B5 - Homeostasis and response

• homeostasis : the regulation of the conditions inside the body
• when the level of glucose and water gets too high or too low the body uses negative feedback to bring it back to normal
• level increase : receptor detects stimulus level is too high, the coordination centre receives and processes the information then organises a response and the effector produces a response which counteracts the change and restores the optimum level. the level decreases.
• level decrease : receptor detects a stimulus level too low, the coordination centre receives and processes the information then organises a response and the effector producer a response which counteracts the change and restores the optimum level. the level decreases
• the effectors will carry on producing the responses for as they are stimulated by the coordination centre. this might cause the opposite problem - making the level change too much. luckily the receptor detects if the level becomes too different and negative feedback starts again
• the nervous system detects and reacts to stimuli
• the nervous system mean that humans can react to their surroundings and coordinate their behaviour
• the central nervous system CNS : brain and spinal cord
• sensory neurones : the neurons that carry information as electrical impulses from the receptor to the CNS
• motor neurones : the neurons that carry electrical impulses from from the CNS to effectors
• effectors : all muscles and glands which respond to nervous impulses
• relay neurone : a neurone that connects sensory and motor together
• receptors are cells that detect stimuli
• effectors respond to nervous impulses and bring about a change
• muscles contract in response to a nervous impulse whereas glands secrete hormones
• the CNS is a coordination centre it receives information from receptors and then coordinates a response. the response is carried about by effectors
• stimuli, receptor, sensory neurone, CNS, motor neurone, effector, response
• the connection between two neurones is called a synapse. 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
• reflexes : are rapid, automatic response to certain stimuli that do not involve the conscious part of the brain
• reflex arc

  A) stimulation

  B) sensory neurone

  C) impuses

  D) relay neurone

  E) motor neurone

  F) synapse

  G) contracts

  
• Reflex arc

  1. Stimulus detected by receptors

  2. Impulses sent along sensory neurone to relay neurone in CNS

  3. Chemicals released at synapse between sensory and relay neurone

  4. Impulses sent along relay neurone

  5. Chemicals released at synapse between relay and motor neurone

  6. Impulses sent along motor neurone

  7. Muscle contracts and moves hand away
• Neurones in reflex arc

  • Go through spinal cord or unconscious part of brain
• Impulses are sent along a sensory neurone to a relay neurone in the CNS
• Chemicals are released at the synapse between the sensory neurone and the relay neurone, causing impulses to be sent along the relay neurone
• Chemicals are released at the synapse between the relay neurone and the motor neurone, causing impulses to be sent along the motor neurone
• Impulses travel along the motor neurone to the effector
• The muscle contracts and moves the hand away from the bee
• when out of the corner of its eye it spots a cat skulking towards it (stimulus) . the receptors in the birds eye are stimulated. sensory neurones carry the information from the receptors to the CNS. the CNS decides what to do about it. the CNS sends information to the muscles in the birds wings ( the effectors) along motor neurones. the muscles contract and the bird flies away safety
• reaction time : time taken to respond to a stimulus but can be affected by age drugs and alcohol
• RULER DROP TEST REQUIRED PRATICAL : person should sit with their arm resting on the table. hold a ruler vertically between their thumbs. then let go without warning reaction time is measured by the number on the ruler where it is caught. the higher the number the slower the reaction time. repeat several times to calculate a mean. the repeat the test but with caffeine the reaction time should be faster.
• hormones are chemical molecules released directly into the blood. they are carried in the blood to other parts of the body but only affect particular cells in particular organs. hormones control things in organs and cells that need constant adjustment
• hormones are produced by various glands called the endocrine system
• pituitary gland : located in the head. produces many hormones that regulate body conditions. it is something called the master gland because these hormones act on other glands directing them to release hormones that bring about change
• thyroid gland : located in the lower neck. produces thyroxine which is involved in regulating things like the rate of metabolism, heart rate and temperature
• adrenal gland : produces adrenaline which is used to prepare the body for a fight or flight response
• ovaries : produces oestrogen which is involved in the menstrual cycle
• pancreas : produces insulin which is used to regulated blood glucose levels
• testes - produces testosterone which controls puberty and sperm production in males
• nerves : very fast action, for a short amount of time and acts on very precise areas
• hormones : slower at acting, act for a long time and act in a more general way