Chapter 7- The Nervous System, Hormones and Coordination

A summary of the 7th Chapter of the AQA GCSE Human Health and Physiology textbook

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7.1 The nervous system

  • The brain is vital for coordinating many actions (eg thinking and learning) and it makes up the central nervous system (CNS) with the spinal cord
  • The CNS receives electrical impulses from sensory nerves, processes them, and send the impulse to the body via motor nerves
  • Nerves are bundles of neurones (nerve cells)
  • Voluntary actions start when your brain thinks about an action, but reflex actions are rapid responses to external stimuli, Both involve sensory and motor neurones (may be linked by relay neurones
  • Receptors are structures at the beginning of sensory neurones that detect stimuli
  • Effectors (eg muscles and glands) respond to stimuli
  • Synapses are tiny gaps between neurones when the impulse stimulates the production of a chemical which crosses the gap
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7.2 The eye

  • The eye is designed to focus light onto the receptor cells in the retina
  • Normally, the light rays from an object are bent and focused on the retina by the cornea and lens to form an image
  • The lens has to be altered to focus on objects (as the cornea cannot change shapes). For distant objects, the lens is thin.
  • To look at something close, ciliary muscles contract and suspensory ligaments slacken in order to make the lens fatter
  • Optometrists will prescribe corrective lenses if you cannot focus properly
  • A cataract occurs when the lens becomes cloudy due to a build-up of protein. They are replaced by clear plastic ones to restore vision
  • Damage to small blood vessels in the retina can be a result of high blood pressure or high blood sugar due to diabetes. Optometrists puff air into the eye to check pressure
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7.3. Hormones and coordination

  • Hormones are produced by endocrine glands, and control many body processes
  • When a gland is stimulated, it releases a hormone into the blood stream, where it is carried to the target area (sometimes whole body- growth hormone, or specific area- FSH to ovary)
  • Endocrinologists investigate imbalances in hormones, which can cause many problems (too little insulin- high blood sugar- diabetes)
  • In Type 1 diabetes, the pancreas stops insulin production, it mainly effects young people, and it is treated with insulin injections and a healthy diet
  • In Type 2 diabetes, the pancreas does produce enough insulin or cells (esp. liver) become insulin resistant and don't absorb blood sugar. This type develops slowly, lifestyle factors are changed first, then medication
  • Insulin can be given in injection form from syringe, pen and pump
  • If blood sugar rises, insulin is released to change glucose into glycogen, reducing the sugar in the blood
  • If blood sugar falls, glucagon is release to change glycogen to glucose, increasing the sugar in the blood
  • Insulin and glucagon are produced by patches of pancreatic cells called islets. Beta cells in islets have receptors for high glucose (release insulin), and alpha cells detect high glycogen levels (release glucagon)
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7.4 Homeostasis

  • Homeostasis is the way that the body maintains a constant internal environment
  • Blood has an important role as it carries heat and materials. If blood temperature rises above 37c, warmer blood flows to the thermoregulatory centre in the brain
  • The brain then sends impulses to body organs to reduce the temperature.
  • Sweat glands produce sweat, which cools when it evaporates. When you sweat a lot, you lose a lot of water, so the kidneys produce less urine. The brain will also detect that more water is needed and you will feel thirsty
  • The hypothalamus contains the thermoregulatory centre. When the temperature rises impulses are sent to arterioles in the skin, they dilate to increase heat loss through the skin. Sweat glands are also stimulated
  • If you have low water levels, the hypothalamus detects it and tells pituitary glands to release antidiuretic hormone (ADH). ADH travels to the kidneys and causes them to reabsorb more water and reduce urine volume
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