What are Neurons?

Orthopaedic & Spine Center

Raj N. Sureja, MD

Neurons are nerve cells that are the basic components of our brain and nervous system.  Although they can vary in shape, size and structure, all neurons have three separate parts – 1) the body of the cell; 2) the axon (transmitter) and 3) the dendrite (receiver).  Nerve cells are structurally and functionally different from other cells in the body in that they receive and transmit electrical and chemical signals (messages) called neurotransmitters.  Other cells in the body cannot do this highly specialized work. 

Would you like to take a guess how many neurons are in the average human brain? 86 billion. That huge number is only the amount in the brain, not the body itself.   Looking at a typical nerve cell under a microscope reminds one of a sort of alien bug, with the cell nucleus on one end, with the dendrite branches coming out of it like the hair of a medusa, and then the axon forming a long tail at the other end, with a small branching area called the synaptic end bulbs.  Most neurons only have one axon, though some can have more.

There are three main types of neurons in the spinal cord (and more lesser types) in the body that have different functions:

  • Motor Neurons – these nerve cells live in the brain, spinal cord and smooth muscles and control all movement in the body – whether that be your heartbeat, walking, breathing, digestion, a bowel movement, lifting a 50-pound weight over your head or playing with your dog in the yard.
    • Motor Neurons are multipolar, with one axon and several dendrites and are divided into two categories –
      • Upper motor neurons travel from the brain to the spinal cord
      • Lower motor neurons travel from the spinal cord to the muscle
  • Sensory Neurons are nerve cells that only have one axon, split into two branches.  They react to an outside stimulus – and respond to all five senses, whether physical or chemical:
    • Taste – the sourness of lemon, the sweetness of a Snickers Bar
    • Touch – a hot stove, a soft, furry kitten, an icy windshield
    • Smell – a freshly cut Christmas tree or chocolate chip cookies in the oven
    • Hearing – a chainsaw, a baby laughing, or a harp playing
    • Sight – a rainbow or a stallion running in a green pasture, a homeless person asleep on the sidewalk

(Isn’t it interesting how just these descriptions can make those senses come alive?)

  • Interneurons – as the name suggests – these nerve cells connect the spinal sensory and motor neurons AND also can communicate between themselves.  They are multipolar and can form complex nerve circuits.

Treating nerve pain comprises a great deal of my practice and I see patients every day who complain of neuropathic issues.  As an Interventional Pain Management Physician, it is important that I understand the intricacies of how nerves function, so that I can better understand why you may be having pain and how to best treat your symptoms, if not uncover the root of the problem completely.