Nervous Systems

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Nervous Systems

• Three Main
• Functions
• 1. Sensory Input
• 2. Integration
• 3. Motor Output

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Two Main Parts of Vertebrate Nervous Systems

• Central nervous system (CNS)
• brain and spinal cord
• integration
•  Peripheral nervous system (PNS)
• network of nerves extending into different parts
  of the body
• carries sensory input to the CNS and motor output
  away from the CNS

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Two Cell Types in Nervous Systems

• Neurons
• Cells that conduct
• the nerve impulses
• Supporting Cells
• Neuroglia

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Figure 48.2x Neurons
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Three Major Types of Nerve Cells

• Sensory neurons
• communicate info about the external or internal
  environment to the CNS
• Interneurons
• integrate sensory input and motor output
• makes synapses only with other neurons
• Motor neurons
• convey impulses from the CNS to effector cells

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Supporting Cells - Neuroglia

• provide neurons with nutrients, remove wastes
• Two important types in vertebrates
• Oligodendrocytes myelin sheath in CNS
• Schwann cells -myelin sheath in PNS

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Myelin Sheath Formation
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Conduction of the Nerve Impulse

• Membrane Potential
• Voltage measured across a membrane due to
  differences in electrical charge
• Inside of cell is negative wrt outside
• Resting potential of neuron -70 mV

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Figure 48.6 Measuring membrane potentials
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Sodium-Potassium Pump
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Excitable Cells

• Neurons muscle cells
• Have gated ion channels that allow cell to change
  its membrane potential in response to stimuli

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Gated Ion Channels

• Some stimuli open K channels
• K leaves cell
• Membrane potential more negative
• hyperpolarization
• Some stimuli open Na channels
• Na enters cell
• Membrane potential less negative
• depolarization

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Gated Ion Channels

• Strength of stimuli determines how many ion
  channels open
• graded response

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Nerve Impulse Transmission
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Action Potentials

• Occur once a threshold of depolarization is
  reached
• -50 to 55 mV
• All or none response (not graded)
• Magnitude of action potential is independent of
  strength of depolarizing stimuli
• Hyperpolarization makes them less likely

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Refractory Period

• During undershoot the membrane is less likely to
  depolarize
• Keeps the action potential moving in one direction

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Propagation of Action Potential

• Action potential are very localized events
• DO NOT travel down membrane
• Are generated anew in a sequence along the neuron

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Saltatory Conduction
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Transfer of Nerve Impulse to Next Cell

• Synapse
• the gap between the synaptic terminals of an axon
  and a target cell

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Transfer of Nerve Impulse to Next Cell

• Electrical synapses
• Gap junctions allow ion currents to continue
• Chemical synapses
• More common
• Electrical impulses must be changed to a chemical
  signal that crosses the synapse

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Synapses
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Neurotransmitters
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Effects of Cocaine
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Integration of multiple synaptic inputs
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Summation of postsynaptic potentials
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Diversity of Nervous Systems
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CNS
Brain and Spinal Cord
Motor Pathways
Sensory Pathways
Sensory neurons registering external stimuli
Sensory neurons registering external stimuli
PNS
Somatic nervous system (voluntary)
Autonomic nervous system (involuntary)
Sympathetic nervous system "fight or flight"
Parasympathetic nervous system "rest and repose"
central nervous system (CNS)
peripheral nervous system (PNS)
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Vertebrate Central Nervous System

• Spinal Cord
• Receives info from skin muscles
• Sends out motor commands for movement response
• Brain
• More complex integration
• Homeostasis, perception, movement, emotion,
  learning

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Vertebrate Central Nervous System

• White matter
• Internal part of brain external part of spinal
  cord
• Myelinated axons
• Gray matter
• Cell bodies of neurons

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Figure 48.16x Spinal cord
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Vertebrate Central Nervous System

• Cerebrospinal Fluid
• Fills central canal of spinal cord and ventricles
  of brain
• Shock absorption

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Functions of Spinal Cord

• Carrying information to and from the brain
• Integration of simple responses
• Reflexes
• Unconscious programmed response to stimuli

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The knee-jerk reflex
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Evolution of Vertebrate Brain

• Evolved from a set of three bulges at the
  anterior end of spinal cord
• Forebrain (cerebrum)
• Midbrain (optic lobe)
• Hindbrain (cerebellum medulla oblongata)
• Regions have been further subdivided structurally
  and functionally

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Vertebrate Brains
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Vertebrate Brains

• The relative sizes of different brain regions
  have changed as vertebrates evolved
• -Forebrain became the dominant feature