CASE 6 - multiple sclerosis Flashcards
what are the 2 main types of cells and their functions in the NS?
glia = insulate, support and nourish neurones
neurones = sense change in the environment, convey info and communicate these changes to other parts of the brain
what are the 2 types of glial cells and their functions?
- microglia — CNS phagocytes
- macroglia — scavenger cells that resemble macrophages and remove debris
what are the 3 types of macro glial cells and their functions?
- Oligodendrocytes — myelin formation around axons in the CNS
- Schwann cells — myelin formation around axons in the PNS
- Astrocytes — provide support for nerve fibres and maintain an appropriate neurotransmitter and chemical environment for neuronal signalling as well as maintaining the blood brain barrier (BBB)
what is the embryo logical origin of microglia?
mesodermal origin
microglia are activated in response to what?
tissue damage
what are the resident macrophages of the brain and spinal cord?
microglia
what can microglia act as if needed?
antigen presenting cells - activate T cells
microglia are very sensitive — how and why?
- act very quickly to recognise foreign bodies, swallow them and act as APCs activating T cells to prevent potentially fatal damage
- microglia are extremely sensitivity to even small pathological changes in the CNS
- they achieve this sensitivity in part by having unique K+ channels that respond to even small changes in extracellular K+
where is the myelin sheath interrupted?
Nodes of Ranvier
how many axons does on oligodendrocyte/schwann cell provide myelin to?
- 1 oligodendrocytes provides myelin to several axons
- 1 schwann cell provides myelin to only a single axon
what is the most numerous glia in the brain and spinal cord?
astrocytes
what are the 2 subtypes of astrocytes and where are they primary found?
- fibrous astrocytes — found primarily in white matter
- protoplasmic astrocytes — found primarily in grey matter
what do astrocytes do?
- metabolic support (can store glycogen and lactate)
- regulation of extracellular ionic environment (remove excess K+ from ECS following neuronal activation)
- neurotransmitter uptake
- modulation of synaptic transmission
- promotion of myelination by oligodendrocytes
- both types send processes to blood vessels, where they induce capillaries to form tight junctions making up the blood-brain barrier
- they also send processes that envelop the synapses and the surface of nerve cells
- fill in the space between neurones — thus decides whether a neuron grows or contracts
- regulates contents of ECF such as K+
- membrane also possesses neurotransmitter receptors that can trigger electrical events inside the glial cell
what is the cell body/soma of a neurone?
- contains the nucleus and the neurone’s intracellular organelles (eg, mitochondria and golgi apparatus)
- the centre of neuronal metabolism
- contains the Nissl substance
what is the Nissl substance?
- in cell body/soma of neurone
= granules containing rough endoplasmic reticulum and free ribosomes, making it the site of protein synthesis
what are dendrites?
- these processes originate from the soma and extend outwards
- they transmit signals received from other neurones to the soma
what is the axon?
- arises from the soma, specifically from an area called the axon hillock, where action potentials are generated
- the action potentials are conducted along the axon to the axon terminal
what is the axon terminal?
- distally the axon branches forming axon terminals
- these make synaptic connections with other neurones
- they contain various neurotransmitters which are released into the synapses to allow signal transmission from one neuron to the next
what are the 4 different types of neurone?
- unipolar
- pseudounipolar
- bipolar
- multipolar
describe unipolar neurones
- not in humans, only in invertebrates
- humans have pseudo-unipolar neurones instead
describe pseudounipolar neurones
- there is one process extending from the cell body, which splits into 2 axonal branches
- exclusive to sensory neurones in humans
- no dendrites (only got the one process leaving from the cell body and the 2 axon branches - one extends from the periphery and one extends into the centre (spinal cord))
describe bipolar neurones
- has one axon and one dendrite extending from the soma
- uncommon, only occur in a few specific places — olfactory epithelium, retina certain nerves within the ear
describe multipolar neurones
- most common
- present throughout a person’s CNS
- only one axon, but each cell has many dendrites, making it easier for the neurone to exchange information
dendrite vs axon
• dendrite: branched projections of a neuron that conduct the impulses received from other neural cells to the cell body
• axon: long slender projection of a nerve cell that conducts nerve impulses away from the cell body to other neurons, muscles, and organs