Neurons

• What are neurons?

  Neurons are nerve cells that process and transmit messages through electrical and chemical signals.
• What is the role of sensory neurons?

  Sensory neurons carry messages from the peripheral nervous system to the central nervous system. They have long dendrites, short axons and the cell body protrudes from the middle of the axon.
• What is the role of relay neurons?

  Relay neurons connect the sensory neurons to the motor neurons or other relay neurons. They have short dendrites, short axons and no myelin sheath.
• What is the role of motor neurons?

  Motor neurons connect the central nervous system to effectors such as muscles and glands. They have short dendrites and long axons, the dendrites protrude from the cell body.
• Fill in the diagram:

  A) Sensory

  B) Relay

  C) Motor

  
• The direction of travel during synaptic transmission can only be one way, this is because neurotransmitters are released from the presynaptic neuron and received by the postsynaptic neuron.
• What happens during excitation?

  This is when positively charged neurotransmitters outweigh negatively charged neurotransmitters, due to this the neuron will continue to fire
• What happens during inhibition?

  This is when negatively charged neurotransmitters outweigh positively charged neurotransmitters, due to this the neuron will stop firing.
• What happens at the start of synaptic transmission?

  A neuron is stimulated by an excitatory neurotransmitter, which creates a positive charge known as an action potential, this action potential travels down the axon towards the end of the neuron.
• What happens in the middle of synaptic transmission?

  Once the action potential reaches the end of the neuron it needs to cross the synapse to get to the next neuron. As soon as the action potential reaches the synaptic vesicles at the end of the neuron they release neurotransmitters, these neurotransmitters diffuse across the synapse and bind to specialised postsynaptic receptor sites on the dendrites of the next neuron and are converted back into an electrical impulse.
• What happens at the end of synaptic transmission?

  If the overall net charge of the postsynaptic neuron is excitatory, the neuron is more likely to become positively charged and create an action potential which starts the whole process again on the next neuron. If the overall net charge is negative the neuron is less likely to fire. This whole process takes fractions of a second.