Exercise 21: Nervous System

• Nervous system is responsible for perception of stimuli, transmission of sensory signals or impulses to the central nervous system, and induction by it for the action of muscles and glands
• Diffuse type

  • other term: nerve net
  • found in radially symmetrical animals except echinoderms
• Diffuse nervous system

  • consists of network of nerve cells almost evenly spread across the body of animal
• Ladder Type

  • found in animals like flatworms
  • nerve cords are arranged along the antero-posterior axis
• Ganglia

  • located in the head region of the ladder type nervous system
  • functional clusters of neurons
• Ganglionic type

  • found in annelids like earthworms and arthropods
• Cerebral ganglion

  • other term for brain in ganglionic type of nervous system
• Ventral nerve cords

  • in ganglionic type, it extends posteriorly from cerebral ganglion
• Each pair of ganglia in each segment is connected by nerve strands in ganglion nervous system
• Tubular type

  • found in vertebrates
• It is referred as "tubular" because of presence of internal spaces in brain and spinal cord
• In the brain of tubular type, internal spaces are called ventricles which continue as central canal in spinal cord
• Unlike the nerve cords of ganglionic nervous system, spinal cord is located dorsally
• what type of nervous system do hydras have?

  Diffuse type
• What kind of nervous system do flatworms have?

  ladder type