1. Anatomy, composition and physiology of neuron, dendrite, axon, and synapses

3. Glial cells/ Astrocyets, Oligodendrocyt, Schwan cells/ Support neuronal cells Produce myelin Act as scavengers Takes up released neurotransmitters Guide migrating neurons and the out growth of axons Form BBB Release growth factor and help nourish nerve cells

4. Neurons type Unipolar cells: single process serving as receptor and releasing terminal e.g. In autonomic nervous system Biplar cells : two process dendrite and axon e.g. in retina, olfactory nerves Pseudo_unipolar cells: e.g. dorsal root ganglia Multipolar cells : most common type e.g. spinal motor neurons,pyramidal cells,pukrinje cells NERONS COULD ALSO BE CLASSIFIED AS : SENSORY MOTOR LOCAL INTERNEURON PROJECTION INTERNEURON NEUROENDOCRINE CELL

6. Structure of a neuron Cell body Dendrites: apical and basal types, are input elements together with the cell body contains nucleus and gives rise to axon and dendrite Axons: transmitting element, could be longer than 3m, covered with myelin interrupted by node of Ranvier is the out put element of neuron single axon may form synapses with as many as 100000 neurons Axon hillock: initial segment of neuron Synapse: presynaptic terminal, synaptic cleft, postsynaptic membrane dendrites cell body axon hillock muscle synaptic connections could be divergent or convergent

12. Functional organization of neurons Input component /receptor or synaptic potential/ : signal electrical input signal is graded in amplitude and duration, proportional to amplitude and duration of stimulus Integrative component : signal electrical action potential is generated only if input signal is greater than spike threshold stimulus intensity is represented by frequency of action potential duration of stimulus is represented by number of action potentials

13. Functional organization of neurons Conductile component/action potential/ : Signal is electrical action potentials are all or none every action potentials have same amplitude and duration information in the signal is represented by frequency and duration Out put component : signal chemical transmitter total number of action potential determine how much neurotransmitter should be released

16. Comparison of local and propagated signals Input signals amplitudesmall duration brief summationgraded signal effect depolarizing propagationpassive Action potential amplitude large durationbrief summationall/none signal effect depolarizepropagation active

19. Cytology of Neurons Nucleus Nuclear envelope Cytoplasm cytosol including cytoskeletal matrix membranous organelle Plasmalemma myelin

20. Membranous organelles Mitochondria and peroxisomes Rough endoplasmic reticulum/smooth endoplasmic reticulum Golgi complex Secretory vesicles, endosomes, lysosomes Most of these structures are abundant in the cell body and dendrite and there are no synthetic function differences between cell body and dendrite. The axon has few mitochondria and smooth endoplasmic reticulum with abundant secratory vesicles

21. Synthesis and trafficking of neural proteins Most proteins are synthesized in the cell body The neuron express more the total genetic material than any other organ Neural cells are engaged in protein synthesis more often than other cells and hence their chromosomes uncoiled Ribosomal and m RNA are synthesized in the nucleus and exported through nuclear pore Some genetic information is also contained in the mitochondria Protein synthesis occurs in cytosol where mRNA ribosome and tRNA form complex Secretory proteins and vacuolar apparatus and plasmalemma are synthesized and modified in the endoplasmic reticulum Secretory proteins are processed further in the golgi complex and then transported

23. cytoskeleton Microtubules largest diameter fibers helical cylinders made of protofilaments undergo cycles of polymerization and depolymerization Neurofilamentsmonomers twist to form dimer protofilament protofibril filament Microfilamentspolymerized actin monomers smallest-diameter fibers undergo cycles of polymerization and depolymerization

26. Anterograde Axonal Transport Fast phase of axonal transport 70-400 mm/d 20-70mm/d 4-20 mm/d Convey mainly plasma membrane proteins such as acetyl cholinesterase mitochondria multivesicular bodies and secretoty vesicles ATPases The physiological properties of fast phase axonal transport has been important for tracing connections in the brain Slow phase of axonal transport 1-4 mm/d 0.2-1.2mm/d Conveys mainly Neurofilaments and Microtubulins Actin and certain glycolytic enzymes

