University:
Kentucky State University
Course:
BIO 301 | Human Anatomy
Academic year:

2019
Views:

143

Pages:

48
Author:

Apolenajz

Ventricular System, The Cerebrospinal Fluid, and the Blood Brain Barrier The lateral ventricle It is Y-shaped cavity in the cerebral hemisphere with the following parts: 1) A central part (body): Extends from the interventricular foramen to the splenium of corpus callosum. 2) 3 horns: - Anterior horn: Lies in the frontal lobe in front of the interventricular foramen. - Posterior horn : Lies in the occipital lobe. - Inferior horn : Lies in the temporal lobe. It is connected to the 3rd ventricle by interventricular foramen (of Monro). Trigone (atrium): the part of the body at the junction of inferior and posterior horns Contains the glomus (choroid plexus tuft) calcified in adult (x-ray&CT). Interventricular foramen trigone body Anterior horn Interventricular foramen Relations of Body of the lateral ventricle Roof : body of the Corpus callosum Floor: body of Caudate Nucleus and body of the thalamus. Stria terminalis between thalamus and caudate. (connects between amygdala and venteral nucleus of the hypothalmus) Medial wall: Septum Pellucidum Body of the fornix (choroid fissure between fornix and thalamus (choroid plexus) Relations of lateral ventricle body Anterior horn Choroid fissure Relations of Anterior horn of the lateral ventricle Roof : genu of the Corpus callosum Floor: Head of Caudate Nucleus Medial wall: Rostrum of corpus callosum Septum Pellucidum Anterior column of the fornix Relations of Posterior horn of the lateral ventricle •Roof and lateral wall Tapetum of the corpus callosum Optic radiation lying against the tapetum in the lateral wall. •Medial wall --- two convexities: Upper (bulb of the posterior horn)  Splenium of the corpus callosum (bulb) Lower (Calcar avis)  Calcarine sulcus.  If Calcar avis is well developed, it obliterates the posterior horn. Bulb of splenium Relations of Inferior horn of the lateral ventricle •Roof tail of the caudate nucleus, amygdaloid body •Lateral wall Tapetum of corpus callosum and optic radiation •Floor medially  hippocampus laterally  collateral eminence (by collateral fissure) Lower part of choroid plexus enter this horn from the temporal part of the choroid fissure Choroid plexus of Lateral Ventricle Choroid plexus projects into the ventricles on its medial aspect. Composed of pia matter covered with ependymal lining of the ventricle. Choroid plexus is made of tela choroidea (two layers of pia matter). Lies between fornix superiorly and thalamus inferiorly. Situated in the inferior horn of the lateral ventricle. Projects into the choroid fissure Formed by posterior choroid branch of PCA (body) and anterior choroid branch of ICA (inferior horn) The lateral ventricle Body Corpus callosum Choroid plexus anterior horn Posterior horn Bulb of post horn Calcar avis Choroid plexus Interventricular foramen Inferior horn Superior view Thalamus Caudate nucleus A B F K G C H I D M E N L J Caudate nucleus Internal capsule Anterior limb Genu Posterior limb Retrolentiform part External capsule Lentiform nucleus Roof The third ventricle It is a narrow slit like cleft between the 2 halves of the diencephalon. Boundaries: - Roof: Thin layer of ependyma stretched between lateral walls containg choroid plexus (1). - More superiorly, fornix, septum pellicidum and corpus callosum - Anterior wall: Columns of fornix (2), anterior commissure (3), Lamina terminalis (4) & - Floor: Hypothalamus [ optic chiasma (5), tuber cinereum (6) Anterior Mammillary body (7)] & wall tegmentum of midbrain. - Posterior wall: Pineal body (8), posterior commissure (9) & aqueduct of sylvius (10). 5 - Lateral wall: Thalamus & hypothalamus. Anterior wall Posterior wall Floor 1 2 Thalamus 3 4 Roof 8 Hypothalamus 6 7 Floor 9 tegmentum of midbrain 10 Posterior wall Connections: It is connected with the lateral ventricle through interventricular foramen & with the 4th ventricle through cerebral aqueduct. Suprapineal Recesses: Recess 1) Optic. 2) Infundibular. 3) Suprapineal. 4) Pineal within the stalk. Optic recess Infundibular recess Pineal Recess Choroid plexus of Third Ventricle Formed of tela choroidea above the roof of the ventricle. Vascular tela choroidea projects downward on each side of the midline, invaginating the ependymal roof of the ventricle. Blood supply of choroid plexus of third ventricle is derived from choroidal branch of posterior cerebral artery The fourth ventricle It is a diamond shaped cavity of the hindbrain. It lies behind the pons & open medulla & in front of the cerebellum. Its superior angle is continuous with the cerebral aqueduct of midbrain & its inferior angle is continuous with the central canal of closed medulla (at the obex). It has 2 lateral recesses which curve around the inferior cerebellar peduncle & open by lateral apertures in the subarachnoid space at the flocculus . The roof: Is tent shaped & is formed of - The superior cerebellar peduncles (SCPs). - the superior medullary velum (SMV) stretching between the 2 SCPs. - The inferior medullary velum (IMV) which has a median aperture (of Magendie) connecting the 4th ventricle to the subarachnoid space. SMV Cerebellum IMV Median aperture Floor of the 4th ventricle Superior Cerbellar peduncle Middle Cerbellar peduncle Inferior cerebellar peduncle 30 T shape. Choroid plexus of Fourth Ventricle Formed of highly vascular tela choroidea. Suspended from the inferior half of the