neurons and synaptic transmission

• Types of neurons


  100 billion neurons in human nervous system, 80% of which located in brain - by transmitting signals electrically and chemically provide nervous system with its primary means of communication

  Three types of neuron:

  • Sensory neuron - carry messages from PNS to CNS, have long dendrites and short axons
  • Relay neurons - Connect sensory neuons to motor or other relay neurons, short dendrites and short axons
  • Motor neurons - connect CNS to effectors such as muscles and glands - short dendrites and long axons
• Structure of neuron


  Cell body includes nucleus which contains genetic material of a cell

  Branchlike structures called dendrites protrude from cell body

  Axon carries impulses away from cell body down length of neuron

  Axon covered in fatty layer of myelin sheath that protects axon and speeds up electrical transmission of impulses from neighbouring neurone towards the cell body

  Axon carries impulses away from cell body down the length of the neutron, axon covered in fatty layer of myelin sheath that protects axon and speeds up electrical transmission of impulse.

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• Synaptic transmission - chemical transmission

  Each neuron separated from next by tiny gap called synapse

  Signals within neurons are transmitted electrically, signals between neutrons transmitted chemically across synapse

  When electrical impulse reaches end of neuron (presynaptic terminal) it triggers release of neurotransmitter from tiny sacs called synaptic vesicles

  Diffuses across synaptic gap and binds to receptor cites on post synaptic nob/next neuron

  triggers reaction in membrane - electrical impulse can pass through the next neuron
• Neurotransmitters


  Chemicals that diffuse across the synapse to next neuron in the chain - once neurotransmitter crosses the gap its taken up by postsynaptic receptor site on the dendrites of the next neuron (axons take signal to synapse, dendrites take signals away)

  The chemical message is converted back into an electrical impulse and process of transmission begins again in this other neuron.
• Excitation and inhibition


  neurotransmitters have either excretory or inhibitory effect on neighbouring neuron for instance serotonin causes inhibition in receiving neuron resulting in neuron becoming more negatively charged and less likely to fire

  In contrast, adrenaline
• Structure of a neuron

  Dendrites extend so neurons close together as possible and carry nerve impulses

  Myelin Sheath surrounds axon to keep nerve impulses inside

  neuron holds genetic material
• Synaptic transmission


  Electrical impulse reaches end of neuron, diffuses across synaptic gap (which is tiny gap between neurons) as chemical neurotransmitter and binds to next neuron.