1. The document discusses various types of innate and learned behaviors in animals, including reflex behaviors, kinesis, taxes, classical and operant conditioning, and imprinting. 2. Examples are provided of specific reflex behaviors like the pupil reflex and gag reflex, as well as examples of kinesis using sowbugs and taxes using male promethia moths. 3. Innate behaviors are described as instinctual, species-specific traits controlled by genes that help animals adapt to their natural environments and are selected through natural selection. Learned behaviors are influenced by environmental experiences.

1. OPTION E:
NEUROBIOLOGY AND BEHAVIOR
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2. Introduction to behavior
Behavior is any action of an organism
that is triggered by a stimulus.
An animal’s behavior is related to its
environment because the environment is
a constant source of stimuli.
There are two types of behavior: innate
and learned. Together they combine to
produce the total behavior of an animal.
Innate behavior – like feeding hungry Learned behaviors – like using sticks to
eaglets – is behavior which normally collect ants - reflect conditions
occurs in all members of a species despite experienced during development.
natural variation in environmental Different members of a species may
influences. develop different learned behavior
according to their unique experiences.
The types of behaviors
Innate Behaviors Learned Behaviors
Reflex behavior is the simplest type of animal Classical conditioning is a change in the behavior
behavior. A sudden stimulus induces an automatic of an animal as a result of the animal associating
involuntary and stereotyped response. (e.g. pain one external stimulus with another.
withdrawal reflex and pupil reflex).
Kinesis is the random movement of an animal in Operant conditioning is the development of a new
which the rate of movement is related to the intensity behavior as a result of the animal being rewarded
of a stimulus but not to its direction. (e.g. the positive (positive reinforcement) or punished (negative
relationship between humidity and the rate of reinforcement) after trial and error behavior.
movement in sowbugs).
Taxis is the movement of an animal in response to the Imprinting is phase-sensitive learning (i.e., it
direction of a stimulus. Movement towards a stimulus occurs during a temporary and sensitive period of
is positive and movement away from a stimulus is development) that is independent of the
negative. (e.g. positive chemotaxis guides male consequences of behavior.
promethia moths towards female pheremones).
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3. Reflex Behavior
• Reflex behavior is the simplest type of innate behavior. There are two types of reflex behavior: the
cranial reflex and the spinal reflex.
o Cranial reflexes involve the brain. Two examples of cranial reflexes are:
1) the pupil reflex and 2) the gag reflex.
o Spinal reflexes do not involve the brain. Two examples of spinal reflexes are:
1) the pain withdrawal reflex and 2) the crossed-extensor reflex.
The pupil reflex
• The pupil reflex is the reduction of pupil size in response to light. It is a normal response to an
increase in light intensity. Emergency room physicians often assess the pupil reflex: lack of the
pupil reflex indicates optic nerve damage or brain death.
o The sensory receptors responsible for the pupil
reflex are photoreceptor cells in the retina. When
the photoreceptor cells are stimulated by light, they
excite sensory neurons of the optic nerve, which
send the message to the brain.
o The brain relays the message to oculomotor
neurons, which synapse with ganglion neurons that
innervate the constrictor muscle (the effector) of
the iris of the eye.
Human eye
The gag reflex
• The gag reflex is a reflex contraction of the back of the throat. The gag reflex prevents objects
from entering the throat except as part of normal swallowing. This helps prevent choking.
Touching the soft palate at the back of the throat can evoke a strong gag reflex to induce vomiting.
o The sensory receptors responsible for the gag
reflex are pressure receptor cells in the soft palate
of the throat. When the pressure receptor cells are
stimulated beyond a threshold, they excite the
neurons of cranial nerve IX, which send the
message to the brain.
o The medulla oblongata relays the message to the
neurons of cranial nerve X, which synapse with
ganglion neurons that innervate muscle (the
effector) at the back of the throat. Pressure receptor in skin
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4. The pain withdrawal reflex and the crossed-extensor reflex
• The pain withdrawal reflex and the crossed-extensor reflex are involuntary actions in which the
body reacts to pain by trying to move itself away from the source of the pain.
o The response is so fast that if you step on a sharp object with your right foot, the pain
withdrawal reflex will cause you to lift your right leg before your brain perceives pain.
• In this example, the effector muscles in your right leg are flexors, which bend the
right leg when they contract.
o The crossed-extensor reflex occurs simultaneously to keep you from falling down.
• In this case, the effector muscles in the left leg are extensors, which strengthen the
left leg when they contract to prepare it for the shift of body weight).
Diagram of the pain withdrawal reflex
• Pain receptor cells in the skin are responsible for the pain withdrawal reflex and the crossed-
extensor reflex. The pain receptors can be stimulated by pressure, cuts, and heat.
o When pain receptor cells are stimulated, they excite sensory neurons, which send the message
to the grey matter of the spinal cord.
o In the spinal cord, the message is passed from the sensory neuron to a motor neuron via an
association neuron.
o The motor neurons carry the message to muscles (the effectors) causing them to contract.
o The series of neurons that link the receptors to the effectors is called a reflex arc.
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5. Example of taxis
• In order to pass on his genes, a male promethia moth must avoid being eaten by predators and he
must find a fertile female to copulate with.
o This isn’t an easy task because females spend most of their time hiding under branches,
and they are distributed very sparsely over large forest landscapes.
• Through natural selection, male promethia moths have adapted two innate behaviors - menotaxis
and chemotaxis - to help them locate mates.
o Menotaxis refers to an animal in motion that maintains a constant angle to a stimulus.
o Chemotaxis is movement in response to chemicals.
Female promethia moth
• Male promethia moths fly at an angle (menotaxis) perpendicular to the direction of the wind
(stimulus). Once a male detects a female’s scent trail (stimulus), he turns upwind and follows the
chemical gradient (chemotaxis) of the trail, which leads to the female.
• The menotaxis response increases the male’s chance of successful reproduction by:
reducing his searching time
lowering his energy costs
decreasing his risk of being eaten by predators
increasing his chance of finding a female.
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6. Example of kinesis
• Organisms that settle in more favorable areas enjoy a reproductive advantage over those settling in
less favorable areas.
o Therefore, natural selection favors animal behaviors that help individuals to move to, and
remain in, ideal habitat.
• Humidity is one factor that affects the reproductive
success and survival of the sowbug.
o Sowbugs are land animals with external gills that
must remain moist.
o Therefore, sowbugs are restricted to humid areas
and are commonly found under damp logs, rocks,
and fallen leaves.
