Download DURAL VENOUS SINUSES Channels within meningal layer of dura

DURAL VENOUS SINUSES
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Channels within meningal layer of dura mater
Function: veins draining brain
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Components: Unpaired & paired sinuses
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Unpaired Sinuses: Superior saggital
Inferior saggital
Straight
Confluence
Occipital
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Venous Flow tends to be
- anterior to posterior
- posterior and downward
- from midline outwards
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UNPAIRED SINUSES
Superior saggital: lies in upper margin of falx cerebri
Terminates in the internal occipital protuberance
Drains into the confluence of sinuses
Paired Sinuses: Cavernous
Transverse
Superior petrosal
Inferior petrosal
Sigmoid
Inferior Saggital sinuses: lies lower margin of the falx cerebri
Joined by the great cerebral vein to form the straight sinus.
Straight sinus: located in the tentorial attachment of falx cerebri
Terminates turning left at internal occipital protuberance & becomes the left
transverse sinus
Occipital sinus: runs superiorly in cranial attachment of falx cerebelli & ends in
the confluence of sinuses.
Confluence of sinuses: The superior & the straight sinus converge at the
confluence of sinuses, from here blood flows laterally on either side in the
transverse sinus.
 PAIRED SINUSES
Transverse sinuses: lies in the attachment of tentorium cerebelli
Each transverse sinus runs forwards to lateral part of petrous temporal bone where it
turns inferomedially towards jugular foramen as sigmoid sinus
Superior petrosal sinus: Located in the anterior attachment of tentorium cerebelli
Connects posterior aspect of cavernous sinus with transverse & sigmoid sinuses
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Inferior Petrosal sinus: overlies petro-occipital fissure of temporal bone
Connects cavernous sinus with internal jugular vein
Cavernous sinus: located on body of sphenoid bone
Interconnected by anterior & posterior intercavernous sinuses
Sigmoid sinus: Continuation of transverse sinus
Drain into internal jugular vein
NB: STUDENTS TO REVISE CRANIAL FOSSA TO REVIEW THE IMPRESSIONS
FORMED BY THE SINSUES.
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Ventricular system
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Cavities within the cerebrum
Includes: Lateral (2); third & fourth ventricle
- LATERAL VENTRICLE
Parts: Central part, Anterior , posterior and inferior horn.
Anterior to interventricular foramen. Its roof & anterior border are formed
by corpus callosum, its vertical medial wall by septum pellucidum. Floor is
formed by the head of caudate nucleus.
Extends from splenium of the corpus callosum; medially, by posterior part
of the septum pellucidum; & below, by parts of caudate nucleus, thalamus,
choroid plexus and fornix.
Extends into occipital lobe. Its roof is formed by fibers of corpus callosum.
It traverses the temporal lobe. Its roof is formed by white substance of
cerebral hemisphere. Along medial border is stria terminalis and the tail of
caudate nucleus. Amygdaloid nucleus bulges into terminal part of inferior
horn. Floor & medial wall are formed by fimbria, hippocampus and the
collateral eminence.
Third Ventricle
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Slit-like structure situated in the diencephalon
Wedged between the thalami and hypothalami in each hemisphere
Connected to the lateral ventricle via the interventricular foramen
Connected to the 4th ventricle via the cerebral aqueduct
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Anterior wall formed by – lamina terminalis and anterior commissure
Roof formed by – thin layer of ependyma (velum interpositum), that stretches
between the medullary stria of the thalami and is lined by
choroid plexus, which passes anteriorly through the
interventricular foramen to become continuous with that of the
lateral ventricle
Posterior wall formed by - habenular commissure, the stalk/infundibulum of
the pineal gland and the posterior commissure,
from superior to inferior
The floor is fashioned from anterior to posterior
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Optic chiasm, infundibulum of the hypophysis, tuber cinereum,
mammillary bodies, tegmentum of the midbrain
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The lateral wall is formed by
- Columns of the fornix, thalamus, hypothalamic sulcus and the hypothalamus
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70% of people present with an interthalamic adhesion (massa intermedia) where
the 2 thalami touch each other, this is not a commissure and has no function
whatsoever.
Fourth Ventricle
The fourth ventricle is a cavity which lies posterior to the pons and upper half of the
medulla oblongata and anterior to the cerebellum. It is continuous with the cerebral
aqueduct (mesencephalic or Sylvius) above and the central canal of the spinal cord in the
lower half of the medulla. On each size, a narrow prolongation, the lateral recess, projects
around the brainstem; its lateral aperture (foramen of Luschka) lies below the cerebellar
flocculus.
The fourth ventricle has lateral boundaries, a roof and a floor.
The lateral boundaries: are formed on each side by the superior cerebellar peduncle, the
inferior cerebellar peduncle and the cuneate and gracile tubercles.
Roof of the fourth ventricle - Formed by thin laminae of white matter. The lower has a
median aperture (foramen of Magendie); cerebrospinal fluid escapes through this opening
and lateral apertures into the subarachnoid space.
The floor of the fourth ventricle, also known as rhomboid fossa, is formed by the dorsal
surfaces of the pons and medulla oblongata.
