Flotte’s Outline of

Neuroscience

Edward R. Flotte, 2006

 

 

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NEUROPHYSIOLOGY

 

 

General Cell Biology

Cell cycle: M & G1 susceptible to radiation.

 

DNA syntyhesis:

·         RNApol (3’-5’) primer > DNApol (moves 3’-5’).

·         Lagging strand – Okazaki frags, 5’-3’. UV – thymidine dimers.

·         Transcription: RNApol 5’-3’.

·         Hydroxyurea blocks ribonucleoside diphosphate reductase & deoxynucleotide/DNA synthesis rate limitng step.

·         UV light makes thymidine dimers.

 

Transcription:

·         RNA polymerase binds to promoter – adds nucleotides 5’ to 3’. Poly-A tail on 3’ end.

·         Terminated by rho.

·         Amanita & rifampin (nonhuman) inhibit RNApol by binding to initiation sites.

·         Elongation inhibited by actinomycin D.

·         Reverse transcription: RNAdep-DNApol makes DNA from RNA.

 

Translation:

·         GTP energizes.

·         Cytoplasmic ribosome 80S (60S+40S). Mitochondrial 70S (50S+30S).

·         Cytosolic proteins: translated by free ribosomes, little modification;

·         Secretory/organelle proteins: translated by ER, extensive modification (ex neuropeptides cleaved in ER/Golgi);

·         Nuclear & mitochondial proteins targeted by posttranslational importation.

·         Inhibited by mercury, dipitheria toxin, erythromycin.

 

Organelles:

·         SER: steroids, lipoprotein synthesis;

·         RER: export protein translation,

·         Ribosomes: cellular proteins translation (N-linked glycosylation),

·         Golgi complex: export protein modification (fatty acid attachment, O-linked sugars, sugar phosphorylation, sulfation of tyrosine),

·         Mitochondria: matrix = Krebs cycle, membrane = electron transport chain

 

Extracellular matrix:

·         Composed of glycosaminoglycans & proteoglycans, collagen/elastin, and “adhesive” proteins: fibronectin (fibroblasts), laminin (epithelium), tenascin (glia).

·         Integrins on cells bind to these (recognize RGQ seuence). 

·         Cell adhesion molecules (CAMs, ie N-CAM & Ng-CAM) bind cells to each other.

 

G-proteins:

·         α unit binds GDP, bg units anchor, inhibits activation by stabilizing binding of GDP and inhibiting GTP binding.

·         Binding of ligand > GDP/GTP transfer > bg units dissociates > protein activates > automatic GTPase > GDP > bg reassociates.

·         Activation of 1 G-protein inhibits activation of other G-proteins in the membrane.

·         Pertussis & cholera ADP-ribosylate, prevent GTP hydrolysis & inactivate.

 

Second messengers: Phosphorylate/ dephosphorylate or directly open/close channels to alter activity.

1. Phospholipase C forms IP3 & DAG from PIP.

·         IP3: releases Ca from ER. Ca binds calmodulin & protein kinase C.

·         DAG: activates PKC w/Ca. Used by a1 & muscarinic receptors

2. cAMP: 

  • Used by b-adrenergic, H2 & D1 receptors, ACTH & TSH.
  • Closes K channels - ­ excitability, activates PKA.
  • Adenyl cyclase forms; Phosphodiesterase degrades.

3. cGMP: stimulated by NO.

4. Arachadonic acid: DAG > AA by phospholipase A2. Then forms prostaglandins, etc. Used by histamine.

 

Steroid hormones: have cytosolic receptors which bind to chromatin affecting mRNA transcription.

 

Cytoskeleton: Actin & spectrin link cytoskeleton to plasma membrane.

Microfilaments: actin. (bg)

Neurofilaments: Neuron-specific intermediate filaments. Form neurofibrillary tangles (paired helical filaments assc w/tau MAP).Nonpolarized.

Microtubules: polymerize w/GTP. Polarized. Depolymerized by colchicine, stabilized by Taxol. Synthesis inhibited by vincristine.

MAPs: microtubule-associated proteins.  Include tau, kinesins, dyneins.

Intermediate filaments: GFAPin astrocytes & Schwann cells

 

 

Nervous System Cell Types

 

Neurons

·         No anaerobic glycolysis. Require O2 & glucose. Don’t require insulin. Glucose crosses BBB by facilitated transport.

·         Dendrites have all organelles except Golgi; axons & hillock lack RER (Nissl), Golgi, ribosomes. Dendrites only have graded potentials, not APs.

Nissl substance = Rough ER.

Psuedounipolar = sensory (dorsal root) ganglia; Bipolar = CN8 ganglia, CN I&II. Multipolar = all others

Golgi I: single long axon, projection. Goligi II: short axon, cortical.

Intrinsic burst firing:  due to low voltage activated (LVA) Ca channels

 

Action Potential:

·         RMP: resting membrane potential mostly from K. Axons –95, neurons –65. 

·         Na open > Na close (absolute refractory) >  K open (relative refractory), Cl unchanged.

·         Na & Ca channels excitatory; K & Cl channels inhibitory.

·         Equilibrium potential: electrical force = chemical force, no net movement of ions across membrane.

 

Na/K pump: 3 Na out, 2 K in. Uses 1 ATP. 2subunits (ab). Inhibited by ouabain. Hyperpolarizes membrane. Electrogenic. Contributes to RMP.

Tetrodotoxin: blocks Na channels; TEA block K channels

Membrane stabilizers: Hypercalcemia, hypokalemia, anesthetics, acidosis. Destabilizers: alkalosis (induces szs), caffeine, strychnine

 

Synapse

·         Ca entry causes release of vesicles.

·         Synaptic Delay 0.5sec. 20-50nm (NMJ) wide.

·         Ca channels in presynaptic  active zone.

·         Ca removed by:

o        1) active transport into SER, mitochondria, & out of cell

o        2) cytosolic binding proteins

o        3) diffusion (not reversal of flow thru Ca channels).

·         Release: Vesicles anchored to actin cytoskeleton by synapsin & rab3A – released by phosphorylation by Calcium-dependant kinase (CAMKII). NT released by fusion pore or exocytosis.

·         Fusion: SNAREs on vesicle (synaptobrevin) & plasma (syntaxin, Rab3 removes Sec1 blocking protein 1st) membranes fuse. Ca binds to synaptotagmin which releases it from SNARE complex, allowing binding & stabilization by SNAPs & NSF. Tetanus & botulinum toxins cleave these proteins.

·         Vesicle recovery: synaptotagmin/AP2/ AP3 causes formation of clatharin coat, Ca/calcineurin activates dynamin – intitiates endocytosis

·         Types: Axodendritic: excitatory, axosomatic: inhibitory, dendrodendritic: olfactory builb only, axoaxonic: inhibitory, ― NT release.

·         Gray type I: excitatory, wide, assymetric (large postsynaptic density), round vesicles. Gray II: inhibitory, narrow, symmetric, oval vesicles.

·         In PNS (not CNS) is surrounded by basal lamina.

 

Nerve transport:

·         Anterograde (- to +) slow = 1mm/d, enzymes/proteins; fast = 100mm/d, organelles, kinesin; retrograde = fast, dynein.

·         Fast = vesicles. Slow = microtubules, neurofilaments.

·         Fast: actin, enzymes, organelles. Inhibited by colchicine.

·         All use microtubles (not neurofilaments).

·         Only fast is ATP dependent.

·