Sowbugs
• To settle in a suitable habitat, a sowbug must perceive, and respond to, changes in humidity.
o When humidity is favorable, a sowbug will remain (more or less) in the same place.
o When humidity is unfavorable, a sowbug will emigrate to a new location.
• Sowbugs respond to humidity with a form of kinesis called hygrokinesis. In hygrokinesis,
sowbugs respond to changes in humidity by altering the rate of locomotion and/or the rate of
change in direction.
o When conditions are ideal, sowbugs move slowly and change directions frequently,
which has the effect of keeping them in the ideal microhabitat?
o When conditions become dry, sowbugs increase their speed of travel and change
direction less frequently, which has the effect of taking them far away.
o Once a sowbug reaches a moister microhabitat it will move slower and change directions
more frequently.
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7. The natural selection of innate behavior
o Innate behavior is under the steady influence of
natural selection because:
1. There is always some variation in the innate
behavior of individuals within a species.
2. Variation of innate behavior in a species is caused
by genetic differences between individuals.
3. Nature selects individuals that have genes that
produce favorable innate behaviors (i.e., ones that
improve an individual’s chance of reproduction). Innate courtship behavior in birds
The importance of innate behavior
o Each innate behavior of a species is normally
present in each member of that species; so we say
that innate behaviors are species specific.
o Innate behaviors determine an animal’s chance of
surviving, reproducing and passing on its genes. By
evolving innate behaviors, a species becomes better
adapted to its environment.
o Innate behaviors are controlled by genes,
independent of the environmental context. This
preprograms an individual for success in its natural
environment. But a sudden change in the Innate copulation behavior in ladybirds
environment can turn a favorable innate behavior
into an unfavorable one.
Summary of innate behavior
1. instinctual
2. species specific
3. controlled by genes
4. inherited from parents
5. adaptats species to their natural environment
6. developed in a species through natural selection
7. developed in an individual independent of
environmental context
8. stereotyped responses (i.e., the same response is given to
the same stimulus on different occasions) Innate grooming behavior in primates
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8. Migration behavior
o Migration is the movement of an animal
population from one ecosystem to another
according to the season of the year.
o Animals migrate in search of optimal
feeding sites and/or to avoid harsh seasonal
conditions such as arid summers or cold
winters.
o Migration is a common behavior amongst
birds, whales and grazing mammals but
rare amongst insects. The Monarch
butterfly, Danaus plexippus, is an
exception.
Monarch migration routes
o In the entire world, no butterflies migrate
like the Monarchs of North America,
which travel up to 5000km between
Canada and Mexico.
o However, unlike birds, individual
monarchs only make the migration once.
o In the spring, monarchs migrate north in
search of milkweed, their favorite food
plant.
o In the fall, low temperatures and
shortening day-length are two factors that
trigger the monarch’s southward migration.
Migrating Monarchs in Mexico
o Fat stored in the abdomen is an essential
energy source for the long journey.
o Navigation probably involves the sun’s
position and/or chemical signals - but
researchers don’t know for sure.
Monarchs in Canada on milkweed
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9. Grooming behavior
• Grooming is a behavior in which one animal uses its fingers or tongue to remove parasites from
the coat of another animal.
o Grooming occurs in rodents, birds, primates
and other animal groups.
o The removal of parasites reduces the
incidence of skin infections and disease.
o Grooming forms bonds and often initiates
sexual behavior.
o Grooming stimulates the secretion of
endorphins in the blood, which lowers stress,
increases happiness and improves the Ground squirrels grooming
immune system.
o In the bonobo, Pan paniscus, grooming is a
social activity that strengthens relationships
and is important for establishing hierarchies
in the troop.
o Individuals lower in the hierarchy tend to
groom members that are higher up, in order
to win their favor.
Female bonobos grooming
o The amount of grooming taking place
between bonobos is a good indicator of group
unity.
o When a troop is small, each member is able
to groom with all the other members; this
results in strong social bonds.
o When a troop becomes large it is impossible
for each member to groom with every other
member; so unity breaks down, conflicts
arise, and the group eventually splits in two. Small troop of bonobos
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10. Communication behavior
• Communication is the transfer of information from one animal to another. Communication may be
vocal (e.g. bird calls) or tactile (e.g. grooming).
o Vocal communication is widespread in the animal kingdom; birds, wolves, whales and primates
have some of the most elaborate vocal communication systems.
o Tactile communication is important in primates for establishing bonds and hierarchies. When
one individual grooms another it signals trust and reinforces feelings that bond them together.
o The golden langur, Trachypithecus geei, lives in small
groups in the jungles of Bhutan and India.
o When feeding, the group will stay in close contact
with one another, either remaining in the same tree or
in neighboring trees.
o Male golden langurs are on constant watch for
predators (tigers, leopards, and humans).
Male golden langur on watch
o When a male suspects that a predator is near, he
makes an alarm call to signal the threat to the other
members of his group.
o The alarm call is a short, low pitched vocalization that
sounds like "nauk-nauk..." This call is emitted by
males with mouths closed. Usually the adult male will
emit the alarm call until other group members get to
safety.
Alarm calls made with closed mouth
o If frightened the male will make a barking alarm call,
which sends the other group members leaping quickly
from tree to tree.
o The barking alarm call is a high pitched vocalization
that sounds like "aeke-ke-aeke-ke..." This call is
emitted in quick succession by adult males by opening
the mouth widely.
o If an infant is frightened it will make a loud screech. Barking alarm calls confirms a predator
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11. Courtship behavior
• Courtship is specialized behavior in animals for attracting mates. Elaborate courtship behaviors are
common in animals, especially amongst birds (e.g. peacocks, sage grouse).
o The North American sage grouse, Centrocercus
minimus, has one of the most elaborate courtship
displays of any bird.
o Each spring, up to 50 male sage grouse gather
together on a common breeding ground called a
lek.
o The males vocalize by repeatedly, filling and
emptying their air sacs, which makes a large Male sage grouse vocalizing
booming sound that attracts females.
o The competition amongst males is intense. Almost
all the mating is done by a small number of
dominant males - so it pays to be aggressive.
o The males display for several hours in the early
morning and evening; strutting around with their
air sacs inflated and their tail feathers spread.
o When males encounter one other, they lower their
tails, release air from their air sacs, and strike at Male sage grouses in combat
one another with their wings and beaks.
o The hens watch the displays and approach the male
they want to mate with. After mating, females leave
the lek to find a nesting site, and males go back to
attract another mate.
o The courtship behavior of the sage grouse has made
it vulnerable to extinction. It is now endangered
due to the loss of sage shrubs, which it requires for
breeding sites.
