(Sample Material) IAS PRE GS Online Coaching : General Science - "The Nervous System"


Sample Material of Our Online Coaching Programme

Subject: General Science

Topic: The Nervous System


Multicellular animals must monitor and maintain a constant internal environment as well as monitor and respond to an external environment. In many animals, these two functions are coordinated by two integrated and coordinated organ systems: the nervous system and the endocrine system. Three basic functions performed by nervous systems are:-

  1. Receive sensory input from internal and external environments
  2. Integrate the input
  3. Respond to stimuli


Receptors are parts of the nervous system that sense changes in the internal or external environments. Sensory input can be in many forms, including pressure, taste, sound, light, blood pH, or hormone levels, that are converted to a signal and sent to the brain or spinal cord.


In the sensory centers of the brain or in the spinal cord, the barrage of input is integrated and a response is generated. The response, a motor output, is a signal transmitted to organs than can convert the signal into some form of action, such as movement, changes in heart rate, release of hormones, etc.


Some animals have a second control system, the endocrine system. The nervous system coordinates rapid responses to external stimuli. The endocrine system controls slower, longer lasting responses to internal stimuli. Activity of both systems is integrated.


  • The nervous system monitors and controls almost every organ system through a series of positive and negative feedback loops.
  • The Central Nervous System (CNS) includes the brain and spinal cord.
  • The Peripheral Nervous System (PNS) connects the CNS to other parts of the body, and is composed of nerves (bundles of neurons).
  • Not all animals have highly specialized nervous systems.
  • Those with simple systems tend to be either small and very mobile or large and immobile.
  • Large, mobile animals have highly developed nervous systems: the evolution of nervous systems must have been an important adaptation in the evolution of body size and mobility.