Structure of Neurons and Synaptic Transmission#

• Motor neuron:

  • Dendrites - Where neurotransmitter receptors are, once the receptor and neurotransmitter bind, this causes an electrical impulse to occur (action potential)
  • Cell body - Includes the nucleus which contains the cell's genetic material
  • Axon - Sends a nerve impulse through the neuron to transmit a message to the next neuron
  • Myelin sheath - Protects axon and speeds up the transmission of the message
  • Nodes of ranvier - Speeds up the transmission by forcing impulse to jump across the gaps of the axon
  • Terminal button - Sends information to the next neuron through the neurotransmitters

  
• Sensory neuron:

  • Location - PNS in clusters known as ganglia
  • Function - Send information from the senses to the brain
  • Structure - Long dendrites and short axons
  • (Cell body in middle)

  
• Relay neuron:

  • Location - CNS
  • Function - Carry nerve impulses between neurons allowing sensory and motor neurons to communicate, involved in analysing the sensations from these neurons and deciding how to respond
  • Structure - Short dendrites, short axons and no myelin sheath

  
• Motor neuron:

  • Location - Cell bodies are found in the CNS but the long axons form part of the PNS
  • Function - Send information via long axons from the CNS to effects such as muscles, glands or organs
  • Structure - Short dendrites and long axons
  • (Cell body at the start)

  
• Process of synaptic transmission:

  1. Begins in the presynaptic neuron: action potentials are sent down the neuron until they reach the presynaptic neuron
  2. This causes neurotransmitters (stored in vesicles and are only located in the presynaptic neuron) to be released into the synapse
  3. The neurotransmitters diffuse across the synapse (from an area of high concentration to an area of low concentration) and then bind with their specific receptor sites that are only present on the postsynaptic neuron
  4. Two outcomes can be achieved after the neurotransmitters have attached to receptor sites
• Two outcomes of synaptic transmission:

  1. The next neuron is ready to fire an impulse, depending on whether the next neurotransmitter has an excitatory or inhibitory effect
  2. The neurotransmitters are recycled back to be stores back in the vesicles in the presynaptic neuron through reuptake
• Excitatory neurotransmitters, e.g. dopamine or adrenaline:

  • When they bind to the postsynaptic neuron, the next neuron becomes positively charged (1)
  • The next neuron is more likely to fire an impulse (1)
  • Increases brain activity in the CNS (1)
• Inhibitory neurotransmitters, e.g. serotonin or GABA:

  • When they bind to the postsynaptic neuron, the next neuron becomes negatively charged (1)
  • The next neuron is less likely to fire an impulse (1)
  • Reduces brain activity in the CNS (1)
• Summation:

  • Occurs when the excitatory and inhibitory influences are added up (1)
  • If the overall effect is mainly inhibitory, it reduces the likelihood the neuron will fire an impulse down the postsynaptic neuron (1)
  • If the overall effect is mainly excitatory, it is more likely that the neuron will fire an impulse down the post synaptic neuron (1)