Female watches males display
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12. Mate Selection
• Mate selection is - choosing an individual of the opposite sex to copulate with. In many animal
species, males need to show off their strength to be selected by females.
o The Canadian bighorn sheep, Ovis canadensis, is a good example of a species in which
the males fight for the right to breed.
o Male bighorns have exceptionally hard and massive
horns. Within the species, however, there is variation
in the size and strength of horns. Individuals with the
best genes have larger and stronger horns and they are
more likely to attract females and pass on their genes.
In this way, natural selection has caused bighorn
sheep to continually evolve bigger horns.
o As the fall rutting season approaches, male bighorns are attracted
to fertile females by pheromones. Several rams may follow a
single ewe, with their noses elevated and their upper lip curled.
o But the female will only mate with one male – the one who
proves to be the strongest during head-butting contests. Fights
occur between rams with similar size horns.
o Two opponents rear back onto their hind legs, then drop to all
fours and charge each other at speeds greater than 30 km/hr. Their
foreheads crash together with a resounding crack.
o After impact, the two combatants pause for about one minute to
regain their senses and then they repeat the ritual many times over
– for up to 20 hours.
o Pieces of horn may chip off and blood may flow from their ears
and noses. Eventually one of the rams, exhausted or injured, will
lower his head in submission; and the winner strides away to
claim the ewe. Thus, horn size and strength determine status.
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13. Social behavior
• An animal species is social if its members form permanent and highly interactive groups of adults that
live together. A social behavior is one that aims to benefit the group and/or keep group members
connected to one another.
o Many insect species - including ants, bees and termites - have highly organized societies, with
individual organisms specialized for distinct roles.
o High sociality is common in many mammals as well – including humans, chimps, dolphins,
wolves, bats and naked mole rats.
Altruistic behavior in naked mole rats and vampire bats
• Altruistic behavior lowers the fitness of an individual (i.e., its chance of passing on genes) whilst
increasing the fitness of another individual. The naked mole rat of East Africa and vampire bats of
South America, provides good examples of innate altruistic behavior.
The naked mole rat has a complex social structure. Colonies are
comprised of 20 to 300 highly related animals living together in intricate
systems of burrows. In each colony, all mating is done by one queen and
1-3 males. There are two castes of non-reproductive mole rats: tunnelers
and soldiers. Naked mole rats display altruism in three ways: 1) mature
females help to raise young that are not their own; 2) tunnelers do all the
work without getting to mate; and 3) soldiers squeak loudly to alert the
colony of danger, which puts them at risk of being eaten by predators.
Under a stricter definition, altruism only includes acts that benefit
unrelated individuals. Altruism between unrelated animals is common
amongst vampire bats, which feed at night by sucking blood from
mammals. On most nights, an individual bat is successful in obtaining
enough food. On occasion, however, a bat might go one or two nights
without feeding success. In such a case, the hungry bat will return to its
cave to get nourishment from the regurgitated blood of another bat. The
act of ‘donating’ blood is altruistic.
Why be altruistic?
• How could natural selection favor altruism if it causes individuals to have reduced fitness? This riddle
is resolved by the selfish gene theory, which states that natural selection acts on the gene pool, not on
individuals. In a mole rat colony, every member is highly genetically related. On average, two mole
rats in a colony share 81% of the same genes. This means that almost all the genes of an individual get
passed on by the breeding of others. So as long as the other mole rats are breeding there is no need for
a virgin mole rat to worry about sex. In fact, a soldier raises the fitness of his genes by squeaking (and
dying for it) if his warning increases the total number of survivors (each of which carries his genes).
• In vampire bats, the act of donating blood is not helpful to the donor in the short term but in the long-
term it is beneficial because the donor may need to be a receiver on another occasion. This is called
reciprocal altruism: one individual acts altruistically knowing that it will be reciprocated later on.
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14. The social behavior of honey bees
• Honey bee colonies are comprised of three social castes: a single queen, thousands of workers and
numerous drones.
o Drones are adult males that are produced from unfertilized eggs. The workers and the queen
are female adults that come from fertilized eggs.
o Worker bees are developed by feeding bee bread (a mixture of honey and pollen) to female
larvae. Queen bees are developed by feeding royal jelly (a nutrient-rich secretion) to female
larvae throughout their development.
Queen bee (in center) Worker bee collecting pollen Drone on the honey comb
There is only one queen in Workers search for pollen A drone’s only function is
a hive and her only job is and nectar, produce honey to mate with virgin
to lay eggs. The queen and wax, feed the young queens.
controls the social and protect the hive against
organization of her colony enemies.
by secreting a pheromone
that maintains tranquility
within the hive and inhibits
ovarian development
among her workers.
• Mature colonies may grow to include as many as 60,000 workers, at
which point the hive will "reproduce" by swarming. This is a
process of colony division in which an established queen emigrates
with a large group of workers to establish a new nest site, while a
young queen and the remaining workers stay behind to occupy the
old nest site. During winter, the workers eat honey to produce
metabolic heat and they crowd around the queen to keep her warm.
Swarming bees
• Honey bees use many signals to communicate with nest-mates.
Workers secrete one kind of pheromone to mark a source of nectar
and another kind to signal alarm when the colony is threatened.
Scout bees that find a good nectar supply return to the hive to
recruit more foragers, which they achieve by performing the waggle
dance: the dancer communicates the distance and direction of the
food supply by the size and angle of her waggles relative to the sun.
Waggle dance of a worker bee
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15. How learning improves the chances of survival
• Learning is the process of modifying behavior through experience. Learning helps animals to achieve a
goal such as obtaining food, avoiding predators, and avoiding toxic plants. Habituation, conditioning
and imprinting are types of learning that increase an animal’s chance of surviving.
• Habituation is a type of learning in which a behavior is
reduced when no reward or punishment follows.
• Deer become habituated in Canada’s National Parks, for
example. Deer are initially frightened by the sound of
highway traffic and therefore run from vehicles.
Individuals that habituate, however, learn to feed near Habituated deer on highway
highways. Therefore, habituated deer gain greater access
to food and produce more offspring than un-habituated
deer.
• Outside the park, habituated deer are likely to be shot by
poachers (so a behavior can be favorable in one
environment and unfavorable in another).
