Stimulus and response Topic E.1. Assessment Statements E.1.1 Define the terms stimulus, response and reflex in the context of animal behaviour. E.1.2.

Stimulus and response

Topic E.1

Assessment Statements

• 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.

Definitions

• Stimulus – a change in the environment (internal or external) that is detected by a receptor and elicits a response

• Reflex – a rapid, unconscious response

• 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

neurons• Sensory neurons carry the impulse toward the spinal cord • 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 the synapse

• Motor neuron carries the impulse to an effector (organ which performs the response)

Spinal cord

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 environment

• Theory of natural selection states that the organism best fitted for the environment is more likely to survive to reproduce

European blackcaps• Small warblers usually migrate between Spain and Germany• 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 blackcaps• 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

blackcaps

• 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 Spanish birds

• 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)

• http://www.wingsoverwetlands.org/• 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 migratory waterbirds.

• 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.

Sockeye salmon

• Species introduced into Lake Washington (deep and quiet) in Washington State

• Some of them migrated to the Cedar River (flows quickly)

• Over a span of 60 years, 13 generations of salmon have been produced

• 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 swimmers

• 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?• ???