Nervous System

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Nervous System
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Divisions of PNS

• Afferent
• Sensory
• Efferent
• Motor
• Somatic
• Autonomic

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• Dendrites
• Cell body
• Nissl bodies
• Axon
• Schwann cells
• Nodes of Ranvier
• Myelin sheath
• Synaptic terminals

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Types of neurons
Multi
Bi
Uni
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• Neuroglia (supporting cells) far outnumber
  neurons
• Secrete circulate CSF (ependymal)
• Physical protection structural support
  (astrocytes oligodendrocytes schwann cells)
• Remove wastes pathogens (microglia)
• Maintain ion nutrient balance

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Neural transmission

• Communication between excitable cells
• Neuron-neuron
• Neuron-muscle
• Neuron-gland
• Via transmission of electrical stimulus (AP)

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Maintenance ofResting Potential
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Types of Potentials

• Resting potential At rest charge difference
  across plasma membrane
• Local (graded) potential Local depolarization of
  cell membrane
• Signal strength dissipates with distance from
  source
• Action Potential Propagated change in membrane
  potential
• Signal strength does not dissipate with distance
• Travels entire length of neuron

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Resting Potential
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Depolarization
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Repolarization
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AP Propagation

• AP generates local currents (depolarizations)
• these depolarize the plasma membrane immediately
  adjacent to the AP

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AP Propagation

• When local depolarizations reach threshold, a new
  AP is produced adjacent to original
• In this manner, AP is propagated along entire axon

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• Myelin sheath determines type of propagation
  speed of propagation

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Continuous vs. Saltatory

• Continuous propagation
• Along unmyelinated axons
• AP depolarizes every mm of plasma membrane
• Slow propagation
• Saltatory propagation
• Along myelinated axons
• AP depolarizes only those portions of the plasma
  membrane that are exposed to extracellular fluid
• Rapid propagation

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The synapse

• Any chemical synapse
• If Na channels open depolarization excitatory
• If K or Cl- channels open hyperpolarization
  inhibitory

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Neurotransmitters

• Excitation or inhibition depends on receptors,
  NOT neurotransmitters
• Ach - Both brain spinal cord, neuromuscular
  junctions
• Serotonin - Both brainstem (widespread effects)
  mood, anxiety, sleep induction
• Too much hallucinations, delusions, withdrawls
• Too little insonmnia

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Neurotransmitters

• Norepinephrine - Both brainstem (widespread
  effects)
• Stimulant (increases heart rate, glycogen
  metabolism dilate pupils blood vessels)
• Coca. and amphet. Increase release block uptake
• Endorphins - Inhibitory throughout CNS PNS
  decrease/dull sensations of pain
• Morphine heroin mimic endorphinsinhibit
  release of neurotransmitters

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