Un-habituated deer in woods
• Conditioning is a type of learning in which an animal
associates two separate stimuli and then modifies its
behavior. Grizzly bears, for example, learn where to
catch fish by associating waterfalls with jumping salmon.
• Another example of conditioning in nature involves birds
that prey on butterflies: birds that can distinguish between
edible and toxic butterflies have a survival advantage. For Monarch butterfly
example, after eating a toxic Monarch butterfly, a
flycatcher feels ill and experiences an unpleasant taste.
The flycatcher learns to avoid monarchs by remembering
the butterfly’s appearance (a visual stimulus) and
associating it with the butterfly’s toxicity (a chemical
stimulus).
• Many poisonous animals have evolved bright colors to
communicate their danger to predators.
Yellow back poison dart frog
• Imprinting is a form of learning that keeps ducklings and goslings near their mother, which helps them
to avoid predators and learn how to feed.
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16. Ivan Pavlov’s experiments on learning: classical conditioning
o Ivan Pavlov was the first researcher to use quantitative
data to show how classical conditioning occurs.
o He observed that dogs naturally salivate to food; and he
called this correlation between food and salivation the
unconditioned reflex.
o The food was called the unconditioned stimulus, and the
salivation was called the unconditioned response.
Ivan Pavlov
• In one of his experiments, Pavlov fed his dogs several times over a period of several days; and on each
occasion, he rang a bell a few seconds prior to presenting the food.
o Before the experiment, the ringing bell was a neutral
stimulus since it had no effect on salivation.
o During the experiment, the ringing bell stopped being a
neutral stimulus and became a conditioned stimulus
because the dogs learned to associate the bell with food.
o As a result, Pavlov could make his dogs salivate just by
ringing a bell; and he called this correlation between the
ringing bell and salivation the conditional reflex.
One of Pavlov’s dogs
• The origins of the two reflexes are different: the unconditioned reflex has its origins in the evolution of
the species, whereas the conditioned reflex has its origins in the experience of the individual animal.
o Pavlov repeated this experiment with other stimuli such as a metronome and vanilla and achieved
the same results.
o It is interesting to note that when Pavlov presented a neutral stimulus after the unconditioned
stimulus, no conditioning took place.
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17. BF Skinner’s experiments on learning: operant conditioning
o BF Skinner is famous for a box that he designed to
perform quantitative research on operant conditioning.
o Operant conditioning is distinguished from classical
conditioning in that it deals with voluntary behavior
explained by its consequences.
o Skinner used reinforcement (positive and negative) to
develop operant conditioning. Reinforcement is a
consequence that causes a behavior to occur with greater
frequency; and punishment is a consequence that causes a
behavior to occur with less frequency.
BF Skinner
o Skinners box was set up with a
small lever that if pressed,
released a pellet of food.
Skinner placed a hungry
pigeon or a rat inside his box to
see how they learned to press
the lever – a behavior he called
the operant response. At first
the animals would move at
random through the box –
occasionally triggering the
lever by accident. By trial and
error, the animals eventually
learned to associate the reward
of food with the pressing of the
lever so the frequency of the
operant response increased
with experience. Skinner also
found that negative
experiences - like shocks or
loud noise - would make the
operant response occur less
frequently.
Rat pressing lever in Skinner’s box
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18. Konrad Lorenz’s experiments on learning: imprinting
o Lorenz was the scientist who coined the term imprinting. A
well known form of imprinting is filial imprinting, in which a
young animal learns To recognize its parent.
o Imprinting is obvious in ducks and geese, which imprint on
their parents and then follow them around.
o The process occurs in humans, beginning in the womb, when
the unborn baby starts to recognize its parents' voices.
Konrad Lorenz
o In his famous experiment, Lorenz divided the eggs of a
graylag goose into two groups: 1) eggs hatched by their
mother and 2) eggs hatched in an incubator.
o After hatching, the chicks that hatched with their mother began
to follow her around. The incubated chicks however, began
instead to follow Lorenz around.
o Then Lorenz placed all the goslings in the same box (to
separate them from their mother and him). When he released
the chicks from the box, they reliably followed their mother (if
they hatched with her) or Lorenz (if they hatched with him). Goslings following Lorenz
o Based on his observations, Lorenz concluded that there is a
critical period in a chick’s development when it learns to
identify its mother. Further research has shown that:
Chicks only imprint on a relevant stimulus (i.e., a moving
object) called the sign stimulus.
Chicks have an innate system (innate releasing mechanism) to
filter out irrelevant stimuli (i.e., non-moving objects).
Different species imprint by different stimuli; so innate Goslings show their
releasing mechanisms and sign stimuli are species specific. attachment to Lorenz
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19. The importance of quantitative data in studies of behavior
• Biologists use the scientific method to learn about animal behavior. First they make a hypothesis, then they
collect, analyze and interpret data, and lastly they make a conclusion.
• Some hypotheses can be answered with qualitative observations but most require quantitative data.
o Quantitative data are collected by counting or measuring and they are expressed as numbers.
o Our understanding of taxis, kinesis, classical conditioning, operant conditioning and imprinting comes
from researchers who collected and interpreted quantitative data.
• Advantages of quantitative data include:
o Numbers obtained from many counts (or precise measurements) can reveal subtle behaviors that are not
observable qualitatively.
o Numbers don’t lie: they represent the way things really are, as opposed to the way we want them to be.
o Numbers can be analyzed using statistics (e.g. Chi square test) to establish confidence levels. A
confidence level allows a scientist to make a conclusion with a known probability of being correct. In
biology – by convention - 95% confidence is the usual requirement for making conclusions.
o Numbers can be displayed in graphs to aid interpretation and to make predictions. The graph below
makes it easy to understand the relationship between humidity and the movements of sowbugs. And it
makes it possible to predict their behavior at a particular level of humidity.
Average speed and mean number of direction
changes made by sowbugs at different humidities
120
Speed (cm/min); turns (#/min)
100
80
turns
60
speed
40
20
0
20 30 40 50 60 70 80 90 100
Percent humidity
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20. Perception of stimuli
• A behavior is an animal’s response to a change in the environment. In order to have behavior an animal
must be able to perceive changes in its environment, which it accomplishes with sensory receptors.
o There are several types of sensory receptors including: mechanoreceptors, chemoreceptors,
photoreceptors, and thermoreceptors.
Each type of sensory receptor functions as an energy transducer, which means the energy of a
stimulus is converted into the electrical energy of a nerve impulse.
