Neurobiology & Behaviour HL & SL Option E

Stimulus & Response E.1.1. Define the terms stimulus, response, and reflex in the context of animal behaviour.

Stimulus, response, and reflex Stimulus (pl. stimuli) A change in external or internal environment that is detected by a receptor and elicits a response Response Is a reaction to a stimulus Reflex Is a rapid, unconscious response e.g. - the response to pain

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Response of animals to pain stimuli E.1.2 Explain the role of receptors, sensory neurones, relay neurones, motor neurones, synapses and effectors in the response of animal to stimuli

Receptors receive the stimulus Receptors Pain Reflex Arc Receptors receive the stimulus Pain, heat, pressure, chemicals Receptors Generate a nerve impulse in the sensory neurons Sensory neurons carry the impulse toward the spinal cord The axons of the sensory neuron enters the spinal cord

Pain Reflex Arc The axon of the sensory neuron enters the spinal cord in the dorsal root It sends a chemical message across a synapse to a relay neuron (interneuron) Synapse – functional connections between neurons or between neurons and other types of cells. Relay neuron (interneuron) is located in the gray matter The motor neuron is located in the ventral root of the spinal cord

Pain Reflex Arc It carries the impulse to an effector An effector is an organ that performs the response Effectors are muscles or glands A reflex is an automatic response following a sensory stimulus. It is not under conscious control and is therefore involuntary (it does not involve the human brain.)

E.1.3 Draw and label a reflex arc for a pain withdrawal reflex, including the spinal cord and its spinal nerves, relay neuron, motor neuron, and effector

E.1.4 Explain how animal responses can be affected by natural selection, using two examples

http://msjensen. cehd. umn http://msjensen.cehd.umn.edu/1135/Links/Animations/Flash/0016-swf_reflex_arc.swf

Effects of Natural Selection Animal behaviour is much more than just single reflex arcs Behavioural changes may be so extreme that a new species is formed Review – Black Peppered Moths

Migration in European Blackcaps Small warblers Migrate between Germany & Spain Breed in Germany in spring Spend the winter in Spain

Migration in European Blackcaps 50 years ago – some blackcap warblers came to UK for winter UK blackcaps left to go back to Germany 10 days earlier than the Spanish blackcaps The earlier the birds arrived in Germany, the more choice of territory they had; the more eggs they laid UK warblers have an advantage

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Migration in European Blackcaps - experiment Eggs collected from UK parent Eggs collected from Spanish parents Young reared without parents All birds in study migrated in the same direction that their parents had gone Supports the hypothesis – blackcaps are genetically programmed to fly in a certain direction Change in migration patterns may cause new species

Sockeye Salmon Video clip

Sockeye salmon were introduced into Lake Washington Some migrated to Lake Cedar River flows quickly – lake is deep & quiet Different aquatic environments

Sockeye Salmon – Lake Washington 13 generations of salmon over 60 years River & lake salmon do NOT interbreed 2 different breeding methods Lake salmon spawn on the beach, females lay eggs in the sand Males have heavy bodies & are inefficient at navigating fast currents in the river

Sockeye Salmon – Cedar Lake Thinner & narrower bodies Females bury their eggs deep in the sandy river bottom – not washed away Fish hatched in the river had little success trying to spawn on the beach

Comparison of the Sockeye Salmon Variations in the 2 populations were selected for by the 2 different environments Original population diverged into 2 different breeding populations. The lake conditions favour one set of traits and the river conditions favour another set of traits Sockeye salmon are now 2 genetically distinct populations