Homeostasis and response

• Homeostasis: Maintaining a stable internal environment.

  Homeostasis is all about the regulation of the conditions inside your body and cells to maintain a stable internal environment in response to changes in both internal and external conditions; your automatic control systems keep your internal environment stable using a mechanism called negative feedback
• Negative Feedback: A process that reduces or stops change by acting against it.
• The nervous system detects and reacts to stimuli:

  Central nervous system: in vertebrates this consists of the brain + spinal cord only; in mammals the CNS is connected to the body by sensory + motor neurones

  Sensory Neurones: The neurones that carry information as electrical impulses from the receptors to the CNS

  Motor neurones: The neurone that carries electrical impulses from the CNS to effectors.
• Effectors: All your muscles and glands which respond to nervous impulses
• Receptors and effectors can form part of complex organs: Receptors are cells that detect stimuli. eg: retina of the eye, is covered in light receptor cells. Effectors respond to nervous Impulses and bring about a change. eg: Muscles and glands. (Muscles contract in response to a nervous Impulse, whereas glands secrete hormones)
• Synapses connect neurones: The nerve signal is transferred by chemicals which diffuse across the gap. These chemicals then set off a new electrical signal in the next neurone.
• Reflexs help prevent injury. Reflex’s are rapid automated responses to certain stimuli that don't involve the conscience part of the brain
• The reflex arc goes through the central nervous system:

  1. Bee stings finger
  2. stimulation of pain receptors
  3. Impulses travel along a sensory neurone
  4. Impulses are passed along a relay neurone via a synapse
  5. Impulses travel along a motor neurone via a synapse
  6. when impulse meets muscle it contracts

  Because you don't have to think about it, is quicker than normal.
• Reaction time can be Measured using a computer: Computers can give a more precise reaction time because they remove the possibility of human error from the measurement as the computer can also remove the possibility that the person can predict when to respond - using the ruler test, the catcher may learn to anticipate the drop by reading the testers body language
• The eye:

  Sclera: tough supporting wall

  Cornea: transparent outer layer -refracts light into eye.

  Iris: controls how much light enters the eye.

  Lens: focuses the light onto the retina

  Capillary muscles + suspensory ligaments: control shape of lens

  Optic nerve: carries impules from the receptors on the retina to the Brain
• Focusing on Near + Distant objects - Reflex:

  The eye focusses light on the retina by changing the shape of the lens - accommodation

  To look at Near object:

  1. Ciliary muscles contract which slackens The suspensory ligaments
  2. The lens becomes More curved
  3. increases the amount by which it refracts lightTo look at Distant objects:

  To look at Distant objects:

  1. ciliary Muscles relax which allows the Suspensory ligaments to pull tight
  2. Makes the lens less curved.
  3. refracts Light by a smaller amount
• some people are long sighted: (hyperopia)

  long sighted people are unable to focus on near objects:

  1. occurs when the lens is the wrong shape + doesn't refract the light enough or the eyeball is too short
  2. The images of near objects are brought into focus behind the retina
  3. glasses with a convex lens to correct it.
  4. lens refract the light rays so they focus on the retina
• some people are short-sighted: (myopia)

  short sighted people are unable to focus on distant objects:

  1. Occurs when the lens is the wrong shape and refracts the light too much or the eyeball is too long.
  2. Images of distant objects are brought into focus in front of the retina.
  3. you can use glasses with a concave lens to correct it so that the light rays can focus on the retina
• There are several Treatments for vision Defects:

  1. contact lenses: lightweight and almost invisible.There are two types; Hard lens + soft lenses. (soft lenses are generally more comfortable but carry a higher risk of eye infections then hard lenses.)
  2. laser eye surgery: A laser can be used to vaporise tissue; changing the shape of the cornea.
  3. replacement lens surgery: the natural lens of the eye is removed and an artificial lens, made of clear plastic is inserted in its place.
• Controlling body Temperatures

  The body has to keep its insides at around 37°c - the optimum temperature for enzymes

  1. Body temperature must be kept constant: the body has to balance the amount of energy gained and lost to keep the core body temperature constant.
  2. Thermoregulatory centre in the brain contains receptors that are sensitive to the temperature of the blood flowing through the brain.
  3. The thermoregulatory centre also receives impulses from temperature receptors in the skin, giving information about skin temperature.
• When you're too hot:

  1. Hairs lie flat.
  2. Sweat is produced by the sweat glands and evaporates from the skin. This transfers energy to the environment.
  3. The blood vessels supplying the skin dilate so more blood flows close to the surface of the skin. This is called Vasodilation. This helps transfer energy from the skin to the environment
• When you're too cold:

  1. Hairs stand up to trap an insulating layer of air
  2. No sweat is produced.
  3. blood vessels supplying skin Capillaries constrict to close of the skins blood supply. This is called vasoconstriction.
  4. When you're cold you shiver too. This needs respiration, which transfers some energy to warm the body
• The Brain:

  we know that different regions of the brain carry out different (functions)

  1. Cerebral cortex: its responsible for things like conscience, intelligence, Memory and language
  2. Medulla: controls unconscious activities like breathing and your heartbeat.
  3. Cerebellum: responsible for Muscle co-ordination.

  Messing with the Brain can have consequences:

  The brain is incredibly complex and delicate: the investigation of brain functions and any treatment of brain damage or disease is difficult. It also comes risks, physical damage or increased problems with brain function.