Type of Function Example
sensory receptor
Mechanoreceptor Perceives changes in pressure Hair cells send nerve impulses to the brain when they detect
caused by mechanical energy vibrations in the cochlea of the inner ear.
(sound, touch, movement)
Chemoreceptor Perceives the presence of chemical Neuro-epithelial cells (taste buds) send nerve impulses to the
substances brain when they detect chemicals on the tongue.
Photoreceptor Perceives levels of light intensity Rod and cone cells in the retina of the eye send messages to
the brain when they absorb light.
Thermoreceptor Perceives temperature Heat sensitive cells on the skin’s surface increase their firing
rate when warm; cold sensitive cells increase their firing rate
when cold.
Bundle of hair cells in cochlea Taste buds on the upper surface of the tongue
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21. The human brain
• An animal’s brain makes sense of inputs arriving from sensory receptors and it carries out the appropriate
responses.
o The human brain is quite possibly the most fascinating object in the universe! What makes the human
brain unique is its amazing ability to: understand concepts; memorize, be creative; solve problems;
communicate with complex language; feel empathy; and love.
o The human brain is comprised of many parts: neuroscientists are only beginning to identify them and to
understand their functions.
Section of human brain
Structure and function of human brain parts
Brain structure Functions
Cerebellum Controls muscle coordination, posture and balance
Medulla oblongata Controls heartbeat, coughing and the gag reflex
Cerebrum Memory, emotion, language, reasoning and sensory processing
Corpus collosum Connects the two cerebral hemispheres; important for language
Hypothalamus Regulates water balance and body temperature
Pituitary gland Controls the activity of other glands in the body
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22. The human eye The human retina
Comparison of rod and cone cells
Rod cells Cone cells
Photoreceptors in the retina Photoreceptors in the retina
More sensitive to light Less sensitive to light
Bleached in bright light Function well in bright light
Absorb all wavelengths of visible light Absorb red/blue/green light only
Monochrome vision Color vision
Give duller vision than cone cells Give sharper vision than rod cells
More widely dispersed in retina Less widely dispersed in retina
Provide wider field of vision Provide narrower field of vision
Groups of rod cells send signals to one Individual cone cells send signals to
neuron of optic nerve one neuron of optic nerve
Processing of visual stimuli
The retina has two halves: one half is on the inside
(i.e., closer to the nose) and the other half is on the
outside (i.e., further from the nose). When rod and
cone cells are stimulated by light, they send impulses
to bipolar cells.The bipolar cells combine the impulses
and forward them to ganglion cells, which are the
sensory neurons of the optic nerve. The left and right
optic nerves intersect near the center of the brain - at a
structure called the optic chiasma -and half the
sensory neurons cross over to the opposite optic nerve.
The neurons that cross over are the ones carrying
impulses from the inside half of the retina (i.e., closer
to the nose). Thus, as each optic nerve continues from
the optic chiasma it carries impulses from both eyes.
The optic nerves end at the thalamus, which processes
the information and forwards it to the visual cortex at
the back of the brain, which forms the final image.
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23. Divisions of the Nervous System
The nervous system of
vertebrates is divided into the
central nervous system (CNS)
and the peripheral nervous
system (PNS). The CNS
consists of the brain and the
spinal cord. The PNS includes
all the nerves outside the central
nervous system. The peripheral
nervous system is divided into
the voluntary nervous system
(VNS) - which is under
conscious control - and the
autonomic nervous system
(ANS) - which is mostly under
unconscious control. The VNS
is comprised of sensory neurons
and motor neurons. The ANS
consists of sympathetic and
parasympathetic motor neurons.
The peripheral nervous system
• The VNS enables an animal to make conscious responses to the environment. Sensory receptors of the
VNS perceive the environment and send messages – via sensory neurons - to the brain. The brain
makes sense of the incoming messages and sends instructions - via motor neurons - to the appropriate
effectors (muscles and glands).
• The ANS functions to maintain the homeostasis and normal functioning of internal organs. It controls
blood vessels, smooth muscles, and organs such as the liver, the heart, the stomach, the intestines, and
the kidneys.
o Although the ANS regulates many body functions that are beyond conscious control (involuntary),
it also controls some that are not completely outside our awareness.
Through learning – operant conditioning - infants achieve conscious control over the
sphincter muscles of the anus and bladder.
Some people can even gain a degree of control over their heart rate. Through yoga, Zen
meditation and other ‘Eastern’ practices, for example, people have learned to slow down their
heart rates and even stop the heart for short periods of time.
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24. Antagonism between the sympathetic and parasympathetic systems
• The roles of the sympathetic nervous system and the parasympathetic nervous system are largely
antagonistic.
o The parasympathetic nervous system is sometimes called the "rest and digest system”. It functions
during non-threatening situations to slow and relax organs and body systems.
o The sympathetic nervous system is sometimes called the "fight or flight system”. It becomes
active during threatening situations and/or to prepare the body for periods of high activity (e.g.
chasing prey, being chased by predators, playing sports).
Examples of antagonism between the sympathetic and parasympathetic systems
Effects of sympathetic motor neurons Effects of parasympathetic motor neurons
Constricts pupil to reduce the influx of light, Circular muscles relax to increase the diameter of
thereby allowing the retina to rest. the pupil. This maximizes the influx of light
thereby increasing the sharpness of vision.
Stimulates saliva production and dilates blood Inhibits saliva production and constricts blood
vessels leading to digestive system so that the vessels leading to digestive system (dilates blood
body can focus on eating and digesting food. vessels leading to heart and lungs so that the body
can focus energy on locomotion).
Reduces heartbeat (both strength and frequency), Increases the frequency and strength of heartbeats,
which conserves energy. which sends more blood to muscles thus
improving muscle performance.
Location and action of peripheral nerves
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25. Synapses and neurotransmitters
• A nervous impulse is transmitted from one neuron to another across a narrow, fluid-filled space called
a synapse. The signal travels across the synapse in the form of special chemicals called
neurotransmitters, of which there are many kinds.
o Two neurotransmitters that control brain activity are glutamate (which increases brain activity)
and GABA (which decreases brain activity).
Glutamate and GABA are strongly influenced by a class of neurotransmitters called
monoamines, which include dopamine, serotonin, acetylcholine and noradrenalin.
o Synapses are classified according to the type of neurotransmitter they use: each synapse uses only
one kind of neurotransmitter.
Synapses that use acetylcholine are known as cholinergic synapses.
Synapses that use noradrenalin are called adrenergic synapses.
