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The Nervous System

  • The Nervous System sends messages using nerve cells or neurons which produce a quick response - nerve impulse- which is electrical. Also has specialised organs - brain & spinal cord
  • The Central Nervous System (CNS) consists of the brain and spinal cord. The CNS is connected to the Peripheral Nervous System (PNS) - sensory and motory neurones
  • Sensory Neurones connect receptors which detect changes in the environment - stimuli
  • Motor Neurones connect the CNS to effectors - muscles - which produce a response
  • In the hormonal system responses are slower and longlasting. Insulin produced by pancreas. Acts on liver, muscles and body cells to take up glucose from blood
  • Neurons are cells specialised for carrying nerve impulses
  • Neurons consist of the cell body which consist of the nucleus and a long axon
  • Axons carry impulses away from the cell body to other nerves and muscles
  • Some axons are cover with an insulating fatty sheath called the myelin sheath
  • Speed of the nerve impulse is affected by:
  • Temperature - faster in warm-blooded animals 
  • Diameter - the wider the axon, the quicker the response
  • Myelin Sheath - presence speeds up the nerve impulse.
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Linking Nerves Together

  • Synapses - small gap between one neuron and the next 
  • As nerve impulse reaches the end of the nerve, it is changed to a chemical signal, which crosses the synapse and sets up an electrical impulse in the next neuron
  • As the nerve impulses reaches the end of the first neuron, a chemical transmitter substance is released
  • Transmitter diffuses across the synapse and binds with receptor molecules on the membrane of the next neuron, triggering a nerve impulse in the next neuron
  • After impulse has been transmitted, chemical transmitter is removed from the synapse (taken back up by neuron or broken down by enzyme)
  • Nervous system responds to changes in the environment called stimuli
  • Stimuli detected by receptors
  • CNS coordinates the response which is made by an effector - glands and muscles
  • Glands make and release chemicals such as enzymes and hormones 
  • Muscles used for movement. Their contraction helps body to move away from dangerous stimuli and towards pleasant ones.
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  • Refelexes are involuntary, rapid and automatic e.g. removing foot automatically away from sharp object. Simple reflexes improve chance of survival
  • Pathway of a reflex action through the nervous system is called the reflex arc
  • Reflexes enable us to respond quickly to stimuli that could harm us:
  • Dropping a hot object, knee-jerk reflex, pupil reflex
  • Baby reflexes: stepping, grasping, sucking
  • Responses are rapid as they use fixed pathways which do not involve the brain making a consious decision. Relay Neurons in the CNS connct with other neurons which run to the brain so we:
  • Know what's happened after reflex action has occured
  • Override an action, e.g. keeping hold of a hot plate when you'd rather not drop it
  • The brain sends a message to motor neurons, which changes the response of the muscles in your hand so you keep hold of the object.
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  • Animals have certain behaviours that help them survive in their environment, both instinctive and learned
  • Instinctive behaviours are controlled by reflex responses. Simple animals have simple nervous systems so cannot learn behaviours
  • A reflex response to a stimulus can be learned by introducing an unrelated stimulus in association with the first. This is known as conditioning
  • Pavlov studied  the behaviour of dogs and noticed they would salivate in response to the smell, sight and taste of food.This is a simple reflex in response to a primary stimulus. A bell was rung before giving dogs food. The dogs salivated  when the bell was rung, even if they couldn't smell the food. They had learned to associate the sound of the bell (secondary response) with the food. The final response has no direct connection to the secondary stimulus
  • Watson's study with eight month old Albert. He like and showed no fear of a white lab rat. He was then shown the rat while Watson made a loud noise which made Albert cry. Later, Albert cried when shown the rat, even if there was no loud noise.
  • Conditioned reflexes help animals survive e.g. association of a plant's bright colours with the fact it's poisonous helps animals avoid it and survive.
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The Brain & Learning

  • The cerebral cortex is involved with intelligence, memory, language and consiousness. A large number of folds increases our ability to process information
  • Neuroscientists map the regions of the brain using invasive and non-invasive methods
  • Invasive methods include studying how a person is affected when a certain part of the brain is damaged; during brain surgery, using electrodes to stimulate parts of the brain electrically and see how patients are affected
  • Non-Invasive methods include producing images and mapping activity with scanning techniques (MRI) These are useful in: 
  • Comparing non-diseased brains with the brains of people with brain disease
  • Looking at activity in the brain when it's stimulated by music, language or images
  • Transmitting impulses in the brain leads to links forming between the neurons (neuron pathway)
  • If experience is repeated, more impulses follow the same pathway, causing it to strengthen. Also strengthened by strong stimuli such as colour, light, smell and sound
  • Learning results from experience where: new neuron pathways form and other pathways are lost; certain pathways in brain more likely to transmit impulses than others
  • Children not presented with appropriate stimuli or those isolated, may not progress in learning e.g. feral children
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  • Memory is the storage and retrieval of information. Short term memory involves info from most recent experiences. Long term memory involves info from earliest experiences onwards that can be stored for a long period of time.
  • You are more likely to remember info if there is a pattern to it. You can use repetition to also remember certain information along with strong stimuli such as colours, strong smells or loud sounds
  • The multi-store model splits memory into sensory memory, STM memory and LTM memory and shows how they work together. If info arrives in a memory store and is not passed or retrieved, the info lost i.e. forgotten
  • Models are limited in explaining how memory works as: memory is more complicated; no models have exact explanation of how LTM works; multi-store model is too linear and doesn't provide subdivisions of STM and LTM; the model does not differentiate between different types of stimulus and the difference in performance of individuals.



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  • Many drugs and toxins work by affecting the transmission of nerve impulses across synapses, stopping the transmission, changing the speed of the transmission or making the impulse stronger or weaker e.g:
  • The antidepressant Prozac, increases levels of the transmitter substance Serontonin
  • Beta blockers are prescription drigs that block the transmitter molecule adrenaline, so they reduce the heart rate. It is used to treat people with problems with their heart rhythm but some people use them to control anxiety
  • Ectasy (MDMA) works on serontonin. It blocks sites in the brain's synapses where serontonin is removed. Following the transmission of a nerve impulse, the transmitter molecules should be removed from the synapse.
  • MDMA blocks the sites on the neuron where MDMA is reabsorbed, increasing its concentration
  • MDMA therefore gives a feeling of well-being because of increased levels of serontonin
  • After taking MDMA, the brain's serontonin is depleted, so person is irritable and tired
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