Cells of nervous system and Neurotransmitters

• label the neuron

  A) impulse

  B) axon

  C) dendrite

  D) cell body

  E) myelin sheath

  
• label the synaptic cleft

  A) impulse

  B) pre-synaptic neuron

  C) vesicle

  D) synaptic cleft

  E) neurotransmitter

  F) post-synaptic neuron

  G) impulse

  H) receptors

  
• myeline sheath is produced by glial cells and support neurons
• myelin sheath insulates axons, which increase speed of impulse conduction
• myelination continues in adolescence so nervous control increases with age
• diseases destroy the myelin sheath which lead to a loss of coordination
• examples of neurotransmitters are:

  • endorphin
  • dopamine
• endorphins reduce intensity of pain, pleasure obtained from eating, sex, prolonged exercise, injury
• dopamine increases pleasure and activates the reward pathway which reinforces behaviour
• recreational drugs can act as agonists or antagonists, this affects the reward pathway
• recreational drugs can affect:

  • mood
  • behaviour
  • cognition
  • perception
• impulse stimulates vesicles containing neurotransmitters to move to and bind to surface of pre-synaptic neuron
• neurotransmitters released into cleft and diffuse across, bind to receptors on post-synaptic neuron, bring about impulse
• agonists bind to and stimulate receptors -> mimic their action
• antagonists bind to and block receptors -> reduce / stop their action
• an effect of the autonomic nervous system (ANS) on the sinoatrial node (SAN) in the heart?

  parasympathetic branch of autonomic nervous system releases chemical acetylcholine which decreases impulse generation of sinoatrial node
• neurons have a high number of mitochondria to provide energy for neurotransmitter (protein) synthesis or receptor synthesis
• neurons increase the number of ribosomes to increase neurotransmitter / enzyme synthesis
• receptors determine if a signal is excitatory or inhibitory
• removal of neurotransmitters:

  • prevent continuous stimulation of post-synaptic neuron by enzymes pr re-uptake
• DAT

  desensitisation

  Decreases number and sensitivity of receptors

  Agonist drugs

  Tolerance - more drug needed to get effect
• SANTA

  sensitisation

  Increased number and sensitivity of receptors

  ANTagonist drugs

  Addiction- crave more drug
• summation is a when series of weak stimuli trigger enough neurotransmitters to reach threshold
• threshold is the minimum number of neurotransmitters bound to receptors to trigger and impulse
• summation is typical in convergent neural pathways
• in summation, receptors can filter out weak stimuli from insufficient neurotransmitter secretion