Midbrain

Midbrain anatomy

• external anatomy review (dorsal)

  • trochlear nerve (CN IV)

  • Inferior/superior colliculus

• external anatomy review (ventral)

  • oculomotor nerve (CN III)

  • cerebral peduncles (crus cerebri)

• Anterior/posterior divisions

  • crus cerebri (cerebral peduncles)

  • tegmentum

  • tectum

Midbrain CN Nuclei

• Mesencephalic branch of trigeminal nerve (CN V)

  • Continuation of original pons nuclei from the Trigeminal Nerve

• Trochlear Nucleus (CN IV)

  • found in caudal midbrain & mid-section of midbrain

  • medial to inferior colliculus & next to periaqueductal gray matter

• Oculomotor Nucleus (CN III)

  • found in mid to rostral midbrain

  • medial and dorsal to oculomotor nerve

Tectum (roof)

• Posterior/dorsal to the cerebral aqueduct

• Contains both superior and inferior colliculi

• Control behavioral responses, visual and auditory responses

Superior Colliculi function

• Visual reflexes, stimulate motor neurons involving head, neck, and eye movement

• Receives input from eyes, inferior colliculus, skin, and cerebral cortex

• Projects to CN nuclei and superior spinal cord

• Visual tracking of moving objects

Inferior Colliculi funciton

• Auditory and olfactory controls

Structures at the superior colliculus in midbrain

• Dorsal

  • Lateral geniculate body (vision)

  • Super colliculus connection

  • Edinger-Westphal Nucleus & Oculomotor nucleus

  • Medial Longitudinal Fasciculus (MLF)

• Ventral

  • Substantia Nigra

  • Crus cerebri (cerebral peduncle)

  • Red nucleus

  • Relay from cortex and cerebellum to spinal cord, inferior olive, reticular formation

  • Helps with contralateral UE movement

Structures at the inferior colliculus of midbrain

• Dorsal

  • Inferior colliculus

  • Cerebral Aqueduct

  • Trochlear Nerve (CN IV)

  • Mesencephalic Nucleus of V

  • Medial Longitudinal Fasiculus

  • Raphe Nucleus

    • Projection of serotonergic fibers to basal ganglia and cortex

• Ventral (Basis Peduncularis)

  • Substantia Nigra

    • melanin cells that produce dopamine and project to basal ganglia

  • Cerebral Peduncles

    • (Crus cerebri with fibers from corticospinal and corticobulbar tracts)

• Inferior

  • Medial geniculate body (auditory)

    • Inferior colliculus connection

  • Lateral leminiscus

  • Cochlear nerve

  • Receives visual input from superior colliculus and retina (both connected to CN II/optic CN) = mental map of physical space

  • Somatosensory input to IC is to allow for coordinated movements to loud sounds and unexpected noises

Structures in Tegmentum

• CN III Nucleus (Edinger-westphal & oculomotor), CN IV

• Red Nucleus

  • receives impact from cerebellum & cerebral cortex

  • rubrospinal tract (UE flexion, contralateral)

• Cerebral Peduncles

• Substantia Nigra

  • Pars compacta (input center - dopamine supply)

  • Pars Reticulata (output center)

  • Interconnected with basal ganglia

  • Reward and movement center

Peri-aqueductal gray

• gray matter around the cerebral aqueduct

• involved in pain suppression (spinomesencephalic tract)

• coordinates somatic and autonomic reactions

  • paint, emotions, threats, etc.

• Activity results in sympathetic system reactions of "fight or flight"

Blood supply to midbrain

• Major supply from basilar artery branch

• Posterior cerebral artery

• Superior cerebellar artery

• Posterior communicating artery

Clinical manifestations of injury/damage in midbrain

• Tumors

  • gradual sx onset

• Hemorrhage

  • instant dysfunction

• Infarcts

  • stroke; sx in specific area (homunculus)

• Hydrocephalus

  • cerebral aqueduct tumor

• Weber's Syndrome (ventral midbrain syndromes)

  • Base of midbrain, CN III, corticospinal tract, oculomotor palsy with contralateral hemiplegia

  • Occlusion of PCA part that supplies midbrain

  • Contralateral hemiplegia of UE/LE and contralateral face, tongue (descending motor tracts through crus cerebri)

  • Ipsilateral efocots in eye motor activity, pupil dilation (CN III)

• Parinaud's Syndrome

  • dosal/superior colliculus: upward gaze palsy (skew deviation)

• Claude's Syndrome

  • Branches of PCA & Basilar Artery

  • CN III, red nucleus, superior cerebellar peduncle fubers

  • Ipsilateral CN III palsy

  • Contralateral hemiparesis

  • Contralateral ataxia

• Benedikt's Syndrome

  • Branches of PCA & Basilar Artery

  • Necrosis in medial reminisces and red nucleus, substantial nigra

  • Ipsilateral pupillary dilations & 3rd nerve palsy

  • Contralateral tremor, chorea, athetosis, ataxia

  • Contralateral hemiparesis