Homeostasis and Response

• What is Homeostasis?

  the regulation of the internal conditions of a cell or organism to maintain optimum conditions for function in response to internal and external changes
• Homeostasis maintains optimal conditions for enzyme action and all cell functions such as:

  • blood glucose concentration
  • body temperature
  • water levels
• What are the features of an automatic control system?

  • stimulus
  • receptor cells
  • coordination center
  • effector
  • response
• The nervous systems consist of two things:

  • central nervous system (spinal cord + brain)
  • other nerves
• The CNS coordinates...

  The responses of effectors, which may be muscles contracting or glands secreting hormones
• How is an electric signal transported around the body

  1. Receptors detect a stimulus
  2. This sends electrical impulses down a neuron to the CNS
  3. The CNS sends electrical impulses down other neurons to effectors
  4. The effectors bring about a response
• What is an effector?

  A muscle that contracts or gland which secretes a hormone
• What are the steps in a reflex arc?

  1. The stimulus is detected by a receptor (heat and skin)
  2. Electrical impulses now pass from the receptor along a sensory neuron to the CNS
  3. At the synapse, a chemical is released, which diffuses across to a relay neuron in the CNS, where it triggers an electrical impulse
  4. Electrical impulse passes across the relay neuron, reaching another synapse, releasing more chemical
  5. This chemical triggers an electrical impulse in a motor neuron
  6. The electrical impulse now passes down the motor neuron to an effector (muscle)
  7. Muscle contracts pulling hand away
• Required practical 7: reaction time

  1. Person 1 sits on a stool with good upright posture
  2. Person 1 places their dominant arm across the table
  3. Person 2 holds the ruler vertically. 0 cm mark between person 1's thumb and first finger
  4. Person 2 drops the ruler at a random time
  5. Person 1 has to catch the ruler using the thumb and first finger as soon as possible
  6. Person 2 records the number above the thumb
  7. Repeat and calculate the mean
  8. Repeat with a different person, environment, or coffee
• What does the brain do?

  Controls complex behaviors. It is made of billions of interconnected neurons and has different regions that carry out different functions
• What is the function of the Cerebral Cortex?

  language, memory, and consciousness
• What is the function of the Cerebellum?

  Controls our balance and co-ordinates our movements
• What is the function of the Medulla?

  Heart rate and breathing rate
• Why is the brain hard to access?

  • Protected by the skull
  • Structures are extremely complex
  • delicate and easy to damage
• How do scientists investigate the brain?

  • electrically stimulate
  • Check the functions of individual areas
  • MRI scanning
• The eye is a...

  Sense organ containing receptors sensitive to light intensity and colour
• What is the Cornea?

  The transparent front of the eye. Starts the focusing of the light rays
• What is the Pupil?

  Light rays pass through this
• What is the Iris?

  The colored part of the eye
• What is the function of the lens?

  to focus the light rays onto the back of the eye. This can change its shape. This is called accommodation
• What is the retina?

  The back of the eye, contains receptor cells detecting light which send electrical impulses down the optic nerve to the brain
• What is the Sclera?

  The white part of the eye. Tough structure protects the eye
• What are the ciliary muscles and suspensory ligaments?

  work with the lens to focus on distant or near objects
• What is the function of the Iris?

  Controls the size of the pupil
• What is Accommodation in the eye?

  The process of changing the shape of the lens to focus on nearer or distant objects
• How do the eyes focus on a near object?

  • Ciliary muscles contract
  • The suspensory ligaments loosen
  • The lens is then thicker and refracts light rays strongly
• How do the eyes focus on a distant object?

  • The ciliary muscles relax
  • the suspensory ligaments are pulled tight
  • The lens is then pulled thin and only slightly refracts light
• What are 2 common defects of the eye?

  • Myopia (short-sightedness)
  • Hyperopia (Long sightedness)
• How are these eye defects generally treated?

  Spectacle lenses which refract the light rays so that they do focus on the retina
• What are some new technologies to fix eyes?

  • Hard and soft contact lenses
  • laser surgery to change the shape of the cornea
  • replacement lens in the eye
• What part of the brain controls body temperature?

  Thermoregulatory centre
• How does the Thermoregulatory centre maintain body temperature?

  Contains receptors which are sensitive to the temperature of the blood
• What does the body do if its temperature increases?

  • Sweat glands release sweat onto the surface of the skin, which evaporates, releasing energy, cooling the body down
  • Blood capillaries dilate, causing vasodilation, meaning heat and energy can be transported out of the body
• What does the body do if its temperature decreases?

  • The blood vessels constrict, causing vasoconstriction, causing the body retains its heat
  • We shiver, causing skeletal muscles to contract, which causes us to generate energy, triggering the cells to increase their rate of respiration
  • Stopping sweating causes the body to contain its energy
• What is the endocrine system composed of?

  Glands which secrete chemicals called hormones into the bloodstream