Synapses

• Approximately how many synapses can a nerve cell have in some brain cells?

  Up to 10,000
• What is the synaptic cleft and what is its significance?

  • 20-50 nm gap between the presynaptic and postsynaptic membranes
  • Allows neurotransmitters to diffuse across
• How many types of neurotransmitters are there?

  Approximately 50 types
• Which neurotransmitter was the first to be discovered?

  Acetylcholine
• What are the key steps involved in neurotransmission?

  1. Action potential arrives at presynaptic membrane
  2. Membrane depolarises
  3. Calcium ion channels open
  4. Calcium ions diffuse into the neuron
  5. Vesicles fuse with presynaptic membrane, releasing neurotransmitters
  6. Neurotransmitters diffuse across synaptic cleft
  7. Bind to receptors on postsynaptic membrane
  8. Sodium channels open, postsynaptic membrane depolarises
  9. Action potential initiated in postsynaptic neuron

  10. Neurotransmitters are reabsorbed, broken down, or diffuse away
• Which types of drugs affect the mechanism of neurotransmission?

  Recreational drugs and antidepressant drugs
• What are the key functions and characteristics of neurotransmitters?

  • Approximately 50 neurotransmitters in the brain
  • Control all bodily functions by passing impulses through synapses
  • Need precise amounts for proper function
  • Changes can severely affect bodily processes
  • The blood-brain barrier protects the brain from harmful substances
  • Only very small molecules like glucose can pass through
• What are the roles of dopamine in the nervous system and how are these affected in Parkinson's Disease?

  • Dopamine is a neurotransmitter secreted by neurons
  • Axons spread throughout the midbrain, spinal cord, brain stem, and frontal cortex
  • Dopamine-secreting neurons in the basal ganglia die in Parkinson's
  • Normally releases dopamine into the motor cortex
  • Less dopamine in the synapse disrupts nerve impulse transmission in the motor cortex
• What are the main symptoms of Parkinson’s Disease?

  • Stiffness of muscles
  • Tremor of muscles
  • Slowness of movement
  • Poor balance
  • Walking problems
• How are dopamine levels related to Parkinson’s Disease and schizophrenia?

  • Parkinson's involves a lack of dopamine in the synapse, leading to motor dysfunction
  • Schizophrenia is linked to an excess of dopamine
  • Antipsychotic drugs that prevent dopamine binding are used to treat schizophrenia