The Nervous System

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The Nervous System
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Nervous System

• Three basic functions
• Sensation
• gather information
• Integration
• process information
• use of multiple sources of information.
• Response
• coordinated action appropriate to environment

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EK3E2 Animals have nervous systems that detect
external and internal signals, transmit and
integrate information, and produce responses.

• a. The neuron is the basic structure of the
  nervous system that reflects function.
• 1. A typical neuron has a cell body, axon and
  dendrites. Many axons have a myelin sheath that
  acts as an electrical insulator.
• 2. The structure of the neuron allows for the
  detection, generation, transmission and
  integration of signal information.
• 3. Schwann cells, which form the myelin sheath,
  are separated by gaps of unsheathed axon over
  which the impulse travels as the signal
  propagates along the neuron.

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The neuron is the basic structure of the nervous
system that reflects function.

• 1. A typical neuron has a cell body, axon and
  dendrites. Many axons have a myelin sheath that
  acts as an electrical insulator.
• 2. The structure of the neuron allows for the
  detection, generation, transmission and
  integration of signal information.
• 3. Schwann cells, which form the myelin sheath,
  are separated by gaps of unsheathed axon over
  which the impulse travels as the signal
  propagates along the neuron.

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• Neurons are similar to other cells in the body
  because
• 1. Neurons are surrounded by a cell membrane.
• 2. Neurons have a nucleus that contains genes.
• 3. Neurons contain cytoplasm with organelles
• 4. Neurons carry out basic cellular processes
  such as protein synthesis and energy production.
• However, neurons differ from other cells in the
  body because
• 1. Neurons have specialized extensions called
  dendrites and axons. Dendrites bring information
  to the cell body and axons take information away
  from the cell body.
• 2. Neurons communicate with each other through an
  electrochemical process.
• 3. Neurons contain some specialized structures
  (for example, synapses) and chemicals (for
  example, neurotransmitters).

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Neuron Trivia

• Neurons are the oldest and longest
  cells in the body! You have many of the same
  neurons for your whole life. Although other cells
  die and are replaced, many neurons are never
  replaced when they die. In fact, you have fewer
  neurons when you are old compared to when you are
  young. On the other hand, data published in
  November 1998 show that in one area of the brain
  (the hippocampus), new neurons CAN grow in adult
  humans.
• Neurons can be quite large - in some
  neurons, such as corticospinal neurons (from
  motor cortex to spinal cord) or primary afferent
  neurons (neurons that extend from the skin into
  the spinal cord and up to the brain stem), can be
  several feet long!

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Neuron Anatomy

• Soma/Cell Body is the metabolic center of the
  neuron, contains the Nucleus and Mitochondrion.
• Dendrites convey incoming messages to the cell
  body.
• Axon generates nerve impulses and topically
  conduct them away from the cell body myelinated
  by either oligodendroglia in CNS or Schwann cells
  in PNS. Each neuron has only one axon.
• Axon Hillock a cone like region from where an
  axon arises.
• Presynaptic terminals The swollen, distal end of
  an axon contains a neurotransmitter substance
  within synaptic vesicles. Also called synaptic
  ending or synaptic bouton.
• Synapse Specialized junctions with other cells
  that are along the length or at end of an axon.

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• Axons
• Take information away from the cell body
• Smooth Surface
• Generally only 1 axon per cell
• No ribosomes
• Can have myelin
• Branch further from the cell body

• Dendrites
• Bring information to the cell body
• Rough Surface (dendritic spines)
• Usually many dendrites per cell
• Have ribosomes
• No myelin insulation
• Branch near the cell body

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Neuron Anatomy
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Neurons can also be classified by the direction
that they send information

• Sensory (or afferent) neurons send information
  from sensory receptors (e.g., in skin, eyes,
  nose, tongue, ears) TOWARD the central nervous
  system.
• Motor (or efferent) neurons send information
  AWAY from the central nervous system to muscles
  or glands.
• Interneurons send information between sensory
  neurons and motor neurons. Most interneurons are
  located in the central nervous system.

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EK3E2 Animals have nervous systems that detect
external and internal signals, transmit and
integrate information, and produce responses.

• b. Action potentials propagate impulses along
  neurons.
• 1. Membranes of neurons are polarized by the
  establishment of electrical potentials across the
  membranes.
• 2. In response to a stimulus, Na and K gated
  channels sequentially open and cause the membrane
  to become locally depolarized.
• 3. Na/K pumps, powered by ATP, work to maintain
  membrane potential.

