Neurons & Glia Lecture 5

Nature of the Nervous System Camillo Golgi The Synctium continuous network no gaps ~

Nature of the Nervous System Santiago Ramon y Cajal The Neuron Doctrine discrete cells communication across gaps synapses ~

Nature of the Nervous System Golgi won Proved himself wrong Golgi Stain - silver chromate Supported Neuron Doctrine Golgi & Cajal shared Nobel Prize (1906) ~

NEURONS Basic functional unit of N.S. Specialized cell All cells have same basic properties information processing Transmits Integrates Stores Regulation of behavior ~

Information Transmission

Integrates information~ Receives information Integrates information~ Stimuli

Axon carries information away from soma Electrical signal Axon terminal releases chemical message~

Neuron Classification Categories overlap ~

Shorthand

By function (connections) Sensory Motor Interneuron

By morphology (# of neurites) Multipolar Bipolar Unipolar

By Morphology By Dendrite Structure Pyramidal Stellate Dendritic Spines Spiny or Aspinous ~

By Axon Diameter Sensory afferents Size: large ---> small Aa, Ab, Ad, C C: small, unmyelinated pain & temperature Aa: not associated with skin receptors proprioceptors in muscle ~

Primary Afferents Speed of conduction larger is faster myelinated faster slowest: C fibers ~

Other Classification Schemes Axon length Golgi Type I - long Golgi Type II - short (local signaling) Chemistry neurotransmitter released ~

Neurons vs. Nerves Neurons - cells microscopic Nerves - bundles of axons seen with naked eye ~

Glia Neural Support Cells

Astrocytes Provide physical support Regulating chemical content of extracellular fluid localizes neurotransmitters K+ concentration Blood-brain Barrier ~

Blood-Brain Barrier astrocytes Typical Capillary Brain Capillary

BBB: Function Maintains stable brain environment large fluctuations in periphery Barrier to poisons Retains neurotransmtters & other chemicals Regulates nutrient supplies glucose levels active transport ~

Myelin Sheath

Myelin Wrap around axon Saltatory Conduction faster transmission CNS: oligodendroglia or oligodendrocytes PNS: Schwann cells ~

Other non-neuronal cells Microglia phagocytosis immune-like function Ependymal cells line walls of ventricles role in cell migration during development ~

Membrane Structure Barrier Compartmentalization Semipermeable selectively leaky Fluid Mosaic Model Phospholipids Proteins ~

<------- Phosphate head Phospholipids <------- Phosphate head hydrophilic <------- Lipid tails hydrophobic

Phospholipid Bilayer Hydrophilic heads -----> Hydrophobic tails ----->

Membrane H20 out & in Pores~ H2O H2O

Membrane Proteins Channels Pumps active transport Receptor protein sites bind messenger molecules Transducer proteins: 2d messenger systems Structural proteins form junctions with other neurons ~

Membrane Proteins: Ionophores Ions Channels Nongated always open Gated chemically-gated electrically-gated mechanically-gated ~

Chemically-Gated Channels ligand-gated Ionotropic receptor protein = channel direct control ---> fast Metabotropic second messenger system indirect ---> slow ~

Membrane Proteins OUTSIDE INSIDE

Membrane Proteins OUTSIDE INSIDE

Metabolic pumps Membrane proteins Pump ions require energy Na+ - K+ Ca++ (calcium) Also various molecules nutrients neurotransmitters ~