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The Brain
Dr Ayman G. Mustafa
CNS = Brain + Spinal cord
Brain is divided into
1.Forebrain
2. Midbrain
3. Hindbrain
Hindbrain:
1. Pons
2. Medulla oblongata
3. Cerebellum
Brainstem:
Midbrain + Pons + Medulla oblongata
Directional terms
Above the brain stem:
Dorsal means superior
Ventral means inferior
Rostral means anterior
Caudal means posterior
Within the brain stem
and below:
Dorsal means Posterior
Ventral means Anterior
Rostral means Superior
Caudal means Inferior
Coverings of the brain
Brain is covered by three
protective layers of
connective tissue called
meninges
1. Dura matter
2. Arachnoid matter
3. Pia matter
Coverings of the brain
1.
•
•
•
Dura matter:
Tough fibrous membrane
Avascular
Composed of two layers
-Endosteal layer
-Meningeal layer
The two layers adhere tightly except in certain
areas to form Dural Sinuses
Coverings of the Brain
Dura matter has sheet like procesess (septa):
-Falx cerebri:
between cerebral
hemispheres
-Tentorium cerebelli:
above cerebellum
-Falx cerebelli:
between cerebellar
hemispheres
Coverings of the brain
2. Arachnoid mater:
Delicate
avascular membrane
Separated from pia mater by Subarachnoid space which
contains Cerebrospinal fluid (CSF)
Arachnoid villi: empty
CSF into superior
sagital sinus
Coverings of the brain
3. Pia mater:
- Innermost layer
- Vascular layer
- Tightly attached
to the brain
surface
Forebrain
Composed of :
1. The Diencephalon:
masses of gray matter
located around third
ventricle
Thalamus, situated dorsally
Hypothalamus, situated ventrally
Pineal gland
Forebrain
2. Cerebrum:
Largest part of the brain
Composed of:
Rt & Lt cerebral hemispheres
Separated by longitudinal
cerebral fissure
connected by corpus
callosum
Cerebral hemispheres
Each hemispheres is composed of :
1. Cerebral cortex:
outer layer
4-6 mm of gray matter
2. White matter
3. Basal ganglia
Masses of gray matter lie deep within
white matter
Each hemisphere is divided
into lobes by:
Central sulcus
Parieto-occipital sulci
Lateral sulcus
And two imaginary lines
Cerebral Hemispheres
External appearance:
• Each hemisphere is
organized into folds
called Gyri
• Gyri are separated
by fissures called sulci
Insular lobe lies deep
within the lateral sulcus
Internal Structure of Cerebral
Hemispheres
White mater: composed of nerve fibers (axons)
and glial cells
Types of fibers:
1. Commissural fibers:
connect regions of the two hemisphers
e.g Corpus callosum, Anterior commissure,
Posterior commissure
Internal Structure of Cerebral
Hemispheres
2. Association fibers:
-Short association fibers: connect adjacent gyri
-Long association fibers: bundled together to make
named structures
e.g Cingulum within cingulate gyrus
Connects frontal and parietal lobes with temporal
lobe
Internal Structure of Cerebral
Hemispheres
3. Projection fibers:
Nerve fibers that pass from
brainstem to the entire
cortex
Internal capsule, External
capsule, Extreme capsule
Corona radiata: optic
radiation, auditory
radiation
Internal Structure of Cerebral
Hemispheres
Septum pellucidum:
Thin sheet of gray and
white matter
Extend from corpus
callosum to fornix
Forms partition between
anterior horns of lateral
ventricles
It is a double membrane
Internal Structure of Cerebral
Hemispheres
3
Corpus callosum:
Large bundle of
commissural fibers
Parts:
2
1.Rostrum
2.Genu
3.Body
4.Splenium
4
1
Ventricles of the Brain
• Four CSF-filled cavities located within the
brain
• Lined by ependyma
• Contain specialized vascular structure for CSF
production (choroid plexus)
- Lateral ventricles (2)
- Third ventricle (1)
- Fourth ventricle (1)
• C – shaped
Lateral Ventricle
• Parts:
1. Body: in parietal lobe
2. Anterior horn: in frontal lobe
3. Posterior horn: in occipital lobe
4. Inferior horn: in temporal lobe
• Each lateral ventricle is
connected to the third
ventricle through foramina of
monro
Third Ventricle
• Narrow cavity located
between the two thalami
• Communicates with lateral
ventricles
• Communicates with fourth
ventricle through cerebral
aqueduct
Cerebral Aqueduct
• ¾ inch long
• Connects third
ventricle to fourth
ventricle
• Does not contain
choroid plexus
Fourth ventricle
• Tent shaped cavity
• Anterior to cerebellum
• Posterior to pons and
medulla oblongata
• Communicates with central
canal of medulla and spinal
cord
• Communicates with
subarachnoid space
through:
-foramen of magendie
-foramena of luschka
T1 weighted
T2 weighted
Choroid plexus
• Components:
-Endothelial layer
(fenestrated)
- Pial membrane
- choroidal epithelial cells
Blood-CSF barrier
CSF
• Made by choroid plexus
500 ml/day
• Active process
• Distributed in ventricles and SAS
• Clear and colorless
• CSF Vs blood serum
• Functions
CSF
Circulation
Arachnoid villi
Location
valve –like
function
Accumulation of CSF:
Hydrocephalus: internal vs external
Functional Localization of Cerebral
Cortex
Funtional Localization of Cerebral
Cortex
General Somatic Sensations
• Primary somesthetic area:
- Postcentral gyrus
- Posterior part of
paracentral lobule
(Brodmann areas 1,2,3)
• Somesthetic association
cortex
- Superior parietal lobule
(brodmann areas 5, 7)
Vision
• Primary visual cortex:
- Surrounds calcarine sulcus
(Brodmann area 17)
• Secondary visual cortex
- Surrounds primary visual area
(Brodmann areas 18, 19)
Hearing
• Primary auditory cortex:
- Inferior wall of lateral sulcus
(Transverse Gyri of heschl’s)
(Brodmann areas 41, 42)
• Secondary auditory cortex
- Posterior part of superior temporal gyrus
(Wernicke’s sensory speech area)
(Posterior part of Brodmann’s area 22)
Taste and Olfaction
• Primary gustatory cortex:
- lower end of postcentral
gyrus in the superior wall of
lateral sulcus
(Brodmann areas 43)
• Primary olfactory cortex
- Insula and uncus
(Brodmann area 34)
Motor cortex
• Primary motor cortex
- Precentral gyrus
-Anterior part of paracentral
lobule
(Brodmann’ s area 4)
• Secondary motor cortex
(Premotor area)
- Lateral aspect of frontal lobe
(Brodmann’ s area 6)
Motor cortex
• Expressive speech area
-Broca’s area
-Consist of Opercular &
triangular gyri)
(Brodmann’s areas 44, 45)
• Frontal eye field
-Lateral aspect of frontal
lobe
-Brodmann’ s area 8
Motor cortex
• Supplementary motor area
-Medial surface of frontal
lobe
-Brodmann’ s area 6