A2 Option Module 8  BEHAVIOUR AND POPULATIONS

Introduction: This option module extends the study of nervous and hormonal physiology in Module 4 to the behaviour of whole organisms. There is also consideration of reproductive behaviour and human growth and development, with an emphasis on the underlying principles of hormonal control. The study of human populations is developed to include a range of public health issues. Candidates are expected to understand the biological background to these issues and to be able to evaluate possible strategies for improvement. In the assessment of this module a knowledge and understanding of relevant  content from Modules 1 to 5 will be assumed.

Innate behaviour

The principal differences between innate and learned behaviour.

Taxes and kineses

Taxes and kineses as examples of innate behaviour.

Reflex actions

The nature of simple reflex behaviour, such as in reflex escape responses.

The linking of a number of simple reflexes to produce a more complex pattern of behaviour as shown by the reflexes involved in the feeding of a new-born human infant.

Modified reflexes

The modification of reflex behaviour by learning as shown by the development of conscious control of bladder emptying.

Learned behaviour

Habituation and imprinting.

Classical conditioning, illustrated by the work of Pavlov on the control of salivation in dogs.

Operant conditioning, illustrated by the work of Skinner on rats.

The importance of reinforcement stimuli and rewards in learning .

Candidates should be able to explain examples of behaviour in terms of classical conditioning and of operant conditioning and to evaluate parallels between animal and human behaviour.

Courtship

Courtship behaviour as a necessary precursor to successful mating. The roles of species recognition, pair bond formation, sexual selection and synchronisation of breeding behaviour.

Sign stimuli and innate releaser mechanisms as components in simple courtship patterns.

The role of hormones and pheromones in courtship behaviour.

Candidates should be able to analyse individual components in simple courtship patterns, and evaluate comparisons between the behaviour of humans and other animals.

Territorial behaviour

The advantages of defending a territory, in relation to breeding success.

The menstrual cycle

The roles of FSH, LH, oestrogen and progesterone in controlling the human menstrual cycle.

The effect of oestrogen and progesterone on the uterine

endometrium.

The role of negative feedback in regulating hormone concentrations.

Contraception

The use of oral contraceptives based on oestrogen and progesterone in controlling fertility.

Candidates should be able to evaluate the different methods of birth control.

Infertility

The treatment of female infertility with extracted and synthetic hormones and with drugs such as clomiphene which stimulate hormone activity.

The key stages in in vitro fertilisation:

• the use of fertility drugs to stimulate ovulation;

• the collection of mature egg cells and their incubation with sperms;

• the insertion of embryos into the uterus.

Pregnancy

Conception

Fertilisation, including capacitation, the role of the acrosome and formation of the fertilisation membrane.

Hormones and pregnancy

The roles of human chorionic gonadotrophin (HCG) and

progesterone in controlling the events of pregnancy.

Confirmation of pregnancy by determining HCG and progesterone levels.

The placenta

The structure of the placenta in relation to its role in the supply of substances to, and the removal of waste products from, the developing foetus.

Physiological changes in the

mother

The changes in the following which take place during the course of a normal pregnancy and their physiological significance:

• body mass;

• plasma volume, red-blood-cell mass and cardiac output;

• kidney function.

Patterns of human growth

The pattern of growth of the whole body, reproductive organs and the brain from infancy to adulthood.

Candidates should be able to represent graphically and interpret data relating to growth and growth rate.

Hormonal control

The roles of thyroxine, growth hormone and sex hormones in the control of human growth from infancy to maturity.

Puberty and the principal physical changes associated with it. The evolutionary importance of a long pre-puberty stage in the human lifespan.

Ageing

The contributions to ageing of changes in physiological function, degeneration of tissue, accumulation of genetic error, and malfunction of the immune system.

Population size and structure

Population growth rates, pyramids, survival rates and life expectancy.

Candidates should be able to:

• interpret population growth curves, survival curves and age pyramids;

• calculate population growth rate from data on birth rate, death rate, emigration and immigration;

• relate changes in the size and structure of human populations to different stages in demographic transition.

Social conditions

The influence of food supply, safe drinking water and effective sewage disposal on mortality.

Infectious disease

Pathogens, including certain bacteria, viruses and fungi, as the cause of infectious disease.

Transmission of pathogens by droplet infection and contact, or in food and water.

Natural immunity as production of antibodies in response to antigens. Immunological memory. (Details of the mechanisms of the immune response not required.)

Artificial immunity by vaccination. The limitations of vaccination related to variability of antigens in pathogens.