Excitatory synapses versus inhibitory synapses
• Different neurotransmitters have different effects on the post-synaptic neuron.
o Excitatory neurotransmitters (e.g. glutamate) stimulate an action potential in the post-synaptic
neuron. Inhibitory neurotransmitters (e.g. GABA) prevent the initiation of an impulse in the post-
synaptic neuron.
When excitatory neurotransmitters bind to receptors on the post-synaptic membrane, gated-
sodium-channels open, causing sodium ions to flow into the post-synaptic neuron. This
depolarizes the post-synaptic neuron, triggering an action potential.
When inhibitory neurotransmitters bind to receptors on the post-synaptic membrane, gated-
chlorine-channels open, causing chlorine ions to flow into the post-synaptic neuron. This
hyperpolarizes the post-synaptic neuron, preventing it from forming an action potential.
o Some post-synaptic neurons synapse with large numbers of both excitatory and inhibitory pre-
synaptic neurons. In this situation, a post-synaptic neuron will form an action potential if it is
receiving more excitatory neurotransmitters (from excitatory pre-synaptic neurons) than inhibitory
neurotransmitters (from inhibitory pre-synaptic neurons).
Parkinson’s disease
• Dopamine has numerous functions in different parts of the brain. It also functions as an inhibitory
neurotransmitter at neuromuscular junctions. In a normal person, dopamine controls muscle
contractions by counteracting the excitatory effects of acetylcholine.
o Parkinson's disease is a degenerative disorder that results in a reduction of dopamine at synapses
that control muscle contraction. The disease results from the death of neurons in a part of the brain
called the substantia nigra.
o Symptoms of Parkinson’s disease include: shaky movement and speech. It is often characterized
by muscle rigidity, tremor, and a slowing of physical movement.
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26. Perception of pain
• Pain is an unpleasant sensation that results when pain receptors are stimulated. Pain improves the
chances of survival because it informs an individual when its tissues are being damaged, which enables
the individual to respond appropriately. And animals that associate harmful experiences with pain can
learn to not repeat them - operant conditioning.
• Pain occurs when pain receptors send nervous impulses to the central nervous system. There are three
types of pain receptors: cutaneous (located in the skin); somatic (located in tendons, ligaments and
bone); and visceral (located in visceral organs). All types of pain receptors are mechanoreceptors.
• When pain receptors are stimulated they trigger action potentials in sensory neurons that carry the
message to the spinal cord.
o At the spinal cord, some of the sensory neurons synapse with association neurons to initiate the
pain withdrawal reflex. Other sensory neurons synapse with neurons of the ascending tract, which
carry the message to the brain.
o When pain signals reach the thalamus of the brain, they may be passed on to sensory regions of
the cerebral cortex, causing conscious pain. There are two kinds of neurons in the ascending tract:
fast (which cause immediate sharp pain) and slow (which produce a delayed burning pain).
Enkephalins and endorphins
• Enkephalins and endorphins are proteins produced by the body in response to pain and strenuous
activity.
• When the brain detects that the pain of an injury is too intense, it sends impulses down the descending
tract of the spinal cord, which trigger the release of enkaphalins.
o The enkaphilins flood into synapses that are transmitting pain signals to the brain.
o The enkephalins attach to calcium gated-channels in the pre-synaptic membrane, which prevents
calcium ions from entering the pre-synaptic neuron.
o Without an inflow of calcium ions, the pre-synaptic neuron can not release its neurotransmitters
into the synapse, which means that the pain signal is not transmitted to the brain (i.e. conscious
pain is reduced).
• Endorphins are produced by the pituitary gland and the hypothalamus to produce a sense of well being.
o Endorphins are released in response to a variety of stimuli including: eating chocolate, laughter,
sunshine, meditation, massage, singing, orgasm.
o Injuries and strenuous exercise activate significant endorphin production. As a result, it is not
uncommon for an athlete to ‘play through’ an injury, and then realize after the game, when
endorphin levels have dropped, that the injury is severe. This phenomenon helps animals to
overcome injuries and escape their predators.
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27. Psychoactive drugs
• A psychoactive drug is a chemical that alters brain function, resulting in temporary changes in
perception, mood, consciousness, or behavior.
o Psychoactive drugs are taken by some people: to treat neurological illnesses; for ‘recreational drug
use’; or for spiritual purposes.
o Psychoactive substances can be habit-forming, causing chemical dependency, often leading to
substance abuse.
o Psychoactive drugs are
grouped into three types
- stimulants, depressants
and hallucinogens -
according to their effect
on the nervous system.
o Some drugs behave in
multiple ways as shown
in the Venn diagram.
o Stimulants are excitatory psychoactive drugs that increase the activity of the sympathetic nervous
system and produces a sense of euphoria or the feeling of being more awake. Stimulants can be
used as recreational drugs, performance-enhancing drugs, or therapeutic drugs to increase
alertness. Examples of common stimulants include caffeine, nicotine, ecstasy and cocaine.
o Depressants are inhibitory psychoactive drugs that diminish the activity of the sympathetic
nervous system and produce a sense of calm, dullness or drowsiness. Depressants can be used as
recreational drugs or therapeutic drugs to relieve symptoms of anxiety or insomnia. Examples of
common depressants include valium, cannabis, and alcohol.
o Hallucinogens are distortatory psychoactive drugs that affect the subjective qualities of perception,
thought or emotion, resulting in altered interpretations of sensory input, alternate states of
consciousness, or hallucinations. Hallucinogens are used by thrill seekers in some cultures or for
spiritual experience in others. Examples of hallucinogens include peyote, mushrooms and LSD.
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28. Effects of psychoactive drugs on synapses
o Psychoactive drugs affect mood,
perception, personality, etc. by
either increasing or decreasing
synaptic transmission in the brain.
o The effect of a psychoactive drug
depends on which neurotransmitter
it affects and in which brain region
(or regions) it acts.
o Psychoactive drugs differ in their
effects depending on whether they
affect excitatory neurotransmitters
or inhibitory neurotransmitters; and
on whether they increase or decrease
synaptic transmission.
A psychoactive drug may affect synaptic transmission in one of five ways:
1. Mimicking a neurotransmitter in structure and function
Valium is an example of a neurotransmitter mimic. Its structure closely resembles that of GABA.
GABA slows brain activity and functions to promote sleep. Valium interferes with synaptic
transmission by binding to GABA receptors on the post-synaptic membrane and stimulating an action
potential in the post-synaptic neuron. Thus valium has a calming effect.
