A01

• What are the three types of neurons?

  Motor, relay and sensory
• What is the role of the sensory neuron?

  - To carry messages from the PNS to the CNS

  - They have long dendrites and short axons
• What is the role of the motor neuron?

  - To connect the CNS to effectors such as muscles and glands

  - They have short dendrites and long axons
• What is the role of the relay neuron?

  - To connect the sensory neurons to the motor neurons or other relay neurons

  - They have short dendrites and short axons
• What is synaptic transmission?

  The process by which a nerve impulse passes across the synaptic cleft from the presynaptic neuron to the postsynaptic neuron
• What is excitation?

  When a neurotransmitter increases the positive charge of the postsynaptic neuron, increasing the likelihood that the neuron will fire - e.g. adrenaline
• What is inhibition?

  When a neurotransmitter makes the charge of the postsynaptic neuron more negative, decreasing the likelihood that the neuron will fire - e.g. serotonin
• What is a neurotransmitter?

  A chemical messenger that helps transfer the electrical impulse across the synapse from the presynaptic to the post synaptic neuron
• What is summation?

  The net result of adding up the excitatory and inhibitory neurotransmitters binding to the receptors - determines whether or not the neuron fires
• Describe the process of synaptic transmission

  - Nerve impulse/ action potential travels down the axon of the presynaptic neuron

  - It stimulates synaptic vesicles to release neurotransmitters which diffuse across the synapse to the postsynaptic neuron

  - Neurotransmitters bind to receptors on surface of postsynaptic neuron - has either inhibitory or excitatory effect

  - Likelihood of cell firing determined by summation
• What is the role of dendrites?

  Carry nerve impulses from neighbouring neurones towards the cell body
• What is the role of the nucleus?

  Contains the genetic material of the cell
• What is the role of the cell body/soma?

  Carries the nucleus
• What is the role of the axon?

  Carries the nerve impulses away from the cell body
• What is the role of the myelin sheath?

  A fatty layer around the axon which protects the axon and speeds up electrical transmission of the impulse
• What is the role of the Nodes of Ranvier?

  Gaps in the myelin sheath which speed up transmission of impulse by forcing it to 'jump' across the gaps in the axon
• What is the role of terminal buttons?

  At the end of the axon that communicate with the next neuron in the chain across the synapse