survival and response

• A stimulus is a detectable (receptor cell) change in the internal or external environment of an organism that produces a response (reaction/action) in the organism. 
• An organisms ability to respond to stimuli increases the chance of survival because they can detect and move away from predators and extremes in temperature, pH, salinity and moisture. 
• The organisms that respond to stimuli are the ones who survive. They have a greater chance of raising offspring and passing their alleles to the next generation. Those who respond appropriately are favoured when selection pressures are applied. 
• Types of innate behaviour:

  • Taxes
  • Kineses
  • Reflex actions 
  • Instincts (complex)
  • Biological rhythms 
  • Courtship 
  • Mating 
  • Aggression 
  • Social hierarchies 
  • Social organisation 
• Taxes is a deliberate movement of the whole organism in response to external stimuli. Can be towards stimulus (positive) or away (negative). Can be classified according to the nature of the stimulus. 

  • Phototaxis
  • Chemotaxis 
  • Hydrotaxis 
• Kinesis is the non-directional movement response where the rate of movement is related to the intensity of the stimulus not direction. Organisms respond to stimuli by moving more or moving less but not in a specific direction - woodlice and humidity. 
• The motor nervous system is divided into: the voluntary nervous system to carry nerve impulses to body muscles and is under voluntary control. The autonomic nervous system that carries nerve impulse to glands, smooth muscle and cardiac muscle which is involuntary. 
• The autonomic nervous system is further split into parasympathetic and sympathetic.
• Simple reflex action involves the two divisions of the nervous system: the CNS and the PNS. The PNS is divided into motor neurons and sensory neurons. 

  • CNS --> motor neurons --> effector (muscle/gland) --> response 
  • Stimuli --> receptor --> sensory neurone --> CNS 
• The reflex arc:

  1. Stimulus 
  2. Receptor 
  3. Sensory neurone 
  4. Relay neurone 
  5. Motor neurone 
  6. Effector 
  7. Response 
• Reflex arcs are rapid, involuntary and innate.