2. Increasing or decreasing the release of a neurotransmitter into a synapse
Alcohol is an example of a drug that increases the presence of a neurotransmitter (GABA) in synapses.
3. Increasing the effectiveness of receptors on the post-synaptic membrane
Alcohol – in addition to increasing GABA - increases the effectiveness of GABA receptors. Together,
these two effects make alcohol a strong depressant. When used over a long time, ethanol changes the
number and type of GABA receptors, which is likely the cause of the violent withdrawal symptoms.
4. Preventing a neurotransmitter from binding to its receptors on the post-synaptic membrane
PCP is an example of a drug that binds to receptors on the postsynaptic membrane. However, it is not
capable of stimulating an action potential in the post-synaptic neuron. As a result it blocks synaptic
transmission.
5. Preventing the re-uptake of a neurotransmitter from the synapse
Prozac improves a person’s sense of well being by preventing the re-uptake of serotonin. Cocaine and
ecstasy are also drugs that work by preventing the normal re-uptake of a neurotransmitter called
dopamine. Dopamine stimulates the pleasure center of the brain and thus functions to give us a sense
of well-being and happiness. When cocaine or ecstasy is in the blood, dopamine accumulates in
synapses, resulting in repeated action potentials in the post-synaptic neuron. This over-stimulates the
pleasure center and the user feels euphoric.
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29. The behavioral effects of some excitatory psychoactive drugs
Nicotine is a natural drug found in many plant species – notably
tobacco. In small doses, nicotine has a stimulating effect that
increases activity, alertness and memory. It also increases heart rate
and blood pressure and reduces the appetite. Repeat users report a
pleasant relaxing effect. This is because shortly after sucking on a
cigarette, nicotine enters the bloodstream and causes a smoker’s body
to release dopamine and adrenaline. Nicotine causes rapid surges, then
rapid depletions, of these chemicals, leaving the smoker happy for a
short while but soon yearning for another cigarette. Smokers end up
with reduced dopamine levels compared to non-smokers so they tend
to feel worse (not better) because they smoke. Repeat users of nicotine very often develop a physical
dependency to the chemical. Physical withdrawal symptoms include irritability, headaches, anxiety, and
sleep disruption. Nicotine is probably the world’s most addictive, abused and dangerous drug. It kills about
half of all the people that use it – plus millions of innocent people too!
Cocaine is made from the leaves of the coca shrub, which grows in
the mountain regions of South American. In Europe and North
America, the most common form of cocaine is a white crystalline
powder. Most users sniff it into the nostrils where it is absorbed
through the thin nasal lining. Crack cocaine is a smokeable form of
cocaine. It is usually smoked in a pipe, glass tube, or foil. Cocaine and
crack are powerful, but short-acting stimulant drugs (the high lasts no
more than 40 minutes). Crack in particular has strong but short-lived
effects. Both drugs tend to make users feel more alert, energetic and
euphoric. Many users say that they feel very confident and physically strong. Common effects include
talkativeness, dry mouth, sweating, loss of appetite, and increased heart and pulse rates. Cocaine –
especially crack – is highly addictive. Repeated use causes depression (from reduced dopamine production)
and excessive doses can cause death from respiratory failure or heart failure.
Amphetamines are synthetic (man-made) stimulants. One example is
methylenedioxymethamphetamine (better known as ecstasy). Ecstasy
interferes with synaptic transmission by stimulating the secretion, and
inhibiting the re-uptake, of serotonin, dopamine and noradrenalin in
the brain. The result is an induced state of euphoria. The user feels
increased openness, empathy, energy, and well-being. Tactile
sensations are enhanced for some users, making general physical
contact with others more pleasurable. The high lasts for 2-4 hours.
Acute dehydration is a risk among users who are highly physically active and forget to drink water, as the
drug may mask one's normal sense of exhaustion and thirst. Ecstasy use is a likely cause of severe long-
term depression as a result of a reduction in the natural production of serotonin.
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30. The behavioral effects of some inhibitory psychoactive drugs
• Cannabis is a genus of flowering plant from northern India. It is smoked in
the form of dried flowers (marijuana) or resin (hashish). The high lasts 2-4
hours and the effects vary amongst individuals: it makes some people
talkative and silly with laughter, while others become quiet and
contemplative. Some users claim to have bursts of creative inspiration
and/or increased tactile sensitivity. Cannabis is known to reduce
concentration and muscle control in the short-term and in repeat users it
can cause lung disease and depression. Since the 1960’s, the average
potency of marijuana has increased 10-fold due to improved growing
methods and artificial selection. Most of marijuana’s psychoactive
properties come from a drug called THC (there are 16 other psychoactive
drugs in Cannabis). Cannabis also contains at least two medicinal drugs
(cannabidiol and cannabinol) which are thought to be effective in the
treatment of some diseases, including certain cancers. Therefore it has
been legalized for medicinal use in many countries. Cannabis plant
• Alcohol is a potent psychoactive drug that is made by alcohol fermentation
of yeast cells. Cell membranes are highly permeable to alcohol, so it
diffuses into nearly every tissue of the body. In the brain, alcohol triggers
the release of dopamine and endorphins, which can cause euphoria.
Alcohol has a biphasic effect on the body, which means that its effects
change over time. Initially, alcohol produces feelings of relaxation and
cheerfulness, but further consumption can lead to feelings of anger or
sorrow, and to blurred vision and coordination problems. Intoxication
frequently leads to a lowering of one's inhibitions, and intoxicated people
will do things they would not do while sober, often ignoring social, moral,
safety and legal considerations. After excessive drinking, unconsciousness
and death can occur by choking on vomit or blood poisoning (a 0.55% Alcohol
concentration in the blood will kill half the population).
• Benzodiazepines (e.g. Valium and Temazepam) are a class of drugs with
sedative (‘sleeping-pill’) effects. They act on the GABA receptor, the
activation of which dampens brain activity. They also have muscle
relaxant properties and they tend to reduce anxiety. They are sometimes
used for short-term relief of severe, disabling anxiety or insomnia. Side-
effects include drowsiness, confusion, slurred speech and impaired
judgment. Long-term use can be problematic due to the development of
tolerance and dependency.
Benzodiazepines
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31. Did you know that caffeine is a drug?
