Blood Supply to the CNS & CSF Flashcards
what are the 5 main pairs of arteries that supply the brain
1. rostral cerebral arteries
2. middle cerebral arteries
3. caudal cerebral arteries
4. rostral cerebellar arteries
= cerebral arterial circle (= circulus arteriosus)
- caudal cerebellar arteries
= basilar artery
what are the arteries shown
cerebrum
cerebellum
what are the arteries labelled
what is the function of the the cerebral arterial circle
anastromic system (junction between vessels) to preserve the brain from dramatic ischemia in case of occlusion of one of the contributing arteries to the circle
passive pressure dissipating system (maintain a constant blood pressure in the end arteries)
what is the cerebral arterial circle
elongated vascular ring at the base of the brain (below the hypothalamus surrounding the infundibular stalk of the pituitary gland)
what structures are shown
what are other sources for arterial blood
- internal carotid arteries
- single basilar artery
- anastomosing ramus from the maxillary arteries to the internal carotid arteries
- connection of the vertebral arteries to the internal carotid arteries
what is the rete mirabile
vascular network of small blood vessels
can be arterial or venous
what is the function of the rete mirabile
thermoregulation
heat exchange between warm blood from the body (rete blood) and the cooler venous drainage from the nasal mucosa (cavernous sinus)
blood is cooled before it reaches the brain
what is the blood supply to the brain in dogs and horses
internal carotid artery
what is the blood supply to the brain in other species
maxillary artery
what do the rostral cerebral arteries supply
medial aspect of cerebral hemispheres
what do the middle cerebral arteries supply
lateral ventrolateral aspects of cerebral hemispheres
what do the caudal cerebral arteries supply
occipital lobes
what do the rostral cerebellar arteries supply
rostral aspects of cerebellum
what do the caudal cerebellar arteries supply
caudal and lateral aspects of cerebellum
what blood reaches the brain in dogs, man and most mammals
carotid and vertebral blood reaches cerebellum and cerebrum
internal carotid arteries –> rostral & middle cerebral artery
basilar artery –> caudal cerebral & cerebellar artery
what is the flow direction in the basilar artery in dog, man
rostral
what blood reaches the sheep and cat brain
little or no vertebral blood reaches the brain
what is the flow direction in the basilar artery in the sheep and cat
caudal
anastomotic branches of the maxiallry artery to the internal carotid artery –> obliterated parts of the internal carotid artery (post-natally)
maxiallary artery = sole input to the brain
what blood reaches the bovine brain
vertebral and maxiallary blood reaches all parts of brain
anastomosing ramus from maxillary artery to internal carotid artery
connection of vertebral artery to internal carotid artery
what is the direction of flow in the basilar artery
caudal
what are the cranial system of the venous sinus divisions
- dorsal system of sinuses
- ventral system of sinuses
- connecting system of sinuses
what does the dorsal system of sinuses drain
drain the dorsal areas of the forebrain (dorsal cerebral veins)
deep dorsal parts of the forebrain (greater cerebral vein)
what does the ventral system of sinuses drain
drain the ventral areas of forebrain (ventral cerebral veins)
drains face, nasal cavity, orbit, upper teeth
what does the connecting system of sinuses drain
(paired) connecting sinus (or signoid sinus)
recieves the dorsal system (via transverse sinus) and the ventral system (via petrosal sinuses) and connects directly with the spinal sinus system
drains mainly via connecting sinus (sigmoid sinus) into maxiallary vein into the system circulation
what are the components of the dorsal system draining the dorsal regions of the brain
1. dorsal sagittal sinus (falx cerebri) drain dorsal regions (dorsal cerebral veins)
2. straight sinus (caudal part of falx cerebri) drain deeper dorsal parts (great cerebral vein)
3. transverse sinus (located in the osseous part of the tentorium cerebelli) dorsal sagittal sinus and straight sinus drain into the transverse sinus
what are the components of the ventral system draining the ventral regions of the brain
- cavernous sinus
- ventral petrosal sinuses (connects cavernous sinus to sigmoid sinus)
- dorsal petrosal sinuses (drains ventral region of the brain)
what regions do the ventral sinus sytem recieve blood from
face, nasal cavity, orbit and upper teeth
what is the connecting system of venous drainage from the brain
sigmoid sinus
S-shaped continuation of the transverse sinus
what blood does the connecting system recieve and where does it drain
dorsal system (transverse sinus) and ventral system (petrosal sinuses) and connects directly with spinal system (vertebral plexus)
drains into the maxillary vein into the systemic circulation
what are the structures shown
what is the arterial blood supply to the spinal cord
lumbar arteries of aorta, intercostal arteries and vertebral arteries supply,
paired spinal arteries supply,
dorsal & ventral root artery per spinal cord segments supply,
superficial and anastomosing arteries of the spinal cord supply,
deep arteries in the spinal cord leading to 3 vascular zones
what are the structures shown
what are the segmental arteries per spinal cord segment
