MIDBRAIN ANATOMY

MidBrain

Dr Kurian Joseph MD

August 23 2010

Ventral – Lateral View

Midbrain

Cerebral peduncles

Pons

Basis pontis

Medulla

Pyramid Olive

Midbrain measures around 2 cms or 0.8 inch in length and connects Pons and Cerebellum with the forebrain.

Features of Midbrain

Ascends through Tentorium Cerebelli,

traversed by Cerebral Aqueduct.

Divided from anterior to posterior

Crus CerebriTegmentum

Tectum

Patterning of the Midbrain

External Structure of Midbrain

1. Optic chiasm

2. Interpeduncular fossa

3. Oculomotor nerve (CN III)

4. Trochlear nerve (CN IV)

5. Pons

6. Cerebral peduncles (crus cerebri)

Ventral surface

(anterior)

External Structure of Midbrain

Quadrigeminal Plate

• Superior colliculus

• Inferior colliculus

Dorsal surface

Cerebellum removed

CN IV

Trochlear nerve

Cranial Nerves of the Midbrain

Anterior exit

CN III (1)

CN VI (5)

Posterior exit

CN IV (2)

MLF - Medial longitudinal fasciculus (7)

Vestibular nuclei (6)

Pons (3)

Internal Structure of Midbrain

Cross section at two levels

• Level of inferior colliculus

• Level of superior colliculus

Lower MidbrainInferior colliculus

hearing

cerebral aqueduct

DORSAL

VENTRAL

cerebral peduncles


Substantia nigra

Melanin-containing cells that produce dopamine Project to the basal ganglia


Substantia nigra

Crus cerebri

(cerebral peduncle)

Basis peduncularis


CN IV Trochlear nerve


CN IV Trochlear nerve

MLF


CN IV

MLF

Dorsal raphe nucleus – projects serotonergic fibers to basal ganglia and throughout cortex


hearing Mesencephalic

nucleus of V

analogous to dorsal root

ganglion but within

CNS

Internal Structure of Midbrain

Cross section at two levels

• Level of inferior colliculus

• Level of superior colliculus

Upper Midbrain

Superior colliculus

vision

Substantia nigra Crus cerebri (cerebral

peduncle)

Upper Midbrain

Superior colliculus

vision

Medial geniculate bodyhearing

Upper Midbrain

Vision

Superior colliculus Lateral geniculate body

Hearing

Inferior colliculus Medial geniculate body

Upper Midbrain

Superior colliculus

vision

Red nucleus – relay from cortex and cerebellum to spinal cord, inferior olive, reticular formation, cerebellum

Controls arm movement

Cranial Nerves of Upper Midbrain

Superior colliculus

vision

Red nucleusCN III Oculomotor

nucleus

Edinger Westfal nucleus

Parasympathetic to ciliary ganglion

Pupillary sphincter ciliary muscles

Cranial Nerves of Upper Midbrain

Superior colliculus

vision

Red nucleus

Edinger Westfal nucleus

MLF

CN III Oculomotor nucleus

Innervation of Eye Muscles

Dorsal view

Cerebellum removed

Innervation of Eyes & Muscles

Lacrimal gland (CN VII)

Superior rectus Inferior rectus Medial rectus Inferior Oblique

(CN III)

Superior oblique (CN IV)

Lateral rectus (CN VI)

Parasympathetic: Edinger-Westfal (CN III) Sympathetic: Superior Cervical Ganglion

Midbrain Tectum• Superior colliculi:

Visual reflexes.

Receive input from eyes, inferior colliculi, skin, cerebrum.

Fibers project to cranial nerve nuclei and to superior cervical portion of spinal cord.

Stimulate motor neurons involved in turning eyes and head.

Involved in visual tracking of moving objects.• Inferior colliculi:

Auditory and olfactory reflexes.

Midbrain TegmentumRed nucleus:

Receives information from the cerebellum and cerebral cortex.

