Homeostasis and Response

• Homeostasis is the regulation of conditions inside the body to maintain a stable internal environment, in response to both internal and external conditions
• The body needs certain conditions in order for enzymes function properly. For example, it cannot be too hot or too cold.
• The nervous system is very fast and precise. It sends electrical impulses through nerves that can respond quickly
• The endocrine system sends hormones through the bloodstream to the entire body. Messages are slower, longer lasting and more generalised
• Negative feedback is when the change in the stimulus causes a change in the response, for example if something is too low, the body will increase it
• There are lots of different types of neurones. They carry electrical impulses from one place to another. They are long and thin and contain branched connections to pass on impulses to other nerve cells.
• For one nerve cell to communicate to another, we need a synapse. When an electrical impulse hits the end of a nerve, it causes the release of some chemicals which diffuse across the gap to the next nerve cell where they can trigger another electrical impulse.
• The central nervous system (CNS) is made up of the brain and spinal cord. All thinking takes place here and orders are sent out to the rest of the body.
• Sensory neurons carry information from receptors to the CNS. Eg, changes in temperature
• The CNS send impulses back to the body through motor neurons to effectors, which are usually muscles or glands
• Reflex Arc:

  Stinky (stimulus)

  Rats (receptor

  Stinky (sensory neuron

  Rats (relay neuron)

  Munch (motor neuron)

  Every (effector)

  Rat (response)
• The cerebral cortex is responsible for consciousnesses, intelligence, memory and language. Also, our senses like hearing and vision.
• The cerebellum is responsible for balance and muscle coordination
• The hypothalamus is responsible for regulating our body temperature and sending signals to the pituitary gland
• A=Cerebellum

  B=Hypothalamus

  C=Cerebral Cortex

  
• The medulla is responsible for unconscious activities such as breathing and the beating of our hearts

  
• Scientists can study the brain by studying people with brain damage. For example, if someone has a stroke and part of their brain is damaged, and it leads to them not being able to hear anymore, then we can guess that that region was responsible for hearing.
• Scientists can study the brain by electrically stimulating different parts of the brain. For example, if zapping a part of the brain results in muscle contraction, the person may move an arm or a leg
• Scientists can study the brain by scanning the brain. For example,

  • CT scan (uses x-rays)
  • PET scan (uses radioactive chemicals)
  • MRI scan (uses magnetic fields)
• The brain is so difficult to treat because:

  • A wide range of things can go wrong, eg tumors, trauma, mental health problems or infection
  • The brain is encased in the skull and surrounding tissue is very fragile, so it is difficult to physically fix anything
  • The brain is so complex so it is difficult to fix with drugs and chemicals
• Light enters through cornea -> passes through lens -> hits retina -> light sensitive cells called rods and cones send electrical impulses along optic nerves -> these signals are processed in the brain -> image formed
• When light first hits the eye, it meets the cornea. It is completely transparent, so has no blood vessels. This means that light can pass through and all the oxygen it needs has to diffuse into it from the outside air. The cornea causes all light to refract.
• The iris is the coloured bit of your eye. It controls how big or small your pupil is. The pupils is gap in the middle of the iris which allows light to pass through into the lens
• The lens can change its shape, so can control how strongly it refracts light. This allows it to focus light perfectly on the retina
• The retina is made from 2 different types of receptor cells:

  1. Cone cells, which are sensitive to the colour of light. But, they don't work well in low light levels
  2. Rod cells, which are more sensitive to light, but only allow us to see in black and white
• The fovea is a spot on the retina that contains only cone cells, this is the region we try and focus light on as it allows us to see more clearly
• The optic nerve takes all of the impulses generated by receptor cells and transmits them to the brain
• Iris Reflex:

  • Bright light levels can cause damage to your retina, so iris is constricted. Circular muscles contract, radial muscles relaxed
  • Low light levels, iris is dilated. Circular muscles relax, radial muscles contract

  
• A=Pupil

  B=Suspensory ligament

  C=Cornea

  D=Iris

  E=Blind spot

  F=Ciliary muscles

  G=Retina

  H=Optic nerve

  I=Lens

  J=Fovea

  K=Sclera

  A) A

  B) C

  C) B

  D) D

  E) E

  F) F

  G) G

  H) H

  I) I

  J) J

  K) K

  
• Close objects need to be refracted a lot, the lens needs to be short and fat so it is more curved and therefore refract more strongly. The ciliary muscle must contract while the suspensory ligaments slacken
• Distant objects don't need to be refracted as strongly, the lens must become less curved. So, the ciliary muscle relaxes and pulls the suspensory ligaments taut, causing the lens to stretch out
• Long-sightedness is when the lens can't refract enough and is unable to focus on nearby objects. We call this hyperopia. We can fix this by using glasses with convex lenses
• Short-sightedness is when the lens refracts too much and is unable to focus on distant objects. We call this myopia. We can fix this by using glasses with concave lenses
• Thermoregulation is the process of maintaining a constant body temperature in response to internal and external conditions
• Our body tries to maintain 37°C as it is the optimum temperature for our enzymes to function at
• The thermoregulatory centre is located in the hypothalamus and acts as a thermostat for our body
• Warming up:

  1. Constrict blood vessels close to skin, vasoconstriction-to conserve heat, less heat energy lost
  2. Contract erector muscles, makes our hairs stand on end, layer of insulating air
  3. Shivering, muscles contract automatically, energy from respiration, heat energy released as waste
• Cooling down:

  1. Expand blood vessels close to skin, vasodilation-more heat energy transferred to surroundings
  2. Erector muscles relax, hairs stand down, no layer of insulating air
  3. Produce sweat, evaporates and takes heat energy away with it
• The endocrine system is made up of glands that secrete hormones into the bloodstream
• The pituitary gland produces many different hormones which tell the body what to do or tell other glands to release their hormones