OCR 21st Century B6

Brain and Mind
Reflexes
1. Simple
  1. the simplest animals rely on reflex actions for the majority of their behaviour
    1. these simple reflex actions are involuntary and help to ensure that the simplest animals respond to a stimulus in a way that is most likely to aid their survival, to include finding food, a mate, sheltering from predators and to avoid harmful or extreme environments
      1. E.g. Woodlouse prefer dark damp conditions to prevent water loss and to provide shelter from predators
  2. Newborn reflexes
    1. Rooting reflex- stroke a babies cheeck and itll turn to find foot
      1. Stepping reflex- support a baby under its arms and it will take steps
        Grasping- hold tight onto your finger and grips stronger if you pull away
        Moro reflex- (startle) when jerked or hears a loud noise . Baby brings arms back together, spreads arms and legs and cries
        sucking- to help the baby feed
    2. Adult simple reflexes
      1. Heat reflex- if you touch a hot object, your muscles will contract to pull away from it to avoid burning yourself
        Gag reflex- object touches the back or your throat, you gag to prevent choking
        Pupil reflex- When a bright light shines in your eye, your pupil constricts to prevent light from damaging the sensitive cells in your retina
        Knee jerk reflex- thigh muscle contracts
        Fight/Flight- your secrete adrenaline when your scared to help you fight or run away
        A nerve impulse always takes the same direct route through the reflex arc so no information is processed. This is why reflexes are involuntary and rapid.
a stimulus is a change in the environment of an organism that causes an organism to produce a response
1. A response is an action or behaviour as a result of an organisms exposure to a stimulus
  1. behaviour is everything an organism does; its response to all the stimulus around it.
The nervous systems use electrical impulses for fast, short-lived responses including simple reflexes
1. The nervous system is made up of Neurones, which are nerve cells that transmit electrical nerve impulses when stimulated. They link receptor cells to effector cells.
  1. An axon is a long extension of the cytoplasm in a neurone and is surrounded by a cell membrane. some axons are surrounded by a fatty myelin sheath, which insulates the neurone from neighbouring cells and increases the speed of transmission of a nerve impulse as the impulse can jump between sheaths
    1. Some receptors are made up of single cells, i.e. pain receptors in your skin, but others are grouped together as part of a complex sense organ, for example your eye.
      1. light receptor cells in the retina of the eye trigger nerve impulses which are sent to the brain
The Reflex Arc
1. 1. Receptor cells
  1. 2. Sensory Nerurone-
    1. 3. Central Nervous system
      1. 4. Relay Neurone
        5. Motor Neurone
        6. Effector
        Effectors respond to nerve impulse and bring about a change. Like receptors, effectors can also form part of a complex organs.
        In multicellular organisms, these effectors are muscles or glands. Nervous or hormonal communication systems have developed as organisms have evolved
        Short term- Muscle cells
        Nerve impulses bring about fast, short-lived responses, e.g. muscle contractions
        Long term- Hormone secreting cells
        hormones are chemicals that are produced in glands, travel in the blood and bring about slower, longer-lasting responses, e.g. insulin and oestrogen
        this arrangement of neurons into a fixed pathway allows reflex responses to be automatic and so very rapid, since no processing of information is required
        The motor neurone carries nerve impulses away from the CNS. They complete the reflex arc by stimulating effectors that carry out a response
        impulses are passed from sensory neurons to motor neurons through relay neurons
      2. The CNS co-ordinates all of the information it receives from your receptors via sensory neurones. information about a stimulus goes either to your brain or spinal cord
        in humans and other vertebrates the central nervous system (CNS) is made up of the spinal cord and brain
    2. The sensory neurone carries the nerve impulses to the CNS from the receptors.
    3. in the mammalian nervous system the CNS (brain and spinal cord) is connected to the body via the peripheral nervous system (PNS) (sensory and motor neurons)
  2. Receptors both inside and outside of the body detect stimuli or changes in the environment.
    1. Examples include: sound, temperature, light, smell, blood sugar and texture
Synapses
1. Neurons do not touch each other, so when nerve impulses pass from one neuron to the next, they have to cross tiny gaps
  1. these gaps are known as synapses and nerve impulses have to be passes across them from one neurone to the next.
    1. 1. An electrical nerve impulse travels along an axon arrives at the synapse
      1. 2. This triggers the nerve-ending of a neurone (presynaptic membrane) to release chemical transmitters called neurotransmitters.
        3. These chemicals diffuse across the synapse
        4. These chemicals bind to receptor molecules on the postsynaptic membrane
        5. The receptor molecules on the second neuron binds only to the specific chemicals released by the first neuron
        6. This stimulates the second neuron to transmit the nerve impulse
2. Drugs and their effects
  1. Serotonin is a chemical that is released into synapses in the brain. An increase in serotonin levels in the synapses makes us feel happier. However, serotonin is normally absorbed by receptor molecules on the other side of the synapse. This prevents the levels of serotonin from increasing.
  2. Prozac is an anti-depressant drug.Prozac causes the concentration of the neurotransmitter, serotonin to build up in the synapse in the brain by blocking the reabsorption of serotonin by the presynaptic membrane. This causes good nerve impulses to be fired down the postsynaptic neuron so you perform happy actions.
    1. Betablockers- nerve impulses stimulate the heart to speed up which can leave the heart painfully starved of oxygen. Beta blockers are drugs that can help people who suffer from angina (chest pain due to a heart condition). They work by blocking the receptor sites on heart muscle cells so impulses from nerves which would speed up the heart are prevented from passing to the heart.
      1. Ecstacy- Ecstasy (also called MDMA) is a drug that blocks the serotonin receptor sites in the synapses in the brain. This prevents the serotonin from being absorbed by the receptor molecules. As a result, the level of serotonin in the synapse increases. This produces a feeling of wellbeing. However, there is evidence to suggest that the use of ecstasy reduces memory and cause damage to the postsynaptic membrane. Ecstasy can also cause severe dehydration which can result in death by suppressing ADH.