Worldwide, the number-one drink is water. But next in line is
tea, followed by coffee, and then soft drinks (sodas). All of
these drinks, besides water, contain caffeine. Caffeine is so
popular because it has powerful effects on us and nearly every
other animal species. Rats, for instance, learn faster when
given caffeine. Caffeine also has major effects on humans –
the best known of which is making us feel awake. Competitive
bicycle racers take caffeine about an hour before their race,
improving their performance by up to 20%. Some cyclists take
their caffeine in the form of suppositories for a time-released
Effect. Caffeine revs up more than just our minds and bodies though; sperm swim faster and wiggle more
vigorously under caffeine’s spell, making them more likely to fertilize an egg. How does caffeine work its
magic? Well, after having a cup of coffee or a can of Coke, caffeine enters your bloodstream and makes a
beeline for your brain. At the brain, caffeine bubbles around between the brain cells. Here, because of a
chance similarity in shape, the caffeine slips into receptors intended for adenosine. Adenosine is a waste
product that brain cells produce when they are active. Adenosine builds up during the daytime and attaches
to your brain cells, causing them to slow down – this makes you feel sleepy. However, if caffeine is
present in your brain then it blocks adenosine from attaching to brain cells – this prevents the feeling of
sleepiness. Amazingly, research shows that moderate consumption of caffeine is generally safe for most
people – at least for now it does – although caffeine makes a lot of people feel jittery. In addition, heavy
caffeine consumers sleep less, which can have negative effects on memory, learning and relationships.
Did you know that chocolate is a drug?
Have you ever noticed the way some people crave the stuff?
Some people go so far as to say they need a chocolate fix, and
we’ve all heard about chocoholics! Why do you suppose this is
so? The answer is that consumption of chocolate, like other
sweet foods, triggers the release of endorphins; the bodies
endogenous opiates. Endorphin-release reduces the chocolate-
eater's sensitivity to pain and probably adds to a warm inner
glow induced in susceptible chocoholics. Oh! And there’s one
more thing - chocolate is chocolate-blocked with psychoactive
drugs! It contains:
Modest quantities of caffeine, which reduces the sense of fatigue.
Small quantities of 3 cannabinoids (anandamide, N-oleolethanolamine and N-linoleoylethanolamine),
which may promote a prolonged feeling of well-being.
A drug called theobromine, which in pure form may be superior to opiates as a cough medicine due to
its action on the vagus nerve.
Tryptophan, an essential amino acid important in regulating production of the mood-modulating
neurotransmitter serotonin. Enhanced serotonin function typically diminishes anxiety.
Tetrahydro-beta-carbolines, which are found in beer, wine and liquor and have been linked to
alcoholism.
Phenylethylamine (PEA), which is a naturally occurring drug in the brain that releases dopamine in the
pleasure-centres. It is known as the "love-chemical" because the brain produces large amounts of PEA
as couples fall in love. This explains the attraction, excitement and euphoria that new couples feel near
the beginning of their relationship. Sadly PEA diminishes as a relationship goes on and is nearly absent
within two years.
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32. Syllabus for Option E: Neurobiology and Behavior (SL)
1. State that the behavior of animals is related to the environmental context.
2. State that innate behavior develops independently of the environmental context, whereas learned
behavior reflects conditions experienced by individuals during development.
3. Explain the role of natural selection in the development of behavior patterns.
4. Explain, using species of birds or mammals (other than humans), one example of each of the
following types of behavior: migration, grooming, communication, courtship and mate selection.
5. Explain the need for quantitative data in studies of behavior.
6. State that sensory receptors act as energy transducers.
7. State that human sensory receptors are classified as mechanoreceptors chemoreceptors,
thermoreceptors or photoreceptors.
8. Describe what is meant by each of the terms in E.2.2 with reference to one named example of each
type of receptor.
9. Draw the structure of the human eye
10. Annotate diagrams of the human retina.
11. Distinguish between rod and cone cells.
12. Outline how visual stimuli are processed in the retina and the visual cortex.
13. Define innate behavior.
14. Outline the pain withdrawal reflex and one other human spinal reflex.
15. Draw the structure of the spinal cord and its spinal nerves to show the components of a reflex arc.
16. Outline the pupil reflex and one other cranial reflex.
17. Draw the gross structure of the brain including the medulla oblongata, cerebellum, hypothalamus,
pituitary gland and cerebral hemispheres.
18. State one function for each of the parts of the brain (listed above).
19. Discuss the use of the pupil reflex in testing for brain death.
20. Some discussion about what is meant by death could be included here.
21. Define taxis and kinesis.
22. Explain, using one example of each behavior, how taxis and kinesis improve animals' chances of
survival.
23. Discuss the importance of innate behavior to the survival of animals.
24. Define classical (Pavlovean) conditioning.
25. Outline Pavlov's experiments on conditioning of dogs (the terms unconditioned stimulus,
conditioned stimulus, unconditioned response and conditioned response should be included).
26. Define operant conditioning.
27. Outline Skinner's experiments into operant conditioning. The terms operant response and
reinforcement should be included.
28. Define imprinting.
29. Outline Lorenz's experiments on imprinting in geese. The terms sign stimulus, species specific
behavior and innate releasing mechanism should be included.
30. Discuss how the process of learning improves the chances of survival.
31. List three examples of animals that show social behavior.
32. Describe the social organization of honey bee colonies.
33. Discuss the role of altruistic behavior in social organizations using two examples.
34. State that the ANS consists of sympathetic and parasympathetic motor neurons.
35. State that the roles of the sympathetic and parasympathetic system are largely antagonistic.
36. State that the ANS serves the heart, blood vessels, digestive system and smooth muscles.
37. Explain the effects of the sympathetic and parasympathetic system by referring to the control of
the heart, salivary glands and iris of the eye.
38. Discuss the relationships between the influence of the conscious part of the brain and automatic
reflexes as shown by bladder or anus control, meditation and yoga.
39. State that synapses of the peripheral nervous system (PNS) are classified according to the
neurotransmitter used, including acetylcholine and noradrenaline.
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33. 40. Explain how presynaptic neurons can either encourage or inhibit postsynaptic transmission by
depolarization or hyperpolarization of the postsynaptic membrane.
41. Outline how pain is sensed and how endorphins and encephalins can act as painkillers.
42. Outline the symptoms of Parkinson's disease and the involvement of dopamine.
43. Explain that psychoactive drugs affect the brain and personality by either increasing or decreasing
synaptic transmission. (An outline of the ways synaptic transmission can be increased or decrease
is expected).
44. Discuss the behavioral effects of the excitatory psychoactive drugs nicotine, cocaine and
amphetamines.
45. Discuss the behavioral effects of the inhibitory psychoactive drugs benzodiazepines, cannabis and
alcohol.
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