3-the brain (cont.)

8/2/2019 3-The Brain (Cont.)

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Today we will finish the brain, we will speak about: the hindbrain, theventricular system (the chambers within the brain) and the vasculature of

the brain (the arterial blood supply to the brain)

The hindbrain is made from three parts:1) the pons (which mean the bridge)2) medulla oblongata3) Cerebellum

What are the structures contributing to the brain stem?1) midbrain

2) pons3) medulla oblongata

PonsPons (the bridge) connects the lower part of the brain to midbrain (I couldnot hear this ward), it is located anterior to the cerebellum and also itcontain axons that connect the two halves of the cerebellum together so itis bridging horizontally and vertically* pons contains nerve fibers that connects the two halves of thecerebellum and it controls the arousal .what we mean by arousal ?(whenwe weak up).

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Medulla oblongata

The second part is medulla oblongata (you DO NOT NEED to knowmore information than I tell you) is a part of brain stem.The medulla oblongata connects the brain with the spinal cord inferiorly at

the level of foramen magnum.Medulla oblongata contains:(1) median fissure (in the middle)and(2) Two bulges, those bulges are made by large motor tract(neurons axons) that descends down. Form where? From whichgyrus in the brain? Where is the motor area? The precentral gyrusthese axons descend in tract (bundle) from the precentral gyrus

passing through the medulla oblongata forming two at the anterioraspect of medulla oblongata which we call it the pyramids. the

pyramid contains bundles or descending part of motor neuronsfrom the precentral gyrus at the lower border of medulla oblongatawhere is continue with spinal cord, these motor tract crossoverfrom left to right and from right to left, we called this thedecussation of the pyramid(it is written in your book you have tofind it) .

The decussation means the crossover of the motor neurons from right toleft &from left to right andwe have also

(3) Two olives: two bulges beside the pyramid laterally .it contains amassof cells nerve body we call it nuclei.Important function of the medulla another than the crossover iscontaining the ascending sensory part to the postcentral gyrus,another important function is containing the cardiovascular system whichhave nuclei (neural cell body )controlling the rate and the force of heart

beating through the cardiovascular center within the medulla oblongataalso there is:(4) The respiratory center: to control the rhythm of the breathing

*so any injury to the medulla oblongata considered serious case,do you rememberwhiplash injury? (The dr. Did not answer but Ianswer instead): injury to the vertebrae in the neck, caused whenthe head jerks backwards, often occurring in a car that is struck

from behind

It results in direct death (the dr. means the injury to the medullaoblongata) .why? Due to injury in the respiratory &cardiovascular centerin the medulla oblongataMotor bundle crossover to opposite side at lower part of the medulla, we

call that decussation

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Cerebellum

Cerebellum which is the 2nd largest part of the brain, it represents tenth ofthe brains weight, however it contains half of the nerve cells of the brain,it is located in the posterior Cranial fossa. Beneath which dura flexion?Tentorium cerebelli so why we call it the cerebelli (and this is the duramatter and this called the falx cerebelli and these two lateral flexion istentorium cerebelli beneath them is the cerebellum and above it the

posterior aspect of the cerebrum separating cerebrum from cerebellum)this is according to the picture below.

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Cerebellum located in the posterior cranial fossa & covered bytentorium cerebelli.

The function of the cerebellum is coordination of muscle tone&movement on same side of the body. e.g. as you touch your nose so thecoordination of muscle movement on the same side of the body becausethere is not decussationAn important case is Ataxia: (Ataxia means: order & and A means:without): loss of muscle coordination due to damage to the cerebellum.So we tell the patient to put his finger over the tip of the nose, he can not.

Ventricular system of the brain

Now we move to another topic Ventricular system of the brain. Do youknow the meaning of the ventricle? Chamber.-we have chambers (like the heart-chambers) of the brain are connected toeach other so we call it ventricular system of the brain. It consists of twolateral ventricles and they are located away from the midline and two inthe midline.The two at the periphery or laterally to the midline we call them thelateral ventricle and those in the midline above each otherwe call themthe 3rd &4th ventricle ,so four chambers in the brain two laterally and twoin the midline.

The main function to these chambers in the brain is to produce thecerebral spinal fluid (CSF) which is contained in the subarachnoid space,Ventricular system of the brain contains choroids plexuses, and itsfunction is the secretion or production of CSF.Choroid (means membrane like) plexuses (network). Choroid plexuses

composed from three layers:

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(1) Projection from the pia matter (part of the meninges) inside theventriclealong with(2) blood capillaries and those blood capillaries are(3) covered

by specific kind of cells we call it ependymal cell(epithelial cell cuboidal

to short columnar cell) surrounds these blood capillaries and they havetight junction between each other to form what we call blood brainbarrier(BBB).How the choroid plexuses produce the CSF? The blood gets into thecapillary, the ependymal cells will filtrate the plasma from the blood to theventricle, by this the plasma becomes CSF, and CSF is mainly plasmacontaining all nutrient requiring.So four chambers in the brain containing choroid plexuses, which iscomposed of three layers and its function is to produce CSF. So this CSF

passes through this ventricle, from lateral ventricle through foramenbetween lateral &3rd ventricles we call it interventricular foramen one inthe right and one in the left, we have two interventricular foraminaconnected the lateral ventricle to the third ventricle then we have a duct

between the third and the fourth ventricle we call it the cerebralaqueduct in the midbrain, so the ventricles connected to each otherthrough interventricular foramina and cerebral aqueduct.When we look to the lateral Ventricle, it is located within cerebrum (in alarge cavity filled with CSF) and it has within it choroid plexuses. Thetwo lateral ventricles separated from each other by a septum (wall like

structure) translucent in it is appearance we call it septum pellucidum.