The herd immunity effect.

Candidates should be able to:

• interpret information relating to the incidence and mortality of diseases;

• evaluate the effectiveness of immunisation programmes and changes in social conditions in preventing epidemics.

Effects of lifestyle on health

The constitution and importance of a balanced diet. The effects of excess fat and salt intakes, and of deficiency of mineral ions (calcium, iron and iodine) and vitamins (vitamins A, C and D).

The relationships between diet, exercise and cardiovascular disease. Atheroma formation, formation of blood clots, aneurysm, myocardial infarction and cerebrovascular accident.

The relationships between air pollution and smoking and chronic bronchitis, emphysema and lung cancer. The development and effects on lung function of bronchitis, emphysema and lung cancer.

The relationship between ultra-violet light and malignant skin tumors. Tumor growth and metastasis.

Candidates should be able to explain the biological effects of the disorders listed, and to evaluate measures that might be taken to reduce the risk factors.

Screening programmes

The principles involved in the use of x-rays, endoscopy, ultrasound and genetic techniques in diagnosis and screening programmes.

Candidates should be able to:

suggest the most appropriate technique to use in the diagnosis or screening of a particular condition;

evaluate the issues arising from the use of screening programmes for inherited conditions.

Patterns of behaviour

Behaviour

Behaviour is what an animal does and how it does it. To some extent all behaviour has a genetic basis but in general, behaviour is a response to some environmental stimulus. Ethology is the correct term for the study of behaviour in its natural habitat. It is mostly a descriptive science.

There are two types of behaviour innate and learned.

• Innate behaviour – little influence from the environment – does not need to be learnt, varies little within species.  (inflexible)

• Learned behaviour – develops from an animals experience of its environment – not passed on genetically

Some behaviours are a blend of both so classification is not always so easy

Innate Behaviours

• inherited, instinctive:

• programmed by genes

• highly stereotyped (similar each time in many individuals)

Types of innate behaviour:

1. Kinesis: "change the speed of random movement in response to environmental stimulus"
2. Taxis: "a directed movement toward or away from a stimulus; positive and negative taxes
3. Reflex: "movement of a body part in response to stimulus".
4. Fixed Action Pattern (FAP): "stereotyped and often complex series of movements., responses to a specific stimulus - Releaser"

Reflex: A simple reflex is movement of a body part in response to stimulus. It is a rapid, innate automatic response to a stimulus. We looked at the nerve pathway involved in a reflex in module 4 and that helps explain why they are quick and the response does not vary. Watch out for synoptic questions on reflexes.

Reflexes can be linked together to produce more complicated behaviours. The example of this that you have to learn is breast-feeding in humans.

There are several reflexes involved in the sequence.

Reflex

Behaviour

Rooting reflex (baby)

Also called nipple-seeking behaviour. When the breast touches the baby it will turn its head with its mouth open until it finds the nipple.

Sucking reflex (baby)

When the baby attaches to the nipple it begins to suck.

Let-down reflex (mother)

The stimulation of the nipples by the baby sucking causes the reflex release of the hormone oxytocin. This hormone triggers smooth muscle contraction in the mammary glands causing the release of milk

Although reflexes are defined as unconscious actions that are performed in their entirety and are automatic – they can in some instances be modified. The most obvious example of this is the control of the sphincters which govern urination and defaecation.

The reflex that empties the bladder is as follows. The full bladder is the stimulus which causes the sphincter muscles around the base of the urethra to relax, these muscles are connected to the autonomic nervous system – to modify it this muscular relaxation has to be prevented.

Learned behaviours develop during an animals lifetime and are not passed on genetically to its offspring. They vary from very simple to the complex social interactions in primates and whales. Since learned behaviours are not “hardwired” they can often be adapted – this adaptation of behaviour forms the basis of animal training.

When a reflex is modified it is because the stimulus that causes the reflex also causes sensory information to be sent to the brain. When the learning has occurred this information causes inhibitory signals to be sent from the CNS preventing the normal reflex response

Learned Behaviour can be divided into different categories:

• Habituation

• Imprinting

• Conditioning:

• classical conditioning

• operant conditioning

• Insight, reasoning

Habituation is perhaps the simplest form of learned behaviour. This is where an animal that normally responds to a certain stimulus learns to stop responding to the same stimulus when it is repeatedly stimulated without reason. For example some spiders lie in wait for prey to one side of their web and when something gets trapped. On the web the spider detects the vibrations of the web a rushed out to kill its prey. This response can be made to occur by simply tapping the web with a pen. However after a few stimuli the spider ceases to respond. We say it has become habituated.

