UNIT 3 NEUROTRANSMITERS

• Dendrites


  Fibres that carry signals to the cell body
• Cell body


  Contains the nucleus and most of the cytoplasm, controls cell activity and has enzymes
• Myelin Sheath


  Surrounds the axon and increases the speed of conduction
• Function of the myelin sheath

  Insulates the axon and increases the speed of conduction
• Importance of the myelin sheath

  Increases the speed of conduction
• Myelin sheath is a fatty material that runs through the axon
• Myelination continues from birth to adolescence
• Myelination continues from birth to adolescence

  Responses to stimuli in the first two years of life are not as rapid or co-ordinated as those of an older child or adult
• Glial cells


  Produce the myelin sheath and support neurons
• Certain diseases (e.g. multiple sclerosis) destroy the myelin sheath causing a loss of co-ordination
• Glial cells help to build the myelin sheath, maintain a homeostatic environment and remove debris
• Three types of neurons

  • Sensory-inform for sensations to CNS
  • Motor-carry impulses to effectors (muscle)
  • Inter-connect sensory and motor within CNS
• Axon


  Carries impulse away from the cell body, is surrounded by a myelin sheath
• Endorphins


  Neurotransmitters that stimulate neurons involved in reducing the sensation of pain
• Endorphin production increases


  In response to prolonged and continuous exercise, eating chocolate and certain foods
• Increased levels of endorphins

  Are linked to feelings of pleasure obtained from activities such as eating, sex and exercise
• Dopamine


  A neurotransmitter that induces feelings of pleasure and reinforces particular behaviour by activating the reward pathway in the brain
• Reward pathway


  Involves neurons which secrete or respond to dopamine, between nucleus accumbens and ventral tegmental area
• Reward pathway is activated


  When an individual engages in a behaviour that is beneficial to them, for example eating when hungry
• Endorphins and dopamine are neurotransmitters that affect mood and behaviour
• Agonists


  Chemicals that bind to and stimulate specific receptors mimicking the action of a neurotransmitter at a synapse
• Antagonists


  Chemicals that bind to specific receptors and block the action of a neurotransmitter at a synapse
• Other drugs act by inhibiting the enzymes that break down neurotransmitters or by inhibiting reuptake of the neurotransmitters causing an enhanced effect
• Alzheimer's, Parkinson's, Schizophrenia, Generalised anxiety, Depression and Drug addiction are neurotransmitter-related disorders
• Drug addiction is caused by repeated use of drugs that act as agonists
• Drug tolerance is caused by repeated use of drugs that act as agonists, leading to a decrease in the number and sensitivity of receptors
• Drug addiction is caused by repeated use of drugs that act as antagonists, leading to an increase in the number and sensitivity of receptors
• Acute tolerance is shown by a decrease in the dopamine response with repeated doses of a drug