephalic child
    When the neural tube doesn't close all the way
  75. Spine bifida
    Incompelete closure of the posterior portion of the neural tube
  76. What are the layers of the neural tube?
    • Ependyma: inner layer
    • Gray matter: central layer
    • White matter: outer layer
  77. Neurotrophins
    • brain tissue growth factors
    • produced as a result of brain ctivity
  78. Step 1 of neural development: Cell proliferation
    • response to induction signals
    • peak neuronal progenitor cell proliferation occurs early in gestation and stops shortly after birth
    • peak glial proliferation occurs later in gestation and after birth
    • neural stem cells continue to proliferate throughout life
  79. Step 2 of neural development: Migration of young post-mitotic neurons
    • guidance dependent on physical cues
    • movement via amoebpoid activity
    • movement facilitates by cilia
    • 96-97% of the neuroblasts arrive at appropriate target tissues
  80. Step 3 of neural development: Aggregation of relevant cells
    • neurons which aggregate don't migrate anymore
    • influenced by cell/substrate adhesion molecules
    • during aggregation neurons become aligned
  81. Step 4 of neural development: Cytodifferentiation
    • capacity to synthesize neurotransmitters
    • development of distinct processes
  82. Step 5 of neural development: Synaptogenesis
    • initial microenvironment influences
    • specific neuronal receptors
    • remodeling of dendritic trees
  83. Step 6 of neural development: apoptosis
    • coincides with the arrival of axons at their target fields
    • ranges from 15-85% with an average of 40-50% of the initial population
    • occurs in both CNS and PNS
  84. Which neural cells are selected for death?
    • developmental errors
    • overproduction of neurons that can't find target tissue
    • competition for essential maintenance factor from target tissue cells
  85. Step 7 of neural development: Process and synapse elimination
    • occurs after apoptosis
    • reduction in the extent of innervations to various tissues
    • occurs in both the CNS and PNS
    • regulated by functional activity
  86. Functional validation
    progressive development of integrated patterns of neuronal function
  87. Steps of neural development
    • Cell proliferation
    • Migration of young post-mitotic neurons
    • Aggregation of relevant cells
    • Cytodifferentiation
    • Synaptogenesis
    • Apoptosis
    • Process and synapse elimination
  88. What are the 3 parts of the brain?
    • Forebrain: cerebral cortex; responsible for thought, voluntary movement, language, reasoning, perception
    • Midbrain: responsible for vision, audition, eye movement, body movement
    • Hindbrain: contains the cerebelium; responsible for movement, balance, posture
  89. Gyril
    brain folds
  90. Sulci
    brain rooves
  91. Meninges
    series of tough membranes covering the brain and spinal cord
  92. Nerve
    bundle of nerve fibers
    • proliferation occurs inside the tube and migrates outward
    • creates 6 layers -outer layer is the youngest
    • glial cells create a latter for the migrating cells to "climb"