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Lecture 13 Nervous Tissues JPHubbard Bio-5. Control/Communication – Two Systems Nervous Endocrine. Organization of the Nervous System. CNS is brain and spinal cord PNS is everything else. Nervous Tissue Neurons – cells responsible for conducting information 3 types

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organization of the nervous system
Organization of the Nervous System

CNS is brain and spinal cord

PNS is everything else

slide4
Nervous Tissue
  • Neurons – cells responsible for conducting information
    • 3 types
  • Neuroglia – responsible for support of neurons
    • 6 types
      • 4 in CNS
      • 2 in PNS
slide5
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

slide6

Cell body (soma)

Dendrites

Axonal hillock – ‘trigger zone’

Axon

Telodendria

Synaptic terminal

synaptic knob

parts of a neuron
Parts of a Neuron

Neuroglial cells

Nucleus with Nucleolus

Axons or Dendrites

Cell body = soma

slide8
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)
slide10

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
slide11
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
gray and white matter
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
slide13
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
multiple sclerosis ms
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
slide16
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
slide17
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
functioning of chemical synapses
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
slide20
Neurotransmitters:
  • various chemical classes
    • Amino acids
    • Modified amino acids
    • Gasses (nitric oxide) – etc. + 50 known
  • Excitatory: stimulate postsynaptic neuron
    • Acetylcholine (loss  Alzheimer’s)
    • Dopamine (loss  Parkinson’s)
    • Serotonin (decrease assoc. with depression)
  • Inhibitory: inhibit signal in postsynaptic neuron
    • GABA
slide21
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
slide22
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