Neurobiology & BehaviourHL & 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

Video

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

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.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

Video

Migration in European Blackcaps - experiment

1) Eggs collected from UK parent2) Eggs collected from Spanish parents3) Young reared without parents4) All birds in study migrated in the same direction that their

parents had gone5) Supports the hypothesis – blackcaps are genetically

programmed to fly in a certain direction6) Change in migration patterns may cause new species

Sockeye Salmon

Video clip

Sockeye Salmon

1) Sockeye salmon were introduced into Lake Washington

2) Some migrated to Lake Cedar

3) River flows quickly – lake is deep & quiet

4) Different aquatic environments

Sockeye Salmon – Lake Washington

1) 13 generations of salmon over 60 years2) River & lake salmon do NOT interbreed3) 2 different breeding methods

a) Lake salmon spawn on the beach, females lay eggs in the sandb) Males have heavy bodies & are inefficient at navigating fast

currents in the river

Sockeye Salmon – Cedar Lake

1) Thinner & narrower bodies2) Females bury their eggs

deep in the sandy river bottom – not washed away

3) Fish hatched in the river had little success trying to spawn on the beach

Comparison of the Sockeye Salmon

1) Variations in the 2 populations were selected for by the 2 different environments

2) Original population diverged into 2 different breeding populations.

3) The lake conditions favour one set of traits and the river conditions favour another set of traits

4) Sockeye salmon are now 2 genetically distinct populations