Young geese (goslings) do not immediately recognise their mother but they imprint on her. There is a sensitive period during the first few days of a goslings life in which it will follow and become attached to any large object, of course in nature this is the mother but in some experiments it has been humans or even a red watering can. When goslings are distressed they will run to whatever object they have imprinted on which usually will be advantageous as it would be their mother but not so helpful if the object was the red watering can.

It breeding programs to replenish rare or endangered animals care is taken to avoid imprint onto humans and habituation to the presence of humans. In fact habituation to human presence is one of the factors that makes zoo and captive bred animals very different to their wild counterparts and is an obstacle to reintroduction.

Conditioning involves the formation of new connections between stimuli and responses, the table below shows a summary of this

Type of conditioning

Summary

Classical

A stimulus leads to a response. Here a new stimulus is given at the same time as the first after time the response occurs even if only the second stimulus is given.

Operant

Trial and reward learning.

Habituation

Habituation is a reduction in a previously displayed response when a stimulus is repeatedly applied with no reward or punishment following.

If you make an unusual sound in the presence of the family dog, it will respond - usually by turning its head toward the sound. If the stimulus is given repeatedly and nothing either pleasant or unpleasant happens to the dog, it will soon cease to respond. This lack of response is not a result of fatigue or sensory adaptation and is long-lasting; when fully habituated, the dog will not respond to the stimulus even though weeks or months have elapsed since it was last presented.

Imprinting

If newly-hatched geese are exposed to a moving object of reasonable size and emitting reasonable sounds, they will begin to follow it just as they would normally follow their mother.

This is called imprinting.

The time of exposure is quite critical. A few days after hatching, imprinting no longer occurs. Prior to this time, though, the results can be quite remarkable. A gosling imprinted to a moving box or clucking person will try to follow this object for the rest of its life. In fact, when the gosling reaches sexual maturity, it will make the imprinted object - rather than a member of its own species - the goal of its sexual drive.

Much of our knowledge of imprinting was learned from the research of Konrad Lorenz

The Conditioned Response

The conditioned response is probably the simplest form of learned behaviour. It is a response that - as a result of experience - comes to be caused by a stimulus different from the one that originally triggered it. The Russian physiologist Ivan Pavlov found that placing meat powder in a dog's mouth would cause it to salivate.

This unconditioned stimulus (US) is probably a simple inborn reflex involving taste receptors, sensory neurons, networks of interneurons in the brain, and motor neurons running to the salivary glands.

Pavlov found that if he rang a bell every time he put the meat powder in the dog's mouth, the dog eventually salivated upon hearing the bell alone. This is the conditioned response.

The dog has learned to respond to a substitute stimulus, the conditioned stimulus (CS).

We assume that the physiological basis of the conditioned response is the transfer, by appropriate neurons, of nervous activity in the auditory areas of the brain to the motor neurons controlling salivation. This involves the development of new circuits, which - we may also assume - is characteristic of all forms of learning.

Pheromones are chemicals released by an organism into its environment enabling it to communicate with other members of its own species.

Humans may have pheromones

It has long been noticed that women living close together (e.g., college roommates) develop synchronous menstrual cycles.

This is thought to be because they release two (as yet uncharacterised) primer pheromones

• one prior to ovulation that tends to speed up the onset of ovulation in others

• one after ovulation that tends to delay the onset of ovulation in other women.

Both pheromones are released from the armpits.

The pheromones are not detected consciously as odours, but presumably trigger the hormonal changes that mediate the menstrual cycle.

Reproductive behaviour

Courtship 

Courtship Behaviour:

• Attraction of mate, (possibly from a considerable distance)

• Allows species recognition

• Allows sex recognition

• Stimulates sexual behaviour / egg production

• Allows recognition of sexually mature / receptive individuals

• Enables choice of fittest individuals

In birds courtship behaviours can include action such as:

• Head Wagging

• Sky Pointing

• Hop Display

• Wing Waving

• Bowing

• Presenting Nest Material

In establishing breeding partners and defending territories members of the same species rarely fight. Instead they take part in behaviour that is stylised and aimed at avoiding the need to fight

Aggressive encounters between individuals of the same species

• Song, Roar etc.

• Display

• Charging

• Pushing & Shoving

• Displacement

Why not just fight?

• Risk of Injury

• Expenditure of energy

• Conclusion predictable

Do they ever fight?....Yes…When

• The stakes are high i.e. it is a life or death situation

• The outcome may not be clear

Types of mating relationships

Monogamous: Male and female form exclusive bond, may be for one breeding season or for life.

