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BRAIN STEM EXTERNAL FEATURES. Dr. Ahmed Fathalla Ibrahim. BRAIN. PROSENCEPHALON (FOREBRAIN): TELENCEPHALON: Cerebral hemispheres (cavities: 2 lateral ventricles) DIENCEPHALON: thalamus, hypothalamus, epithalamus & subthalamus (cavity: 3 rd ventricle) MESENCEPHALON (MIDBRAIN)

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BRAIN STEM EXTERNAL FEATURES

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BRAIN STEM

EXTERNAL FEATURES

Dr. Ahmed Fathalla Ibrahim


BRAIN

PROSENCEPHALON (FOREBRAIN):

  • TELENCEPHALON: Cerebral hemispheres(cavities: 2 lateral ventricles)

  • DIENCEPHALON: thalamus, hypothalamus, epithalamus & subthalamus(cavity: 3rd ventricle)

    MESENCEPHALON (MIDBRAIN)

  • Cavity: cerebral aqueduct

    RHOMBENCEPHALON (HINDBRAIN)

  • METENCEPHALON: Pons & cerebellum

  • MYELENCEPHALON: Medulla

  • Cavity: 4th ventricle


BRAIN STEM

COMPONENTS:

  • Midbrain: most rostal part

  • Pons

  • Medulla oblongata: most caudal part

    EMBRYOLOGICAL ORIGIN:

  • Midbrain: arises from mesencephalon

  • Pons & medulla: arise from rhombencephalon or hindbrain (together with cerebellum)


BRAIN STEM

SITE:

  • It lies on the basilar part of occipital bone (clivus)

  • The midbrain is continuous rostrally with diencephalon of forebrain

  • The pons is continous rostrally with midbrain & caudally with medulla

  • The medulla is continuous caudally with spinal cord at the margin of foramen magnum


BRAIN STEM

CONNECTION TO CEREBELLUM:

  • Midbrain:by superior cerebellar peduncle

  • Pons:by middle cerebellar peduncle

  • Medulla oblongata:by inferior cerebellar peduncle


BRAIN STEM

IMPORTANCE:

  • Pathway of tracts between cerebral cortex & spinal cord

  • Site oforigin of nucleiof cranial nerves (from 3rd to 12th)

  • Site of emergence of cranial nerves (from 3rd to 12th)

  • Contains groups of nuclei & related fibers known as reticular formation responsible for: control of level of consciousness, perception of pain, regulation of cardiovascular & respiratory systems


BRAIN STEMVENTRAL SURFACE


BRAIN STEMVENTRAL SURFACE


BRAIN STEMVENTRAL SURFACE

MEDULLA:

  • Ventral median fissure:

  • It divides the medulla into 2 halves

  • Its lower part is masked by decussation of pyramidal (corticospinal) fibers

  • Pyramid:

  • It lies on either side of ventral median fissure

  • It is an elevation produced by corticospinal tract


BRAIN STEMVENTRAL SURFACE

MEDULLA:

  • Olive:

  • It lies lateral to the pyramid & separated from it by the ventrolateral sulcus

  • It is an elevation produced by inferior olivary nucleus

    Nerves emerging from Medulla (4 nerves):

  • Hypoglossal (12th): between pyramid & olive

  • Glossopharyngeal (9th), vagus (10th) & cranial part of accessory (11th): dorsolateral to olive (from above downwards)


BRAIN STEMVENTRAL SURFACE


BRAIN STEMVENTRAL SURFACE

PONS:

  • Basilar sulcus:

  • It divides the pons into 2 halves

  • It is occupied by basilar artery

  • Transverse pontine (pontocerebellar) fibers:

  • Originate from pontine nuclei

  • Cross midline & pass through contralateral middle cerebellar peduncle to enter the opposite cerebellar hemisphere


BRAIN STEMVENTRAL SURFACE

PONS:

Nerves emerging from Pons (4 nerves):

  • Trigeminal (5th): from the middle of ventrolateral aspect of pons, as 2 roots: a small medial motor root & a large lateral sensory root

