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Neural Activity - Relationships with Behaviour - Psych Lecture October 5th 2011.docx

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Iuliana Baciu

th Neural Activity: Relationships with Behaviour: Psych Lecture Oct. 5 , 2011 Nervous System: Function  Info processing  Communication syst.  Behaviour as a response to environment and as changing environment Nervous System: Anatomy  Signals are received, transmitted, and integrated  Nervous tissue  Neurons – info processing o Communicate with other neurons, with receptors from sensory organs, and with skeletal muscles  Glia – provide support for neurons and… (recent research) Neuron:  Anatomy:  Soma (cell body) with nucleus and chemical apparatus that cells need for their maintenance  Dendritic trees – specialized in receiving info  Axon – specialized in sending away info to other neurons, muscles, glands The Axon:  Wrapped in myelin sheath between Ranvier nodes, which speeds up transmission of electrical signals along axon  Ends up in terminal buttons, which secrete neurotransmitters (chemical messengers that may activate other neurons)  Meets with a dendrite or other cells through synapses, where info is transmitted from a neuron to the other Synaptic Transmission:  Specific neurotransmitter can bind only to receptor sites that its molecular structure will fit into (key in a lock). Therefore, neurotransmitter fits and can bind to postsynaptic membrane at receptor sites at left, but not at other sites. Exceptions:  Not all neurons have an axon, and other neurons have multiple axons  Synapses can be between an axon and a soma or another axon, not only between an atom and a dendrite Glia:  Outnumber neurons, account for more than 50% of brain volume  Helps with supplying nourishment to neurons and with removing the waste  Provides insulation around axons (myelin sheaths are a form of special glial cells)  Role in organizing development of NS in the embryo Glia – Recent Research:  Receive and send chemical signals (Fields, 2004)  Role in memory formation (Bains & Oliet, 2007)  Role in experiencing chronic pain (Banks & Watkins, 2006)  Deterioration: Alzheimer’s disease (Streit, 2005)  Role in amyotrophic lateral sclerosis and Parkinson’s disease (Lobsiger & Cleveland, 2007)  Impaired glial-neural communication may lead to schizophrenia (Hashimoto et al., 2005) and mood disorders (Lee et al., 2007) Neural Activity – Neurons and How They Work – Video (Mcgraw-Hill):  Neurons don’t touch each other – synapse (gap) in between  *neuron networks*  There are 100 billion neurons in the brain  2/3 of all neurons live in cortex (newer part of brain; controls senses, thoughts)  Ions create electrical potential  Serotonin, adrenaline, substance p, morphine, ect. Neural Impulse: Neuron at Rest:  Ions (electrically charged atoms and molecules) floating inside and outside the neurons -  Cell membrane permits movement through it of some ions (semi-permeable): Na+, K+, Cl , but these ions don’t cross at the same rate  Inside the cell there is a higher concentration on negatively charged ions (Cl )  Neuron at rest is charged negatively (resting potential) (battery) Action Potential:  Neuron is stimulated  the membrane becomes permeable to positive ions that go inside the neuron  An action potential = shift in electrical charge of the neuron; it travels along the axon  The membrane becomes semipermeable again and it needs time to become permeable to positive ions after an action potential (= absolute refractory period, ARP)  This ARP is followed by a relative refractory period: the neuron can fire only for more intense stimulation (higher threshold) The All-or-None Law:  Neuron’s action potentials are all the same size  The stimulation has to reach a certain threshold to produce an action potential (weaker stimuli – no action potential)  Info about the strength of a stimulus – by varying the rate of firing action potentials (for stimuli that reached the threshold)  Speed of neural impulse varies with the thickness of the axon (thick axons – faster impulses) Impulse Transmission: The Synapse:  Neurons in synapse: synaptic cleft (gap)  The impulse has to cross this gap for neurons to communicate  Action potential at terminal buttons  release of neurotransmitters from synaptic vesicles  Neurotransmitters diffuse across synaptic cleft to the membrane of the receiving cell  Neurotransmitters bind with special molecules (not with all) at the receptor site Postsynaptic Potential:  When a neurotransmitter and a receptor molecule bind  voltage change  Do not follow the all or none law, but are graded (vary in size, increasing and decreasing the probability of a neural impulse as a function of voltage change) Types of Messages:  Inhibitory – negative voltage shift, decreases the likelihood of an action potential from the postsynaptic neuron  Excitatory – positive voltage shift that increases the likelihood that the postsynaptic neuron will
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