B1 Revision~ Coordination and Control

• The NERVOUS SYSTEM has RECEPTORS which detect STIMULI.

• The receptors are found in the SENSE organs e.g eye, ear, tongue, nose and skin.

• Light can stimulate receptors in the eye and ELECTRIC IMPULSES then pass to the brain along NEURONS (nerve cells).

• The brain and spinal cord form the CENTRAL NERVOUS SYSTEM (CNS).

• NERVES contain neurons.

• SENSORY NEURONS carry impulses from the receptors to the CNS.

• MOTOR NEURONS carry impulses from CNS to effector organs (muscle or glands). The muscle responds by contracting. The glands react by releasing chemicals. 

• REFLEX ACTIONS are rapid, automatic responses to stimulus. These protect us from damage.
• Main Steps are...
• A RECEPTOR detects STIMULUS (sharp pain).
• A SENSORY NEURON transmits the impulses to the CNS.
• A RELAY NEURON passes the impulses on.
• A MOTOR NEURON is stimulated
• The impulse passes on to an EFFECTOR (muscle or gland)
• Action is taken (the response)
• At the junction between the receptor to the effector is a REFLEX ARC.

• The MENSTRUAL CYCLE takes 28 days, with ovulation abput 14 days into the cycle.

• This cycle is cintrolled by 3 hormones.

• FOLLICLE STIMULATED HORMONE (FSH) is made in the PERTUITARY GLAND and causes the egg to mature and oestrogen to be produced.

• OESTROGEN is produced by the OVARIES and stops further production of FSH. It stimulates the womb lining to develop to recieve fertilised egg. It also stimulates the production of LH.

• LUTEINISING HORMONE (LH) is made by the pirtuitary gland and stimulates the mature egg to be released from the ivary (OVULATION)

• The CONTRACEPTIVE PILL may contain oestrogen and progesterone.
• It prevents the production of FSH so no eggs mature.
• If a woman cannot produce mature eggs then FSH and LH can be given. This is known as 'fertility treatment'

• Advantages
• Contraceptive pills have helped to reduce famiily size which reduces poverty. Also it allows women to plan their pregnancy.
• Fertility drugs help infertile couples who are having IVF.

• Disadvantages
• Contraceptive pill can cause side effects. Some poeple object to its use due to ethical or religious reasons.
• Expensive process, unethical when older women have babies by IVF. Extra embryos may be stored or destroyed.

• The body controls its INTERNAL ENVIRONMENT these include:
• Water Content
• Ion content 
• Temperature
• Blood sugar level 

• Water is constantly leaving our body in RESPIRATION and as sweat. Also we lose water in our urine (which is produced by the KIDNEYS)

• We also lose ions in our sweat and URINE.

• We must keep our body temperature constant, otherwise the ENZYMES in our body will not work properly or denature. 

• The sugar in the blood is the energy source for cells. The level of sugar is controlled by the PANCREAS.

• Plants respond to light, gravity and moisture. 
• Plants shoots lean towards the light. This is called PHOTOTROPISM.
• Roots grow towards gravity. This is called GRAVITROPISM. Roots also grow towards water.
• AUXIN is the hormone which controls Phototropism and Gravitropism. 
• Unequal distribution of auxin causes unequal growth. This leads to the bending of the shoot or root.

Summary

In Women

• It is important to evaluate the advantages and disadvantages of using hormones to control reftility.
• Contraceptive pills help to prevent pregnancy.
• Other women use hormones to help them become pregnant. 
• Sometimes hormone treatment is used to help older women become pregnant. This may involve using an egg donor who is goven hormones to produce extra eggs.

In plants

• Can be used by farmers and gardeners.
• Weed killers are used to kill unwanted plants on lawns.
• When cuttings are taken from plants, hormones are used to encourage roots to grow before the cutting is planted.
• If plant hormones are used incorrectly they can cause damage to the environment.