Neuroanatomy L2: Biomechanics of the brain Flashcards
What are the 3 components of the brain?
- Cerebral hemispheres
- brainstem (midbrain, pons , medulla)
- Cerebellum
Brain tissue is _____. What are the 4 components in brain tissue?
inhomogenous
- neurons (axons behave differnetly to cell body) and glial cells (more- contributes to biomechanics)
- grey matter
- white matter (axons- myelinated)
- 70% water
Why is brain tissue ___ (densely/sparsely) vascularised. Why?
Densely (vasculature affects behaviour)
What is perfusion?
how much it is perfused, blood volume
What are the 3 meningeal layers?
- Pia
- Subarachnoid
- Dura
What is the pia mater?
- Cloe to gyri
- very delicate
What is the subarchanoid mater?
close to dura
What are the different layers in the brain?
- Meningeal layers
- Subarachnoid space
- Potential spaces (extradural and subdural)
What happens if the menigeal artery is ruptured?
The epidural (extradural) space (which is normally a potential space) is created
What does the middle menigeal artery supply?
Dura mater
What happens if the bridging veins are ruptured?
Subdural space (normally a potential space) is created
What connects the cerebral vein and the venous sinus?
Bridging vein
What does the bridging vein do?
Connect the cerebral vein and the venous sinus (very delicate)
Is it a true or potential space? - Epidural - Subdural - Subarachnoid
potential; potential; true
What is parenchyma?
(substance of brain- grey and white) small arterioles and arteries
What are 3 types of hematomas that can occur, when a brain haemorrhage occurs?
- subarachnoid
- subdural
- epidural
What is the consequence of when cerebral arteries or veins rupture?
The blood readily mixes with the CFS
What are the 3 function of cerebrospinal fluid?
- provides buoyancy for the brain within the skull (1500g brain net weight ~50g)
- cushioning of mechanical forces
- provide good environment, transport
How does the CSF provide buoyancy for the brain within the skull?
mechanical function- to reduce about of mechanical force on brain
What is the purpose of the dural folds?
(leaves extra room for bleeding, tumour = increasing pressure of brain on skull
What are the 4 mechanical properties or brain tissue?
- Very soft
- Incompresisble
- Viscoelastic
- Very low permeability ~4 x 10-12 m4/Ns
Why is brain tissue very soft and how does it relate to being a mechanical property?
Able to be deformed low modulus of elasticity for compresios, shear and tension (modulus of elasticity- how much stress is required for relative amount of strain)
Why is brain tissue incompressible and how does it relate to being a mechanical property?
Made up of 70% water (which is incompressible) cannot decrease volume- but still soft
- Eg. if compressed vertically, it will expand radially/horizontally = no change in volume
Why is the brain tissue viscoelastic and how does it relate to being a mechanical property?
strain rate sensitive
- want to know about injuries which occur at high rates of strain
Why does the brain have a very low permeability and how does it relate to being a mechanical property?
a lot of force for flow to pass through resistance to fluid flow through it
What is the general threshold for strain for the brain?
At a high strain rate > 10s-1
- Injury threshold ~ strain > 20%
- Tract-orientated strain threshold for injury ~b (white matter in axons- viscoelastic; strain rate dependent; can’t strain very much = break, rupture)
What is the effect of strain rate of compression (compression tests) on the stiffness of the brain (modulus of elasticity)?
As strain rate of compression was applied fast rate = stiffer brain (increase modulus of elasticity); reach higher values of stress for a given strain rate (this happens in viscoelastic materials)
“white matter behaviour is _____ (more/less) anisotropic than gray matter.
more
“different degrees of anisotropy exist within the white matter” –> correlates with the neurostructural organisation –> affect biomechanics
What is an anisotrophic object?
response different depending on orientation of force
Brainstem and internal capsule are________ oriented
vertically
Corona radiata is ______orientated. What does this mean?
multi-axially; fan out= radiate
Corpus callosum has a _______ orientation. What does this mean?
L-R; (uniform- all fibres go L-R)
What is the order for level of isotrophic from most to least? (grey matter; CR; CC)
Grey > corona radiata > corpus callosum
What is the level of isotrophy (shear) between grey matter and corpus callosum?
grey &CC significantly different
- grey matter almost 2x CC stiffness
- CC is more compliant- undergo more strain when subjected to shear- more vulnerable (can’t strain more than 6-7% before yield)
Is grey matter anisptrophic or isotrophic?
Isotrophic
What is the level of anisotropy between corpus callosum and corona radiata?
CC > CR
(matches with degree of alignment of axons)
Corpus callosum has higher _________ (parallel/perpendicular) shear modulus than ________ (parallel/perpendicular). Still compliant to shear - vulnerable.
parallel; perpendicular
______ forces and ______loading are related to brain mass.
Shearing; inertial
(brain is vulnerable to shear - axons vulnerable to tensile (rapid rate))
Smaller brains can tolerate much ______ (greater/smaller) acceleration/deceleration forces. Why?
greater; large brain mass = greater inertia
How does the alignment of the brain in quadrupeds and human differ?
brain and spinal cord almost at right angles which may increase rotational shearing forces
(stiff stalk with large mass on top (rotation, shear and tensile forces)
So for a given impact, the brain deforms in _____ (sensitive in rotation) makes it more sensitive to _____ than linear translation
shear; rotation
(brain bulk modulus (compression) = 5 x shear modulus)
What are 2 factors of external loading to the head that may affect the intracranial contents?
- Direct contact: displacing or deforming the skull or intracranial partitions high focal KE and relatively low cranial momentum
- Differential motion between skull / dura and the intracranial contents acceleration/deceleration forces impart large-momentum, rotational, tensile and shear forces but relatively low kinetic energy
What is “direct contact” as an external loading to the head that may affect the intracranial contents?
Local injury displacing or deforming the skull or brain.
High focal KE and relatively low cranial momentum.
What is “differential motion” as an external loading to the head that may affect the intracranial contents?
between skull, dura and brain.
Low KE, but acceleration/deceleration impart large momentum, rotational, tensile and shear forces.
Brain lagging behind the skull motion during head acceleration (inertia).
Contents _____ behind the motion of the skull during _____ of the head (inertial or impulsive phenomena)
lags; acceleration
______ impact is most common. This produces both ____ & _____ head kinematics. Brain is more sensitive to ______ than _____ translation
Oblique; linear; rotational; rotation; linear
Would you rather be hit in the head mid air, or when your head is against a wall?
Better to have head on wall
- If head is free to move and then impacted by rapid, strong oblique force –> forces go to brain than skull (loss of consciousness, diffused axonal = poor outcome)
- Impact to a head that is free to move (and change in velocity) produces loss of consciousness more often than one that is constrained, with the latter being more likely to cause localised defects of the skull and brain
What is the level of isotrophy (shear) for grey matter and corona radiata?
Grey has similar shear modulus to corona radiata.
White matter is _______(isotrophic/anisotrophic). Grey matter is _______ (isotrophic/anisotrophic).
anisotrophic; isotrophic
