Why does the nervous system need so much protection?
-it is vital and relatively fragile, CNS= composition of a yoghurt
What is the protection of the CNS?
-skull (bony cavity) -meninges including CSF
What are the negatives about having the brain inside a skull?
-it is a cavity of a fixed volume,if the tissue increase in volume than damage! pressure increase, you push things around and that's bad, blood flow into brain is compromised if pressure is increased -dangers brought about by eodema
What are the meninges and what do they look like?
-the meninges provide a space for things to circulate, it can communicate with the endocrine system, also it's a way of things to leave the brain like if something bad in there -dura=thick connective tissue -arachnoid=there is fluid, the cerebrospinal fluid, like rarefired blood plasma without protein and any big molecules, lot of the major blood vessels that can be seen on the outside of the brain are there,arachnoid has the little extensions that join on to the pia -pia -protective coverings of the brain,meninges have own blood supply, tough structure, none of the detail of the brain is visible when the meninges on. -there is fluid all around the CNS, in a sense it is floating in this casing of fluid -all also in around the spinal cord
What is the superior saggital sinus?
-saggital plane= the midline the dura there splits in half leaving space in the middle= the space call vena sinus =vein but niot floppy, it is filled with blood -in between the hemispheres there is a large vein -you can see there is a communication between the arachnoid layer and the vena sinus so that CSF can leak to the venus sinus into the blood
How is the CSF removed from the subarachnoid space?
-CSF is made all the time and fixed volume and CSF is removed via the granulations in the vena sinus so it is taken away with the blood
What are the two types of matter in the brain and what composition are they?
-section through the frontal lobes and bit of brain stem -blue= ventricles, the black thingy is the connection to the third ventricle -white matter quite hard, grey matter quite soft
Why is white matter white?
-because of the insulating myelin sheaths, in the CNS this is produced by the oligodendrocytes and in the PNS by the Schwann cells --layers and layers of membranes that insulate the axons, = membranes are lipids and those are white -lot of fatty insulations, most axons the re myelinated
What are the little dots in the picture and what do they tell us?
-collagen bundles= thanks to that can tell it's peripheral nervous system -PNS protects itself by the collagen wrapped around it
How do oligodendrocytes differ from the Schwann cells?
-this is in the CNS= oligodendrocytes -oligo= mini, denrocytes= branches -they branch out unlike schwann cells -the condensed cell membranes of the myelin sheath are mostly lipid and give the white matter its white fatty appearance
Which is more vascularised the grey or the white matter?
-grey matter more vascularised than white matter -brain extremely vascularised -white matter= the axons grey matter the neurons and synapses= need more energy so more vascularisation -every neuron is about 10-20 microns away from a capillary= that is how well they are supplied for (the picture:put in latex into the vessels and then dissolve all the tissues so you can see the vessels)
How much of the cardiac output goes to the brain?
-15-20%, high energy demand (to a structure that is about 1,5 kg of your body weight)
What sort of O2 metabolism does the brain have?
-obligate aerobic metabolism, O2 is essential -only adrenal gland needs more O2 -loss of O2 for a few minutes, glucose for 10-15min is fatal for neurons (and neurons are vital)
What sort of energy source does the brain use?
-glucose (only that) -totally dependent on glucose supply via blood -can only use glucose, when you're fasting, gluceogenesis is really just for the benefit of the brain other tissues can use other things -brain has a dominant role over how the metabolism supports the body
What supplies the brain with energy?
-the mitochondria via glucose (aerobic respiration)
What are the three major arteries of the brain?
-anterior cerebral artery -middle cerebral artery -posterior cerebral artery -most of the oxygen (in the blood) goes from the outside of the brain to the inside -it has major arteries, they form 3 territories -all of those come from the middle corrotid artery, aortic arch into the head
What do the arteries look like from below?PIC9
What is the circle of Willis?
-the circle= it allows the pressure to equalise (circle of Willis) lot of people however don't have it so it cannot be that important
Do the regions supplied for by different arteries overlap?
-not very much, each region is distinct -if one artery damaged then the entire region dies and it cannot be supplied for by another artery
What are the CVAs?
-cerebrovascular accidents or strokes are disruptions of the brains' blood supply. Loss of adequate flow causes loss of neuronal function and neuronal death. CVAs are the most common cause of neurological disorder
What are the two causes of CVAs?
