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Chapter 2 - Principles of Neural Science

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Chapter 2 Principles of Neural Science Synaptic Plasticity and localisation of mRNA translation in axons Nuerobiology

Glial Cells

Functions:
  • Nourishment to neurons
  • Structure
  • Dev — migration cues by radial glia
  • Myelin Sheath
  • Blood Brain Barrier
  • Scavengers
  • Signalling
  • Pre-synaptic terminal control
Types:
Microglia
  • Immune cells arising from macrophages, embryologically and physiologically diff from other merve cells
  • Unknown rest conditions, stouter process when activated after injury
  • Produce antigens, active in MS and AIDS-related dementia
Macroglia
  • Oligodendrocytes and Schwann cells
    • Provide insulation through myelin sheath
    • not very branched, myelin by each differes in chemical composition
  • Astrocytes
    • Not very processed
    • Has end feet
    • Brings nutrients
    • Blood-brain barrier
    • Maintains K-ion conc. in ECM

Neurons

Ramon y Cajal
  • Silver Staining method of staoining neurons
  • Established that neurons are distinct and do not for synctium
  • Principle of dynamic polarisation Unidirectional transmission of nerve signals from soma to axon
  • Principle of connectional specificity Connections between neurons arew not random but specific
  • Shape-based classification into unipolar, bipolar and multipolar
Specific signaling network — control specific behaviour
  • Four types of connections - sensory, motor, inhibitory (to opposing muscles for example) and conveyance to brain
  • in knee-jerk reflex Stretching of extensor muscle | (Sensory info) Dorsal root ganglion |(Interneuron helps) Motor neuron for extensor (activated) & Flexor (opposing) inhibited | Contraction of extensor
  • Feedback and feed-forward inhibition
Components of signal in neuron and uniformity in all of them
  • Four types of signals in all cells - input, trigger, signalling, output
  • Action potential, Na+-K+ pump
  • Neuronal convergence(integration of instructions by motor neurons) and divergence(affecting diverse cells at once)
Amplitude of signals decrease along distance (graded receptor and synaptic potential)
  • Receptor potential generated locally— strength depends solely on amplitude and duration of triggering muscle stretch
  • Also synaptic potential - graded — depends on amount and duration of neurotransmitters released
  • Both decay with distance
Trigger component starts action potential
  • Trigger zone — impulse initiation zone
  • sums up activity of all receptor potentials
  • Highest density of Na+ channels (voltage sensitive ones) – lowest threshold
  • once input potential crosses threshold, action potential generated, whose frequency is decided by duration of input potential
All-or-none principle
  • All action potentials are the same in amlitude and duration - does not decay as periodically regenerated
  • Only frequency changes with input duration — produces stronger sensation or speed of movement
  • Must cross threshold to be generated
Neurotransmitter
  • Graded output signal
  • No. of neurotransmitters depends on no. and freq. of action potential
  • Generates synaptic potential in post-synaptic cell
  • Whether excitatory or inhibitory effect determined by receptor on the postsynaptic cell and not on the neurotransmitter itself
Molecular difference b/w Neurons
  • differ in whether they produce action potential
  • what ion channels they use (leads to diff. signals and thresholds)
  • differ in what neurotransmitters they use and can recept
Specific Networks — Unique info. transmission
  • Localisation of brain func.
  • Two kinds of neural maps - sensory and motor
  • Parallel processing single behaviour — different groups of neurons work simultaneously to convey similar info — increases speed and reliability of CNS
  • complexity of connection and not complexity of neurons themselves — responsible for unique messages
How the specific conn. change — Adaptability of behaviour
  • Plasticity Hypothesis Changes in chemical synapses
    • Short term - Physiological changes like alteration of strength of synapse connection (day long)
    • Long term - Anatomical changes like pruning of pre-existing connection and development of new connections (learning and memory formation or dev)
  • potential for plasticity responsible for individuality