The Nervous System

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The Nervous System

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Organization
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The Brain The control center

• Human brain-100 billion cells (neurons)
• Information processing
• fMRI-functional magnetic resonance imaging-allows
  observation of functional brain
• Neurons-grouped to perform specific tasks

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Nervous System organization in animals

• Smallest animals (cnidarian)-nerve nets
• Larger, more complex-nets AND nerves (fiber-like
  extensions)
• Cephalization-clustering of neurons near anterior
• Ganglion-clusters of neurons

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CNS versus PNS

• CNSCentral Nervous system, brain long nerve
  cords simple organisms have too!
• PNS-Peripheral Nervous system-connects CNS to
  rest of body

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Processing information

• 3 stages of processing
• Sensory input-sensory neurons transmit info from
  sensors to CNS
• Integration-interneurons in CNS integrate and
  interpret input
• Motor output-leaves CNS thru motor
  cells-communicates with effector cells-response!

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Neuron Structure

• Nucleus, cell organelles in cell body
• 2 types of extensions
• Dendrite-receives signals from other neurons
• Axons-longer than dendrites, transmits signals to
  other cells

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Nervous Tissue - Neurons

• Dendrites -IN
• Cell body with nucleus organelles makes
  neurotransmitters.
• Axon -OUT to stimulate OR inhibit a neuron,
  muscle, or gland.
• - ends at synapse.
• - myelin sheath to speed up impulse

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More about nerve cells

• Myelin sheath-layer that surrounds axons
• Synaptic terminal-end of axon that communicates
  with another cell
• Presynaptic celltransmitting cell,
• Postsynaptic cell-receiving cell
• Neurotransmitters-chemical messengers

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Supporting the nervous system

• Glial Cells (glia) attach neurons together
• Many types of glia
• Astrocytes-in CNS, regulate concentrations of
  ions neurtotransmitters
• Formation of blood-brain barrier
• -Radial glia-in embryo, forms a track that
  neurons form around to make CNS
• -Oligodendrocyte-in CNS, Schwann cells-in PNS,
  form myelin sheath around axons, insulating the
  axon

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Neurotransmitters Chemical signals

• Bind to specific receptors
• Some have many different receptors
• may have different effects
• Transmission may be direct ( binds directly to
  receptor/channel that opens) or indirect
  (transmitter binds to a receptor that is not
  attached to the channel)

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Major neurotransmitters
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More neurotransmitters
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Peripheral Nervous System

• Lies outside the CNS
• - Cranial nerves connect to the brain
• - 31 pairs of spinal nerves off of spinal cord.
• Some are sensory, some are motor nerves
• Spinal nerves conduct impulses to and from the
  spinal cord.
• somatic nervous system and autonomic

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Somatic System

• Motor (move) commands from CNS to skeletal
  muscles.
• Voluntary control of muscles involves the brain.
• Reflexes involve brain or spinal cord.
• Reflexes are automatic, involuntary responses.
• Response occurs due to sensory neuron stimulation
  of several Interneurons.
• Impulses extend to the cerebrum, making person
  conscious of stimulus and reaction.

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Pathway of Reflex Arc

• Sensory receptors generate an impulse in sensory
  neuron.
• Moves along sensory axons toward spinal cord.
• Sensory neurons pass impulse to Interneurons.
• Impulses travel along motor axons to an EFFECTOR
  that responds to stimulus.
• Muscles contract to withdraw from source of pain.

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Autonomic System has 2 compontents

• Sympathetic Division
• Emergency Fight or Flight
• Increase heartbeat, dilates bronchi
• Inhibits digestion.
• Neurotransmitter is mainly norepinephrine,
  similar to epinephrine (adrenaline)

• Parasympathetic System
• Housekeeper System
• Promotes internal responses resulting in relaxed
  state.
• Causes constriction of eye pupil, controls
  digestion, slows heartbeat.
• Acetylcholine is neurotransmitter.

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Sympathetic vs parasympathetic

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Transmission of Nerve Impulse

• Resting potential membrane at rest has
  potential equal of 65mV
• - inside of neuron more negative than outside.
• - Higher concentration of K ions inside higher
  concentration of Na outside membrane.
• Sodium-potassium pump is an active transport
  system at moves Na ions out K ions into axon.
• Pump always working to overcome diffusion.

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The Resting Neuron

• Resting potential membrane at rest has
  potential equal of 65mV
• - inside of neuron more negative than outside.
• - Higher concentration of K ions inside higher
  concentration of Na outside membrane.
• Sodium-potassium pump is an active transport
  system at moves Na ions out K ions into axon.
• Pump always working to overcome diffusion.

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Action Potential

• When an axon carries a nerve impulse, there is a
  rapid change in the membrane polarity this is
  called action potential.
• Threshold value must be reached to open sodium
  potassium gates in membrane.
• Depolarization phase cytoplasm more positive
  than tissue fluid.
• Repolarization phase return to resting.