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OPTION E:

NEUROBIOLOGY AND BEHAVIOR

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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 eaglets – is behavior which normally occurs in all members of a species despite natural variation in environmental influences.

Learned behaviors – like using sticks to collect ants - reflect conditions experienced during development. Different members of a species may 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 behavior. A sudden stimulus induces an automatic involuntary and stereotyped response. (e.g. pain withdrawal reflex and pupil reflex).

Classical conditioning is a change in the behavior of an animal as a result of the animal associating one external stimulus with another.

Kinesis is the random movement of an animal in which the rate of movement is related to the intensity of a stimulus but not to its direction. (e.g. the positive relationship between humidity and the rate of movement in sowbugs).

Operant conditioning is the development of a new behavior as a result of the animal being rewarded (positive reinforcement) or punished (negative reinforcement) after trial and error behavior.

Taxis is the movement of an animal in response to the direction of a stimulus. Movement towards a stimulus is positive and movement away from a stimulus is negative. (e.g. positive chemotaxis guides male promethia moths towards female pheremones).

Imprinting is phase-sensitive learning (i.e., it occurs during a temporary and sensitive period of development) that is independent of the consequences of behavior.

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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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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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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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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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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 environment can turn a favorable innate behavior into an unfavorable one.

Innate copulation behavior in ladybirds

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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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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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 immune system.

Ground squirrels grooming

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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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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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 booming sound that attracts females.

Male sage grouse vocalizing

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 one another with their wings and beaks.

Male sage grouses in combat

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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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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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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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 a hive and her only job is to lay eggs. The queen controls the social organization of her colony by secreting a pheromone that maintains tranquility within the hive and inhibits ovarian development among her workers.

Workers search for pollen and nectar, produce honey and wax, feed the young and protect the hive against enemies.

A drone’s only function is to mate with virgin queens.

• 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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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 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).

Habituated deer on highway

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 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.

Monarch butterfly

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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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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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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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

releasing mechanisms and sign stimuli are species specific.

Goslings show their attachment to Lorenz

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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

0

20

40

60

80

100

120

20 30 40 50 60 70 80 90 100

Percent humidity

Spee

d (c

m/m

in);

turn

s (#

/min

)

turns

speed

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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 sensory receptor

Function

Example

Mechanoreceptor

Perceives changes in pressure caused by mechanical energy (sound, touch, movement)

Hair cells send nerve impulses to the brain when they detect vibrations in the cochlea of the inner ear.

Chemoreceptor

Perceives the presence of chemical substances

Neuro-epithelial cells (taste buds) send nerve impulses to the 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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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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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 neuron of optic nerve

Individual cone cells send signals to 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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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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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, thereby allowing the retina to rest.

Circular muscles relax to increase the diameter of the pupil. This maximizes the influx of light thereby increasing the sharpness of vision.

Stimulates saliva production and dilates blood vessels leading to digestive system so that the body can focus on eating and digesting food.

Inhibits saliva production and constricts blood vessels leading to digestive system (dilates blood vessels leading to heart and lungs so that the body can focus energy on locomotion).

Reduces heartbeat (both strength and frequency), which conserves energy.

Increases the frequency and strength of heartbeats, which sends more blood to muscles thus improving muscle performance.

Location and action of peripheral nerves

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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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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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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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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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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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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% concentration in the blood will kill half the population).

Alcohol

• 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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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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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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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.