Ionotropic Receptors Postsynaptic potentials
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Postsynaptic potentials Depending on the type of ion channel which opens, the postsynaptic cell membrane becomes either depolarized or hyperpolarized. Ions will tend to follow the concentration from high to low concentration, and the gradient electrostatic gradient towards the opposite charge. Excitatory postsynaptic potentials (EPSPs) Opening of ion channels which leads to depolarization makes an action potential more likely, hence “excitatory PSPs”: EPSPs. Inside of post-synaptic cell becomes less negative. Na+ channels (NB remember the action potential) Ca2+ . (Also activates structural intracellular changes -> learning.) Inhibitory postsynaptic potentials (IPSPs) Opening of ion channels which leads to hyperpolarization makes an action potential less likely, hence “inhibitory PSPs”: IPSPs. Inside of post-synaptic cell becomes more negative. K+ (NB remember termination of the action potential) Cl- (if already depolarized) Postsynaptic Ion motion Neuronal firing: the action potential The action potential is a rapid depolarization of the membrane. It starts at the axon hillock and passes quickly along the axon. The membrane is quickly repolarized to allow subsequent firing. Requirements at the synapse For the synapse to work properly, six basic events need to happen: Production of the Neurotransmitters Storage of Neurotransmitters Release of Neurotransmitters Binding of Neurotransmitters Generation of a New Action Potential Removal of Neurotransmitters from the Synapse Arvid Carlsson discovered dopamine is a neurotransmitter. Carlsson also found lack of dopamine in the brain of Parkinson patients. Paul Greengard studied in detail how neurotransmitters carry out their work in the neurons. Dopamine activated a certain protein (DARPP-32), which could change the function of many other proteins. Eric Kandel proved that learning and memory processes involve a change of form and function of the synapse, increasing its efficiency. This research was on a certain kind of snail, the Sea Slug (Aplysia). With its relatively low number of 20,000 neurons, this snail is suitable for neuron research. Overview Course introduction Neural Processing: Basic Issues Neural Communication: Basics Vision, Motor Control: Models Motor Control Basics Reflex Circuits Usually Brain-stem, spinal cord based Interneurons control reflex behavior Central Pattern Generators Cortical Control Hierarchical Organization of Motor System Primary Motor Cortex and Premotor Areas Primary motor cortex (M1) science-education.nih.gov Flexor- Crossed Extensor Reflex (Sheridan 1900) Reflex Circuits With Inter-neurons Gaits of the cat: an informal computational model The discovery of mirror neurons in the frontal lobes of monkeys, and their potential relevance to human brain evolution — which I speculate on in this essay — is the single most important "unreported" (or at least, unpublicized) story of the decade. I predict that mirror neurons will do for psychology what DNA did for biology: they will provide a unifying framework and help explain a host of mental abilities that have hitherto remained mysterious and inaccessible to experiments. Ramachandran, Reality Club Lecture 2001 What are mirror neurons? What is the promise? Why the excitement? What challenges are faced in fulfilling that promise? F5 mirror neurons Shared goal-simulation = Action understanding Representations in the premotor cortex (Rizzolatti et al). Shift from thinking about movement representations to action representations. Neurons in F4, F5 coding action primitives such as grasping, pinching, pulling A Grasping with the mouth B Grasping with the cl. hand C Grasping with the ipsil. hand Goal-related neuron in area F5 90’s: Shift to perceptual responses of F5 neurons Three classes of neurons 1. movement/action neurons Respond only when animal moves 2. “canonical” neurons Respond when object is presented alone 3. mirror neurons Respond when observing action towards object. Same neurons activated during production and perception of an action. A: Effective Action B:Mimicked Action C: Action with tool Gallese et al. Brain 1996 Umiltà et al. Neuron 2001 A: Full vision to object B: Hand fades C: Full vision, no object D: Hand fades, no object Audio-Visual Mirror Neurons Kohler et al. Science (2002) Vision+Sound Vision alone Sound alone Movement Murata et al. J Neurophysiol. 78: 2226-2230, 1997 The fronto-parietal networks The F5c-PF circuit Links premotor area F5c and parietal area PF (or 7b). Contains mirror neurons. Mirror neurons discharge when: Subject (a monkey) performs various types of goal-related hand actions and when: Subject observes another individual performing similar kinds of actions Somatotopy of Action Observation Buccino et al. Eur J Neurosci 2001 MEG study comparing pianists and non-pianists. Pianists show activation in primary motor cortex when listening to piano. Activation is specific to fingers used to play the notes. Colored region: MEG signal for pianists minus non-pianists. Vision Physiology of Color Vision © Stephen E. Palmer, 2002 Cones cone-shaped less sensitive operate in high light color vision Rods rod-shaped highly sensitive operate at night gray-scale vision Two types of light-sensitive receptors The Microscopic View No stimuli: Stimuli in center: ON-center-OFF-surround fires rapidly OFF-center-ON-surround doesn’t fire Stimuli in surround: OFF-center-ON-surround fires rapidly ON-center-OFF-surround doesn’t fire Stimuli in both regions:
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