1.2 Coordination and Control

An animal’s response to a stimulus is coordinated by their central nervous system (CNS).

Receptors are groups of specialised cells that can detect changes in the environment called stimuli.

Receptors located in sense organs ---- Stimuli

• ·         Eyes (sight) --- Light
• ·         Ears (sound) --- Sound
• ·         Mouth (taste) --- Chemicals
• ·         Skin (touch) --- Preasure/Temperature
• ·         Nose (smell) --- Chemicals

The CNS consists of the brain and spinal cord. When a receptor is stimulated it sends a signal along the nerve cells, also called neurones, to the brain. The brain then coordinates the response.

Sensory Neurons carry impulses from receptors to CNS. Motor Neuron carry impluses from CNS to effector organs(muscles/glands). The muscles respond by contracting. Glands respond by secreating (releasing) chemicals.

Peripheral nervous system (PNS) In some cases when the Sensory neurons are stimulated we need a quick reaction which wouldn't happen if we sent messages all the way round the CNS. This is why animals have the Relay Neuron (Interneurone) to speed up our reactions

Sensory and Relay neurone connect through synapses, as do the Motor neuron

The menstrual cycle in women is a recurring monthly process in which the lining of the uterus (the womb) is prepared for pregnancy. If pregnancy does not happen, the lining is shed at menstruation.

Follicle stimulating hormone, FSH

The hormone FSH is secreted by the pituitary gland.

• it causes an egg to mature in an ovary
• it stimulates the ovaries to release the hormone oestrogen.

Oestrogen

The hormone oestrogen is secreted by the ovaries.

• it stops FSH being produced - so that only one egg matures in a cycle
• it stimulates the pituitary gland to release luteinizing hormone (LH), which triggers ovulation (the release of the mature egg from the ovary).
• it cause the Uterus linning to thicken.

Luteinising hormone, LH

Made in pituitary gland. It stimulates the mature egg to be released from the ovaries. (ovulation)

Human fertility is controlled by hormones. This means that knowledge of hormones can be used to decide to increase, or reduce, the chances of fertilisation and pregnancy.

The pill, greatly reduces the chances of mature eggs being produced. It contains oestrogen or progesterone (another hormone). These hormones inhibit the production of FSH, which in turn stops eggs maturing in the ovaries.

Ads: Couples can choose when the start and stop having children.           Disads : Original pills had high levels of Oestrogen, causing side effects (changes in wieght, mood, blood pressure).

IUD (Interuterine Device) / Coil, sits inside uetrus and stops fertilised eggs from implanting.

Ads: Doesn't distrupt hormone cycle.     Disads: Ethical views, IUD's are killing already fertilised eggs.

Fertility treatments

Some women have difficulty becoming pregnant because they don't produce enough FSH to allow their eggs to mature. Fertility drugs contain FSH and LH, which stimulate eggs to mature in the ovary.

In vitro fertilisation (IVF)                      

This is where the egg is fertilised outside the woman’s body and then implanted back into her uterus. As FSH can also be used to encourage the production of several mature eggs at once, it is used as part of IVF to increase the number of eggs available for fertilisation.

Some people worry about the ethical implications of IVF. They are concerned that couples may want 'designer babies' with 'desirable' qualities, so may only want certain fertilised eggs. For example, they may want a girl if they have lots of boys in the family, or they may wish to avoid producing a baby with an inherited defect.

The internal environment of the body is controlled by the nervous system and hormones. The maintenance of a constant internal environment is called homeostasis. Here are some of the internal conditions that need to be controlled.

Ion (salts) content of the body

• Ion levels are controlled to protect cells from too much water entering or leaving them. Ion content is controlled by the loss of ions from:
• the skin - through sweating
• passing urine - produced by the kidneys.

Temperature of the body

• This is controlled to maintain the temperature at which enzymes work best. Body temperature is controlled by sweating, shivering, and controlling blood flow to the skin.

Blood sugar levels

• This is controlled to provide cells with a constant supply of energy. Blood sugar level is controlled by the release and storage of glucose controlled by insulin.

Plants produce hormones and respond to external stimuli, growing towards sources of water and light, which they need to survive.

Phototropism, stem will grow towards the light source to optimise production of photosynthesis.

 Gravitropism (also called a 'geotropism'), roots of plant will always grow in the direction of gravity or towards moisture.

Plant hormone called  AUXIN.

Unequal distribution of AUXIN cause unequal growth, resulting in the bending of the root or shoot of a plant.

Uses of AUXIN

• Used to stimulates fruit growth, help ripens the plants.
• Used to stimulate root growth of cuttings
• Used as weed killers to kill any unwanted plants.

In WOMEN

• Contraceptive pill to prevent pregnancies (helps plan a baby)
• Injection of hormones helps other women become pregnant.

Taking hormones for a long time can lead to side effets

In PLANTS

• Hormones used by farmers and gardeners
• Weed killers to kill unwanted plants on lawns
• Hormones used to encourage root growth of plant cuttings
• Fruit growth and ripening

Hormones used incorrectly can cause damage to enviroment.