Head full of blood Flashcards
Brain represents how much of body weight? How much CO does it get? Responsible for how much O2 & glucose consumption?
- 2% of body weight
- 15% of CO
- 20% of O2 consumption
- 25% of glucose consumption
What are the 3 types of fluid in the head?
- arterial supply
- venous drainage
- cerebrospinal fluid
What is the venous drainage system good for?
- to decrease likelihood of increased intercranial P
- it is a series of valveless sinuses with collateral channels
What is the CSF good for?
- allows brain to float in the skull
- acts as lymphatic system in brain (?)
What are the meninges? What are the layers?
- CT covering that encloses & protects the brain & spinal cord
- dura mater, arachnoid mater & pia mater (exterior to interior)
What is the dura mater?
-‘tough mother,’ tough fibrous sack that surrounds brain & has firm attachment points to skull & sacrum, creates dural folds & venous sinus system of the brain
What is the arachnoid mater?
- fine, web-like appearance
- middle layer of meninges
- CSF flows underneath in the subarachnoid space
- forms arachnoid villi, responsible for reabsorbing CSF & returning it to the blood stream
What is the pia mater?
- ‘soft mother’
- very thin
- adheres to the brain & spinal cord
- impermeable to fluid
- covers every surface of the brain except some areas of the ventricular system
What are the 4 dural folds?
- falx cerebri- located in longitudinal fissure, separates hemispheres of cerebrum
- tentorium cerebelli- separates cerebellum from occipital lobe
- falx cerebelli- separates cerebral hemispheres in posterior cranial fossa
- sellar diaphragm- covers pituitary in it’s fossa
What are the denticulate ligaments?
- specialized structures of the pia mater
- are thin, ligamentous structures that emerge from the pia of the spinal cord & attach it to the dura mater
- thought to stabilize motion of the spinal cord
What is the filum terminale?
-CT cord, continuous with the pia mater, that extends from the lowest tip of the spinal cord (the conus medullaris) to anchor the spinal cord at the level of the sacrum & coccyx
What does the subarachnoid space contain?
CSF
What area do you do lumbar punctures on?
-cauda equina area, ALWAYS insert needle below L3 vertebra
What are the properties of CSF?
- small volume: 150 ml
- low pressure: 10 mmHg
- choroid plexus produces 450-500 ml/day
- CSF propelled cranially by brain movements & pulsations of surface arteries
What does the brain ‘float’ in? Why does it float in this? What is the weight of the brain normally vs in CSF?
- CSF
- 1400 g brain is 45 g when suspended in CSF
- cranial nerves & blood vessels are not crushed
- arachnoid trabeculae keep brain in place
What does the CSF move through?
-ventricles (intracerebral spaces)
What are the lateral ventricles & how many are there?
- lateral ventricles, 2
- C-shaped spaces derived from neural tube
- spaces curve from the medial part of the hemispheres around into the temporal lobes
Where does CSF flow? (order of flow)
lateral ventricles—> 3rd ventricle via interventricular foramen (above medulla, lie between halves of thalamus & hypothalamus)—> cerebral aqueduct (through midbrain)—> 4th ventricle (by/right in front of the cerebellum)—> into spinal canal or exit into subarachnoid space
How does CSF enter the subarachnoid space?
-exits the 4th through foramina of Luschka & Magendie
After CSF exits into the subarachnoid space what happens to it?
-ascends to superior sagittal sinus to be reabsorbed by the arachnoid granulations
What does the choroid plexus do?
- modifies ependymal cells that surround capillaries
- generates CSF in lateral, 3rd & 4th ventricles by filtering blood from capillaries that run through it
What is the blood-CSF barrier?
- tight junctions b/w choroidal epithelial cells
- prevents passage of large molecules
- O2, CO2, glucose can go in freely
What is the brain-CSF barrier?
-minimal restriction between ventricles & brain interstitium b/c needs to be getting metabolites, O2, glucose, etc through CSF
What are ependymal (glial) cells?
- line the interior of ventricles
- not connected by TJs
- fluid passes freely b/w brain interstitium & ventricles
- metabolites of neurotransmitters can move from brain to ventricles & be detected in spinal taps (catecholamines are lower in CSF of Parkinson’s)
What are arachnoid villi/arachnoid granulations?
- membranous filters that allow CSF to pass into venous blood of the superior sagittal sinus
- protrusions into dura created by the villi
- cerebral veins also drain into dural sinuses
What branches off the aorta to supply blood to the head? What are the branches afterwards?
Arch of aorta–>common carotid artery–>vertebral artery–>middle cerebral artery
Where does the internal carotid artery come from? What do they split into? What do they supply?
- ascends from brachiocephalic artery or arch of aorta
- internal carotid splits from external carotid at carotid sinus
- IC then splits into anterior & middle cerebral arteries
- supply most of cerebral hemispheres
Where does the vertebral artery come from?
- ascends from subclavian artery
- passes through transverse foramina of vertebrae C1-6
- penetrates atlanto-occipital membrane and dura
What does the basilar-vertebral system supply? What are the 2 arteries?
- spinal cord, brain stem, inner ear, cerebellum, occipital & temporal lobes
- vertebral arteries: unite to form the basilar artery on ventral medulla, spinal arteries & posterior inferior cerebellar arteries branch from here
- basilar artery: ascends on ventral surface of brainstem, anterior inferior cerebellar, pontine, superior cerebellar & posterior cerebral arteries all branch off of basilar artery
What are spinal arteries?
