Neuroscience Meninges Ventricles Lecture 1
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- embryological origin of meninges
- mesoderm
- Endosteal layer of cranial dura
- adherent to inner surface of cranium Not continuous w/ dura of spinal cord
- Meningeal layer of dura
- Continuous w/ dura of spinal cord
- Dura mater septa
- Septa: inward reflections of dura 4 locations in brain: Falx Cerebri Tentorium cerebelli Falx cerebelli Diaphragma sellae
- Falx cerebri
- Located in longitudinal fissure b/t cerebral hemispheres Ends just above corpus callosum
- Tentorium cerebelli
- Horizontal b/t the occipital lobes and cerebellum Attached to falx cerebri olong median plane posteriorly Lateral borders attached to skull Tent-like--> "tent"orium
- tentiorium incisure
- opening in anterior tentorium cerebelli for midbrain
- posterior cranial fossa
- space inferior to tentorium cerebelli
- supra and infra tentorial lesions
- refer to lesions above or below tentorium cerebelli
- Falx cerebelli
- dural fold between the two hemispheres of the cerebellum
- diaphragma sellae
- forms roof of hypophyseal fossa, stalk of pituitary passes thru this dural sheath
- venous sinuses
- endothelium lined blood channels b/t two layers of dura found b/t endosteal and meningeal layers or two meningeal layers
- superior sagittal sinus
- located within attaced borders of falx cerebri formed b/t endosteal and meningeal layers of dura Receives: branches from the superior cerebral veins on convexity of cerebral hemispheres veins from the meninges, bone, scalp, nose--providing route for infecting CNS site where cerebrospinal fluid is returend to systemic circulation
- inferior sagittal sinus
- extends along inferior free margin of falx cerebri, formed b/t two meningeal layers of dura drains medial aspect of brain
- straight sinus
- posterior continuation of the inferior sagittal sinus Empties into transverse (lateral) sinus Formed by great vein of galen and inferior sagittal sinus Supratentorial space-occ lesion can block and impede venous outflow from brain--> perivenous compression hemorrhage
- Transverse sinus
- Also called lateral sinus continuation of straight sinus around lateral aspect of hemispheres
- Arachnoid villi
- Protrusions of meningeal dura into venous sinuses; main site of CSF passage into systemic circ.; large numbers of arachnoid villi found in sagital sinus
- Arachnoid granulations
- macroscopic structures formed by groups of arachnoid villi which often calcify w/ age.
- Pia
- innermost meningeal layer, thin vascular membrane that adheres closely to the surface of brain and spinal cord. Covers ventricals
- vasculature of pia
- blood vessels in subarachnoid space on surface of pia.vessels pass into brain w/ sleeve of pia and perivascular space
- choroid plexus
- structure primarily involved in production of CSF; pia is part of it. Telachoroidea + ependyma = choroid plexus.
- ventricles
- CSF filled cavities in the brain
- ependyma
- thin, one layer of lining epithelium (called cuboidal epithelium b/c of appearance)
- telachoroidea
- vascular tufts of pia invaginated into ventricles
- Locations where CSF is found
- ventricles, subarachnoid space, cisterns
- function of CSF
- cushioning of brain in solid vault
- CSF protein content
- 15-45mg/100ml
- CSF glucose content
- 40 - 80 mg/100 ml, 2/3 of blood glucose level
- CSF cell content
- 0-5 lymphocytes per mm^3
- CSF volume
- 125-175 ml
- ion content of CSF relative to blood
- more Na and CL, less glucose and K, very little protein
- pink CSF significance
- blood in CSF, usually bleeding aneurysm in subarachnoid space
- yellow, clotting CSF significance
- increased protein content (sometimes b/c tumor), also may be from lysis of red blood cells w/ hemoglobin --> bilirubin
- cloudy CSF significance
- cloudy white --> bacterial meningitis (neutrophils), increased protein & dec glucose. Slightly Cloudy--> viral meningitis (lymphocytes) near normal protein and glucose
- Gram's stains/cultures on normal CSF
- negative
- Mechanism of CSF secretion
- cuboidal cells secrete Na; glucose and protein not very diffusable; low K b/c possible active K transport in opposite direction
- brain-CSF barrier
- barrier of tight junctions of ependymal cells, but CSF diffuses into parenchyma. Alcohol and other lipid solubles enter brain from CSF. Hangover from toxic effect on meninges and neurons, maybe swelling and stretching of meninges w/ dehydreation
- CSF rate of production
- continually produced, 500-750 mls/day. 4-5 x Volume at any time (125-175 ml)
- Sites of CSF production
- formed by choroid plexus primarily in lateral ventricles, also in fourth ventricle
- CSF circulation
- 1) produced in lateral ventricles, passes trhu septum pellucidum (interventricular foramen of Monro) 2) Enter 3rd ventricle, passes posteriorly thru cerebral aqueduct (aqueduct of sylvius) 3) Enters 4th ventricle, thru two lateral foramina of Luschka and medial foramen of Magendie in roof of 4th vent. 4) Enters subarachnoid space, around brain, central canal of spinal cord (small hole in middle of spinal cord) which is continuous w/ 4th ventricle
- Return of CSF to circulation
- 1) thru arachnoid villi which project from the subarachnoid spaces into the dural venous sinuses (primarily the superior saggittal sinus) 2) arachnoid villi contain trabeculae and CSF 3) one way valves for CSF
- Subarachnoid hemmorage causes
- usually from aneurysm, most common aneurysm is berry (saccular) aneurysm at arterial jx's in circle of willis--often during exertion. Also subarachnoid hemm from trauma, leakage of AVM, angiomas
- Symptoms of subarachnoid hemmorhage
- sudden headache, stiff neck (nuchal rigidity), altered level of consciousness
- nuchal rigidity
- stiff neck seen in number of neurological conditions. From irritation of meninges in posterior fossa and cervical canal, stimulating nerve roots resulting in reflex spasm and contraction of posterior neck muscles
- Types of hydrocephalous
- non-communicating hydrocephalous, communicating hydrocephalous
- Non communicating hydrocephalus characteristics
- 1) fluid flow out of ventricles or 4th ventricle is blocked
- most common cause of non-communicating hydrocephalous in adults
- blockage of canal of sylvius (from supratentorial space occupying lesion) causes fliuid to build up in lateral and 3rd ventricles
- Common cause of non-communicating hydrocephalous in children
- aqueductal stenosis in infants whose mothers had mumps or rubella
- Dandy Walker malformation
- from developmental arrest of hindbrain; cyst develps producing grossly enlarged posterior fossa and hydrocephalou
- Arnold Chiari malformation
- displacement of brainsten and/or cerebellum into cervical canal closing off foramina in the roof of 4th ventricle
- manifestations of brain damage from non-communicating hydrocephalous in infants and adults
- infants:head enlarges, may or may not be brain dammage 2) adults brain is flattend against skull w/ brain dammage. Brain herniation and death follow.
