topic 5

• homeostasis is regulation of a stable internal environment
• cells need the correct conditions to be able to properly function
• the body has an automatic response system which includes a receptor, co-ordination centre and effector
• organisms need to react to stimuli
• single celled organisms can just respond to the environment
• multicellular organisms need to communicate and have developed a nervous and hormonal system
• the central nervous system consists of the spinal chord and brain - it is connected with a sensory and motor neurone
• a motor neurone sends electrical impulses from the CNS to the effector
• a sensory neurone sends electrical impulses from the receptor to the CNS
• effectors are all the muscles and glands that respond to nervous impulses
• receptors are cells that detect stimuli
• effectors are cells that co-ordinate a response
• the synapse is the gap between 2 neurones
• electrical impulses are transferred by chemicals which diffuse across the synapse and the chemicals set off a new electrical impulse in the other neurone
• reflexes are a rapid and automatic response that dont include the conscious part of the brain
• the passage of information in a reflex is called a reflex arc
• stimuli is detected by receptors which send electrical impulses up the sensory neurone which meets the relay neurone at a synapse where chemicals diffuse across, impulses run through relay neurone to the synapse at the motor neurone, motor neurone sends electrical impulses to effectors
• neurones in reflex arc go through spinal chord or unconscious brain
• investigating reaction time

  1. place arm at the edge of a table with your hand hanging over the edge
  2. hold a ruler vertically level with 0cm against the persons hand
  3. drop the ruler with no warning
  4. measure distance moved
  5. repeat and find mean
• a more precise way to measure reaction time would be using a computer and clicking a mouse, this would reduce human error and give a more accurate number
• the cerebral cortex is the outer wrinkly layer of the brain and controls conscious activities like your memory and language
• the medulla controls the unconscious part of the brain like breathing
• the cerebellum controls muscle co-ordination
• studying the brain

  1. MRI scan
  2. looking at brain damage
  3. electrically stimulating
• we can use brain damage to study the brain as we can see which parts of the brain effects different things
• we can use MRI scans to study the brain as it shows us a detailed image of the brain so we can see which parts of the brain are active while doing tasks like listening to music and recalling memory
• electrically stimulating the brain is when small electrodes are pushed into the tissue and a small zap of electricity in sent - the effect shows us what that part of the brain does
• if you send an electric impulse in motor area it will cause the muscles to move
• messing with the brain can lead to loss of speech
• electric impulses can help reduce muscle tremors caused by nervous system disorder like parkinsons disease
• the sclera is the white tough supporting wall
• the cornea is the transparent layer that refracts light into the eye
• the retina contains receptor cells which are light sensitive
• the ciliary muscle and suspensory ligament control the shape of the lens
• the iris is a muscle that controls the diameter of the pupil
• the lens focuses light onto the eye
• the optic nerve carries receptor cells from sensitive retina to brain
• light receptors detect a very bright light causing a reflex action to be triggered meaning the circular muscles contract and the radial muscle relax this allows less light to enter the eye
• near objects


  ciliary muscle contracts and suspensory ligament slackens, making lens become fat - more light is refracted
• distant objects 


  suspensory ligament contracts and ciliary muscle slackens, causing lens to become thin - less light is refracted