Reflexes

• The simplest form of nervous response to a stimulus is a reflex action
• Reflex arc

  The shortest pathway taken by the impulses in a simple reflex, typically involving one or two synapses
• Reflexes involve either the spinal cord or the brainstem
• The sensory and motor neurones are linked by a relay neurone (or interneurone) within the spinal cord
• A simple reflex is innate and always results in the same response to a particular stimulus
• Examples of reflex actions

  • Knee-jerk reflex-aids balance
  • Swallowing reflex-prevents choking
  • Pupiliary reflex-controls light intensity reaching the retina
• Importance of simple reflexes

  • They are involuntary actions that do not involve decision-making areas of the brain, leaving them free to carry out more complex responses
  • They are very rapid, as they involve fast electrical impulses and very short neurone pathways
  • They are usually concerned internally with the control of continuous and repetitive actions, such as breathing, control of heart rate etc, essential for survival
  • They are effective from birth and do not have to be learned, protecting the body from harmful stimuli and increasing survival chances
• Most spinal reflexes involve three neurones, with two synapses
• A reflex action is a rapid, short-lived response to a specific stimulus
• Reflexes allow the body to react very quickly to potentially dangerous situations by taking defensive action of some form
• Spinal reflexes

  • Involve either the spinal cord or the brainstem
  • Most spinal reflexes involve three neurones, with two synapses
  • The sensory and motor neurones are linked by a relay neurone (or interneurone) within the spinal cord