Brain and Mind

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Stimuli and Responses

   In order to survive organisms need to
    monitor and respond to changes in the
   A stimulus is any change in the
   Animals move towards food and away
    from toxins.
   Plants grow towards light and water
    and are affected by gravity.
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.
     Central Nervous System

   Coordination of
    responses is through
    neurones linking
    receptors and
    effectors via a central
    nervous system.
   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.
   Receptor cells send impulses along sensory
    neurones to the CNS.
   There are gaps between neurones called
   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.
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.
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.
Reflex Arcs
      Sensory Neurone



                              Motor Neurone

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
   The secondary response is nothing to
    do with the primary response.
Conditioned Reflexes

 Conditioned reflexes provide
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.

   Mammals have large brains with billions of
   Learning is the formation of neurone
   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.
The Brain

   The cerebral cortex is the part of the
    brain associated with memory,
    intelligence, language and
   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)

   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

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