The cerebral aqueduct is a narrow canal in the midline connecting the third and fourth
ventricle.
CEREBROSPINAL FLUID
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CSF is a colourless , odourless fluid formed by choroid plexus
Choroid plexus is composed of pia mater, ependyma & capillaries. Found in all
ventricles of brain
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Circulation of CSF
Lateral ventricle
Interventricular foramen
Third ventricle
Cerebral aqueduct
Fourth ventricle
Medial &
lateral foramen
Subarachnoid space
Central canal
REABSORPTION OF CSF
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Arachnoid granulations which project into superior sagittal sinus & small venous
lacunae
FUNCTION OF CSF
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Supports & cushions CNS against trauma
Provides buoyancy
Removes waste products
Controls microenvironment of neurons & glial cells.
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Diencephalon
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Area of the brain wedged between 2 cerebral hemispheres, above the midbrain of the
brainstem
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Main components include:
Thalamus
Epithalamus
Metathalamus
Hypothalamus
Subthalamus
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Thalamus
Inner chamber or bedroom
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2 grey collections of nuclei in the lateral walls of the 3rd ventricle
Comprises approximately 80% of the diencephalon
Surfaces include: superior, inferior, medial and lateral
Anterior and posterior extremities
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Anterior extremity
- bordered by the interventricular foramen and the columns of the fornix
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Posterior extremity
- Ends in the pulvinar
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The medial surface
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forms the postero-superior part of the lateral wall of the
3rd ventricle
covered by ependyma
At the superomedial border of the thalamus, where the ependyma is reflected
medially to form the roof of the third ventricle, it forms a fold in which a fibre bundle
– the stria medullaris thalami, is embedded
The superior surface – lies in relation to the central part of the lateral ventricle , the
fornix and the caudate nucleus
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The striae terminalis and the thalamostriate vein are located in the interval between
the thalamus and caudate nucleus
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The lateral surface – is covered by the posterior limp of the internal capsule and the
hypothalamus abuts against the inferior surface from below
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The hypothalamic sulcus depicts the line of separation between the thalamus and
hypothalamus
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The thalamus
- largest relay station for afferent impulses to the cortex
- involved in the integration of motor activity for impulses between the basal
nuclei, cerebellum and the cerebral cortex
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The 4 basic roles of the thalamus include
- All sensory tracts, except olfactory nerves, have direct projections to the
thalamus. In turn the thalamic nuclei project to the sensory cortex. The conscious
awareness of the crude aspects of pain, touch, pressure and temperature are
realized in the thalamus
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The thalamus has vital motor connections that relay critical influences from the
basal nuclei and cerebellum to the motor and premotor areas of the cortex
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Essential in processing cerebral cortical rhythms (EEG) and phases of the sleepwake cycle.
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Involved in aspects of emotion and behavior through connections with the limbic
system and prefrontal cortex. This contains structures essential to cortical activity
such as though, symbols of communication and creativity
The internal medullary laminae divide the thalamic nuclei into 4 groups.
i.e. anterior, medial lateral and intralaminar nuclei
Epithalamus
 Above the thalamus
 Consists of the pineal gland, habenular nucleus, medullary stria of the thalamus
Metathalamus
 Composed of the medial and lateral geniculate nuclei
auditory pathway
optic tract and relay
Subthalamus
 Below the thalamus and lateral to the hypothalamus
 Continuous with the tegmentum of the midbrain
Hypothalamus
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Situated beneath or ventral to the thalamus and forms the base of the diencephalon
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The antero-inferior part of the lateral wall of the 3rd ventricle forms its medial relation
- the subthalamus and internal capsule lies lateral to it
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The anterior border is formed by the lamina terminalis, and the anterior commissure
and hypothalamic sulcus lies superior to it
 The structures forming its floor or base have been described with the 3rd ventricle.
 The nuclei of the hypothalamus are:
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Controls parasympathetic nuclei
Preoptic nucleus
Synthesis & secretion of
Supraoptic nucleus
vasopressin. Lesions of this
nucleus can cause diabetes
insipidus.
Receives retinal input & projects
Suprachiasmatic nucleus
to pineal gland. This controls
circadian rhythms.
Involved in response to
Anterior nuclei
temperature & sexual
preference.
Synthesis & secretion of oxytocin
Paraventricular nucleus
(milk ejection reflex and uterine
contractions). It also regulates food
intake.
Dorsomedial nucleus
Ventromedial nucleus
Arcuate nucleus
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Both of these may be involved
with paraventricular nucleus in
inhibiting eating and drinking
(satiety centre). Lesions of these
nuclei can cause eating disorders.
Function is unknown.
The hypothalamus occupies a strategic area between the cerebrum and brainstem
It has vast connections with visceral (sympathetic and parasympathetic) and somatic
systems.
It plays an important role in the following activities
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Regulation of body temp
Emotional behavior
Hunger and thirst
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Sexual activity and procreation
Autonomic activities
Endocrine activities and Biorhythms
REFERENCES:
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Crossman, AR and Neary D, Neuroanatomy, An illustrated colour text
Snell,R. Clinical Neuroanatomy, 6th ed.
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