By Lydia Chang, Lauren Lee, and Diana Zheng

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The Nervous System

• By Lydia Chang, Lauren Lee, and Diana Zheng

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Evolution of the Nervous System

• Porifera no nervous system
• Cnidaria nerve net all throughout bodycan react
  to stimuli from all sides
• Platyhelminthes cephalization ganglia,
  eyespots, two main ventral nerve cords
• Rhynchocoela dorsal nerve cord, two lateral
  nerve cords
• Nematoda ring of nervous tissue around pharynx
  attached to dorsal and ventral nerve cords
• Annelida pair of brain-like cerebral ganglia and
  subpharyngeal ganglion
• Mollusca ranges from simple nervous system to
  relatively complex systems that rival those of
  mammals
• Arthropoda cerebral ganglion (brain!) sense
  organs concentrated on head
• Echinodermata decentralized nervous no brain
  but have ganglia along radial nerves in some
  species sensory neurons within podia

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Evolution of the Nervous System

• Vertebrates very centralized and cephalized
  well-developed sensory organs dorsal, hollow
  nerve cord (spinal cord)
• Lampreys and hagfishes no myelin sheath
• Fish enlarged cerebellum
• Amphibians growing importance of forebrain, but
  midbrain still important
• Reptiles/Birds many connections between thalamus
  and hemispheres
• Birds larger cerebellum
• Mammals brain completely dominated by cerebral
  hemispheres large surface area controlled
  mainly by cortex large thalamus

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The Human Nervous System

• Brain about 2 human body mass
• Neocortex outer layer of brain
• Human cerebral cortex (aka pallium) flat sheets
  of cells in six layers
• Frontal lobe reasoning, speech, motor cortex
• Parietal lobe speech, taste, reading,
  somatosensory cortex
• Temporal lobe hearing, smell, auditory
• Occipital lobe sight
• Cerebellum ballistic movements, balance,
  coordination, helps in learning and remembering
  motor skills

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From Vertebrate Nervous System
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The Brain, contd

• Diencephalon major integrating centers
  information, act as relay stations for info flow
• Thalamus main relay center for sensory
  information
• Hypothalamus maintains homeostasis
• Brain stem includes the pons, medulla oblongata
• transfers info between peripheral and central
  nervous systems
• helps coordinate large-scale body movements (e.g.
  running)
• nerve crossing right side of brain controls left
  side of body and vice versa
• Midbrain/RAS (reticular activating system)
  centers for receiving and integrating several
  types of sensory info
• Corpus callosum connects brain hemispheres

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From Wikipedia
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Evolutionary Trends

• More complex!
• This system is necessary for complexity and
  sophisticated behaviors/responses to environment
• Increases chance of survival more complex NS
  more complicated nerve connections, behaviors,
  movements
• The nervous system controls all other body
  systems!! Except maybe skeletal

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Neurons

• Neurons
• Sensory neurons
• Interneurons
• Motor neurons

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How Neurons work

• Resting potential negative relative to the
  outside
• Sodium-potassium pumps in the plasma membrane
• Transport sodium out of the cell and potassium
  into it
• Very few sodium channels
• Net negative charge inside cell

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Action Potential

• Depolarization
• Rising phase of the action potential
• Falling phase of the action potential
• Undershoot Potassium channels close to bring it
  back to the concentration needed to be at resting
  potential
• refractory period

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Conduction of the Action Potential

• Action potential a wave from dendrite to axon
• Speed is determined by axon diameter
• Evolutionary trend Because vertebrate axons have
  narrow diameters, vertebrates have adapted the
  myelin sheath to enable more efficient conduction
• Nodes of Ranvier (nodes between gaps in myelin
  sheath) allows for saltatory conduction
• current jumps from node to node

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Synapses

• Electrical synapses contain gap junctions to
  allow electrical currents to flow from one neuron
  to another
• Chemical synapses (most synapses)
  neurotransmitter
• Examples of neurotransmitters acetylcholine,
  biogenic amines (serotonin)

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Disorders and Diseases

• Cerebrovascular accident (stroke)
• Parkinson's disease
• decreased stimulation of the motor cortex by the
  basal ganglia caused by the insufficient
  formation and action of dopamine
• Multiple sclerosis immune system damages the
  myelin
• When myelin is lost, the axons can no longer
  effectively conduct signals

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Works Cited and Consulted

• AP Bio book
• http//faculty.washington.edu/chudler/nsdivide.htm
  l
• http//parasitology.informatik.uni-wuerzburg.de/lo
  gin/n/h/0941.html
• http//www.daviddarling.info/encyclopedia/V/verteb
  rate_nervous_system.html
• http//infusion.allconet.org/webquest/PhylumMollus
  ca.html
• http//www.mindcreators.com/Images/NB_Neuron.gif 
• http//en.wikipedia.org/wiki/FileNeurons_big1.jpg