homeostasis

• the structure of the nervous system:

  1. receptor cells convert a stimulus into an electrical impulse
  2. this impulse travels along sensory neurons to CNS
  3. the information is processed and an appropriate response is coordinated as an electrical impulse sent along motor neurones to effectors
  4. the effectors carry out the response
• reflex arc:

  1. a stimulus is detected by receptors
  2. impulses sent along sensory neurone to spinal cord
  3. in the spinal cord the impulse passes to a relay neurone
  4. impulses are sent along a motor neurone
  5. the impulse reaches an effector resulting in appropriate response
• synapses are the gaps between the two neurons where neurotransmitters are diffused across to continue electrical impulses
• Cerebral cortex: controls consciousness, intelligence, memory and language

  Cerebellum: controls fine movement of muscles

  Medulla: controls unconscious actions such as breathing and heart rate

  
• Why is investigating brain function and treating brain damage difficult?


  • it is complex and delicate
  • it is easily damaged
  • drugs given to treat disease don’t always reach the brain due to membranes that surround it
  • it is not fully understood what parts of the brain do what
• How do neuroscientists map out the regions of the brain?

  • studying patients with brain damage
  • electrically stimulating different parts of the brain (using an electrode) but this can cause mental or physical changes in the individual
  • using MRI
• the retina is a layer of light sensitive cells (rods and cones) which send impulses to the brain when stimulated
• the optic nerve leaves the eye and leads to the brain, it carries impulses from the retina to the brain to create an image
• the sclera is the white outer layer which supports the structures inside the eye, it is strong to prevent damage
• the cornea is transparent layer at the front of the eye which allows light through, the curved surface bends and focuses light onto the retina
• the iris is made up of circular and radial muscles that contract or relax to alter the size of the pupil.
• What do the muscles in the iris do to adjust to bright light?

  The circular muscles contract and the radial muscles relax to make the pupil smaller, to avoid damage to the retina.
• What do the muscles in the iris do to adjust to dim light?

  The circular muscles relax and the radial muscles contract to make the pupil large, so more light can enter to create a better image.
• To focus on a near object (accommodation)?

  1. The ciliary muscles contract
  2. Suspensory ligaments slacken
  3. The lens is then thicker and more curved to refract the light more
• To focus on a distant object (accommodation)?

  1. The ciliary muscles relax
  2. Suspensory ligaments tighten
  3. The lens then becomes thinner, refracting light less
• 
  
• type 1 diabetes:

  1. pancreas cannot produce enough insulin
  2. glucose is excreted with urine, lots of urine produced leaving person thirsty

  treatment:

  1. insulin injections at meal times
  2. advised to limit intake of simple carbohydrates (diet)
  3. attempting pancreatic cell transplants
• type 2 diabetes:

  1. body no longer responds to insulin
  2. obesity and age is a risk factor

  treatment:

  1. reducing simple carbohydrates in diet
  2. losing weight
  3. increasing excersise
• maintaining water balance:

  1. if water concentration of the blood increases then cells in the body take up water
  2. as concentration of water in bloodstream is higher than concentration in cells, so water moves into cells by osmosis
  3. cells then expand as they take up more water, may eventually burst
• maintaining water balance:

  1. if water concentration of the blood decreases then cells in the body lose water
  2. as the concentration of water in the bloodstream is lower than the concentration of water in cells
  3. so water moves out of cells by osmosis, so they shrink
• testosterone:

  • main male reproductive hormone
  • produced by the testes
  • stimulates sperm production
• FSH (follicle stimulating hormone)

  • causes maturation of an egg in the ovary, within a follicle
  • produced in the pituitary gland
  • stimulates the ovaries to produces oestrogen
• oestrogen:

  • causes the lining of the uterus to grow again
  • produced in ovaries
  • secreted due to FSH
  • stimulates production of LH and inhibits secretion of FSH
• LH (luteinising hormone)

  • produced in pituitary gland
  • produced as a result of oestrogen
  • releases steroid in ovulation
• in the kidneys, blood is ultrafilterated of urea, water and salts into the nephron tubule; blood cells and proteins remain in blood as they are too big to move across capillary walls. then selective reabsorption occurs of useful substances back into blood stream, so all urea, excess salts and excess water is left in the tubule to form urine.
• amino acids are the products of the digestion of protein, which are deaminated in the liver to form ammonia. ammonia is toxic so the body converts it to urea for safer storage.
• adh (anti-diuretic hormone) is involved in controlling the loss of water as urine
• ADH:

  • released from pituitary gland into pancreas when a brain receptor detects blood is too concentrated
  • how: travels through bloodstream to tubules, increases permeability of tubules to water so more reabsorbed from the tubule and back into blood
  • results in a smaller volume of more concentrated urine and less concentrated blood
  • example of negative feedback loop