D Neuro Gross Part1a

7/18/2019 D Neuro Gross Part1a

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G r o s s A

n a t o m y

G r o s s A

n a t o m y

o f t h e B r a i n

o f t h e B r a i n

P a r t 1 P a r t 1



Neurobiology – Gross Anatomy of the Brain (part I)

On the external surface of the brain are the cerebral and cerebellar cortices

which are coered by the three meningeal layers (dura! arachnoid and pia)" #he

surface topography consists of eleations (conolutions) called gyri! shallow

depressions called sulci and deeper indentations called fissures" #he cerebrumis also diided into fie lobes! four of which (frontal! parietal! temporal and

occipital) are readily isible and the insula which is hidden in the depths of the

lateral fissure" It is all protected by the scalp!s$ull and meninges"



#he s$in on the head is firmly connected to the epicranial aponeurosis! which

moes freely oer the surface of the pericranium and cranium due to the

presence of a layer of interening loose %&#'" #his epicranial aponeurosis is

actually the intertendon of the occipitofrontalis muscle" #he word scalp is

actually the acronym for the

following for s$in with

numerous hair follicles!

sweat and sebaceous

glands! & for the dense

%&#'! A for the epicranial

aponeurosis between thefrontalis and occipitalis

muscles! * for the layer of

loose %&#' that proides

mobility to the s$in and +

for the pericranium

(forming the externalperiosteum of the cranial

bones)"



#here are eight cranial bones and fifteen facial bones that ma$e up the s$ull"

#he eight cranial bones are the four midline singular bones (frontal! ethmoid!sphenoid and occipital) and the two bilateral paired bones (parietal and

temporal)" #he fifteen facial bones are the three midline singular bones

(mandible! ethmoid and omer) and six bilateral paired bones (maxillae!

inferior nasal conchae! ,ygomatic! palatine! nasal and lacrimal)" #he only

moable bone is the mandible that forms the temporomandibular -oint (#./)

connecting the neurocranium (protecting the brain) and iscerocranium"



#o add protection and support for the brain! neres and essels inside the s$ull!

certain bones are reinforced to withstand force" #he three most notable are the

occipital! frontonasal and ,ygomatic arch0lateral orbital margin butresses" In

order to compensate for the increased density of these strong pillars of bone!

some s$ull bones are less mechanically stressed and become pneumati,ed (%air

filled')"



#he s$ull is composed of a neurocranium or calaria (protects the brain) and the

iscerocranium (forms the framewor$ of the face)" .ost of the neurocranium

deelops by intramembranous ossification whereas the iscerocranium is often

referred to as the chondrocranium due to its cartilaginous origin" #he lateral

aspect of the s$ull demonstrates the arious pro-ections! indentions! opening

and lines (including sutures and lines for muscle attachments)"



#he anterior aspect of the s$ull demonstrates the arious pro-ections! indentions!

opening and lines (including the sutures! arious foramina for neres and essels

and details of the orbit and nasal caities)"



#he inferior aspect of the s$ull possesses numerous foramina! pro-ections and

articular surfaces of interest"



#he iew of the floor of the cranial ault demonstrates the openings that were

also seen on the inferior iew" #he floor of the cranial ault is diided into three

cranial fossae (anterior! middle and posterior)"



#he anterior cranial fossa houses the frontal pole of the frontal lobe of the

cerebrum1 the middle cranial fossa houses the temporal pole of the temporal

lobe of the cerebrum and the posterior cranial fossa houses the cerebellum"



2ith an initial lateral iew of the brain! the lobes and lines of diision are

apparent" 3pon further reiew! the

specific gyri and sulci can be

identified and then correlated

with their specific functions"



2ith an initial medial iew of the brain! the lobes and lines of diision are

apparent" 3pon further reiew! the

specific gyri and sulci can be

identified and then correlated

with their specific functions"



Also! when loo$ing at the

brain from a %entral' or

%inferior' iew! the brain

stem and cranial neres are

obious" #he frontal!temporal and occipital poles

are also apparent"



4eep to the cortex! three types of &N white matter fiber tracts exist including

associational 5 connect parts within same hemisphere

commissural 5 connect right and left hemispheres (ex corpus callosum)

pro-ectional 5 ascending 6 descending tracts from and to the spinal cord



*ocated een deeper are the cerebral (basal) nuclei which represent the deep

gray matter which are still sometimes referred to as basal ganglia eenthough

they are a &N component" #hese structures are areas that inhibit moement

as a result of releasing the neurotransmitter dopamine and they include the

corpus striatum made up of the caudate nucleus and the lentiform nucleus! the

latter of which is in turn made up of the putamen and the globus pallidus" #heclaustrum and the amygdaloid body ma$e up the rest of the collectie basal

nuclei"



#he second of the fie secondary

brain esicles is the

diencephalon which is

composed of the epithalamus!

