How Do Organisms Respond to External Stimuli?

When external stimuli affects an organism's nervous system, it transports the information in the form of action potentials, and then the brain processes and perceives it. External stimuli come in a variety of formats. As such, they illicit various responses within organisms.

When an external stimulus is applied to an organism, it usually receives information via its nervous or endocrine system. From there, it can produce a variety of responses:

  • Reflex responses
  • - Organisms can automatically respond to their stimuli with a reflex response. Usually, this causes a muscle or appendage to move.

  • Orientation
  • - Orientation behaviors include swimming, walking and flying. Organisms consciously choose them based on the environment around them and their need to move.

  • Taxis
  • - A simpler organism may automatically move or rotate itself towards external stimuli. For example, moths naturally move towards light.

  • Secretion
  • - When an external stimulus causes input in the form of taste, glands may secrete saliva to make digestion easier. In addition, people sweat in response to heat and the adrenal glands secrete adrenaline in response to fear.

  • Brain reactions
  • - As the brain processed nervous system input, EEG brain waves occur when it receives action potentials.

  • Sodium gated channels
  • - At a neurological level, sodium gated channels open in response to external stimuli to allow action potentials to travel.