-occlusive= due to the narrowing or closure of vessels (result of atheroslecrosis, thrombosis,) -haemorrhagic= due to rupture of vessels (aneurysm, elevated BP, trauma, infection)
What do the CVAs result in?
-results in tissue ischemia (reduced blood) and HYPOXIA(low oxygen)/ ANOXIA(no oxygen) -the vascular pattern is consistent between individuals as ins the functional organisation of the brain, therefore strokes in a particular location produce characteristic loss of function
What can you see in this picture?
-the region supplied for by middle cerebral artery died off, atrophied -middle cerebral artery CVA-occlusion
What can you see in this picture?
--lot of blood= fatal -midline is all wrong, high pressure and trying to move brain trough tissues that won't move -intraparechymal CVA. haemorrhage of middle cerebral artery
What do you see in this picture?
-it took out the whole pons -cardiovascular and so on is controlled in the pons, so even a small strong in pons is likely to be fatal -CVA in pons, probably due to rupture of vessels arising from the Basilar artery
What are the effects of raised intra-cranial pressure?
1.Haemorrage 2.Vasogenic Odema 3. Cytotoxic Odema 4.Hydrocephalus 5.CBF(cerebral blood flow) often reduces as the ICP (intracranial pressure) increases cerebral perfusion pressure= arterial BP-ICP =how much profusion can occur(how much blood can flow) =is the blood pressure- the intracerebral pressure, so to keep brain supplied for with blood= the blood pressure has to go up
What is a Haemorrage?
-extravasion of blood (various types defined by location of bleeding in relation to meninges and brain parenchyma(the brain and glial cells)
What is a vasogenic odema?
-increase in vessel permeability, increased ECF volume (extracellular fluid) (head injury, meningitis)
What is a cytotoxic odema?
-swelling of cells, reduced ECF volume (asphyxia =choking can't get air into lungs, or hypoxia= low oxygen in blood)
What's a hydrocephalus?
-over-secretion of CSF(cerebrospinal fluid) or impaired absorption of CSF or obstruction in the circulation of CSF (esp. at the aqueduct) -blocked outflow of CSF -can happen during development, at birth
What is the blood-brain barrier?
-brain is untypical in that it has capillaries that don't leak -O2 CO2 and glucose can go in but rest cannot that is what the blood brain barrier is= at the capillary level things don't cross over very much
How was the presence of a blood-brain barrier proven?
1. Ehrlich's dye experiments=put dye in the blood of the chicken, then everything is blue except for the CNS= evidence of the barrier 2.Goldmann's dye experiments=if you put sth into the CSF then it stays in the CNS and doesn't get out, as well as putting in the body and then doesn't get into the CSF
How does the blood-brain barrier arise?
-in most tissues the capillary cells don't meet up perfectly, they leave little gaps
-but in the CNS they form tight linkages= tight junctions=nothing big can leak through
-capillary endothelial cell is lined with protein that makes it non leaky
-astrocytes= structural support of the capillaries and signals the capillary to form the tight junction
-some astrocytes create blood-feet telling the capillaries= don't leak!
What are the astroglia (astrocytes)?
-have numerous functions including recycling of neurotransmitters and maintaining the ionic composition of the extracellular fluid -some create blood-feet telling the capillaries= don't leak!
Which one is a cerebral capillary?
-left= skeletal muscle capillary with fenestrae -right= cerebral capillary with the blood brain barrier
What determines if a molecule can get through the blood brain barrier?
-size -lipid solubility -things that cna go in= lipd soluble (doesn't matter that the membrane is there) even partially lipd soluble (alcohol, nicotine) -or really really small and can go through the tight junction -heroin gets in really easily, morphine doesn't -some have transport channels= glucose, L Dopa
What are the microglial cells?
-another highly branched cell that is not a neural cell in the brain -the immune cells of the brain= when something goes wrong -neurons, oligodendrocytes and astrocytes form from neuroepithelium in the embryo,but then during development some cells that form in the egg sack invade the embryo=microglial cells,effectively monocyte macrophage lineal cells, so they are part of the immune system they are of mesodermal origin and take up residence in the nervous system -as many as 1 in 10 arre there cells
What is the role of oligodendrocytes?
-glial cell -myelination of axons in the CNS (Schwann cells in the PNS)
What are the roles of astrocytes?
-roles in neurotransmitter metabolism, ionic homeostasis, synaptic transmission and blood brain barrier
What is the role of the microglia?
-small macrophage-like cells that invade the developing brain and reside as immune surveillance cells