structure and function of neurons

• neurons


  building blocks of nervous system and transmit messages through electrical and chemical signals

  100 billion in human nervous system, 80% in brain

  provide ns with primary means of communication
• sensory neuron


  long dendrites and short axons

  found in sensory receptors and carry nerve impulses to CNS

  convert external stimuli into electrical impulses

  reach brain and translate into sensations

  not all reach brain, stop at spinal cord for quick reflex reactions
• relay neuron 


  found in CNS and visual system

  allow sensory and motor neurons to communicate

  short dendrites and axon
• motor neuron


  found in CNS

  carries nerve impulses from CNS towards effectors (muscles and glands)

  when stimulated, release neurotransmitters that trigger response from muscles causing movement

  short dendrites and long axons
• dendrites


  branch like structures that carry nerve impulses towards cell body
• cell body 


  nucleus (DNA)
• myelin sheath 


  axons covered in fatty layer to protect
• axon terminals 


  end of axon, synaptic connections with other cells
• axon 


  long fibre carries nerve impulses away from cell body
• nucleus 


  contains genetic material
• Process of synaptic transmission

  1.Action potential reaches presynaptic terminal

  2.neurotransmitters released from synaptic vesicles not synapse and diffuse across gap

  3.neurotransmitters bind to specialised post synaptic receptor site

  4.excitatory and inhibitory neurotransmitters are summer

  5.process ends with ‘re-uptake’
• neurotransmitters

  chemicals that diffuse across synapse to next neuron and have specialised functions
• why can neurons only transmit in one direction at the synapse

  synaptic vesicles only present from presynaptic membrane

  receptors only present on postsynaptic membrane

  binding of neurotransmitter to receptor enables information to be passed on
• excitatory neurotransmitters

  increase positive charge of post synaptic neuron

  increases likelihood neuron fires electrical impulse

  adrenaline and glutamate
• inhibitory neurotransmitter

  increases negative charge of post synaptic neuron

  decreases liklihood neuron fires electrical impulse

  serotonin and GABA
• Summation

  Decides whether post synaptic neuron fires eleclerical impulse

  Influence of excitatory and inhibitory neurotransmitters summed and if net effect inhibitory less likely to fire