dr nyamapfene basic biology of nerve

Dr Nyamapfene

BASIC BIOLOGY OF NERVES

FACTS

• 100 BILLION NERVES (10^11) nerves• 10 -50 times glial cells• 40 % of genes participate in the formation of

CNS

NUERONE

• 4 SEGMENTS • RECEPTOR DENDRITIC REGION • SOMA• INITIAL SEGMENT• AXON

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

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

ASTROCYTES

2 TYPES PROTOPLASMIC -GRANULAR CYTOPLASM AND

FOUND IN GRAY MATTERFIBROUS-INTERMEDIATE FILAMENTS AND

WHITE MATTER

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

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]

Diagnosis

• NERVE CONDUCTION STUDIES –DECREASED CONDUCTANCE

• CSF OLIGOCLONAL BANDS• MRI – SCARRING OF CORTEX

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

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

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

RETROGRADE AXONAL TRANSPORT

• 200MM/DAY• SYNAPTIC VESICLE RECYCLE• ENDOCYTOSIS eg nerve growth factor