The 3rd ventricle located within diencephalon. What is the diencephalon?Thalamus & hypothalamus.The thalamus makes the lateral wall of the 3 rd ventricle, and the floor ofthe 3rd ventricle made by hypothalamus.So the wall of the 3rd ventricle is:*lateral wall by thalamus*interthalamic connection passing through the 3rd ventricle

*and the floor is made by hypothalamus

3rd ventricle communicate with the 4th chamber through cerebral aqueduct(in the cross section in the lab you should see the 3rd ventricle with its wall&the cerebral aqueduct)

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4th ventricle located between brain stem anteriorly & cerebellumposteriorly, it is actually in the hindbrain contains 3 foramina:in its roof, one in the midline foramen of Magendie's and two lateral tothe ventricle foramina of losochka, you do not need to know these names

just that there is three foramina in the 4th ventricle that communicate the4th ventricle with the subarachnoid space to drain the CSF from the 4th

ventricle to the subarachnoid (space between arachnoid and pia matter)

and this actually is the circulation of CSF.

The circulation of CSF: the plasma filtrates from the blood to theventricle and then to the subarachnoid space through these foramina andfrom the subarachnoid space it retains to the blood through sagittal sinusor the venous sinus. Where is it? In the dura matterbetween the periosteal& meningeal layer of dura.So the arachnoid makes projections to the venous sinuses mainly the

sagittal sinus to drain CSF

so if there is obstruction for one of these openings in the subarachnoid orin the ventricles( in the cerebral aqueduct ) leading to increase in theintracranial pressure which we call it hydrocephalus which means waterin the brain (hydro :water,cephalus:head).

hydrocephalus : excess CSF in the ventricle or the subarachnoid spaceleading to enlargement of the head in the infants ?because the skull boneis not closed yet in the infant. So the intracranial pressure increasingaffects the brain and the soft area leading to enlargement in the head.

*the condition is more sever when it is affecting the adult .why? becausethere is a compression on the brain this lead to:

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(1) Sever convulsion () due to the sever pain,(2) Mental disability

Hydrocephalus is life threatening condition in adults, we need emergency

treatment, we have to drain the CSF directly from the brain even ininfants.Usually the treatment is surgical to drain the CSF to a body cavity or toretain it to the subarachnoid cavity, usually we drain it to the peritonealcavity and go back to the brain circulation we call that shunt.

The causes of hydrocephalus are:(1) Over production of CSF (the choroids plexuses secretes too muchCSF.

(2) Obstruction of CSF flow.(A) If it is in the interventricular foramen, the enlargement is in the

lateral Ventricle.(B) If it is in the cerebral aqueduct, the enlargement is in the lateral

&the 3rd ventricle.(C) If it is in the foramina of the 4 th ventricle, the enlargement is in the

all the ventricular chamber(D) If it is in the connection between arachnoid &venous sinus, the

enlargement is in the ventricles &subarachnoid space

(3) Interference with CSF absorption (obstruction in the connectionbetween arachnoid &the venous circulation).

*In infants: it increases the size of the head

*In adults: it leads to sever convulsion and mental disability

The treatment is surgical to drain the CSF.

Arteries of the brain

Arteries of the brain, we know the arteries to the meninges are anteriorMiddle & post. Meningeal arteries however we have cerebral & otherarteries that provide blood supply to the cerebrum, the diencephalons andto the mid brain

The two main arteries to the brain are the two internal carotid arteries.From which artery? Common carotid artery. They enter through carotid

canal in the middle cranial fossa, and we have two vertebral arteries,

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vertebral arteries are branches of the first part of subclavian artery andthey pass to the brain throughforamen magnum.you have to read your text book for detailed anatomy of arterial bloodsupply to the brain

(1)2 internal carotid(2)2 vertebral arteries

Internal carotid when it inters the brain through carotid canal it gives fivebranches:(1)ophthalmic artery (not related to the brain ),from its name where itgoes ?to the orbit, it is passing through optic canal with optic nerve

providing blood supply to the eyes ball and another structure in the orbitand it terminates by forming supraorbital & supratrochlear arteries they

provide blood supply to forehead region( anterior half of the skull)Two important arteries to the cerebrum from internal carotid artery first

branch goes to the anterior aspect we call it(2) Anterior cerebral arteries from the right & left side and theycommunicate with each other by a small arteries the anteriorCommunicating branches (which is a small arteries connecting the twoanterior Cerebral arteries in each side) and they (the anterior cerebralarteries) go forward in the longitudinal fissure to provide blood supply tothe medial surface of the cerebellum until the level of paritoccipital sulcus

they pass around a structure we call it corpus callosum (corpus meansbody and callosum means hard).The corpus callosum contains white matter axons connecting the twohalves of the cerebrum also provide blood supply to the superior LateralHalf of the cerebrum ,around 2.5 cm on the lateral aspect so foot region inthe precentral gyrus receives blood supply from the anterior Cerebralarteries (because the inverted manner in the precentral gyrus foot above&head below)So it provides blood supply to the:

*the medial surface of the cerebellum until the level of paritoccipitalsulcus

* also provide blood supply to the superior Lateral half of the cerebrum.