27. Retrograde Axonal Transport Toxins, drugs, heavy metals Neurotropic viruses Nerve Growth Factors and neurotrophines Mitochondria, endosomes

28. Axonal vs dendrite transport Axonal Nerofilaments abundant Microtubules are of tau type Microtubules are uniformly arranged Dendrite Microtubules abundant MAP-2 type Microtubules are bidirectionaly arranged These difference in arrangement explain the polarization of organelles

31. myelin Insulate axons and facilitates speed of action potential transmission Arranged in concentric bimolecular layers Has a composition similar to plasma membranes Schwan cells form myelin of peripheral nerves and Oligodendrocyts that of central nerves Schwan cells express their myelin gene in response to contact with axon while Oligodendrocytes depend also on the presence of Astrocytes

33. Myelin Proteins Myelin Basic Proteinimportant for myelin compaction strongly immunogenic used to produce experimental allergic encephalomyelitis Myelin Associated glycoproteinsupper family of immunoglobulin involved in cell to cell recognition is an adhesion molecule that initiate myelination Protiolipidsimportant for compaction of myelin mutation in the gene causes hypomyelination and degeneration Myelin protein zeromajor protein in peripheral myelin immunoglobulin family important for myelin compaction mice that lack the protein have poor motor coordination Peripheral myelin protein 22encoded by chromosome 17 DNA duplication results in CMT disease

34. Ion channels Conduct ions at fast rate Selective for specific ions Ion channels are proteins that span the cell mme Flux of ions through the ion channel is passive Opening and closing of ion channel involves conformational change Open and close in response to specific stimulus Voltage –gated Ligand –gated Mechanically –gated Gap-junction channels The binding of exogenous ligands /toxins, poisons and drugs/can make channels open or close Ion channels are composed of several subunits Channels are also important targets of diseases myasthenia gravis hyperkalemic periodic paralysis

36. Synaptic transmission The average neuron makes 100000 connections Two basic forms of transmission Chemical Electrical Electrical transmissions are Short lasting Only excitatory Do not induce long lasting postsynaptic changes Gap junction channels Bidirectional transmission Chemical transmissions are Variable signaling :inhibitory or excitatory Produce complex behavior Longer lasting / delay in transmission Amplify signals Modify post synaptic receptors both functionally and anatomically Ionotropic receptors :conformational change that opens the channels on binding transmitter Metabotropic receptors: act by altering intracellular metabolic reaction

38. Chemical transmitters Classical Acetylcholine Cathecolamines Glutamates GABA Serotonine histamine Peptides Substance p Enkephaline Endorphine Prolactin, oxytocine, vasopresin Soluble gases NO

39. Cellular basis of connectionist approach Principle of dynamic polarization : electrical signals within a nerve flow only in one direction Principle of connectional specificity : nerve cells do not connect indiscriminately with one another to from a network

40. Specificity and modifiability of neuronal connections Specific networks Brain has at least two types of neuronal map/ motor and sensory maps/ which are interconnected with each other by interneuron. The neurons that make up these map do not differ greatly in their electrical properties. Rather, They have different function because of the connections they make. Parallel processing: deployment of several neuron groups or several pathways to convey similar information Plasticity : functional transformation in neurons as a result of appropriate stimulation

41. How dose nerve cells differ ? Lack of axon Location of synaptic in puts on the cell cell body dendrite axon hillock type of target cell Difference in cell body size and shape, distribution of axon and dendrite tree Expressing different combination of ion channels providing them with different thresholds,excitability and firing patterns. Thus,neurons with different ion channels encode the same class of synaptic potential into different firing patterns and thereby convey different signals

42. Cont. Chemical transmitter The type of neurotransmitter they use The type of Receptors they have Myelin content Location in the nervous system –central/peripheral These differences and others may account for different patterns of disease