Homeostasis and response

• What is homeostasis?

  Regulation of the internal conditions of a cell or organism to maintain optimum conditions for function in responses for internal and external changes
• What are receptor cells?

  Detect changes in environment
• A change to the environment is called a stimulus
• The receptor cells detect a stimulus and send electrical impulses down neurons to the central nervous system
• What does the coordination centre do?

  Receives and processes information
• The coordination centre sends electrical impulses down neurons down to effectors which bring about a response
• What is the job of the effector (muscle or gland)?

  Carry out the response or restore optimum level
• What happens when you touch a hot object ?

  1. Stimulus (heat) is detected by a receptor (in the skins)
  2. Electrical impulses now pass from the receptor along the sensory neuron to the CNS
  3. At the end of the sensory neurone there is a synapse, which releases a chemical
• 3.This chemical now diffuses across to a relay neuron in the CNS, where it triggers an electrical impulse

  4.The electrical impulse now passes across the relay neuron and reaches another synapse, where another chemical is released

  5.This chemical triggers an electrical impulse in a motor neuron, which passes down the motor neuron to an effector

  6.In this case the effector is a muscle, the muscle now contracts and pulls the hand away from the heat (response)
• In the case of reflexes there is no decision making in the conscious part of the brain- which makes them automatic and rapid
• 1. Cerebral cortex- language, memory and consciousness
  2. Cerebellum- balance and coordinates movement
  3. Medulla- heart rate and breathing rate

  A) Cerebral cortex

  B) Cerebellum

  C) Medulla

  
• Why is it difficult to study the brain, or treat brain damage and diseases?

  -Tricky to access (protected by the skull)

  -Complex structures

  -Delicate and easy to damage
• What are the three ways scientists use to investigate the brain?

  -Looking at patients suffering brain damage, they can try to link the part of the brain to its function

  -Electrically stimulate different parts of the brain and look at the effects it has on the persons behaviour

  -MRI scanning
• *Light rays pass through the cornea (transparent layer of the eye that starts the focusing of the eye)

  *The light rays then pass through the pupil in the centre of the iris (coloured part of the eye)

  * The light rays pass through the lens (focus the light rays onto the back of the eye)

  *The light rays are now focused on the retina (back of the eye which contains receptor cells for light)

  *The receptor cells in the retina now send electrical impulses down the optic nerve to the brain

  
• Sclera- white part of the eye that surrounds the iris and protects the eye

  Ciliary muscle and suspensory ligaments- allow us to focus on distant or near objects
• What happens when you enter a dark room?

  -The amount of light entering the eye is low

  -Light receptors in the retina senses the drop in light intensity

  -These send electrical impulses to the brain

  -The brain sends electrical impulses to muscles in the iris

  -These muscles contract causing the pupils to become larger

  -Allows more light to enter the eye
• What is accommodation?

  The ability to change the shape of the lens to focus on near or distant objects
• What happens when you focus on distant objects?

  -The ciliary muscle relaxes and the suspensory ligaments are pulled tight

  -The lens is now pulled thin, because of this the light rays are only slightly refracted
• What happens when you focus on near objects?

  (light from near objects needs to be focused a large amount)

  -Ciliary muscle contracts and this causes suspensory ligaments to loosen

  -Now the light rays are more thicker and refracts the light rays more strongly
• What is long sightedness (hyperopia)

  -Not able to focus on nearby objects because the eye ball is too short so the light is focused at a point behind the retina or the lens becomes less elastic
• How can hyperopia be treated?

  By using glasses with convex lenses, these partially focuses the light before it enters the eye

  
• What is short sightedness (myopia)?

  -Cannot focus on distant objects, because the eye ball can be long so the light is focused at a point in front of the retina or the lens is too thick
• How can myopia be treated?

  Using glasses with a concave lenses to partially unfocus the light before it enters the eye
• What are other ways to treat myopia or hyperopia?

  Contacts lenses and laser surgery can be used to change the shape of the cornea
• What is the thermoregulatory centre?

  Is the part of the brain which controls the body temperature
• What happens when your body temperature gets too high?

  -Sweat gland release sweat onto the surface of the skin

  -The sweat evaporates and takes energy from the body

  -Cooling it down
• What happens when your body temperature gets too high (flushing)?

  -When we get too hot the blood vessels supplying the capillaries dilate (get wider) - also referred to as vasodilation

  -This means that more blood flows through the capillaries

  -Heat can now transfer out of the blood so body temperature returns to normal level
• What happens when body temperature is too low?

  -We shiver, which causes out skeletal muscles to contract

  -To generate energy for this contraction the muscle cells increase their rate of respiration

  -This releases heat which warms the body
• What happens when the body temperature is too low?

  -Blood vessels supplying the capillaries constrict (narrower)- called vasoconstriction

  -Less blood now flows through the capillaries and less heat is lost
• The endocrine system consists of a number of glands, which secrete hormones directly into the blood stream. The blood carries the hormones all around the body. Each hormone only acts on specific target organs, where it produces an effect.
• What are the key differences between the endocrine system and nervous system?

  -NS uses electrical impulses --> down neurons

  -ES uses hormones (chemicals) -->carried in blood stream

  -Es much slower effect but much longer lasting
• • Pancreas- releases hormones that control blood glucose levels
  • Ovaries and testes- hormones involved in puberty and reproduction
  • Thyroid glands- hormones involved in growth and regulation of the body's basal metabolic rate (how rapidly body's reactions take place)
  • Adrenal glands- releases adrenaline
  • Pituitary gland- act on other glands which causes other hormones to be released

  
• Glucose is needed by every cell to release energy by respiration
• The hormone insulin is used to control the blood glucose concentration
• Insulin triggers body cells to take up glucose from the blood
• Insulin triggers liver and muscle cells to store excess glucose as glycogen
• Pancreas monitors blood glucose concentration
• After a meal rich in carbohydrates, pancreas produces insulin to lower blood glucose concentration
• Type 1 diabetes:

  • Pancreas does not produce enough insulin
  • Blood glucose concentration rises and stays high
  • Treatment involves monitoring blood glucose and injecting insulin when needed
• Type 2 diabetes:

  • Body cells stop responding to insulin
  • Blood glucose levels can rise too high
  • Treatment involves controlled diet and exercise
  • Major risk factor is obesity