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. 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 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. 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. Synapses 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 Receptor Synapse Motor Neurone Effector 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. 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. 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. 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) 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.