Lecture 3- Where is the nervous system?

Question 1

Why does the nervous system need so much protection?

Answer 1

-it is vital and relatively fragile, CNS= composition of a yoghurt

Question 2

What is the protection of the CNS?

Answer 2

-skull (bony cavity) -meninges including CSF

Question 3

What are the negatives about having the brain inside a skull?

Answer 3

-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

Question 4

What are the meninges and what do they look like?

Answer 4

-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

Question 5

What is the superior saggital sinus?

Answer 5

-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

Question 6

How is the CSF removed from the subarachnoid space?

Answer 6

-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

Question 7

What are the two types of matter in the brain and what composition are they?

Answer 7

-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

Question 8

Why is white matter white?

Answer 8

-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

Question 9

What are the little dots in the picture and what do they tell us?

Answer 9

-collagen bundles= thanks to that can tell it’s peripheral nervous system -PNS protects itself by the collagen wrapped around it

Question 10

How do oligodendrocytes differ from the Schwann cells?

Answer 10

-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

Question 11

Which is more vascularised the grey or the white matter?

Answer 11

-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)

Question 12

How much of the cardiac output goes to the brain?

Answer 12

-15-20%, high energy demand (to a structure that is about 1,5 kg of your body weight)

Question 13

What sort of O2 metabolism does the brain have?

Answer 13

-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)

Question 14

What sort of energy source does the brain use?

Answer 14

-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

Question 15

What supplies the brain with energy?

Answer 15

-the mitochondria via glucose (aerobic respiration)

Question 16

What are the three major arteries of the brain?

Answer 16

-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

Question 17

What do the arteries look like from below?PIC9

Answer 17

-

Question 18

What is the circle of Willis?

Answer 18

-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

Question 19

Do the regions supplied for by different arteries overlap?

Answer 19

-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

Question 20

What are the CVAs?

Answer 20

-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

Question 21

What are the two causes of CVAs?

Answer 21

-occlusive= due to the narrowing or closure of vessels (result of atheroslecrosis, thrombosis,) -haemorrhagic= due to rupture of vessels (aneurysm, elevated BP, trauma, infection)

Question 22

What do the CVAs result in?

Answer 22

-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

Question 23

What can you see in this picture?

Answer 23

-the region supplied for by middle cerebral artery died off, atrophied -middle cerebral artery CVA-occlusion

Question 24

What can you see in this picture?

Answer 24

–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

Question 25

What do you see in this picture?

Answer 25

-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

Question 26

What are the effects of raised intra-cranial pressure?

Answer 26

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

Question 27

What is a Haemorrage?

Answer 27

-extravasion of blood (various types defined by location of bleeding in relation to meninges and brain parenchyma(the brain and glial cells)

Question 28

What is a vasogenic odema?

Answer 28

-increase in vessel permeability, increased ECF volume (extracellular fluid) (head injury, meningitis)

Question 29

What is a cytotoxic odema?

Answer 29

-swelling of cells, reduced ECF volume (asphyxia =choking can’t get air into lungs, or hypoxia= low oxygen in blood)

Question 30

What’s a hydrocephalus?

Answer 30

-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

Question 31

What is the blood-brain barrier?

Answer 31

-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

Question 32

How was the presence of a blood-brain barrier proven?

Answer 32

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

Question 33

How does the blood-brain barrier arise?

Answer 33

• 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!

Question 34

What are the astroglia (astrocytes)?

Answer 34

-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!

Question 35

Which one is a cerebral capillary?

Answer 35

-left= skeletal muscle capillary with fenestrae -right= cerebral capillary with the blood brain barrier

Question 36

What determines if a molecule can get through the blood brain barrier?

Answer 36

-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

Question 37

What are the microglial cells?

Answer 37

-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

Question 38

What is the role of oligodendrocytes?

Answer 38

-glial cell -myelination of axons in the CNS (Schwann cells in the PNS)

Question 39

What are the roles of astrocytes?

Answer 39

-roles in neurotransmitter metabolism, ionic homeostasis, synaptic transmission and blood brain barrier

Question 40

What is the role of the microglia?

Answer 40

-small macrophage-like cells that invade the developing brain and reside as immune surveillance cells