NEUR 2.2 - Neurons and their communication

• Parkinson's Disease

  Define: Loss of dopamine in basal ganglia deep in brain

  Effect: Primarily affects movement = slow movement

  
  

  
  

  Dopamine: important for motor function + motor control and associated with reward + reinforcing behaviour

  
  

  Highlight: To treat Parkinson's, once L-DOPA passes through the blood-brain barrier, it's turned into dopamine in the brain, replacing neurotransmitter dopamine in the basal ganglia
• EG: Serotonin - Antidepressant Drugs

  
  

  NOT ALL DRUGS ACT ON THE BRAIN BY REPLACING NEUROTRANSMITTER

  • act on processes that break down serotonin from the synaptic cleft

  
  

  
  

  • SSRIs: suppress action of neurotransmitter reuptake pump for serotonin - leaving serotonin longer in the synaptic cleft

  
  

  • MAOIs: inhibit action of one of the major enzymes that will break down serotonin, increasing serotonin signal

  
  

  
  

  Highlight: both don’t replace serotonin, but signalling of serotonin can be BOOSTED by allowing the serotonin to remain longer in the synaptic cleft and have a larger effect
• Synapses Recap

  Join together axon terminals (neuron 1) to dendrites (neuron 2) for transmission of signals

   

   

  1. input to dendrites
  2. signals go down axon
  3. axon terminals
  4. across synapses
  5. into dendrites of another neuron

   

   

  Neural signals go 1 way
• Neurotransmitter release

  
  

  Depolarisation triggers release of neurotransmitters

  • Neurotransmitters join with receptors of post-synaptic neuron (dendritic spine)

  = open ligand-gated channels allowing signal pass neuron-to-neuron
• Re-uptake pump

   

  Important for clearing neurotransmitter OUT of the synaptic cleft --> stop neurotransmitters signalling to the post-synaptic neuron

   

  Re-uptake pump: sucks the neurotransmitter OUT of the synaptic cleft for repackaging into the vesicles
• Enzymes: chemicals that float around in synaptic cleft facilitate chemical reaction by breaking down neurotransmitter --> changing its molecular shape (no longer act and bind with receptors)

   
• Oligodendrocytes

  • Produce myelin sheath that wraps around axons
  • Essential for the propagation of signals along the axon
• Importance of oligodendrocytes and myelin for neural communication

  Clearly seen in multiple sclerosis disorder: progressive neurodegenerative disorder

  
  

  • Involves loss of myelin in the body
  • Disruption of efficient neural communication
  • Debilitating effects start with some loss of control of movement and later with cognitive changes
• Astrocytes

  • Supply nutrients from blood to neurons
  • Maintain the blood-brain barrier - (Brain has natural barrier that prevents certain substances from the blood from entering the brain)
• Microglia

  • Brain's immune system - (Blood-brain barrier means normal body immune system doesn't operate in the brain)
  • Clean up foreign / toxic substances
• Sodium potassium pump

  Overall positive charge OUT of cell (3Na+ out, 2K+ in)

  
  

  Maintains negative resting membrane potential - imbalance of positive ions + requires energy = not stable equilibrium state
• Voltage-gated ion channels - Depolarisation

  
  

  Voltage less negative = closer to 0

  • CLOSED at resting potential
  • Na+ channels OPEN when threshold reached - sodium rushes IN
• Voltage-gated ion channels - Repolarisation

  1. Na+ channels close

  2. K+ channels open after depolarisation

  3. K+ flows OUT of cell

  
  

  More negative potential
• Summary

  1. Single neuron integrates action potentials

  • Can be excitatory/inhibitory, strong/weak

   2. Determine if it will fire + send signal to brain
• Ligand-gated ion channels - Excitatory

  
  

  • EPSP: Excitatory Post-synaptic Potential
  • closer to threshold for action potential
  • Depolarisation: (Na+ flows IN)
• Ligand-gated ion channels - Inhibitory

  • IPSP: Inhibitory Post-synaptic Potential
  • further from threshold for action potential
  • Hyperpolarisation: (more negative / further away from threshold) - K+ flows OUT / Cl- flows IN
• Graded potentials

  Depend on strength of connection: excitatory + inhibitory combine via dendrites