roof. Blood supply: Posterior inferior cerebellar arteries. (vertebral arteries) Subarachnoid cisternes 1- Cerebello-medullary cisterna (Cisterna magna) Between cerebellum and roof of 4th ventricle Receives foramen of magendie 2- Pontine (ponto-medullary) cisterna In front of pons and medulla Contain basilar and vertebral arteries Receives foramens of luchka Transversed by roots of lower 8 cranial nerves 3- Interpeduncular cistern Lies over interpeduncular fossa Contains circle of willis Transversed by roots of 3rd and 4th cranial nerves 4- Cistern of lateral fissure Contains the middle cerebral vessels 5- Callosal cistern Lies above corpus callosum Contains anterior cerebral vesseles 6- Chiasmatic cistern Lies around optic chiasma The Cerebrospinal Fluid (CSF) It is the fluid filling the ventricles & central canals of the CNS and subarachnoid spaces around brain and spinal cord. Production of CSF: It is secreted by the choroid plexuses in the medial wall of the lateral ventricles & the roof of the 3rd & 4th ventricles Circulation of CSF: It circulates in the ventricles & central canals of the CNS. It leaves the lateral ventricle through interventricular foramen to the 3rd ventricle then to the 4th ventricle through cerebral aqueduct of midbrain & leaves the 4th ventricle through its 3 apertures to the subarachnoid space forming a water cushion to protect the brain & spinal cord. Absorption of CSF: It is absorbed by arachnoid villi & granulations to be excreted into the dural venous sinuses. Not an exam material Properties •Clear, colorless, transparent fluid •Normal Volume is 150ml (varies between 100 – 200 ml) •Rate of formation : 0.3ml /min (550ml/day) •Specific gravity : 1005 •Reaction : alkaline Functions •Supports the weight of the brain •Distributes the force of blows on the head •Mechanical shock absorber •Maintains the intracranial pressure •Nutrient •Removal of wastes Lumbar Puncture Procedure by which CSF is taken out from the subarchnoid space. CSF is drawn by introducing a needle between the 3rd and 4th lumbar vertebrae. (because the spinal cord terminates at lower border of L1 & subarachnoid space is wider ). Purpose of Lumbar puncture: •For diagnostic purposes •Spinal anesthesia •To measure CSF pressure Hydrocephalus accumulation of cerebrospinal fluid (CSF) within the brain. Not an exam material headaches, double vision, poor balance, urinary incontinence, personality changes, or mental impairment. In babies there may be a rapid increase in head size. Other symptoms may include vomiting, sleepiness, seizures, and downward pointing of the eyes (sunset eyes). Types of hydrocephalus Not an exam material Communicating (non obstructive) impaired cerebrospinal fluid reabsorption in absence of any CSF-flow obstruction between the ventricles and subarachnoid space. functional impairment of the arachnoid granulations Causes :subarachnoid/intraventricular hemorrhage, meningitis and congenital absence of arachnoid villi. Non-communicating (obstructive) caused by a CSF-flow obstruction. Foramen of Monro aqueduct of Sylvius dilation of both lateral ventricles and third ventricle. Fourth ventricle (e.g., Chiari malformation). foramina of Luschka and foramen of Magendie may be obstructed due to congenital malformation (Dandy-Walker malformation: cystic dilatation of 4th ventricle. Chiari malformation Chiari malformations (CMs) are structural defects in the cerebellum. They consist of a downward displacement of the cerebellar tonsils through the foramen magnum causing noncommunicating hydrocephalus as a result of obstruction of cerebrospinal fluid (CSF) outflow Signs&symptoms: Headache, tinnitus, dysphagia May be paralysis. Not an exam material Papilledma •Optic nerves are surrounded by piamatter, arachnoid mater and dura mater. •Subarachnoid space is extending around optic nerve to the back of eyeball. •Rise in CSF pressure compress retinal vein. •Congestion of the retinal vein and bulging of the optic disc. •Optic atrophy and blindness. The blood brain barrier barrier present between the brain and the blood Structure •The capillaries of the brain consist of endothelial lining which have tight junctions which close the pores in the blood vessels •Astrocytes completely cover the capillaries and make it less porous •The blood vessels have a thick basement membrane. •Exists in all parts of the brain except hypothalamus, pineal gland and area posterema The blood CSF barrier Blood CSF barrier: barrier between the blood and CSF exists at the choroid plexus whose function is similar to blood brain barrier. Doesn't allow the entry of substances into the CSF from the blood Queckenstedt sign Not an exam material The normal CSF pressure on lying on side is 60-150 mm water. In case of obstruction , normal variation of pressure due to pulse or respiration is absent. Compression of Jugular veins in the neck raises cerebral venous pressure and inhibits CSF absorption producing rise in CSF pressure. Faiure of this phenomenon is referred as positive queckenstedt sign. Kernicterus In fetus, newborn or premature the blood brain barrier is not fully developed. Toxic bilirubin enters CNS and produce yellowing of the brain. Drugs and BBB Easily pass (Chloramphenicol and tetracyclins, lipid soluble anestheia) + L-dopa (treatment of parkinsonism Don't pass (water soluble norepinephrine, and Dopamine)

Ventricular System, The Cerebrospinal Fluid, and the Blood Brain Barrier

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