Stimulus and response
Transcript Stimulus and response
Stimulus and response
• E.1.1 Define the terms stimulus, response and reflex in the
context of animal behaviour.
• E.1.2 Explain the role of receptors, sensory neurons, relay
neurons, motor neurons, synapses and effectors in the
response of animals to stimuli.
• E.1.3 Draw and label a diagram of a reflex arc for a pain
withdrawal reflex, including the spinal cord and its spinal
nerves, the receptor cell, sensory neuron, relay neuron, motor
neuron and effector.
• E.1.4 Explain how animal responses can be affected by
natural selection, using two examples.
• Stimulus – a change in the
environment (internal or external) that
is detected by a receptor and elicits a
• Reflex – a rapid, unconscious
• Response – a reaction to a stimulus
Pain reflex arc
• Animals respond to stimuli with a reflex
• Receptors receive the stimulus
• Receptors generate a nerve impulse in the sensory
• Sensory neurons carry the impulse toward the spinal
• Axon of sensory neuron enters the spinal cord in the
dorsal root and sends a chemical message across a
synapse to a relay neuron located in the gray matter
• Relay neuron synapses with a motor neuron within the
ventral root and transfers the impulse chemically across
• Motor neuron carries the impulse to an effector (organ
which performs the response)
Effects of natural selection
• Animal behavior is a series of responses to the
environment in which they live
• Genetically programmed behavior can have variations
• Variation will allow one group of organisms to survive
and reproduce better than another in a changing
• Theory of natural selection states that the organism best
fitted for the environment is more likely to survive to
• Small warblers usually migrate between Spain and
• Breed in Germany in the spring and summer and spend
the winter in Spain
• About 50 years ago, blackcap warblers were coming to
the UK instead of Spain for the winter
• Orinthologists noticed that the UK blackcaps left to go
back to Germany 10 days earlier than the Spanish
• Also noticed that the earlier the birds arrived in
Germany, the more choice of territory they had, and the
more eggs they laid
• UK blackcaps had a distinct advantage over the Spanish
• Did behavior have a genetic basis?
• Eggs were collected from parents who had been in the
UK the previous winter and other eggs collected from the
• Young reared and direction of migration recorded
• No parents were around to teach the young in what
direction to fly
• All of the birds in the study tended to migrate in the same
direction that their parents had gone
• Supports the hypothesis that blackcaps are genetically
programmed to fly in a certain direction
• What could be the environmental benefit of migrating to
the UK for some birds?
Wings Over Wetlands (WOW)
• The WOW is a partnership among international
conservation organizations and national
governments, which aims to improve and conserve
healthy and viable populations of African-Eurasian
• This will be achieved by assisting a wide range of
partners to conserve the key critical wetland areas that
these birds require to complete their annual migrations
across Africa and Eurasia, by improving international
cooperation and by building local professional capacity.
• Species introduced into Lake Washington (deep and
quiet) in Washington State
• Some of them migrated to the Cedar River (flows
• Over a span of 60 years, 13 generations of salmon have
• DNA evidence has shown that river salmon and lake
salmon have stopped interbreeding
• How did this happen?
• Lake and river salmon differ in their breeding methods
• Lake salmon spawn on the beaches; females lay their
eggs in the sand; males have heavy bodies, perfect for
hiding in the deep waters of the lake, not efficient
• River salmon bury their eggs deep in the sandy river
bottom so that they will not be washed away; male
salmon bodies are thinner and narrow for better
maneuvering in the current;
Global warming effects?
• Migrations of fish and other animas in the ocean?
• Emergence of new species?