Ionotropic Receptors Postsynaptic potentials Depending on the type of ion channel which opens, the...
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Ionotropic Receptors
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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 gradient from high to low concentration, and the electrostatic gradient towards the opposite charge.
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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.)
inside
outsideNa+ Ca2+
+
-
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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)
K+
Cl- +
- inside
outside
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Postsynaptic Ion motion
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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.
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Requirements at the synapse
For the synapse to work properly, six basic events need to happen: Production of the Neurotransmitters
Synaptic vesicles (SV) Storage of Neurotransmitters
SV Release of Neurotransmitters Binding of Neurotransmitters
Lock and key Generation of a New Action Potential Removal of Neurotransmitters from the Synapse
reuptake
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Overview
Course introduction Neural Processing: Basic Issues Neural Communication: Basics Vision, Motor Control: Models
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Motor Control Basics
• Reflex Circuits– Usually Brain-stem, spinal cord based– Interneurons control reflex behavior– Central Pattern Generators
• Cortical Control
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Hierarchical Organization of Motor System
• Primary Motor Cortex and Premotor Areas
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Primary motor cortex (M1)
Foot
Hip
Trunk
Arm
Hand
Face
Tongue
Larynx
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postsynapticneuron
science-education.nih.gov
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Flexor-Crossed ExtensorReflex(Sheridan 1900)
Painful Stimulus
Reflex CircuitsWith Inter-neurons
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Gaits of the cat: an informal computational model
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Vision and Action
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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
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1. What are mirror neurons?
2. What is the promise? Why the excitement?
3. What challenges are faced in fulfilling that promise?
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F5 mirror neuronsF5 mirror neurons
Gallese et al. 1996
Action observation
Action execution
Shared goal-simulation = Action understandingShared goal-simulation = Action understanding
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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
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AA Grasping with the mouth
BB Grasping with the cl. hand
CC Grasping with the ipsil. hand
Goal-related neuron in area F5Goal-related neuron in area F5
(Rizzolatti et al. 1988)
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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.
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F5 Mirror NeuronsF5 Mirror Neurons
A: Effective Action
B:Mimicked Action
C: Action with tool
Gallese et al. Brain 1996
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Umiltà et al. Neuron 2001
A: Full vision to A: Full vision to objectobject
B: Hand fadesB: Hand fades
C: Full vision, no C: Full vision, no objectobject
D: Hand fades, no D: Hand fades, no objectobject
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Audio-Visual Mirror NeuronsAudio-Visual Mirror Neurons
Kohler et al. Science (2002)
Vision+Sound
Vision alone
Sound alone
Movement
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Murata et al. J Neurophysiol. 78: 2226-2230, 1997
F5 Canonical NeuronsF5 Canonical Neurons
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Rizzolatti et al. 1998
A New PictureA New Picture
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The fronto-parietal networks
Rizzolatti et al. 1998
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F5c-PFF5c-PF
Rizzolatti et al. 1998
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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
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Somatotopy of Action ObservationSomatotopy of Action Observation
Foot ActionFoot Action
Hand ActionHand Action
Mouth ActionMouth Action
Buccino et al. Eur J Neurosci 2001
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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.
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Vision
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Overview of the Visual System
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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
cone
rod
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The Microscopic View
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How They Fire
• No stimuli: – both fire at base rate
• 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:– both fire slowly