Rubrospinal tract:

Neurons contribute to upper limb flexion.

• Cerebral peduncles

• Interpeduncular fossa

• Substantia nigra:

Interconnected with basal ganglia.

Involved in coordinating movement and in muscle tone.

Midbrain Tegmentum

• Oculomotor complex:

Nucleus of CN III

Edinger-Westphal nucleus:Parasympathetic control of pupillary sphincter and ciliary muscle.

• Nucleus of CN IV

Periaquaductal Gray of Midbrain

• Gray matter surrounding the cerebral aqueduct.

• Involved in pain suppression.

• Coordinates somatic and autonomic reactions to pain, threats, and emotions.

• Activity results in flight-or-flight reactions and in vocalization during laughing and crying.

Blood Supply to the Midbrain

The major blood supply to the midbrain is derived from branches of the basilar artery;

1. Posterior cerebral artery.2. Superior cerebellar artery.3. Quadrigeminal, a branch of the posterior cerebral, provides support for the tectum.

4. Posterior communicating artery, derived from the internal carotid,Contributes to the interpeduncular plexus

Blood Supply to the MidbrainThe paramedian arteries, derived from the posterior communicating andposterior cerebral, form a plexus in the interpeduncular fossa, enter the through the posterior perforated substance, this system supplies raphe region, raphe region, oculomotor complex, oculomotor complex, medial longitudinal fasiculus, medial longitudinal fasiculus, red nucleus red nucleus substantia nigra substantia nigra crus cerebricrus cerebri

Blood Supply to the MidbrainThe short circumferential arteries originate from the interpeduncularplexus and portions of the posterior cerebral and superior cerebellararteries, this system supplies crus cerebri, crus cerebri, substantia nigrasubstantia nigramidbrain tegmentummidbrain tegmentum

Blood Supply to the MidbrainThe long circumferential branches originate mainly from the posterior cerebral artery, one important branch, the quadrigeminal (collicularartery) supplies the superior and inferior colliculi.

Blood Supply to the Midbrain

The posterior choroidal arteriesoriginate near the basilar bifurcation into the posterior cerebral arteries. In additionto providing reinforement tothe midbrain short and longcircumferential arteries theymove forward to supply portionsof the diencephalon and thechoroid plexus of the third and lateral ventricles

Applied anatomical

aspects

Traumatic InjuryMidbrain form upper end of narrow stalk of the brain or brainstem. It ascends through small rigid opening in tentorium cerebelli and is valnerable to traumatic injury. It is the more common site for tumors, hemorrhage or infarcts.

Blockage of cerebral aqueductCavity of midbrain, cerebral aqueduct is prone for blockage due to tumor of midbrain or tumor outside midbrain and produce hydrocephalus and produce signs and symptoms specific for oculomotor and trochlear nerve nuclei, together with descending corticospinal and corticonuclear tracts features.

Vascular Syndrome of Midbrain

Weber’s Syndrome.

Benedikt’s syndrome.

Claude’s syndrome.

Northangel’s Syndrome.

Parinaud syndrome.

A ‘Top of the basilar’ syndrome.

A caudal paramedian midbrain syndrome.

Weber’ Syndrome

Occlusion of branches of posterior cerebral artery that supplies mid brain and may cause superior alternating hemiplegia (or Weber’s syndrome)characterized by;

A lesion in one of the cerebral peduncle produces

1. Contralateral hemiplegia of the limbs and contralateral faceand tongue, due to damage to the descending motor tracts(crus cerebri).

2. Ipsilateral deficits in eye motor activity, including pupil dilatation, caused by damage to the oculomotor nerve,.

Benedikt’s Syndrome

Necrosis involving medial lemniscus and red nucleus producing ipsilateral 3rd nerve lesions, including pupil dilations and contralateral termor, chorea and athetosis.

Thank you..

Health & Medicine

MIDBRAIN ANATOMY