topic 5- homeostasis and response

• Homeostasis


  Maintaining a stable internal environment
• The conditions inside your body need to be kept steady, even when the external environment changes
• Homeostasis is all about the regulation of the conditions inside your body (and cells) to maintain a stable internal environment in response to changes in both internal and external conditions
• Automatic control systems in the body

  • They regulate internal environment, including body temperature, blood glucose level, and water content
  • They are made up of receptors, coordination centres (including the brain, spinal cord and pancreas), and effectors
• Negative feedback

  1. Receptor detects a stimulus

  2. Coordination centre receives and processes the information, then organises a response

  3. Effector produces a response, which counteracts the change and restores the optimum level
• The effectors will just carry on producing the responses for as long as they're stimulated by the coordination centre, which could cause the opposite problem
• Negative feedback happens automatically, without conscious thought
• Nervous system

  Allows organisms to react to their surroundings and coordinate the body
• Parts of the nervous system

  • Central Nervous System (brain and spinal cord)
  • Sensory neurones
  • Motor neurones
  • Effectors (muscles and glands)
• How the nervous system responds to a stimulus

  1. Receptors detect the stimulus

  2. Sensory neurones carry information to the Central Nervous System

  3. Central Nervous System coordinates a response

  4. Motor neurones carry information to effectors

  5. Effectors produce a response
• Synapse


  The connection between two neurones, where nerve signals are transferred by chemicals
• Reflex

  Rapid, automatic responses to certain stimuli that do not involve the conscious part of the brain
• Reflex arc

  1. Receptor detects stimulus

  2. Sensory neurone carries impulses to relay neurone in the Central Nervous System

  3. Relay neurone passes impulses to motor neurone

  4. Motor neurone carries impulses to effector (muscle), causing it to contract
• Reaction time


  The time it takes to respond to a stimulus
• Caffeine can speed up a person's reaction time
• Measuring reaction time using a ruler

  1. Person sits with arm resting on table, ruler held vertically between thumb and forefinger

  2. Ruler is dropped without warning

  3. Person tries to catch ruler as quickly as possible

  4. Distance ruler falls before being caught is measured, giving reaction time
• Computers can give a more precise and accurate measurement of reaction time compared to the ruler test
• The brain

  • Part of the central nervous system, made up of interconnected neurones
  • Responsible for complex behaviours and functions of the body
  • Different regions carry out different functions
• Regions of the brain

  • Cerebral cortex
  • Medulla
  • Cerebellum
• Methods used to study the brain

  • Studying effects of brain damage
  • Electrical stimulation of the brain
  • MRI scanning
• Knowledge of how the brain works has led to treatments for nervous system disorders, but the brain is incredibly complex and delicate
• Scientists use brain imaging to find out what areas of the brain are active when people are doing things like listening to music or trying to recall a memory
• Knowledge of how the brain works has led to the development of treatments for disorders of the nervous system
• Electrical stimulation of the brain can help reduce muscle tremors caused by nervous system disorders such as Parkinson's disease
• The brain is incredibly complex and delicate - the investigation of brain function and any treatment of brain damage or disease is difficult
• Investigating the brain carries risks, such as physical damage to the brain or increased problems with brain function (e.g. difficulties with speech)
• Sclera


  The tough, supporting wall of the eye
• Cornea


  The transparent outer layer found at the front of the eye that refracts (bends) light into the eye
• Iris


  Contains muscles that allow it to control the diameter of the pupil (the hole in the middle) and therefore how much light enters the eye
• Lens

  Focuses the light onto the retina (which contains receptor cells sensitive to light intensity and colour)
• Ciliary muscles


  Control the shape of the lens
• Suspensory ligaments


  Control the shape of the lens
• Optic nerve


  Carries impulses from the receptors on the retina to the brain
• Iris reflex - adjusting for bright light


  1. When light receptors in the eye detect very bright light, a reflex is triggered that makes the pupil smaller

  2. The circular muscles in the iris contract and the radial muscles relax, reducing the amount of light that can enter the eye

  3. The opposite process happens in dim light, where the pupil widens
• Focusing on near and distant objects

  1. To look at near objects: Ciliary muscles contract, slackening the suspensory ligaments, making the lens fatter (more curved) to increase the amount it refracts light

  2. To look at distant objects: Ciliary muscles relax, allowing the suspensory ligaments to pull tight, making the lens thinner (less curved) to refract light by a smaller amount
• Long-sightedness (hyperopia)


  Occurs when the lens is the wrong shape and doesn't bend the light enough or the eyeball is too short, so the images of near objects are brought to focus behind the retina
• Short-sightedness (myopia)


  Occurs when the lens is the wrong shape and refracts the light too much or the eyeball is too long, so the images of distant objects are brought into focus in front of the retina
• Treatments for vision defects

  • Glasses
  • Contact lenses
  • Laser eye surgery
  • Replacement lens surgery
• Thermoregulatory centre


  In the brain, contains receptors sensitive to the temperature of the blood flowing through the brain and receives impulses from temperature receptors in the skin
• Thermoregulation when too hot

  1. Sweat glands produce sweat that evaporates from the skin, transferring energy to the environment

  2. Blood vessels supplying the skin dilate, increasing blood flow close to the skin surface to transfer energy from the skin to the environment