dr nyamapfene basic biology of nerve
TRANSCRIPT
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Dr Nyamapfene
BASIC BIOLOGY OF NERVES
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FACTS
• 100 BILLION NERVES (10^11) nerves• 10 -50 times glial cells• 40 % of genes participate in the formation of
CNS
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NUERONE
• 4 SEGMENTS • RECEPTOR DENDRITIC REGION • SOMA• INITIAL SEGMENT• AXON
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CELLULAR ELEMENTS OF CNS
• Glia (glue) –connective tissue of CNS• Glia continue to divide throughout life• Evidenced by proliferation after brain injury, seizures
, inflammation as they mop up debris[AIDS DEMENTIA,MULTIPLE SCLEROSIS,PARKINSON’’S DZZ]
• microglia and macroglia• Microglia-migratory, monocyte ,macrophage• Macroglia- 3 types –oligodendrocytes , astrocytes ,
schwannoma
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SCHWANN and Oligodendrocytes
1;1 WITH NUERONEPNS MYELINATION100 TIMES WRAPPING OF MYELIN AND CLOSES
WITH Po proteinNodes of Ranvier , saltatory conductionOligodendrocytes 1:15 CNS myelination
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ASTROCYTES
2 TYPES PROTOPLASMIC -GRANULAR CYTOPLASM AND
FOUND IN GRAY MATTERFIBROUS-INTERMEDIATE FILAMENTS AND
WHITE MATTER
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FUNCTION OF ASTROCYTES
• FORMATION OF BLOOD BRAIN BARRIER• POTASSIUM HOMEOSTASIS [REPETITIVE FIRING
OF NERVES LEADS TO HIGH ECF K+ via voltage gated channels leading to HYPERPOLARISATION and leads to failure to conduct impulses of which it is rapidly absorbed by astrocytes ]
• Uptake of nuerotansmitter• Trophic to nerves eg nerve growth factor
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MULTIPLE SCLEROSIS
• AUTOIMMUNE AGAINST MYELIN• 3 MILLION PEOPLE• 20 TO 50 YEARS • M;F 1; 2• GENETIC VS ENVIRONMENTAL (EBV, measles,HSV) • Weakness , fatigue ,speech , bladder dysfunction
and sensory disturbance• Exacerbated by change of weather from cold to
heat {from north pole to zimbabwe]
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Diagnosis
• NERVE CONDUCTION STUDIES –DECREASED CONDUCTANCE
• CSF OLIGOCLONAL BANDS• MRI – SCARRING OF CORTEX
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PROTEIN SYNTHESIS
• MAINLY SOMA AND SLIGHTLY DENDRITES• TRANSLATION FROM 5’ to 3’• STARTS FROM N TERMINAL • 2 TYPES OF TRANSLATIONAL MODIFICATION
NAMELY CO-TRANSLATIONAL {N –ACYLATION AND POST TRANSLATIONAL]
• POST-TRANSLATIONAL-PALMITOYLATION,UBIQUITIN,ISOPRENALINATION
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AXONAL TRANSPORT
• NUERONES ARE SECRETORY AT THE END OF THE AXON BOUTON
• PROTEIN SYNTHESIS USUALLY AT THE SOMA mainly and the dendrites
• Soma maintains cell function and structure• If axon is cut, Wallerian degeneration occurs• Orthograde [anterograde ] transport• Retrograde transport
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ORTHOGRADE AXONAL TRANSPORT
• FAST AXONAL ANTEROGRADE TRANSPORT IS MEDIATED BY KINESIN
• 400mm /day = I RULER A DAY• Transport of organelles and secretory proteins• SLOW AXONAL ANTEROGRADE TRANSPORT• =1 CM /DAY• CYTOSKELETAL PROTEIN AND CYTOSOLIC
PROTEINS
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RETROGRADE AXONAL TRANSPORT
• 200MM/DAY• SYNAPTIC VESICLE RECYCLE• ENDOCYTOSIS eg nerve growth factor