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Brain and Mind Revision. Stimuli and Responses. In order to survive organisms need to monitor and respond to changes in the environment. A stimulus is any change in the environment. Animals move towards food and away from toxins.

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Stimuli and Responses

  • In order to survive organisms need to monitor and respond to changes in the environment.

  • A stimulus is any change in the environment.

  • Animals move towards food and away from toxins.

  • Plants grow towards light and water and are affected by gravity.


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Receptors and Effectors

  • Receptors receive stimuli.

  • Effectors bring about a reaction.

  • Receptors can form part of complex organs such as the retina of the eye.

  • Effectors can also form complex organs such as a hormone secreting gland or a muscle.


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Central Nervous System

  • Coordination of responses is through neurones linking receptors and effectors via a central nervous system.


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Neurones

  • Neurones are cells where the cytoplasm forms fibres covered in a membrane called an axon.

  • Some axons are covered in fatty sheaths which insulate and speed up impulses.


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Synapses

  • Receptor cells send impulses along sensory neurones to the CNS.

  • There are gaps between neurones called synapses.

  • When impulses reach the end of sensory neurones chemicals are produced that diffuse across the synapse and bind to receptors on the motor neurone.

  • This causes the motor neurone to produce a new impulse.



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Drugs and Synapses

  • Some drugs affect the transmission of impulses across synapses.

  • Drugs such as Ecstasy and Prozac prevent the re-uptake of serotonin by blocking re-uptake channels in the sensory neurone leading to a feeling of well being.

  • Toxins such as curare block the receptors on the motor neurone and prevent transmissions of the impulse across the synapse causing paralysis.


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Simple Reflexes

  • Reflex arcs produce rapid involuntary responses called reflexes.

  • Simple animals rely on reflexes for the majority of responses.

  • These reflexes enable the animal to respond to food, predators, mates etc.

  • The disadvantage of such responses is that they stop the animal responding to new situations.


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Reflex Arcs

Sensory Neurone

Receptor

Synapse

MotorNeurone

Effector


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Conditioned Reflex

  • A new response can be learned by associating a secondary stimulus with a primary stimulus.

  • Pavlov got dogs to associate a bell ringing with food.

  • The dogs then salivated when the bell rang.

  • The secondary response is nothing to do with the primary response.


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Conditioned Reflexes

  • Conditioned reflexes provide advantages

    eg a bird will avoid colourful caterpillars that have an unpleasant taste.

  • The brain can adapt reflexes in certain situations eg holding on to a hot plate.

  • This provides the ability to adapt to new situations.


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Learning

  • Mammals have large brains with billions of neurones.

  • Learning is the formation of neurone pathways.

  • The large number of potential pathways provides the ability to adapt.

  • Strengthening pathways by repetitions helps develop learning.

  • Certain pathways only develop at certain ages, eg learning speech in young children.


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The Brain

  • The cerebral cortex is the part of the brain associated with memory, intelligence, language and conciousness.

  • Three main methods have been used to map the areas of the brain.

    • Patients with brain damage

    • Electrical stimulation of parts of the brain

    • Magnetic Resonance Imaging (MRI)


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Memory

  • Memory can be divided into short-term and long-term.

  • Humans remember information if

    • There is a pattern.

    • There is repetition.

    • There is a strong stimulus asscoiated with the information eg colour, smell.

  • Scientists have produced models for the human memory but these are inadequate.


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