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How neurons conduct impulses

• Membrane potential (as seen in muscle cells)
• K diffuses out of neurons faster than Na
  diffuses in,
• Na-K pump moves 3Na back out for 2K back in
• Cl-, phosphate, protein anions balance cations
• Resting potential -70mV
• Nerve Impulse

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Rate of conduction

• Saltatory Conduction
• Action Potential occurs only in nodes,
• "leaps" from node to node
• Ion attraction and diffusion stimulate new A.P.
  in each node
• Saltatory conduction much faster than continuous
  conduction in unmyelinated fibers.
• up to 100 m/sec

• Unmyelinated axons
• Action potential propagates at 2-3 meters per
  second (m/sec)

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EK3E2 Animals have nervous systems that detect
external and internal signals, transmit and
integrate information, and produce responses.

• c. Transmission of information between neurons
  occurs across synapses.
• 1. In most animals, transmission across synapses
  involves chemical messengers called
  neurotransmitters.
• Acetylcholine
• Epinephrine
• Norepinephrine
• Dopamine
• Serotonin
• GABA
• 2. Transmission of information along neurons and
  synapses results in a response.
• 3. The response can be stimulatory or inhibitory.

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How does impulse get from cell to cell?

• Chemical synapses, 2
• Axon ( A.P.) ends short of next cell,
• Synaptic knob (axon end) releases chemical
  transmitter

• Electrical synapses
• Gap junctions, tiny holes connect cytoplasm of
  adjacent cells
• A.P. continuous from cell to cell

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Neurotransmission

• When Action Potential reaches synaptic knob,
• Synaptic vesicles unite with membrane,
• Release neurotransmitter,
• Neurotransmitter diffuses across synaptic cleft,
• Neurotransmitter binds to receptors in
  postsynaptic membrane,
• Chemically gated channels open
• Chemical Signals
• Mouse Party

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Synapse

• Neurotransmitter can't remain in cleft (would
  continue to stimulate uncontrollably)
• ACh removed by acetylcholinesterase (AChE)
• Acetate choline reabsorbed by axon end,
  resynthesized to ACh
• Other neurotransmitters taken back by axon or
  diffuse away

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Neurotransmitters may be

• Excitatory
• depolarize postsynaptic membrane
• Excitatory Postsynaptic Potential (EPSP)
• Inhibitory
• hyperpolarize postsynaptic membrane
• Inhibitory Postsynaptic Potential (IPSP)

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• Reward Pathway
• Reflex Arc

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EK3E2 Animals have nervous systems that detect
external and internal signals, transmit and
integrate information, and produce responses.

• d. Different regions of the vertebrate brain have
  different functions.

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• LO 3.43 The student is able to construct an
  explanation, based on scientific theories
• and models, about how nervous systems detect
  external and internal signals,
• transmit and integrate information, and produce
  responses.
• LO 3.44 The student is able to describe how
  nervous systems detect external and
• internal signals.
• LO 3.45 The student is able to describe how
  nervous systems transmit information.
• LO 3.46 The student is able to describe how the
  vertebrate brain integrates
• information to produce a response.
• LO 3.47 The student is able to create a visual
  representation of complex nervous
• systems to describe/explain how these systems
  detect external and internal
• signals, transmit and integrate information, and
  produce responses.
• LO 3.48 The student is able to create a visual
  representation to describe how
• nervous systems detect external and internal
  signals.
• LO 3.49 The student is able to create a visual
  representation to describe how
• nervous systems transmit information.
• LO 3.50 The student is able to create a visual
  representation to describe how the
• vertebrate brain integrates information to
  produce a response.

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Resources

• Action Potential Tutorial
• AP Text, 2
• Essential Study partner Links
• Parts of a Neuron Review
• Anatomy Drill
• Body Smart Nervous System
• Campbells Activity Quiz
• Human AP Lessons
• Cerebral Commando
• Synaptic Transmission Tutorial
• Drugs, Brains Behavior
• Parts of the Brain, 2
• Video Quiz - Making Brain Cells
• Video Quiz - ALS Lost Nerve Power
• Video Quiz - Wild Young Brains
• Video Quiz - Vanishing Brain
• Video Quiz - Meth and the Brain
• Video Quiz - Paralysis Push