Homeostasis-biology

• Homeostasis is the maintenance of a constant internal environment in order to maintain optimum conditions for enzyme and cellular function
• The function of a receptor is to detect changes in the environment (stimuli)
• Two types of responses used in body control systems are nervous and chemical
• The function of an effector is to bring about responses to stimuli (muscles or glands)
• Conditions maintained by homeostasis in the body

  • Blood glucose concentration
  • Body temperature
  • Water levels
• Three components of all control systems

  • Receptors
  • Coordination centres
  • Effectors
• The function of a coordination centre is to obtain and process information from receptors
• The nervous system allows the body to react to its surroundings and coordinate an appropriate response
• Reflex pathway vs. conscious pathway

  Within a reflex pathway, the coordination centre is a relay neurone found in the spinal cord/unconscious parts of the brain. In a conscious pathway, the coordination centre is in the conscious part of the brain
• Sequence of events in the nervous system

  • Stimulus → receptor → coordinator → effector → response
• Reflex actions aid survival by preventing harm to the body
• Stimulus to response process

  1. Stimulus is converted into an electrical impulse by the receptors

  2. The electrical impulse passes along sensory neurones to the central nervous system (CNS)

  3. The CNS coordinates an appropriate response and an electrical impulse is sent along motor neurones to the effector, which carries out the response
• A reflex action is an automatic and rapid response which does not involve any conscious input from the brain
• Reflex arc process

  1. The stimulus is detected by a receptor

  2. An electrical impulse passes along a sensory neurone to the spinal cord (part of the CNS)

  3. At a synapse between a sensory neurone and a relay neurone, a chemical diffuses across the gap and stimulates a new impulse which passes along the relay neurone

  4. The same process occurs at a synapse between a relay neurone and a motor neurone

  5. At the effector, an appropriate response is carried out
• Cerebellum

  • Controls muscular coordination
• Reasons why the investigation and treatment of the brain is difficult

  • The brain is a complex and delicate organ
  • The brain is easily damaged and destroyed
  • Certain membranes prevent drugs from reaching the brain
  • The exact function of each part of the brain is not known
• Cerebral cortex


  • Controls consciousness, intelligence, memory, and language
• Medulla

  • Controls unconscious activities e.g. breathing, heart rate
• In a conscious pathway, the coordination centre is in the conscious part of the brain
• Stimuli receptors of the eye are sensitive to

  • Light intensity
  • Colour
• Methods used by scientists to determine brain function

  • Studying patients with brain damage
  • Electrical stimulation of the brain
  • MRI scans
• Retina

  The retina is a light-sensitive layer found at the back of the eye. Light stimulates the retinal cells, resulting in impulses being sent to the brain
• Main functions of structures found within the eye

  • Focusing on near or distant objects - accommodation
  • Adaptation to dim light
• A relay neurone is found in the spinal cord/unconscious parts of the brain
• Retina

  Light-sensitive layer found at the back of the eye
• Cornea structure and function

  Curved transparent layer at the front of the eye, lets light into the eye and allows light to be focused onto the retina
• Optic nerve structure and function

  Connects the eye and the brain, carries impulses to the brain for visualizing images
• Accommodation is the alteration of the lens' shape to focus on near or distant objects
• Ciliary muscles and suspensory ligaments structure and function

  Hold the lens in place and control its shape
• Iris structure and function

  Controls the size of the pupil by contracting or relaxing, allowing the eye to adjust to bright and dim lighting
• Retina function

  Light stimulates the retinal cells, resulting in impulses being sent to the brain
• How the iris alters the size of the pupil in bright and dim light

  Bright light: circular muscles contract and radial muscles relax, making the pupil smaller to avoid retinal damage. Dim light: circular muscles relax and radial muscles contract, making the pupil larger to allow more light to enter the eye
• Sclera structure and function

  Tough outer layer of the eye that protects its internal structures
• Myopia can be treated using glasses with a concave lens, which spreads out light rays so they can be focused on the retina
• Myopia (short-sightedness) usually occurs when the lens of the eye is too curved. As a result, light is focused in front of the retina so images appear blurry
• Hyperopia can be treated using glasses with a convex lens, which brings the light rays together so they can be focused on the retina
• Types of contact lenses

  • Hard - rigid material, last a long time, must be kept sterile
  • Soft - flexible material, last for a shorter time, more comfortable
• Hyperopia (long-sightedness) usually occurs when the lens of the eye is too flat. As a result, light is focused behind the retina so images appear out of focus
• How does the eye focus on a far away object?

  1. Ciliary muscles relax

  2. Suspensory ligaments tighten

  3. Lens becomes thinner - light rays are refracted weakly
• Laser eye surgery is the use of lasers to fix visual defects in adults. To treat myopia, lasers reduce the thickness of the cornea so light is refracted less strongly. To treat hyperopia, lasers alter the curvature of the cornea so that light is refracted correctly