Polygamous: Animals have several mates at the same time ~ 2 classes:

• Males have several female mates = polygynous. e.g. red deer

• Females have several male mates = polyandrous. e.g. starlings

The Hormonal Control of the Female Menstrual Cycle

Pituitary Hormones - released from the pituitary gland in the brain

• FSH:  Follicle Stimulating Hormone

• LH:  Lutenising Hormone

Ovarian Hormones - released from the ovaries (the examiners usually think of oestrogen as been released from the follicle and progesterone as been released from the corpus luteum - however there is actually some overlap)

• Oestrogen;  This repair the uterine lining.

• Progesterone;  This maintain the uterine lining

The sequence

• FSH stimulates growth of the follicle.

• The developing follicle in the ovary produces oestrogens

• Rising oestrogen levels inhibit FSH and promote LH production

• LH stimulates follicle development and its conversion into the corpus luteum

• Rising oestrogen levels stimulates an increase in FSH

• A surge of FSH and LH brings about ovulation

• LH stimulates progesterone production

• Progesterone inhibits FSH and LH

Summary of effects

Hormone

Effects

FSH

• stimulates the growth & development of the follicle

• stimulates secretion of oestrogen

• enhances effect of LH in stimulating ovulation

LH

• stimulates the final development of the follicle

• stimulates ovulation

• stimulates the development of the corpus luteum

• stimulates production of progesterone

Oestrogen

• stimulates repair of uterine lining

• at high conc. inhibits FSH, however during 'pituitary hormone surge' it stimulates further FSH production

• as conc. peaks stimulates release of LH

Progesterone

• maintains uterine lining

• inhibits release of FSH

• inhibits release of LH

• fall in conc. results in menstruation

• fall in conc. removes inhibition of FSH and a new cycle begins.

Fertilisation Summary:

Fertilisation is the fusion of two gametes to form a zygote.  In humans this takes place near the top of the oviduct. Hundreds of sperm reach the egg and use their tails to swim through the follicle cells (shown in this photo). When they reach the jelly coat surrounding the ovum they bind to receptors and this stimulates the rupture of the acrosome membrane in the sperms, releasing digestive enzymes, which make a path through the jelly coat. When a sperm reaches the ovum cell the two membranes fuse and the sperm nucleus enters the cytoplasm of the ovum. This triggers a series of reactions in the ovum that cause the jelly coat to thicken and harden, preventing any other sperm from entering the ovum. The sperm and egg nuclei then fuse, forming a diploid zygote.

Copulation and Fertilization

For fertilization to occur, sperm must be deposited in the vagina within a few days before or a day or two after ovulation. Sperm transfer is accomplished by copulation.

Semen is a fluid containing the sperm and liquid added by the seminal vesicles, Cowper's glands, and the prostate gland. These fluids provide a source of energy (fructose) and perhaps in other ways provide an optimum chemical environment for the sperm. The semen passes through the urethra and is expelled into the vagina.

Once deposited within the vagina, the sperm proceed on their journey into and through the uterus and on up into the fallopian tubes. It is here that fertilization may occur if an "egg" is present (strictly speaking, it is still a secondary oocyte until after completion of meiosis II).

Although sperm can swim several millimetres each second, their trip to and through the fallopian tubes may be assisted by muscular contraction of the walls of the uterus and the tubes. There is some evidence that the egg may release a chemical attractant for sperm. In any case, sperm may reach the egg within 15 minutes of ejaculation. The trip is massive for the sperm and many don’t make it. An average human ejaculate contains several hundred million sperm but only a few hundred reach the egg. And of these, only one will succeed in entering the egg and fertilizing it.

Before sperm can fertilise an egg a process called capacitation must take place. This is where a coating surrounding the sperm is removed it occurs over a period of a few hours and is triggered by the conditions within the female reproductive tract. Once capacitation has occured the acrosome is capable of releasing its enzymes.

Fertilization begins with the binding of a sperm cell to the outer coating of the egg (called the zona pellucida). Enzymes released by the acrosome at the tip of the sperm head digest a path through the zona and enable the sperm to enter the cytoplasm of the egg.

Once a single sperm has penetrated, the cell membrane of the egg calcium ions move into the egg cell. This causes exocytosis of cortical granules from the egg. The granules fuse with the zona pellucida, forming a fertilisation membrane. This prevents the entry of other sperm. The other sperm die within 48 hours. Thus the cortical reaction ensures that only one sperm fertilizes the egg.

