Stimuli are detected by the body and lead to a response

• Stimulus
  • detectable change in environment (internal or external) of any organism that produces a response in that organism
• Receptor
  • Cells or organs that detect stimuli
• Effector
  • Cells, tissues, organs or systems that carry out the response
• Tropism
  • a growth movement of part of a plant in response to a directional stimulus.
• Phototropism
  • Response to light.
• Geotropism
  • Response to gravity

• Hydrotropism
  • Response to water
• Taxis
  • Movement that is orientated in relation to the direction of a stimulus
• Kineses
  • behaviour pattern in which the animal responds ti a change in stimulus intensity or decreasing it activity.
    • Orthokinesis
      • speed of movement depends on stimulus intensity
    • Klinokinesis
      • rate of turning depends on stimulus intensity
• Central Nervous system (CNS)
  • consists of brain and spinal cord

• Peripheral nervous system
  • made up of pairs of nerves that originate from either the brain or the spinal cord which link to receptors and effectors
• Sensory neurones
  • Carry nerve impulses from receptors to CNS
• Motor neurones
  • Carry nerve impulses from CNS to effectors.
• Voluntary Nervous System
  • carries nerve impluses to body muscles
• autonomic Nervous System
  • carries impulses to glands, smooth muscle and cardiac muscle.
• Reflex
  • An involuntary respnse to a sensory stimulus

• Reflex Arc
  • pathway of neurones involved in a reflex

• Responding to a stimulus increases organism chances of survival
  • this increases chances of reproduction and passing alleles to next generation
  • Therefore, there is always a selection pressure favouring organisms with more appropriate responses
  • Animals use the nervous system as a more rapid method of communication

Stimulus--> Receptor --> Co-ordinator --> Effector --> Response

• Plants often respond to an external stimulus acting from a particular direction
  • movement involves directional growth
    • caused by more growth in one region than another
  • such growth is caused tropism
• Type of response named after stimulus:
  • Phototropism
    • Shoots = positively phototropic
    • roots =negatively phototropic
  • Geotropism
    • Shoots = negatively geotropic
    • Roots = Positively geotropic
    • allows seeds to be orientated correctly.
  • Hydrotropism
    • Roots = positive hydrotropism
    • Within soil root systems will grow where most water.

• Taxis
  • motile organism responds to environmental changes
  • classified according to whether movement is away or towards stimulus.
    • positive or negative taxis
• Kineses
  • the more unpleasant the stimulus, the more rapidly it changes direction.
  • Kineses causes increase in random movement
  • designed to bring organism into favourable conditions.
  • Types of kinesis:
    • Orthokinesis
    • Klinokinesis

Nervous system divided into two parts:

• Central Nervous system
• Peripheral Nervous System

Peripheral Nervous system is divided into:

• Sensory neurones
• Motor neurones

The motor nervous system can be further subdived into:

• Voluntary nervous system
• Autonomic nervous system

Column of nervous tissue that runs along the back and lies inside the vertebral colomn for protection.

• emerges at intervals along the spinal cord as a pair of nerves.

1. Nerve from receptor

2. to sensory neurone

3. to intermediate neurone

4. to effector.

Receptor --> Peripheral nerve --> CNS --> Peripheral nerve --> Effector

• Reflex passes along a reflex arc
  • involves 3 neurones
    • e.g spinal reflex
  • main stages of spinal reflex:-

stimulus-->receptor-->sensory neurone --> intermediate neurone --> motor neurone --> effector -->response

• involuntary
  • means brain is left for more complex disicisions
• Protects body from harmful stimuli
• Fast
  • short neurone pathway
  • 1 or 2 synapses