Case 6 Flashcards
Describe MS (name, disease type, brief mechanism, end result).
MS = Multiple Sclerosis
Slow progressive CNS disease characterised by destruction of the myelin sheath around the axons in the brain and spinal cord.
Complex immune/genetic disease.
Mediated by autoimmune response - Auto-immune attack of oligodendrocytes (CNS) and/or schwann cells (PNS).
Inflammation of the CNS white matter (axons).
Glial scarring.
In the action potential, what causes hyper polarisation, and what is its purpose?
Hyper-polarisation results from K+ channels remaining open after re-polarisation (downstroke). This allows resistance to further action potentials. So need more EPSP’s (from dendrites) to reach threshold for another action potential.
In the action potential, what is the purpose of the Na+/K+ ATP pump after re-polarisation?
At the end of action potentials, ions are switched around. (extracellular Na+ rushed inside during upstroke, and intracellular K+ rushed outside during downstroke). So pump swaps ions around to re-establish previous gradient.
How big is Node of Ranvier compared to Myelin Sheath?
Node of Ranvier much smaller. 1-2um vs 1mm.
What is the composition of the myelin sheath?
Lipids: galactocerebroside Glycoproteins: myelin basic protein (MBP) myelin oligodendrocyte glycoprotein (MOG) myelin associated glycoprotein (MAG)
What is saltatory conduction? Where are the Na+ voltage gated ion channels found?
Action potentials jump from node to node. Voltage gated Na+ channels found only at nodes of Ranvier.
What are the pathological END results of MS (on neuronal cells and brain/body)?
1) Loss of nerve fibres.
2) Pockets of inflammation (Lacunar white dots - breakdown of BBB - sign of local oedema associated with inflammation)
3) Glial scarring or sclerosis (Astrocytes)
4) Several neurological symptoms including loss of sensation (touch, taste), motor co-ordination impairment (cerebellum affected), vision impairment (visual tracts - involuntary eye movements)
What neurological effects can be caused by MS and what is the reason for them (axons)?
Weakness and clumsiness, Stiffness and gait disturbances, Visual disturbances, Mental disturbances All caused by degradation of the myelin sheath around axons leading to axonal degradation.
Is MS more common in men or women? What race?
Women. Unknown why.
Caucasians
What is the aetiology of MS?
Unknown but some factors associated with increased incidence.
Combination of genetic and environmental factors
What environmental factors are thought to be associated with/triggers for MS?
1) Viruses & bacteria: part of pathogenesis theory of MS (measles, rubella, mumps and herpes).
2) Nutritional and dietary factors: animals, minerals, chemical agents, metals, solvents
How is chromosome 6 involved in MS?
Chromosome 6 found to carry genes for myelin proteins like MOG & MAG. Also found to contain MHC class genes
What is MHC? Which cells are involved?
MHC = Major Histocompatibility Complex
Execution of immune system (1st line defence)
Cass 1, 2 and 3 (depending on nature of infectious agents)
Found on surface of APC cells (antigen-presenting-cells)
APC blood: Macrophages & monocytes
APC skin: dendritic cells
APC liver: Kupfer cells
How do APC’s used MHC’s to initiate immune response?
APC’s phagocytose pathogens, and use MHC’s to present antigen of pathogen to immune system (epitopes). T cell receptor detects MHC-epitope complex and release inflammatory mediators to initiate immune response.
What does a MHC-T cell receptor immune repose involve?
Inflammatory mediators released by T cell.
Leads to clonal expansion - proliferation (T cytotoxic cells)
Leads to activation of B cells (antibodies)
What is molecular mimicry and how is it related to MS?
Molecular mimicry is the homology between foreign proteins (e.g. viral or bacterial) and self proteins (in this case myelin - MBP, MOG, MAG)
With regards to molecular mimicry: what are the two types of homology? Describe them.
1) Sequence homology: Same sequence of amino acids in gene (in a row).
2) Structural homology: Amino acids are in same “position” within a sequence of gene (not in a row).
Generally, what is the blood brain barrier?
A membrane that controls the passage of substances for the blood into the CNS.
It is a physical barrier between the local blood vessels and most parts of the CNS.
Thus, CNS normally inaccessible to T lymphocytes.
How is the blood brain barrier involved in MS?
Blood brain barrier thought to be disrupted in MS, for reasons not fully understood.
Explain briefly the accepted pathogenic pathway of MS.
1) Infection by virus/ bacteria
2) Antigen gets into bloodstream, digested by APC
3) Macrophage (APC) displays antigen with MHC molecule
4) MHC-antigen complex recognised by T cell receptors
5) Activated Th cells crosses BBB to CNS
6) In CNS, Th cells encounter local APC’s (microglia)
7) APC’s present MHC-protiein complex with myelin antigens
8) Th cells are RE-ACTIVATED by local APC’s (due to recognition of epitope-self-proteins of MBP, MOG, MAG.
9) Th cell releases cytokines (microglia, astrocytes, macrophages and B-cells from periphery, antibodies) and complement system (mediates myelin sheath attack)
10) results in demyelination and oligodendrocyte degradation.
What are microglial cells?
Neuronal glial cells.
Found in brain and spinal cord (CNS)
Local macrophage and APC
What are the types of MS?
1) Benign
2) Relapsing-remitting and relapsing-persistent
3) Relapsing-remitting followed by secondary progression (2ndry prog)
4) Primary chronic progression.
5) Progressive relapsing
Explain benign MS.
10-20%.
short episodes or mild neurological symptoms.
Symptoms do not worsen.
Returns to normal between attacks.
Explain relapsing-remitting and relapsing-perssistant MS.
85-90%
Unpredictable relapses, lasting 24h or more.
Followed by months-years of remission with no new signs of disease activity.
Period between relapse may decrease.
Symptoms become more severe.
relapsing-remitting: no progression between attacks
relapsing-persistant: progression between attacks (partial recovery).
