unit 5 bio

• Homeostasis


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

  • Regulate internal environment
  • Include both nervous and hormonal communication systems
  • Examples: body temperature, blood glucose level, water content
• Components of automatic control systems

  1. Receptors

  2. Coordination centres (including brain, spinal cord, pancreas)

  3. Effectors
• Negative feedback mechanism


  1. Receptor detects a stimulus

  2. Coordination centre receives and processes 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
• Nervous system


  Allows organisms to respond to stimuli (changes in the environment) and coordinate their behaviour
• Parts of the nervous system

  • Central Nervous System (brain and spinal cord)
  • Sensory neurones
  • Motor neurones
  • Effectors (muscles and glands)
• Receptors and effectors


  • Receptors detect stimuli
  • There are many different types of receptors
  • Receptors can form part of larger complex organs
  • Effectors respond to nervous impulses and bring about a change
• How the Central Nervous System coordinates a response

  1. Receptors detect a stimulus

  2. Sensory neurones carry information to the CNS

  3. CNS decides what to do

  4. Motor neurones carry information from CNS to effectors

  5. Effectors (muscles) respond
• Synapse


  The gap between neurons where nerve signals are transferred by chemicals
• Reflex


  Automatic responses to certain stimuli that don't involve the conscious part of the brain
• Reflex arc


  1. Stimulus detected by receptors

  2. Impulses sent along sensory neurone to relay neurone in CNS

  3. Impulses passed to motor neurone

  4. Impulses travel to effector (muscle) which contracts
• Reflexes are quicker than normal responses because you don't have to think about the response
• Reaction time


  The time it takes to respond to a stimulus, often less than a second
• Measuring reaction time using a ruler

  1. Person sits with arm resting on table

  2. Ruler dropped between thumb and forefinger

  3. Person tries to catch ruler as quickly as possible

  4. Reaction time measured by distance ruler fell
• Caffeine can speed up a person's reaction time
• Measuring reaction time using a computer

  1. Person has to click mouse or press key when they see a stimulus on screen

  2. Computer can give more precise reaction time in milliseconds
• The brain


  • Part of the central nervous system
  • Responsible for all complex behaviours
  • Different regions have different functions
• Methods used to study the brain

  • Studying effects of brain damage
  • Electrical stimulation
  • MRI scanning
• Knowledge of how the brain works has led to treatments for nervous system disorders
• The brain is incredibly complex and delicate, so investigation and treatment carries risks
• Parts of the eye

  • Sclera
  • Cornea
  • Iris
  • Pupil
  • Lens
  • Retina
  • Optic nerve
• Messing With the Brain Can Have Consequences
• 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 and carries risks, such as physical damage to the brain
• Sclera


  The tough, supporting wall of the eye
• Cornea


  The transparent outer layer found at the front of the eye that bends (refracts) 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 and 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 detect very bright light, a reflex is triggered that makes the pupil smaller by the circular muscles in the iris contracting and the radial muscles relaxing

  2. The opposite process happens in dim light, with the radial muscles contracting and the circular muscles relaxing to make the pupil wider
• Focusing on near and distant objects

  1. To look at near objects: the 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: the ciliary muscles relax, allowing the suspensory ligaments to pull tight, making the lens thinner (less curved) to refract light by a smaller amount
• As you get older, the lens loses its ability to spring back to shape, meaning it can't be focused well for viewing, so older people have to use reading glasses
• Short-sightedness (myopia)


  The eye is unable to focus on distant objects because the lens is the wrong shape and doesn't refract the light enough, or the eyeball is too long
• Long-sightedness (hyperopia)


  The eye is unable to focus on near objects because the lens is the wrong shape and refracts the light too much, or the eyeball is too short
• Treatments for vision defects

  • Wearing glasses
  • Contact lenses
  • Laser eye surgery
  • Replacement lens surgery