WEEK 7 Nervous system 3 Flashcards
Where is the blood supply to brainspinal cord from
- from vertebral and internal carotid arteries
- deliver nutrients and oxygen
What are Vertebral Arteries and location
- branches of subclavian arteries
- ascend through neck via foramina transversaria of cervical vertebrae
- vessels loop over atlas (C1)
- enter skull via foramen magnum
What are internal carotid arteries and location
- branches of common carotid arteries
- ascend through neck in carotid sheath
-pass through carotid canal & enter cranial cavity
Explain how blood is supplied to spinal cord
via vertebral arteries
- branches fuse to form anterior & posterior spinal arteries
- medullary branches from the aorta join these spinal arteries
- posterior spinal artery supplies ascending [sensory] pathways
- anterior spinal artery supplies descending [motor] pathways
What is the Vertebral arteries Intracranial Course blood supply to brain
- right & left vertebral arteries run on medulla
- 2 fuse on ventral surface pons(now 1) – form basilar artery
- numerous branches to pons & cerebellum
- labyrinthine artery - internal ear
- basilar artery terminates as posterior cerebral arteries
What is the Internal Carotid Arteries Intracranial Course blood supply to brain
- Emerge on either side of pituitary fossa
Branches: - anterior cerebral artery
- middle cerebral artery
- ophthalmic artery - accompanies optic nerve into orbit
- Supplies pituitary gland & hypothalamus, amygdala, hippocampus, thalamus & midbrain
What is the circle of willis
- formed by anastomotic connections between cerebral arteries of each side
- the brain can receive blood from either the carotid or the vertebral arteries, reducing the likelihood of a serious interruption of circulation
- achieved through anterior & posterior communicating arteries
Describe how circle of willis formed
- From the ICA:
- Anterior cerebral artery passes forward & posterior communicating artery passes posteriorly
- anteriorly circle completed by anterior communicating artery
- posteriorly circle completed by anastomosis between posterior cerebral artery & posterior communicating arteries
What 2 branches does cerebral arteries have and functions
- cortical branches-> supply surface [cortex] of cerebral hemispheres
- central branches -> these penetrate into deeper tissues
- central branches are end arteries
- no anastomoses between end arteries & neighbouring vessels
Describe the cortical branches of anterior cerebral artery
- medial surface of hemisphere above corpus callosum
- includes olfactory bulb & tract, and parieto-occipital sulcus
- branches to superior border & narrow strips of lateral surface
includes sensory & motor areas of lower limb - during occlusion: sensory deficits & motor paralysis of contralateral lower limb
Describe the cortical branches of Middle cerebral artery
- most of external [lateral] surface of cerebral hemispheres
- corpus striatum [motor nuclei] & internal capsule [projection fibres]
- ruptures in internal capsule common cause of paralytic stroke
- during occlusion: affects upper limb
- can cause aphasia from damage to Broca’s & Wernicke’s areas
Describe the cortical branches of Posterior cerebral artery
- occipital lobe - calcarine branch significant – visual cortex
- branches to temporal lobe, thalamus & hypothalamus
- terminal branches to calcarine & parieto-occipital sulci
Describe strokes, causes
- also known as cerebral vascular accident (CVA)
- death/damage brain tissue - vascular aetiology – arterial
- can be occlusive & haemorrhagic
What is olccusive
- blockage in vessel (thrombus)
- causes insufficient blood supply - ischaemia
- transient ischaemic attack (TIA): resolves ± 24 hours
- severe/prolonged = infarction
What is haemoorhagic
- rupture/leak of blood vessels
- occur at branching points
- form hematomas
What are the 3 types of haematomas
->epidural – between dura & skull – middle meningeal artery
->subdural – between dura & arachnoid – rupture of bridging veins
->subarachnoid – between arachnoid & pia – rupture of aneurysm of cerebral artery
Where does the venous drainage of brain in external or superficial system occur
in subarachnoid space
Describe the venous drainage of brain in Internal or deep system
- deep veins on each side form internal cerebral vein
- internal cerebral veins unite to form great cerebral vein (of Galen)
- veins draining the brain enter into dural venous sinuses
What are Dural venous sinuses
- dilated channels
- walls: dura, periosteum, lining of endothelium
- terminate at jugular foramen in internal jugular vein
How are ventricles of the brain formed and locations
-in embryo, neural tube encloses neurocoele
-neurocoele expands to form chambers (ventricles) lined with ependymal cells
- each cerebral hemisphere contains one large lateral ventricle
-> separated by medial partition (septum pellucidum)
- third ventricle in diencephalon
communicates with each lateral ventricle via interventricular foramen
where is the 4th ventricle of the brain
- extends into medulla oblongata
- joins central canal of spinal cord
- connects with third ventricle via narrow canal in midbrain (cerebral aqueduct)
What is cerebrospinal fluid and 3 functions
- surrounds all exposed surfaces of CNS
- functions to
- support brain
- cushion delicate neural structures
- transport nutrients, chemical messengers, and wastes
How does Choroid plexus produces CSF
- specialized ependymal cells surround capillaries
- secretes about 500 ml of CSF into ventricles per day
- removes waste products from CSF
- adjusts composition of CSF
Describe the path of circulation for csf
from choroid plexus->ventricles->central canal of spinal cord
->materials diffuse between csf+interstitial fluid of cns across ependymal cells
- into subarachnoid space
->via two lateral apertures and one median aperture in roof of fourth ventricle
- to surround brain, spinal cord, and cauda equina
What are arachnoid villi
- extensions of arachnoid membrane
- extend through meningeal layer of dura mater into superior sagittal sinus
What are Arachnoid granulations
- large clusters of arachnoid villi in adults
- absorb CSF into venous circulation
What is the blood brain barrier, and materials can diffu
- isolates CNS from general circulation
- formed by network of tight junctions between capillary endothelial cells in CNS
-only lipid-soluble compounds like O2, CO2, steroids, prostaglandins, and small alcohols can diffuse into interstitial fluid of CNS
how is blood brain barier regulated
astrocytes
- releasing chemicals that control permeability of endothelium
What is the Blood CSF barrier
- formed by specialized ependymal cells connected by tight junctions
that surround capillaries of choroid plexus - limits transfer of substances to CSF
- allows chemical composition of blood and CSF to differ
BBB absent in protions of hypo allows?
allows hypothalamic hormones into circulation
BBB absent in post pit allows?
allows ADH and oxytocin into circulation
BBB absent in pineal gland allows?
allows pineal secretions into circulation
BBB absent in choroid plexus allows?
where specialized ependymal cells maintain blood CSF barrier
