L5 - Synapses and Neural Integration

Question 1

Neuron Signals:

Answer 1

• Electrical Signals
  
  • Within-neuron: Action Potential, electrical signal from axon hillock, along axon, to pre-synaptic axon terminal
• Chemical Signals
  
  • Between-neurons: Neurotransmitter signal across synapse

Question 2

The Synapse:

Answer 2

Question 3

Neurotransmitters:

Answer 3

Amino Acids

• Glutamate: Excitatory – used in 90% of synaptic transmissions
• Gamma-aminobultyricacid: Inhibitory – used in 9% of synaptic transmissions

Monomines and Acetylcholine (the other 1%)

• Cholinergic System
  
  • Uses Acetylcholine (Striatum)
  • Important for arousal, vigilance and memory
  • Reduced activity implicated in Alzheimer’s
• Dopaminergic System
  
  • Uses Dopamine (Substantia Nigra)
  • Important for motor control
  • Reduced activity linked to Parkinson’s
• Noradrenergic System
  
  • Uses Norephinephrine (Locus cerelus of the brainstem)
  • Important for attention and executive control
  • Reduced activity implicated in ADHD
• Serotonergic System
  
  • Uses Serotonin (Raphe Nuclei of the brainstem)
  • Important for sleep, aggression and memory
  • Reduced Activity implicated in depression

Question 4

“Lock and key” - neurotransmitter receptors:

Answer 4

• Each receptor only binds to a specific type of neurotransmitter
• Neurotransmitters only “activate” their specific type of receptor
• Important for drug effects
  
  • Drugs can act on specific receptors to cause specific effects (eg. L-DOPA for Parkinson’s disease replaces dopamine in the brain)

Question 5

Anti-Depressant Drugs - Serotonin

Answer 5

Question 6

Ligand-Gated ion channels:

Answer 6

• Neurotransmitter receptors open ion channels when neurotransmitter binds
• Different neurotransmitters bind to and open different ion channels (Na+, K+,Cl-) to change membrane potential in different ways
• Receptor binding:
  
  • Can cause depolarisation (less negative) e.g. Na+ flows in
  • Can cause hyperpolarisation (more negative) e.g. K+ flows out or Cl- flows in

Question 7

Excitatory and Inhibitory Post Synaptic Potentials:

Answer 7

• Excitatory (EPSP) and inhibitory (IPSP) post synaptic potentials feed into the dendrites of a neuron
• The influence of EPSP and ISPS vary depending on the strength of the synaptic connection between the neurons
• Graded potential: The resulting potential at the axon hillock determined on the sum and timing of inputs (EPSPs and IPSPs).
  
  • Depolarisation: Less negative and closer to 0 (and the AP threshold) - Excitatory
  • Hyperpolarisation: More negative and further from 0 - Inhibitory
• If enough excitatory inputs occur together close enough in time, membrane potential will exceed AP threshold level and the neuron will fire an AP
• Neural integration: The summation of all sensory or higher inputs to determine motor output