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Richard Ennis

25 September 2012 NEUROPSYCHOLOGY THE NEURON A single cell that is responsible for much of what happens in our brain (thoughts, feelings, and actions). Three parts: 1) Soma – The nucleus of the cell body. 2) Dendrites – Branch-like fibres that come out of the cell body and between neurons. 3) Axon – Elongated part that comes out of cell body; varies in size. Ends of them have terminal endings.  Information comes into the neuron from the dendrites (this process is called afferent).  Information leaves the neuron through the axon (this process is called efferent). Three kinds: 1) Sensory neurons – Carry messages from tissues/sensory organs inwards to brain and spinal cord.  Sensation process (taking the environment in) is an afferent process  Its dendrites are outside the central nervous system while axons are inside it  2-3 million sensory neurons 2) Motor neurons – Efferent process – information leaves the neuron through the axon  Allows us to perform actions by sending message to muscles  Dendrites are in the central nervous system while axons are in the muscles and glands  2-3 million 3) Interneurons – Between sensory input and motor output, information is processed in brain's internal communication system via interneurons  Exist entirely the central nervous system  Have no connections to sensory processes or muscles; only have contact with other neurons  10-100 billion Neuronal Conduction THE E LECTRICAL COMPONENT  Electrical charge travels down neuron's axon to transmit messages (called action potential).  Opposition said that a slight electrical charge would activate all the neurons instead of sending a message to one specific neuron. THE C HEMICAL C OMPONENT  The way neurons communicate is solely chemical.  Galvani: Italian physicist believed in electrical theory o Experimented using a dead frog, attached a wire to its legs and passed direct current through frog's legs and saw that it would jump.  Loewi: tried to do an experiment to prove it was only chemical. o Filled a beaker with distilled water, took a freshly removed heart from a frog and put it in the water, attached electrode to heart and passed electrical stimulus through it, and the heart started beating. o In a second beaker, he had a second heart without water or electricity; he poured the water from the first beaker into the second one and that one began beating (chemicals in distilled water). After Transmission - 1950s: British neurologists theorized neuron communication is both electrical and chemical. Neurotransmitters  The meeting point between neurons is called a synapse; dendrites and axons don't quite touch, but are separated by synapses.  When action potential reaches the terminals at the end of an axon, chemical messengers are released (neurotransmitters). o These messengers close the gap for a split second, and then the sending neuron reabsorbs the excess neurotransmitters (this process is called reuptake).  Excitatory signals must overtake inhibitory signals to trigger an action potential. 25 September 2012  Neurotransmitters can control depression, euphoria, hunger, addiction, etc.  Our brain naturally produces opiates in response to pain and vigorous exercise – these are called endorphin
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