Lecture 2 Flashcards
White vs grey matter
Spinal cord: white matter outside, grey matter inside
Cerebrum: grey matter outside, white matter inside
Division of CNS on macroscopic level
White matter:
myelinated axons, very few cell bodies, pale due to myelin
Bundles of axons within CNS:
tracts (=nerves in PNS)
Grey matter:
pericaria of neurons (multipolar, interneurons, motorneurons), unmyelinated fibers, astrocytes, microglia cells
Clusters of nerve cell bodies in CNS:
nuclei (=ganglion in PNS)
CNS consistency:
jelly-like, minimal extracellular matrix
CNS support
connective tissue layers and fluid
4 protective mechanisms
- Bone structure
- Protective membranes (meninges)
- Cerebrospinal fluid (CSF)
- Blood-brain barrier
Neurons: terminally differentiated, little extracellular matrix
- Bone structures
Enclosed by hard, bony structures
- Cranium (skull) encases brain
- Vertebral column surrounds spinal cord
- Meninges:
- protection and nourishment
- Dura mater (durus: hard)
> Dense connective tissue, inelastic - Arachnoid mater (arachnoideus: spiderweb-like)
- Pia mater (pius: gentle)
Damage in relation to the meninges
- Cerebrospinal Fluid (CSF)
Surrounds and cushions brain and spinal cord
Exchange of materials between neural cells and interstitial fluid surrounding brain
CSF major function
Serves as a shock-absorbing fluid to prevent brain from bumping against hard skull
Anchored by the meninges, floating in CSF
- Brain floats
> Neurons and synaptic vessels in a special environment
CSF generates by
Formed primarily by choroid plexuses
choroid plexuses
Richly vascularized masses of pia matter tissue that dip into pockets formed by ependymal cells
- filtrates and modifies fluid
CSF forms as a result of
selective transport mechanisms across membranes of choroid plexuses
Choroid plexus located in
In roof of 3rd ventricle
CSF constitutions
- Lower in K+, slightly higher in Na2+, almost no proteins, up to 3 leucocytes/ml
- CSF volume: 125-150 ml, replaced more than 3x/day (500-700 ml)
- If >6 leucocytes/ml = inflammation/meningitis
CSF generated and reabsorbed
CSF circulation
from arachnoid villus into venous sinus
Ciliary beating, 10 mm HG
Choroid plexus (arteries) –> 4 ventricles and central canal –>entering subarachnoidal space at 4th ventricle –> flows between meninges –> entire surface of brain and spinal chord –> arachnoid villi –> venous sinus –> blood stream –> choroid plexus
CSF dysfunction:
hydrocephalus
(fluid on the brain)
= Intracranial pressure
- Damage of brain tissue
Pressing on brain stem into foramen magnum>affecting breathing centre
- Blood Brain Barier (BBB)
- Highly selective interface between the blood and the CNS
- Endothelium in CNS with tight junctions
- Drug delivery sometimes difficult (dopamine as L-dopa)
- Some things diffusable through phospholipid bilayer, or must be transorted = very controlled environment
Blood-Brain Barrier (BBB) functions
- Protects brain from chemical fluctuations in blood
Strictly limits exchange between blood and brain - Minimizes possibility that harmful blood-borne substances might reach central nervous tissue
- Prevents certain circulating hormones that could also act as neurotransmitters from reaching brain
- Limits use of drugs for treatment of brain and spinal cord disorders
- Many drugs cannot penetrate BBB
What can get through the BBB?
Lipid soluble substances: O2, CO2, alcohol, steroid hormones, small water molecules
drug abuse
Tight junctions
Sealing off intercellular diffusion
(in BBB)
ZO: zonula occludens = tight junction
BBB
Cancer
Neurons are terminally differentiated do not form tumours
Sources for brain tumours of neural origin:
- glia cells–> glioma
- astrocytes–> astrocytoma
- ependyma cells –> ependymoma
Sources for brain tumours of non-neural origin:
- meningiomas
- metastasized cancers
Astrocytoma (infiltrative homogeneous lesion)
Glioblastoma multiforme (cystic change, necrosis, hemorrhage)
Meningioma
- origin: meningothelial cells from dura
- push rather than infiltrate
