Stimulus and Response

1
Stimulus and Response

• Jonas Theis Jensen

2
Reflexes

• One of the basic activities of the nervous system
  is the coordination of rapid responses to
  stimuli, including reflexes.

• What is stimulus?
• Stimulus is a change in the environment, either
  internal or external, that is detected by a
  receptor and elicit as a response.

3
Reflex arc

• Receptors - to detect a stimulus receptors can
  be sensory cells or nerve endings of sensory
  neurons
• Sensory neurons - to receieve messages across
  synapses, from receptors and carry them to the
  central nervous system (spinal cord or brain)
• Relay neurons - to recieve messages, across
  synapses, from sensory neurons, and pass them to
  the motor neurons that can case an appropriate
  response

4
Reflex arc    

• Motor neurons - to receive messages, across
  synapses, from relay neurons and carry them to an
  effector
• Efffectors - to carry out a response after
  receiving a message from a motor neuron
  effectors can be muscles, which respond by
  contracting, or glands, which respond by
  secreting.

5
Natural selection and responses

• Animal responses can be altered by natural
  selection if they are genetically programmed and
  affect the animal's chances of survival and
  reproduction. 
• Two examples related to global warming are given
  here, but there are many others from all around
  the world.

6
An example

• Migration in Sylvia atricapilla (blackcap)
• This bird breeds in the early summer across much
  of central and northern Europe. It then migrates
  to warmer areas before teh winter. 
• Until recently, populations in Germany migrated
  to Spain or other Mediterranean areas. Recent
  studies have shown a chagne in migration pattern,
  with 10 of the birds migrating to the UK.
• An experiment with eggs have shown that the
  direction of migration is genetically programmed
  and inherited.

7
Components of a reflex arc

•