- treatment of noncommunicating hydrocephalous
- shunt made b/t lateral ventricle and cistern, or lateral ventricle to peritoneal cavity. w/ adults hydrocephalous secondary to another disorder
- communicating hydrocephalous
- caused by either impaiired return of CSF (i.e. excess protein block arachnoid villi) to circulation or increased CSF
- communicating hydrocephalous treatment
- medication to reduce CSF production or surgically destroying choroid plexus
- cerebral edema definition
- swelling of the brain due to increase in fluid
- three major types of cerebral edema
- 1) vasogenic edema, 2) cytotoxic edema 3) interstitial edema
- vasogenic edema
- cerebral edema caused by increased permeability of brain capillary endothelial cells, causes extracellular volume increase
- cytotoxic edema
- cerebral edema with increased intracellular fluid volume
- interstitial edema
- CSF movement from ventricles into surrounding brain tissue due to increased CSF tissue
- meningitis
- inflammation of meninges
- common symptoms of meningities
- high fever, irritability, lethargy, severe headache, vomiting, extreme sensitivity to light (photophobia), nuchal rigidity, and "twitching"
- routes of infection of CNS
- cardiopulmonary system, nasopharynx and sinuses (including dural venous sinuses), middle ear, skull fracture, scalp and face, and along nerves
- Meningeal space involved in meningitis
- commonly arachnoid/subarachnoid space/ pia
- leptomeninges
- arachnoid and pia
- adhesions (CNS)
- adhesion b/t pia and arachnoid, complication of meningitis, interferes w/ circulation of CSF in the subarachnoid space, can impede return of CSF, causes communicating CSF
- cause of severe head and neck headache of meningitis
- due to inflammation and stretching of dura, which receives trigeminal (supratentorially) and cervical (infratentorially) innervation, results in pain being referred to forehead and face, head and back of neck
- meningoencephaloyentriculitis
- encephalitis and ventricular inflamation, west nile virus may cause this
- hygromas
- pooling of CSF, may result in arachnoid tearing from trauma
- types of brain herniation
- tonsillar (tonsil into foramen magnum) and uncal (uncus into tentorial incisure)
- signs of uncal herniation
- decreased consciousness, dilation of the pupil of the eye on the side of herniation (from compression of parasympathetic fibers w/in CNIII)
- signs of tonsillar herniation
- may be unconscious (neurons in the medullary reticular formation control conciousness), abnormalities in heart rate and breathing (medullary portion of reticular formation controls vital functions)
- hemorrhage involving meninges/sinuses in infants description
- tearing of veins as they enter the superior sagittal sinus or from tearing of venous sinuses, rapid compression may tear attachments of falx cerebri from tentorium cerebri
- epidural hemorrhage
- between the endosteal and menigeal layers of dura, or between bone and endosteal dural if fracture rips dura from bone; side of the head--> middle meningeal artery
- brodmann area compressed by hemmorahage of midle meningeal artery
- compression of primary motor cortex (area 4), difficulty performing volantery motor movement contralaterally
- subdural hemorrhage
- bleeding between dura and arachnoid, most commonly from tearing of superior cerebral veins at point of entrance into superior sagittal sinus (bridging veins), usually blow to front or back of head, more comon in elderly
- contusion CNS
- bruise of surface of brain, usually hemorrhages of variable size
- concussion
- transient disruption of brain function
- contents of subarachnoid space
- trabeculae, CSF, Blood vessels
- Trabeculae of subarachnoid space
- bridge arachnoid and pial membranes, resemble spiderweb
- CSF
- fluid which bathes the brain tissue and helps to distribute and equalize pressure w/in the skull
- Blood vessels location in meninges
- all major blood vessels of brain lie in subarachnoid space before entering brain parenchyma
- cistern definition
- regions of subarachnoid space where pia and arachnoid are widely separated, contain pools of CSF
- major cisterns
-
1 cerebomedullary cistern (cisterna magna),
2 pontine cistern,
3 interpeduncular cistern,
4 lumbar cistern - cerebellomedullary cistern
- cistern which spans the space over the cerebellum and the part of the brainstem called the medulla
- pontine cistern
- cistern which lies over the pons
- interpeduncular cistern
- cistern which lies over the interpeduncular fossa (ventral brain surface)
- lumbar cistern
- extends from vertebral levels L1/L2 to S2