Ionotropic Receptors Postsynaptic potentials



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Ionotropic Receptors

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.

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
  • outside
  • Na+
  • Ca2+
  • +
  • -

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

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
    • 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

Three Nobel Prize Winners on Synaptic Transmission

  • 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)
  • Foot
  • Hip
  • Trunk
  • Arm
  • Hand
  • Face
  • Tongue
  • Larynx
  • postsynaptic
  • neuron
  • science-education.nih.gov
  • Flexor-
  • Crossed
  • Extensor
  • Reflex
  • (Sheridan
  • 1900)
  • Painful Stimulus
  • Reflex
  • Circuits
  • With
  • Inter-neurons
  • Gaits of the cat: an informal computational model

Vision and Action

  • 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

  • Gallese et al. 1996
  • Action
  • observation
  • Action
  • execution
  • 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
  • (Rizzolatti et al. 1988)
  • 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.
  • F5 Mirror Neurons
  • 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
  • Rizzolatti et al. 1998
  • A New Picture
  • The fronto-parietal networks
  • Rizzolatti et al. 1998
  • F5c-PF
  • Rizzolatti et al. 1998
  • 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
  • Foot Action
  • Hand Action
  • Mouth Action
  • 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

Overview of the Visual System

  • 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

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


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