Lecture 13 Nervous Tissues JPHubbard Bio-5

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Lecture 13 Nervous TissuesJPHubbardBio-5
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• Control/Communication Two Systems
• Nervous
• Endocrine

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Organization of the Nervous System

• CNS is brain and spinal cord
• PNS is everything else

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• Nervous Tissue
• Neurons cells responsible for conducting
  information
• 3 types
• Neuroglia responsible for support of neurons
• 6 types
• 4 in CNS
• 2 in PNS

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• Neuron Structure
• Cell body
• Control metabolic functions/Integration
• Dendrites
• Receive information from other
  neurons/environment
• transmit towards cell body
• Axonal hillock trigger zone develops nerve
  impulse
• Axon
• Conduct nerve impulse away from cell body
• Terminates at synaptic bulb
• Collaterals may form
• Telodendria

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• Cell body (soma)
• Dendrites
• Axonal hillock trigger zone
• Axon
• Telodendria
• Synaptic terminal
• synaptic knob

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Parts of a Neuron
Neuroglial cells
Nucleus with Nucleolus
Axons or Dendrites
Cell body soma
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• Three Structural Types of Neurons
• Multipolar one axon and several dendrites
• Cell bodies within CNS
• Includes interneurons and motor neurons (efferent
  neurons)
• Unipolar one process from cell body branches
  into axon and dendrite
• Nuclei in ganglia outside CNS
• Most sensory (afferent) neurons
• Bipolar one axon and one dendrite
• Found in special sensory organs (eyes, ears, nose)

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Functional Classification of Neurons

• Sensory cell body outside CNS axon extends
  into CNS
• Interneuron entirely within CNS
• Motor cell body in CNS (also in autonomic
  ganglia) axon extends to effector

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• Neuroglia of CNS
• Astrocytes
• Blood brain barrier
• Control interstitial environment
• Guide development, Repair, Framework of CNS
• Oligodendrocytes
• Form myelin covering (white matter) on one or
  more axons
• Microglia
• security guards
• Ependymal
• Secretion and circul. Of cerebrospinal fluid

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Gray and White Matter

• White matter myelinated processes (white in
  color)
• Gray matter nerve cell bodies, dendrites, axon
  terminals, bundles of unmyelinated axons and
  neuroglia (gray color)
• In the spinal cord gray matter forms an
  H-shaped inner core surrounded by white matter
• In the brain a thin outer shell of gray matter
  covers the surface is found in clusters called
  nuclei inside the CNS

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• Neuroglia of PNS
• Schwaan Cells
• form myelin covering around single axon
• May also enclose multiple unmylenated nerve
  fibers together
• Guide and stimulate nerve fiber repair
• Satellite Cells
• Regulate nutrient/waste product exchange

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Multiple Sclerosis (MS)

• Autoimmune disorder causing destruction of myelin
  sheaths in CNS
• sheaths becomes scars or plaques
• 1/2 million people in the United States
• appears between ages 20 and 40
• females twice as often as males
• Symptoms include muscular weakness, abnormal
  sensations or double vision
• Remissions relapses result in progressive,
  cumulative loss of function

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• Neurons and Nerve Impulses
• Excitability ability of cell membrane to conduct
  electrical impulse
• Neurons
• Muscle fibers
• Action potential wavelike depolarization -
  movement of ions across axon membrane
• Spreads from soma towards synaptic bulb of
  neurons
• Trigger development of threshold potential
  sufficient stimulation
• Factors affecting speed of transmission
• /- myelin sheath
• Diameter of axon

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• Synapses
• Site of communication between neruron and another
  cell
• Usually chemical
• May involve
• Two neurons
• Neuron and another cell type neuroeffector
  junction
• One-way signal direction
• Presynaptic neuron to postsynaptic neuron
• Occur between synaptic bulb of presynaptic neuron
  and
• Dendrites/soma/axon of postsynaptic neuron

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Functioning of Chemical Synapses

• Action potential reaches end bulb triggering
  release of neurotransmitter
• Neurotransmitter crosses synaptic cleft
• Binding of neurotransmitter alters membrane
  potential in postsynaptic neuron
• One-way information transfer
• Neurotransmitter removed
• Action is transitory

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• Neurotransmitters
• various chemical classes
• Amino acids
• Modified amino acids
• Gasses (nitric oxide) etc. 50 known
• Excitatory stimulate postsynaptic neuron
• Acetylcholine (loss ? Alzheimers)
• Dopamine (loss ? Parkinsons)
• Serotonin (decrease assoc. with depression)
• Inhibitory inhibit signal in postsynaptic neuron
• GABA

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• Neurotransmitter Effects
• Neurotransmitter effects can be modified
• synthesis can be stimulated or inhibited
• release can be blocked or enhanced
• removal can be stimulated or blocked (agonist vs.
  antagonist)
• Prozac serotonin reuptake inhibitor
• receptor site can be blocked or activated

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• Terms (see table 13.1 p 332 5th ed)
• Ganglion (pl Ganglia) Mass of cell bodies in
  PNS
• Plexus Network (of nerves)
• Center Group of neuron cell bodies in the CNS
  with common function
• Nucleus center with defined boundries
• Tract Bundle of axons within the CNS sharing
  common origin, destination and function
• Column A group of tracts found within a specific
  region of the spinal cord
• Pathway centers and tracts connecting brain with
  organs/systems in body