Neurons – A briefing – Anatomy and Physiology



Neurons, yay! These little guys respond to electrical excitement! Don’t they just sound like the life of the party? They respond to a change in the environment ( but it has to be powerful enough to start the ball rolling on action potential), this is called a stimulus, and then turn that response into action potential! Action potential is a nerve impulse – an electrical charge that moves all the way along the surface of the membrane of a neuron!
How the hell does it move? Easy! The movement of Na and K, ions, between the interstitial fluid and the inside of a neuron through specific ion channels in its plasma membrane. A nerve impulse travels at the same quick speed through the journey. Some Neurons are really short, and some are super long! like form your waste to your ankle.

Neurons are made up of three parts:

  1. Cell Body (Perikaryon or Soma) contains a nucleus surrounded by cytoplasm
  2. Dendrites (like little trees, there is usually multiple dendrites and only one axon) are the part that receives the signal, the plasma membranes contain reception sites for binding the chemical messages from other cells. Dendrites are usually short but with lot of branches.
  3. Axon (or since there is only one of them usually per neuron – Axis) of a neuron starts the outgoing nerve impulse towards another neuron, gland cell or muscle fibre. An axon is long and thin cylinder shaped, it joins to the cell body at the cone shape (axon hillock), the closes to this part of the axon is called the initial segment. The nerve impulse starts between the axon hillock and the initial segment, this is called the trigger zone. The cytoplasm of the axon, axoplasm, is covered by plasma membranes – axolemma, a bit like a husk. The communication between neurons occurs in the synapse

Now for the interesting bit:

Structural Classification of Neurons:

  • Multipolar neurons: these have lots of dendrites and one axon, mainly the neurons of the brain and spinal cord and all motor neurones fit in this category.
  • Bipolar neurons: one dendrite and one axon, found mainly in the eye, ear and olfactory area of the brain
  • Unipolar Neurons: have some dendrites and one axon that have fused together to become a single process. These ones detect the feeling sensations : touch, pressure, pain or thermal. These can be found in the spinal cord.
    There are is also a functional classification for these neurons too*
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