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BRAIN STEM EXTERNAL FEATURES PowerPoint PPT Presentation


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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

BRAIN STEM

EXTERNAL FEATURES

Dr. Ahmed Fathalla Ibrahim


Brain

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

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 stem1

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 stem2

BRAIN STEM

CONNECTION TO CEREBELLUM:

  • Midbrain:by superior cerebellar peduncle

  • Pons:by middle cerebellar peduncle

  • Medulla oblongata:by inferior cerebellar peduncle


Brain stem3

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 stem ventral surface

BRAIN STEMVENTRAL SURFACE


Brain stem ventral surface1

BRAIN STEMVENTRAL SURFACE


Brain stem ventral surface2

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 stem ventral surface3

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 stem ventral surface4

BRAIN STEMVENTRAL SURFACE


Brain stem ventral surface5

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 stem ventral surface6

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 stem ventral surface7

BRAIN STEMVENTRAL SURFACE


Brain stem ventral surface8

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 stem dorsal surface

BRAIN STEMDORSAL SURFACE


Brain stem dorsal surface1

BRAIN STEMDORSAL SURFACE

MEDULLA

  • Divided into 2 portions:

  • Caudal 2/3: Closed Medulla:

  • Rostral 1/3: Open Medulla


Brain stem dorsal surface2

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 stem dorsal surface3

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 stem dorsal surface4

BRAIN STEMDORSAL SURFACE


Brain stem dorsal surface5

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 stem dorsal surface6

BRAIN STEMDORSAL SURFACE


Brain stem dorsal surface7

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 ventricle1

FOURTH VENTRICLE


Fourth ventricle2

FOURTH VENTRICLE


Fourth ventricle3

FOURTH VENTRICLE


Fourth ventricle4

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 ventricle5

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 ventricle6

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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