- vertebral artery: anterior (1, runs medially down the spine) & posterior spinal arteries (2, dorsal, run on either side)
- radicular branches of intercostal arteries
Symptoms of Occlusion (SOs) for anterior/posterior spinal arteries:
-loss of spinal cord fxn at level of occlusions (paralysis, loss of sensation)
SOs for posterior inferior cerebellar artery (PICA):
-wallenberg syndrome= loss of pain & temp sensation on contralateral side of body/torso &ipsilateral side of face
SOs for anterior inferior cerebellar artery (AICA):
lateral pontine syndrome= sudden onset of vomiting/vertigo, ipsilateral loss of sensation to face & ipsilateral facial paralysis
SOs for superior cerebellar artery:
ipsilateral limb dysmetria (lose ability to make smooth movements), contralateral loss of sensation
SOs for pontine artery:
-contralateral paralysis & loss of sensation, often results in death, several outcomes possible depending on size of infarct
SOs for labyrinthins artery:
ipsilateral hearing loss & vertigo
What is the circle of Willis?
- communicating branches from anastomoses b/w cerebral arteries
- anterior communicating: connects anterior cerebral arteries
- posterior communicating: connects middle to posterior cerebral arteries
Where is the middle cerebral artery?
- heads out laterally from internal carotid
- along lateral fissure & lateral surface of cerebral cortex
What are the two branches of the middle cerebral artery? What happens with occlusion (stroke) to each?
- cortical branches to lateral surface of cortex; paralysis & sensory loss to contralateral side, damage to dominal side usually results in aphasia (difficulty speaking)
- lateral striate arteries to internal capsule & basal ganglia (hemiplegia)
Where is the anterior cerebral artery? What does occlusion cause? What is abulia?
- along medial surface of cerebral cortex, including cingulate gyrus (part of limbic system)
- paralysis & sensory loss in contralateral leg & foot
- abulia: lack of will or initiative, pronounced passivity, reduced social interactions, reduced emotional responsiveness, reduced spontaneous motions
Where does the posterior cerebral artery project to? What can occlusions cause?
- projects to the occipital & temporal lobes
- occlusions can cause: visual field defects, prosopagnosia (face blindness), contralateral deficits of the facial, vagus & hypoglossal n. & ipsilateral deficits of the occulomotor n.
Where do the veins drain in the brain?
- blood from cerebral hemispheres & brain stem drain outwardly into surface veins
- cerebral veins drain venous blood into dural sinuses
What are dural sinuses?
- compartments w/in dura mater
- spaces b/w periosteal & meningeal dural layers convey venous blood (meningeal dural layers from falx cerebri & tentorium cerebelli)
- located at junction of dural folds or b/w bone & dura
Where is the superior sagittal sinus?
-where falx attaches to interior of frontal, parietal & occipital bones
Where is the inferior sagittal sinus located?
-on the free edge of the falx
What are straight sinuses for & where are they?
-connect inferior sagittal sinus w/the confluens along the intersection of falx cerebri & tentorium cerebelli
What are the dural sinuses associated with?
-tentorium cerebelli & anterior cranial base
Where are the confluens?
-on the inside of the occipital bone, at the intersection of falx cerebri & tentorium cerebelli
Where does the transverse sinus extend to?
-extends outward from the confluens along the intersection of the tentorium cerebelli & interior surface of the occipital bone
What is the sigmoid sinus an extension of?
-extension of transverse sinus that drops down into the jugular foramen & becomes the internal jugular vein
Dural sinuses associated with the anterior cranial base?
-cavernosus sinus & inferior & superior petrosal sinuses
Where are the cavernous sinuses, what do they do & what do they contain?
- on either side of the body of the sphenoid bone
- receives blood from local sinuses, orbital veins–> RELATIONSHIP= BAC CAN SPREAD TO BRAIN
- communicates w/pterygoid plexus in lateral pterygoid muscle
- surrounds pituitary gland
- several structures pass through from inferior of the neurocranium, through meingeal dural layer, through sinus & then through posterior dural layer to exit through foramina in cranial base (internal carotid artery, CN: III, IV, V, VI)
- infections entering sinus can affect those structures
Where are the inferior & superior petrosal sinuses from & what do they do?
-drain blood from cavernous sinus posteriorly & into the transverse sinus
What are the spinal veins?
- anterior & posterior longitudinal sinuses
- basivertebral vein
What are the anterior & posterior longitudinal sinuses?
- valveless veins around dura
- blood flows up or down vertebral column
What are the basivertebral veins?
- drains vertebral body
* *how prostate cancer metastasizes into vertebrae
What are the emissary veins good for?
- venous blood can flow freely b/w scalp & dural sinuses
- thermoregulation: brain needs to be at constant temp
- during hyperthermia, cooler blood from surface travels internally through emissary veins to cool the brain
What is the BBB?
- consists of endothelium, pericytes, astrocyte feet & basal lamina
- prevents passage of large, water soluble molecules (ex. proteins) into brain
- capillary endothelial cells sealed by high resistance TJs
- BBB TJs maintained and induced by astrocyte feet
- peripheral endothelial cells more permeable to solutes
What gets taken in through the BBB and how?
- glucose & a.a.s penetrate endothelial cells via transporters
- gases (O2, CO2) penetrate directly through lipid membranes
Where does the BBB not exist in the brain? What does this allow?
- hypothalamus, area postrema & other periventricular regions
- capillaries permit passage of larger molecules
- hormones contact hypothalamic cell receptors
- digested poisons stimulate area postrema’s pathway to vomiting center
