neurons and synaptic transmission

• Motor neurons

  connect the CNS to effectors such as muscles and glands. short dendrites and long axons
• Relay neurons

  connect the sensory neurons to the motor neurons. short dendrites and short axons
• Sensory neurons

  carry messages from the PNS to the CNS. long dendrites and short axons
• Cell body

  includes a nucleus, dendrites attached to the cell body carry nerve impulses from other neurons
• Axon

  carries impulses away from the cell body and down the neuron
• Terminal buttons


  communicate with the next neuron in the chain across the synapse
• location of a motor neuron

  cell body in the CNS but the axons form part of the PNS
• location of relay neurons

  make up 97% of all neurons and most are found within the brain and the visual system
• location of sensory neurons

  located outside of the CNS in the PNS in clusters known as ganglia
• process of electrical transmission

  when a neuron is in its resting state the cell is negatively charged

  when the neuron is activated by a stimulus it is positively charged = action potential

  this creates an electrical impulse which travels down the axon to the neuron
• chemical transmission

  signals between neurons are transmitted chemically across the synapse

  when the electrical impulse reaches the end of the neuron it triggers the release of the neurotransmitter
• Neural networks

  neurons communicate with each other within groups
• neurotransmitters

  chemicals that diffuse across the synapse to the next neuron in the chain.

  once a neurotransmitter crosses the gap it is taken up by the postsynaptic neuron
• what is the direction of travel for a neurotransmitter

  the direction of travel is only one way. released from the presynaptic neuron and received by the postsynaptic neuron
• what is meant by lock and key structure

  each neurotransmitter has its own specific molecular structure that fits perfectly into a postsynaptic receptor site
• excitation

  when a neurotransmitter increases the positive charge of the postsynaptic neuron.

  this increases the chance that the postsynaptic neuron will pass on the electrical impulse
• inhibition

  when a neurotransmitter increases the negative charge of the postsynaptic neuron.

  this decreases the likelihood that the postsynaptic neuron will pass on the electrical impulse
• summation

  whether a postsynaptic neuron fires is decided by summation

  the action potential is only triggered if the sum of the excitatory and inhibitory signals at any time reach threshold