lumbar artiers of aorta
intercostal arteries
vertebral arteries (supply paired spinal arteries which divide into –> dorsal and ventral root artery per each side)
what are the 3 longitudinal trunks in the spinal cord blood supply
dorsolateral arteries & ventral spinal artery
anastomosing arteries (sparse & irregular network) connects the dorsolateral and ventral spinal arteries (run through the whole length)
what do the vertical arteries of the spinal cord arise from and where do they run
ventral spinal artery and pass in ventral fissure towards centre of spinal cord
where do the radial arteries arise from
from all other arteries on the surface of the cord
what structures are shown
what structures are shown
inner vascular zone (vertical arteries only)
middle vascular zone (both vertical and radial artery)
outer vascular zone (radial arteries only)
how does venous drainage of the spinal cord occur
ventral spinal vein (drains into the spinal cord)
drains into
vertebral venous sinus –> segmental spinal veins –> vertebral veins (nec, C1-T4), azygos vein (thorax, T4-L3) & cadual vena cava (abdomen, L4-L7) –> systemic venous circulation
what does the ventral spinal vein drain
spinal cord and vertebral bodies
escorts ventral spinal artery along in ventral fissure of spinal cord
what structures are shown
what does the vertebral venous sinus drain
ventral spinal vein
valvless
in epidural space longitudinal on the floor of vertebral canal
linked to the sinus system of the brain
what is a fibrocartilage embolism
secondary embolism
–Acute onset of paresis / plegia
–Non-progressive
–Non-painful (most of the time)
–Most patients will be better rapidly depending on the severity of the lesion
–Secondary to embolism of fibrocartilage within the spinal cord artery (source of fibrocartilage assumed to be the intervertebral disc)
–Infarction
– ischaemia of the area of the spinal cord supplied by occluded artery
what is the blood brain barrier
barrier between the plasma (blood) and the intersitital spaces (brain)
highly selective barrier which prevents substances (toxins, drugs) from passing between 2 compartments
how is the BBB formed
non-fenestrated brain capillaries with tight junctions between endothelial cells of the capillary wall
surrounded by thick basement membrane and by a layer of foor processes from astrocytes
what structures are shown
what does transport between blood and brain depend on
physiological mechanisms within the endothelial cells
- diffusion
- carrier-mediated transport (glucose, fatty acids)
how are drugs transported between blood and brain
- simple diffusion if drug is small, unbound and lipophilic
- concentration gradient for less lipophilic drugs
- less likely carrier-mediated transport
where is the BBB present except a small number of discrete regions situated at margins of ventricles and the hypothalamus (circumventricular organs)
neurons in these regions need access to molecules circulating in the blood such as hormones or some potentially noxious molecules
throughout CNS except a small number
what are circumventricular organs
what is CSF
cerebrospinal fluid
clear, colourless fluid that surrounds entire CNS (located in subarachnoid space)
where does CSF originate from
capillaries throughout CNS
how is CSF produced
by selective ultrafiltrate of blood plasma (+active transport mechanisms)
major production site choroid plexus of lateral, third, and fourth ventricles
what is the function of CSF
- physical support (buoyancy)
- protection against trauma
- modulates pressure changes within the skull
- nutrition (transport metabolites, nutrients and neurotransmitters)
- chemical buffer (maintains ionic balance)
what structures are shown
how does the CSF flow
caused by blood pulsatations and motile cilia of the surface of ependymal cells
where does CSF flow
passes from lateral ventricles through the interventricular foramina into the 3rd ventricle
flow through the mesencephalic aqueduct into the 4th ventricle
flow into central canal of spinal cord or through the lateral apertures to the subarachnoid space
with each arterial pulsation CSF pressure rises and surges towards the lateral apertures
how is the CSF absorbed
by arachnoid villi in venous sinuses
venules in sub-arachnoid space
or by lymphatic vessels of cranial and spinal nerve roots
what structures are shown
what are the structures shown
how does communication occur in the ventricular system
lateral apertures
what structure is indicated
lateral apertures
what can altered CSF flow patterns lead to
syrinx formation (syringomyelia)
subarachnoid diverticula
hydrocephalus
what is the central canal
continuous with 4th ventricle
surrounded by grey matter
lined with ependymal cells
what is the subarachnoid space
contains CSF
contiguous with ventricular system circulation of CSF
a real space with clinical significance
what is the dubdural space
between dura and arachnoid
a virtual space in the normal live animal but that can be created by introduction of materials such as –> hemorrhage or injection of image contrast material
where can CSF be collected
cervical
flexion of neck required
enter in mid-line between skull and C1
stop advancing needle as enter CSF space
where is lumbar CSF collected in dogs, cats, horses, cow
dog: L5-L6
cat: L6-L7
horse: L7-S1
cow: L7-S1
what are the structurse shown