Soon the head of the successful sperm enlarges. At the same time, the egg (secondary oocyte) completes meiosis II. The male and female nuclei move toward each other. Their nuclear envelopes disintegrate. A spindle is formed, and a full diploid set of chromosomes assembles on it. The fertilized egg or zygote is now ready for its first mitosis.

Pregnancy

Pregnancy

Embryonic development begins while the fertilized egg is still within the fallopian tube. The developing embryo travels down the tube, reaching the uterus in about a week. As a result of repeated mitotic divisions and some migration of cells, a hollow ball of cells is formed called the blastocyst. Approximately one week after fertilization, the blastocyst embeds itself in the endometrium, a process called implantation. With implantation, pregnancy is established.

The blastocyst has two parts the inner cell mass and the trophoblast. Between them these two parts will develop into the:

• baby

• amnion

• placenta

• umbilical cord

and secrete the pregnancy hormone human chorionic gonadotropin (HCG).

Human Chorionic Gonadotropin

HCG behaves much like LH because it stimulates the corpus luteum to secrete progesterone but has one crucial difference: it is NOT inhibited by a rising level of progesterone. So HCG prevents the deterioration of the corpus luteum at the end of the fourth week and enables pregnancy to continue beyond the end of the normal menstrual cycle.

Because only the implanted embryo makes HCG, its early appearance in the urine of pregnant women provides the basis for the most widely used test for pregnancy (which can provide a positive signal even before menstruation would have otherwise begun).

As pregnancy continues, the placenta becomes a major source of progesterone, and its presence is essential to maintain pregnancy.

The Pregnancy Test
This test is usually the first test conducted when you suspect that you may be pregnant. There are a variety of home testing kits available over-the-counter and all detect a protein hormone called human chorionic gonadotropin (hCG). When an egg is fertilized, the embryo begins to produce hCG. Levels of hCG increase after conception and can be detected in the mother's urine. By 10 days after conception, hCG levels are about 25 milli-International Units (mIU).

Typically, the home test is a urine test for hCG:

1. You collect a sample of urine. You would usually use the first urine in the morning, when hCG levels are the most concentrated, or wave the test wand through the urine stream.
2. If you collected the urine, you can either dip the test wand into the cup or place a drop on the test wand.
3. The test wands or dipsticks have a plastic coating embedded with antibodies to hCG.
4. The test wands also have a second antibody to hCG linked with some colour tag (e.g., coloured latex beads, enzyme that produces a colour reaction).
5. If sufficient levels of hCG are present in the urine (more than 25 mIU), then the hCG will bind with the second antibody and cause a colour reaction to occur (i.e., a positive test result).

If a positive test occurs, you generally call your doctor and a second test is performed at the office to confirm the pregnancy. The doctor may also order a blood test to determine the precise quantity of hCG present, which can be used to assess the baby's health.

The placenta

The placenta grows tightly fused to the wall of the uterus. Its blood vessels, supplied by the foetal heart, are literally bathed in the mother's blood. Although there is normally no mixing of the two blood supplies, the placenta does facilitate the transfer of a variety of materials between the foetus and the mother.

Table showing exchange of materials across the placenta

Mother to Foetus

Foetus to Mother

• Oxygen
• Glucose
• Amino acids
• Lipids, fatty acids and glycerol
• Vitamins
• Ions; Na, Cl, Ca, Fe
• Alcohol, nicotine + other drugs
• Viruses
• Antibodies

• Carbon dioxide
• Urea
• Other waste products

The placenta is an organ of exchange and therefore requires a large surface area – to achieve this it has chorionic villi (the cells of which have microvilli and many mitochondria)

The metabolic activity of the placenta is almost as great as that of the foetus itself.

The placenta is also an endocrine organ and it secretes hCG, progesterone and oestrogen

During pregnancy prenatal diagnosis of genetic disorders can be made using the procedures of amniocentesis and chorionic villus sampling (CVS) – see later screening section for details.

Renal System

Kidney Function
Blood flow through the kidney can increase from 25-50% and blood urea also increases as foetal urea is added via the placenta. The kidney accommodates for these changes by increasing in size (length can increase by 1cm). Volume of urine production is not greatly increased (though frequency of urination usually is) therefore the concentration of urine is normally increased.

Body Mass

The average weight gain during pregnancy is about 12kg (or 25-35 pounds). The table below shows some typical mass changes that may occur if I became pregnant (ok I know it’s impossible but it gives an idea of proportion)