The other artery is the (3) lateral or middle cerebral artery the largestbranch and it runs in the lateral sulcus Providing blood supply to thelateral aspect of the cerebrum except small area in superior &inferiorAspect of the cerebrum (the superior Receives from anterior cerebralarteries and the inferior From the posterior cerebral arteries ).

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The middle cerebrum runs in the lateral Sulcus and provides blood supplyto most of the lateral Aspect of the cerebrum.Small communicating branch from posterior aspect of internal carotidmakes connection between the internal carotid and posterior cerebral

artery.

We have mainly three cerebral arteries in the brain anterior, middle&posterior. The anterior & the middle one are branches from internalcarotid and the posterior Branch from the basilar artery.

(4)Posterior communicating arteries are communicating internalcarotid with posterior cerebral arteries

The last one (5) the choroidal artery: it is deep in the brain, and goes tothe floor of the lateral Ventricle where it ends in choroid plexus (the bloodcapillaries in the choroid plexus is from the choroidal artery which is

branch from the internal carotid)*you should know the five branches of the internal carotid

the arteries over the brain are the vertebral arteries one in each sideentering the foramen magnum passing over medulla oblongata until the

junction between the medulla & the pons when they unit to form a large

artery the basilar artery (it pass over the pons), however the two vertebralarteries when they unit to form basilar artery over the medulla oblongataregion it gives several branches:(1) The posterior Meningeal branch to the meninges specifically, the partwhich separate the two cerebral hemispheres which enter the cerebellum,what we call it? Falx cerebelli.

And it gives:

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(2) Anterior & posterior Spinal arteries which they pass over the spinalcord(3) Inferior Cerebellar artery to where? To the cerebellum(4) medullary artery to the medulla oblongata.

Do you remember another posterior Meningeal artery? Arise in the jugularforamen (the dr. Did not answer) (I searched for the answer, I didnot find it!!!(But I found in some sources that is a branch from occipitalartery & my friend found in another one that is a branch from ascending

pharyngeal artery) Please try to find the answer, I will ask the dr.)

The vertebral arteries give 4 branches(1) Meningeal artery to the meninges(2) Spinal artery to the spinal cord(3) Cerebral artery to the cerebellum(4) Medullary artery to the medullaAfter they unit to the basilar artery one of the most important arteries inthe brain, basilar artery it continue on the pons (I could not hear it)

between pons and midbrain they terminate in which we call it (1) post.Cerebral artery

The posterior cerebral artery turns backward at the level of midbrain andgoes to give blood supply to:

(a) The occipital lobe

(b) The lower aspect of the temporal lobe(C) The midbrain because it turns at the level of midbrain.

Also it gives(2) several branches, arteries to the cerebellum as anterior Inferiorcerebellar artery (the book said posterior inferior cerebral artery)

(3) It gives a labyrinthine artery: this artery passes deep in the skullthrough internal acoustic meatus to provide blood supply to inner ear

so they call it labyrinthine artery: a branch from basilar artery to theinner ear. Passes through which foramen? Internal acoustic meatus.sohow many structures pass through this foramen? 2 nerves,1 artery

.what are the two nerves ? (The dr. Did not answer) I answer instead:(A) Facial nerve(B)Vestibulocochlear nerve(4) Gives several arteries over the pons, pontine artery to the pons

Read the exact details because I will ask you about

these details exactly.

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last thing which I would like you to know is the circulus arteriosus(circle of Willis), since the blood supply to the brain is very important,if there is any problem in these arteries we have to compensate for that,in order to compensate we need another blood supply,these arteriescommunicate with each other to make anastomosis to make a circle to

provide blood supply when we have a shortage in blood supplycircle of Willis is the anastomosis between branches from internal

carotid and the vertebral artery .it composed of :*the anterior Communicating branch anteriorly between the twoanterior Cerebral arteries ,then*anterior cerebral arteries ,then* internal carotid ,then* posterior Communicating branch then posterior Cerebral, then*basilar artery

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So when you look at the brain, basilar artery divides to two posteriorcerebral arteries then to two posterior Communicating branches whicharise from internal carotid then anterior Cerebral arteries join togetherwith anterior Communicating branches.

middle cerebral artery is not included in circle of Willis .Anterior communicating branches join what? Anterior Cerebral arterythen internal carotid then posterior Communicating then posteriorCerebral then basilar.*middle (lateral )cerebral artery and vertebral artery are not included

in circle of Willis

DONE BY: HEBA GHOZLAN

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3-the brain (cont.)

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