Chapter 4 - Neural Science

• deals with degree of localisation in brain

• explanaing behaviour as properties of specific nerve cells and interconnections in particular regions of brain

• Talks about how neurons are different because of polarisation, excitability, and molecules they produce, along with compartmentalisation which helps in effective and quick conduction of signals

Neurons similar to epithelial cells

• neurons develop from epithelium
• basolateral surface ‒ cyton part with dendrite & apical surface - part from which axon arises
• plasmalemma with asymmetric bilayer, same cytosolic housekeeping proteins; extra is some special ones, like ones used to degrade neurotransmitters

Selective distribution of organelles and molecules throughout cell

• 
• Vesicular pathways - exocytic (membrane proteins secreted by RER - Golgi incorporated into plasmalemma, secretory pathway) & endocytic (membrane taken in from plasmalemma shuttled back by vesicular recycling, or taken to lysosomes for degradation by endosomes)

Shape of neuron determined by cytoskeleton

• cytoskeleton - microtubules, neuronal filaments, actin
• microtubules - made of tubulin (GTPase); poylmerisation happens due to binding of GTP bound tubulin dimers. After polymerisation, GTP is hydrolysed to GDP and depolymerisation happens. Normally this would be very unstable and would lead to catastrophic depolarisation , but des not happen due to MAP Microtubule Associated Proteins that stabilise it - these are different in cyton and axon
• neuronal filaments - interfilaments made of neuronal proteins called cytokeratins that are responsible for producing in interfilaments in other cell types as well and very stable and fully polymerised

[!note] neurofibrillary tangle in Alzheimer’s and other neurodegenerative disorders #ReadLater

• Actins- short polymers near the plasmalemma; controls dynamical processes, responsible for growth cone mediation, development of pre- and post- synaptic morphological specialisation

SNS and motor neuron systems

nothing very new

• homonymous and synergistic muscles
• central neurons - intensive dendritic branching because of regulation by input from many neurons; spines in dendrites to increase area for reception
• mRNA localisation at dendritic spinces, dendrons more of an extension of the cell body, more closely related than to axon — conc. of proteins and mRNA essential for synaptic plasticity
• recurrent collateral branches in axons - responsible for going back to motor neuron and modifying activity, or may go back to Renshaw cell in spine and inhibit firing in motor neuron

One motor neurons – several muscle cells

• Many synapses in cell body and dendrons(more) - inhibitory ones closely in cell body and excitatory ones on dendrons
• Sensory - motor info flow both convergent (100 sensory to one motor) & divergent (1 sensory to 500-1000 motor)
• Low innervation ratio (no. of muscles by an axon) - more precision
• acetylcholine transmitter - essential molecules reqd. to be present

Defects in Myelin

Demyelinating diseases

[!Note] #ReadLater

• shiverer (recessive mutation for MBP gene exon deletion)& trembler mutants of mice

• three classes of myelin proteins -

  • Myelin Basic Proteins(MBP) - 7 related proteins formed from a single MB gene, elicits strong immune response when injected(demyelination) & scanty myelination
  • Myelin Associated Glycoproteins(MAG) - homophilic adhesion molecule helping in myelin compaction in axon, belongs to superfamily related to immunoglobulin; again, isoforms of same MAG generated from a single gene by alternative RNA splicing

  [!Note] Alternative RNA Splicing (?)

  • PLP - jimpy mice, Merzbacher disease due to PLP mutations, resulting in demyelination
  • Myelin Protein 0 - membrane spanning domain of Schwann cell, extracellular domain affected by mutation, also helps in compaction and adhesion, deletion leads to trembler mutants
  • PMP22 - compaction of myelin

Hippocampus Pyramidal Neurons

• CA1 and CA3 regions
• CA3 regions have axons comprising the Schafer-collateral pathway, that runs through the stratum radiatum, forming connections to the dendritic spines (excitatory) of CA1 regions – intensive branching (pyramidal cells have two dendritic trees) and excitatory connection
• all dendritic spines of CA1 very compartmentalised, useful in memory formation and learning