B1.2 Nerves And Hormones

Mind Map by killthemoment, updated more than 1 year ago
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GCSE Biology (B1) Mind Map on B1.2 Nerves And Hormones, created by killthemoment on 08/01/2014.

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B1.2 Nerves And Hormones
1 B1.2.1 The Nervous System
1.1 The nervous system and hormones enable us to respond to external changes. They also help us to control conditions inside our bodies.
1.1.1 Cells called receptors detect stimuli (changes in the environment). Receptors and the stimuli they detect include: receptors in the eyes that are sensitive to light; receptors in the ears that are sensitive to sound; receptors in the ears that are sensitive to changes in position and enable us to keep our balance; receptors on the tongue and in the nose that are sensitive to chemicals and enable us to taste and to smell; receptors in the skin that are sensitive to touch, pressure, pain and to temperature changes. Light receptor cells, like most animal cells, have a nucleus, cytoplasm and cell membrane. Information from receptors passes along cells (neurones) in nerves to the brain. The brain coordinates the response. Reflex actions are automatic and rapid. They often involve sensory, relay and motor neurones. In a simple reflex action: impulses from a receptor pass along a sensory neurone to the central nervous system; at a junction (synapse) between a sensory neurone and a relay neurone in the central nervous system, a chemical is released that causes an impulse to be sent along a relay neurone; a chemical is then released at the synapse between a relay neurone and motor neurone in the central nervous system, causing impulses to be sent along a motor neurone to the organ (the effector) that brings about the response; the effector is either a muscle or a gland, a muscle responds by contracting and a gland responds by releasing (secreting) chemical substances.
2 B1.2.2 Control In The Human Body
2.1 Internal conditions that are controlled include: the water content of the body – water leaves the body via the lungs when we breathe out and via the skin when we sweat to cool us down, and excess water is lost via the kidneys in the urine; the ion content of the body – ions are lost via the skin when we sweat and excess ions are lost via the kidneys in the urine; temperature – to maintain the temperature at which enzymes work best blood sugar levels – to provide the cells with a constant supply of energy.
2.1.1 Many processes within the body are coordinated by chemical substances called hormones. Hormones are secreted by glands and are usually transported to their target organs by the bloodstream. Hormones regulate the functions of many organs and cells. For example, the monthly release of an egg from a woman's ovaries and the changes in the thickness of the lining of her womb are controlled by hormones secreted by the pituitary gland and by the ovaries. Several hormones are involved in the menstrual cycle of a woman. Hormones are involved in promoting the release of an egg: follicle stimulating hormone (FSH) is secreted by the pituitary gland and causes eggs to mature in the ovaries and stimulates the ovaries to produce hormones including oestrogen; luteinising hormone (LH) stimulates the release of eggs from the ovary; oestrogen is secreted by the ovaries and inhibits the further production of FSH. Hormones are used to control fertility. Oral contraceptives inhibit FSH production so that no eggs mature. They may contain oestrogen and progesteroneThe first birth-control pills contained large amounts of oestrogen which resulted in significant side effects so birth-control pills now contain a much lower dose of oestrogen, or are progesterone only. A 'fertility drug' containing FSH and LH is given to a woman whose own level of FSH is too low to stimulate eggs to mature, for example in In Vitro Fertilisation (IVF) treatment. IVF involves giving a mother FSH and LH to stimulate the maturation of several eggs. The eggs are collected and fertilised. At the stage when they are tiny balls of cells, one or two embryos are inserted into the womb.
3 B1.2.3 Control In Plants
3.1 Plants are sensitive to light, moisture and gravity: their shoots grow towards light and against the force of gravity their roots grow towards moisture and in the direction of the force of gravity.
3.1.1 Plants produce hormones to coordinate and control growth. Auxin controls phototropism and gravitropism (geotropism). The responses of plant roots and shoots to light, gravity and moisture are the result of unequal distribution of hormones, causing unequal growth rates. Plant growth hormones are used in agriculture and horticulture as weed killers and as rooting hormones.
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