Homeostasis + response

• Homeostasis


  The regulation of conditions inside the body to maintain a stable internal environment, in response to changes in internal and external conditions
• Conditions inside the body need to be kept steady for cells to function properly and for enzymes to work properly
• Automatic control systems in the body

  • Nervous communication systems
  • Hormonal communication systems
• Components of automatic control systems

  • Receptors
  • Coordination centres
  • Effectors
• Negative feedback

  1. Used to keep the internal environment stable

  2. When the level of something gets too high or low, negative feedback is used to bring it back to normal
• Negative feedback process

  1. Receptor detects a stimulus (level is too high or low)

  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 (level decreases or increases)

  4. Effectors carry on producing the response as long as they’re stimulated by the coordination centre, which might cause the opposite problem, and negative feedback will start again
• Nervous system

  Allows humans to react to their surroundings and coordinate their behaviour
• Parts of the central nervous system

  • Brain
  • Spinal cord
• Types of neurons

  • Sensory neurons
  • Motor neurons
• Effectors

  • All muscles and glands, which respond to nervous impulses
• Receptors


  Cells that detect stimuli
• Types of receptors

  • Taste receptors
  • Sound receptors
• Synapses


  The connection between two neurons where nerve signals are transferred by chemicals
• Reflexes are rapid, automatic responses to certain stimuli that don’t involve the conscious part of the brain
• Reflex arc

  1. Neurons go through the spinal cord or an unconscious part of the brain

  2. Stimulus is detected by receptors, impulses are sent along a sensory neuron to a relay neuron in the CNS

  3. Impulses travel to the effector (usually in a muscle) producing a response
• Reaction time is the time taken to respond to a stimulus, affected by age and drugs
• Investigating Reaction Time

  Practical steps to measure reaction time using a ruler and caffeine consumption
• Computers can be used to measure reaction time more precisely
• The brain is part of the central nervous system
• Mouse reaction to a stimulus

  King the mouse when they see a stimulus
• Precision in measurement


  • Removes the possibility of human error
  • Records in milliseconds for more accurate measurement
  • Removes the possibility of predicting responses using body language
• The Brain


  Part of the central nervous system, contains billions of interconnected neurons, in charge of all complex behaviour
• Parts of the Brain

  • Cerebral cortex
  • Cerebellum
  • Medulla
• Studying the Brain - Brain damage

  If a small part of the brain is damaged, the effect on the patient can indicate the function of the damaged part
• Studying the Brain - Electrically stimulating the brain


  A tiny electrode can be used to observe the effects of electrical stimulation on brain tissue
• Studying the Brain - MRI scans


  Magnetic resonance imaging scanner produces detailed pictures of the brain's structure to identify active areas for specific tasks
• Knowledge of the brain has led to the development of treatments for disorders of the nervous system
• Electrical stimulation of the brain can reduce muscle tremors caused by disorders like Parkinson's disease
• Investigation and treatment of the brain is difficult and carries risks such as physical damage or increased problems with brain function
• The Eye


  Contains various structures like the sclera, cornea, iris, lens, retina, ciliary muscles, suspensory ligaments, and optic nerve
• Iris Reflex


  Response to bright light triggers pupil constriction, while dim light triggers pupil dilation
• Focusing

  Accommodation involves changing lens shape to focus light on the retina for near and distant objects
• Correcting Vision Defects

  • Long-sightedness
  • Short-sightedness
• Vision Correction Methods

  • Glasses
  • Contact lenses
  • Laser eye surgery
  • Replacement lens surgery
• Controlling Body Temperature

  The body balances energy gain and loss to maintain core body temperature
• Thermoregulatory centre in the brain contains receptors sensitive to blood temperature, regulating body temperature
• Controlling Body Temperature

  1. Body has to balance the amount of energy gained and lost to keep the core body temperature constant

  2. Thermoregulatory centre in the brain contains receptors sensitive to blood temperature

  3. Receives impulses from temperature receptors in the skin

  4. Temperature receptors detect core body temperature changes

  5. Thermoregulatory centre acts as a coordination centre, receiving information from temperature receptors and triggers effectors automatically

  6. Effectors produce a response and counteract the change

  7. Some effectors work antagonistically to achieve precise temperature, allowing a more sensitive response
• ALTERING TEMPERATURE

  1. Cooling: Sweat produced by sweat glands and evaporates from the skin, transferring energy to the environment

  2. Blood vessels supplying the skin dilate for vasodilation, transferring energy to the environment

  3. Heating: Hair stands up to trap an insulating layer of air

  4. No sweat is produced

  5. Blood vessels supplying the skin close off - vasoconstriction

  6. Shivering, which needs respiration, transfers some energy to the body
• The Endocrine System

  1. Hormones are chemical molecules released into the blood and carried to other parts of the body, affecting cells in specific organs

  2. Hormones control things needing constant adjustment

  3. Produced in and secreted by endocrine glands, having relatively long-lasting effects

  4. Glands: Pituitary, Thyroid, Adrenal, Pancreas, Ovaries, Testes

  5. Nerves act quickly, for a short time in a precise area

  6. Hormones act slowly, for a long time in a more general way
• Controlling Blood Glucose

  1. Eating foods with carbohydrates puts glucose into the blood

  2. Normal metabolism removes glucose from the blood, vigorous exercise removes more

  3. Excess glucose stored as glycogen in the liver and muscles

  4. Glucose level kept steady, controlled by the pancreas

  5. Glucose too high: Insulin secreted, glucose moves into liver and muscle cells, turned into glycogen

  6. Glucose too low: Glucagon secreted, glucose released into the blood by the liver, liver turns glycogen into glucose

  7. Diabetes affects blood sugar control: Type 1 - little or no insulin, Type 2 - resistance to own insulin

  8. Kidneys make urine by filtering waste products out of the blood, selective reabsorption of useful substances like glucose, ions, and water