The Brain
1. the cerebral cortex is the outer wrinkled part of our brain most concerned with intelligence, memory, language and consciousness
  1. scientists can map the regions of the brain to particular functions (including studies of patients with brain damage, studies in which different parts of the brain are stimulated electrically, and brain scans such as MRI, showing brain structure and activity).
    1. MRI brain scans Modern imaging methods such as MRI (Magnetic Resonance Imaging) scans can show details of brain structure and function. Patients are asked to perform various tasks and, by looking at the scan, scientists can see which parts of the brain are active when the task is carried out. (Active parts have a greater blood flow).
    2. Studying brain damage.
      1. Electrical stimulation-Scientists have stimulated different parts of the brain with a weak electrical current and then asked patients to describe what they experienced. If the motor area is stimulated, the patient makes an involuntary movement which allows scientists to map which muscles are controlled by specififc parts of the motor cortex.. If the visual area is stimulated, they may see a flash of colour.
        Scientists study patients who are partly destroyed by injuries or diseases. By monitoring behaviour and assessing the affected area, scientists can draw consluions about what areas of the brain are responsible for characteristics.
Conditioned Reflexes
1. a reflex response to a new stimulus can be learned by introducing the secondary (new) stimulus in association with the primary stimulus, and that this is called conditioning
  1. When a secondary neutral stimulus becomes a conditioned stimulus new neural pathways are laid down to assoiciate the secondary stimulus with the final response.
    1. conditioned reflexes are a form of simple learning that can increase an animal’s chance of survival
      1. e.g. Bitter tasting caterpillars are usually brightly coloured. A bird that tries to eat one learns that these brightly coloured caterpillars have an unpleasant taste and so after the first experience the bird will avoid eating them, helping caterpillars to survive.If the caterpillar happens to be poisonous, this reflex helps the birds to survive. The colour of the animals is the secondary stimulus.
        In some circumstances, the brain can modify a reflex response. Thi is called conscious control. It does this by sending an impulse from the brain along a motor neurone of the reflex arc. This enables us, for example, to hold onto a hot dinner plate when normally we would drop it.
2. Pavlovs dog
  1. 1. Before conditioning- Pavlovs dog salivated when presented with food. The food is the unconditioned stimulus and salivation is the unconditioned response.
    1. 2. Pavlov rang a bell. This bell was a neutral stimulus and didn't cause the dog to salivate.
      1. 3.Pavlov rang a bell whilst his dog was eating. After a while the dog salivated when the bell was rung. This is a conditioned reflex as Pavlovs dog was conditioned to associate the sound of abell with the arrival of food.
        4. Pavlov would ring the bell even if there was no food and his dog would salivate as it had linked the primary stimulus of food with the secondary stimulus (the bell) to produce the response, salivation. Despite the fact that salivation had no direct connection to the secondary stimulus.
Complex behaviour
1. the evolution of a larger brain gave early humans a better chance of survival i.e. tools or protection and food as well as a language
  1. mammals have a complex brain of billions of interconnected neurones that allows learning by experience, including social behaviour
2. Neurones are connected to form complicated pathways. These pathways develop when a nerve impulse travels along a particular pathway for the first time, from one neurone to the next. This establishes a connection between the neurones. New experiences set up new pathways in the brain.
  1. If the experience is repeated, or the stimulus is strong, more nerve impulses follow the same neural pathway strengthening the connection between the neurones. Repetition strengthens the connections between neurones and makes it easier for impulses to travel along the pathway.
    1. For example learning to ride a bike requires practice and repetition to learn a new set of skills. To do thi you need to create new neural pathways then strengthen thenm through repitition
      1. Visualisation works because thinking about using muscle triggers nerve impulses to that muscle. This strengthens the pathways the impulse takes. After a period of visualisation, the actual movement is easier to perform
    2. strengthened connections are more likely to transmit impulses than others. After about 10 years, the unused pathways die off which is why its difficult for older people to learn new things
  2. Learning is important to an animal's survival. It enables the animal to adapt and survive in new situations. Human babies learn not to touch hot objects, for instance. This helps the baby to survive.
Memory
1. Memory is the ability to store and retrieve information.
  1. Short-term memory lasts for about 30 seconds. If more information arrives than can be held in the short-term memory then some is lost (forgotten). If you're losing your short term memory then you'll forget simple things like the date
    1. Long-term memory may last the whole of your life. When you sing the words of a favourite song, you are using your long-term memory. Although we often complain about how hard it is to learn new things, there is no limit to how much information you can store in your long-term memory.
      1. People with Alzheimer's disease suffer a loss of short-term memory. They may not remember what day of the week it is, but they can remember details of their childhood.
        Individuals with brain damage may lose their long-term memory and even forget who they are, but their short-term memory still works. This shows that the two types of memory must work in different ways.
        humans are more likely to remember information if:
        a. they can see a pattern in it (or impose a pattern on it)
        c. there is a strong stimulus associated with it, including colour, light, smell, or sound
        enconding changes sensory information so that we can understand it
        b. there is repetition of the information, especially over an extended period of time
      2. Rehearsal can move information from your STM to your LTM.
        models are limited in explaining how memory works

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OCR 21st Century B6

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