Nerves and hormones

Nerves and hormones Nerves and hormones Click to continue

Overview • The nervous system and hormones enable us to respond to external changes. They also help us to control conditions inside our bodies. • Hormones are used in some forms of contraception and in fertility treatments. • Plants also produce hormones and respond to external stimuli. Click to continue

The nervous system The nervous system enables humans to react to their surroundings and coordinate their behaviour. It does this by having receptors that detect stimuli (changes to the environment). What changes in the environment is it important to react to? Click to continue

Receptors 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 What are the other two? Click to continue

Receptors 2 The other receptors are: • 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 Information from receptors passes along cells (neurones) in nerves to the brain. The brain coordinates the response. Give some examples of voluntary actions and the receptors involved. Click to continue

Receptors 3 Click to continue

The reflex arc 1 Sometimes a faster reaction is required than a voluntary action and this can be coordinated directly by the spinal cord. For a hand placed onto a hot object, the pathway is as follows: • a stimulus is detected by a temperature receptor in the skin • a signal is sent along a sensory neurone to the spinal cord • the signal is transferred to a motor neurone via a relay neurone • the signal travels along the motor neurone to the effector, in this case a muscle that causes the hand to move Click to continue

The reflex arc 2 This diagram shows the neurones involved in a spinal reflex. Click to continue

Synapses At the junction (synapse) between relay neurones and either a sensory or motor neurone, the impulses are transmitted across the gaps by a chemical. Click to continue

Homeostasis — keeping internal conditions constant To keep us alive, internal conditions have to be constantly monitored and controlled. These include: • water content of the body — water leaves the body via the lungs when we breathe out, via the skin when we sweat, and in urine • 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 Click to continue

Hormones 1 Hormones are chemical messengers produced by glands and released into the blood. Hormones travel to all parts of the body, but affect only certain target cells. Here are some examples of glands and their associated hormones: • The pancreas produces insulin, which regulates blood sugar levels. • The testes produce male sex hormones. • The ovaries produce female sex hormones, which control menstruation. • The pituitary gland is the ‘master’ gland. It produces hormones that control many other glands. What others do you know? Click to continue Click to continue

Hormones 2 How adrenaline can affect the heart Click to continue

The menstrual cycle 1 Hormones secreted by the pituitary gland and the ovaries regulate the monthly release of an egg from a woman’s ovaries and the changes in thickness of the lining of her womb as part of the menstrual cycle. How does the cycle work? Click to continue

The menstrual cycle 2 The hormones that promote the release of an egg are: • follicle stimulating hormone (FSH), secreted by the pituitary gland. It causes eggs to mature in the ovaries and stimulates the ovaries to produce hormones including oestrogen • luteinising hormone (LH), which stimulates the release of eggs from the ovary • oestrogen, which is secreted by the ovaries and inhibits the further production of FSH Click to continue

The menstrual cycle Click to continue

Using hormones to reduce fertility 1 As the menstrual cycle is controlled by hormones, it can be disrupted by artificially changing the levels using a contraceptive ‘pill’. Contraceptive pills may contain: • progesterone • a combination of oestrogen and progesterone These hormones inhibit FSH production so no eggs mature. Are there any side effects? Click to continue

Using hormones to reduce fertility 2 The first birth control pills contained large amounts of oestrogen that caused the women taking them to have side effects. Modern pills have much lower levels or are progesterone only (POP) with fewer side effects. Sebastien Maleville/Fotolia What are the potential side effects of ‘the pill’? Click to continue

Using hormones to increase fertility Infertility caused by a woman having low hormonal levels of FSH can be treated by giving fertility drugs. IVF (in vitro fertilisation) treatment involves the following: • FSH and LH are given to stimulate the production of several eggs. • The eggs are collected from the mother and fertilised by sperm from the father. • The fertilised eggs develop into embryos. • When they are big enough, one or two embryos are inserted into the womb where they grow into babies. Click to continue

Plant hormones Plant hormones control plant growth and react to changing conditions. These responses are caused by unequal distributions of hormones causing opposite sides of the roots or shoots to grow at different rates. • Plants have been shown to respond to gravity with their roots growing downwards and shoots upwards (geotropism). • Plant shoots also grow towards the light (phototropism). • Plant roots grow towards moisture. Plant hormones can be used as weedkillers and as rooting hormones to enable cuttings to grow roots. Click to continue

Nerves and hormones