  • Abducent (6th): at junction between pons & pyramid

  • Facial (7th) & vestibulocochlear (8th): at cerebellopontine angle (junction between medulla, pons & cerebellum). Both nerves emerge as 2 roots: from medial to lateral:motor root of 7th , sensory root of 7th , vestibular part of 8th & cochlear part of 8th


BRAIN STEMVENTRAL SURFACE


BRAIN STEMVENTRAL SURFACE

MIDBRAIN:

  • It is formed of a large column of descending fibers (crus cerebri or basis pedunculi), on either side

  • The 2 crura cerebri are separated by a depression (interpeduncular fossa)

    Nerve emerging from Midbrain (one):

  • Occulomotor (3rd): from medial aspect of crus cerebri


BRAIN STEMDORSAL SURFACE


BRAIN STEMDORSAL SURFACE

MEDULLA

  • Divided into 2 portions:

  • Caudal 2/3: Closed Medulla:

  • Rostral 1/3: Open Medulla


BRAIN STEMDORSAL SURFACE

CLOSED MEDULLA

  • Contains the rostral continuation of central canal

  • Composed of:

  • Dorsal median sulcus: divdes the closed medulla into 2 halves

  • Fasciculus gracilis: on either side of dorsal median sulcus

  • Gracile tubercle: an elevation produced at the upper part of fasciculus gracilis, marks the site of gracile nucleus

  • Fasciculus cuneatus: on either side of fasciculus gracilis

  • Cuneate tubercle: an elevation produced at the upper part of fasciculus cuneatus, marks the site of cuneate nucleus


BRAIN STEMDORSAL SURFACE

OPEN MEDULLA

  • Forms the lower part of floor of 4th ventricle

  • On either side, an inverted V-shaped sulcus divides the area into 3 parts (from medial to lateral):

  • Hypoglossal triangle: overlies hypoglossal nucleus

  • Vagal triangle: overlies dorsal vagal nucleus

  • Vestibular area: overlies vestibular nuclei


BRAIN STEMDORSAL SURFACE


BRAIN STEMDORSAL SURFACE

PONS

  • Forms the upper part of floor of 4th ventricle

  • Separated from the medulla by an imaginary line passing between the caudal margins of middle cerebellar peduncle

  • On either side, a sulcus divides the area into 2 parts (from medial to lateral):

  • Medial eminence: overlies abducent nucleus

  • Vestibular area: overlies vestibular nuclei


BRAIN STEMDORSAL SURFACE


BRAIN STEMDORSAL SURFACE

MIDBRAIN:

  • Marked by 4 elevations:

  • Two superior colliculi: concerned with visual reflexes

  • Two inferior colliculi: forms part of auditory pathway

    Nerve emerging from Midbrain (one):

  • Trochlear (4th): just caudal to inferior colliculus (The only cranial nerve emerging from dorsal surface of brain stem)


FOURTH VENTRICLE


FOURTH VENTRICLE


FOURTH VENTRICLE


FOURTH VENTRICLE


FOURTH VENTRICLE

  • Cavity of hindbrain

  • Diamond (rhomboid) in shape

  • Triangular in cross section

  • Communications:

  • Rostrally: with cerebral acqueduct (cavity of midbrain)

  • Caudally with central canal (cavity of spinal cord)

  • Lateral walls (boundaries): superior & inferior cerebellar peduncles


FOURTH VENTRICLE

  • Roof:

  • Upper part:superior cerebellar peduncle & superior medullary velum(a layer of pia & ependyma bridging the space between the 2 peduncles)

  • Middle part: cerebellum

  • Lower part: inferior medullary velum (a layer of pia & ependyma), has a central defect that forms the median aperture of 4th ventricle


FOURTH VENTRICLE

  • Floor (rhomboid fossa):formed of:

  • Whole dorsal surface of pons

  • Open medulla (dorsal surface of rostral 1/3 medulla)

  • Apertures:provide communication between 4th ventricle & subarachnoid space for circulation of CSF

  • One median aperture (Foramen of Magendi): in the roof of 4th ventricle

  • Two lateral apertures (Foramena of Luschka): at cerebellopontine angle


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