thalamus! and hypothalamus"#he epithalamus possesses the

pineal gland (epiphysis) which is

associated with 785hour

circadian rhythms that affect our

day5to5day actiities" #he

thalamus is the ma-or relaycenter for all sensory input! with

the exception of smell! and some

motor function integration"

9inally! the hypothalamus is

associated with some seen or

eight ma-or body functions andis connected to the pituitary

gland by the hypothalamo5

hypophyseal portal system (the

adenohypophysis) or by two

hypothalamic nere tracts (the

neurohypophysis)"

A b tt i f th di h l d th b i t i i f th idli



A better iew of the diencephalon and the brainstem is a iew of the midline

section of the brain" #he internal structures obsered include the corpus

callosum (rostrum! genu! body and splenium)! the basal nuclei (ganglia) which

are deep gray matter areas! the anterior and posterior commissures! the

interthalamic adhesion (a$a" massa intermedia or middle commissure)! the

fornix! the septum pellucidum (lucidum)! the limbic %lobe' or system and thefiber tracts (white matter associational! commissural and pro-ectional)"



upport and protection of the brain is primarily due to the presence of the

meninges which are the %&#' coerings of the &N" #he tough! outer dura

mater (referred to as the pachymeninx) around the brain has both a periosteal

and a meningeal layer (which split to form the dural sinuses) superficial to themiddle arachnoid

which possesses

arachnoid illi

(granulations) and

trabeculae that

connect to the innerpia mater which is

adhered directly to

the brain tissue and

along with the

arachnoid! it is ery

delicate (collectiely!they are referred to as

the leptomeninx)"



#he dura mater is tough! inelastic"! fibrous! outermost layer that splits in two

(outer or endosteal layer adheres to bone and is asculari,ed and inner or

fibrous layer that is less ascular) and forms dura (enous) sinus and arious

reflections" #he arachnoid is the central layer separated from dura by subdural

space containing capillaries" It is! as mentioned preiously! a delicate! thin! non5

ascular membrane with thin trabeculae and made up of simple s:uamousepithelium with subarachnoid space containing with &9" #he arachnoid illi

which pierce the dura! return &9 to the blood (ia dural sinuses which possess

enous blood)" #hr pia mater is the ery delicate! fragile membrane that actually

dies deep into sulcii of the brain" It is composed of networ$ of collagenous

fibers superficially (the epipial tissue) and reticular and elastic fibers adhering to

neural tissue (the intima pia which surrounds blood essels as they pass intothe brain substance)"



On this figure! note the features of the dura! especially its relationship to the

arachnoid and the enous structures" #he arachnoid is basically transparent so

that the gyri and sulci of the cerebral hemisphere are isible" Also note the

anterior and posterior branches of the middle meningeal artery which due to their

external location on the dura! the inside surface of the parietal bone will hae

corresponding indentations"



#he meningeal layer of the dura mater sends extension as flat partitions deep

into the cerebral longitudinal fissure! the space between the inferior surface of

the occipital lobe and superior cerebellar surface! the ermal indention of the

cerebellum and forming the roof of the sella turcica ($nown as the falx cerebri!

tentorium cerebelli! falx cerebelli! and the diaphragma sellae! respectiely)"

#hese membranous dural partitions separate specific parts of the brain andproide additional stabili,ation and support to the entire brain"

#he entricles are the caities or expansions within the brain that are deried



#he entricles are the caities or expansions within the brain that are deried

from the lumen (opening) of the embryonic neural tube" #hey are continuous

with one another as well as with the central canal of the spinal cord and the

four entricles in the brain in the brain include two lateral entricles within the

telencephalon (separated by a thin medial partition called the septum

pellucidum)! the third entricle within the diencephalon which communicateswith the lateral entricles through openings called the interentricular

foramina (of .onro)! a thin! minute tubular cerebral (mesencephalic) a:ueduct

which connects to the fourth entricle shared by the metencephalon (the

pons and cerebellum) and the myelencephalon (medulla oblongata)"



& b i l fl id (&9) i l l l li id th t i l t i th



&erebrospinal fluid (&9) is a clear! colorless li:uid that circulates in the

entricles and subarachnoid space" It bathes the exposed surfaces of the

central nerous system and completely surrounds it performing seeral

important functions including buoyancy! protection and enironmental stability"

It is released from the speciali,ed capillaries called choroid plexus in each

entricle by the secretion of a fluid from the ependymal cells (coering thecapillaries) that originates from the blood plasma and is therefore similar to

blood plasma in its composition"

#he &9 leaes the

entricles through three

openings in the fourth

entricle" #wo lateralapertures (of *usc$a) and

a midline! medain

aperture (of .agendie)

allow for the &9 to

escape the entricles and

gain access to the

subarachnoid space

where it will eentually

reach the enous blood in

the dural sinuses"

Approximately ;<< ml of

&9 are made each day"

D Neuro Gross Part1a

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