Brainstem Amadi O. Ihunwo, PhD School of Anatomical Sciences
Lecture Outline Constituents Basic general internal features of brainstem External and Internal features of Midbrain Pons Medulla
Constituents of Brainstem External Features
Basic internal features of brainstem in a cross section Ascending/descending tracts Cranial nerve nuclei Intrinsic nuclei Neuromodulatory nuclei Tegmental/Reticular nuclei
Ascending and Descending fibre pathways These fibres carry information in the form of ascending sensory, or descending motor pathways. E.g. Ascending trigeminal sensory pathway and the Descending pyramidal motor pathway.
Location of the cranial nerve nuclei in the brainstem Functions: motor, sensory (general & special), parasympathetic
Intrinsic Nuclei IO Cross section of medulla Form connections and undertake functions within regions of the brainstem. E.g. Inferior olive (IO) Correlation of impulses from cerebellum, spinal cord, cerebral cortex, and corpus striatum and channels into the cerebellum for the coordination of learned patterns of movement.
Neuromodulatory Nuclei Modulate neuronal activity over large parts of the entire brain. Function: Control over levels of consciousness, perception of pain, regulation of CVS and Respiratory system. Connect with cranial nerve nuclei, cerebellum, brain stem and spinal motor mechanisms and so influence movement, posture and muscle tone. Doya K (2002) in Neural Networks
RETICULAR FORMATION (RF) Ill-defined collections of neurones and fibres with diffuse connections traversing the whole brainstem. Continuous below with the reticular intermediate spinal grey laminae. Modulate motor, pain & autonomic functions associated with respiratory and cardiovascular systems
Swellings Mammary bodies & Colliculi Tuber cinereum & infundibulum Crus cerebri Cranial Nerves III & IV Interpeduncular (Anterior Perforated space) Superior cerebellar peduncle Midbrain External Features
Interpeduncular Fossa of Midbrain Boundaries Anterior: optic chiasma Anterolateral: optic tract Postero-lateral: crus cerebri Behind: antero-superior surface of pons Contents posterior perforated substance mammillary bodies tuber cinereum infundibulum arterial circle of Willis
Midbrain: Internal features at levels of superior colliculus Component parts & contents Tectum/Colliculi Tegmentum Substantia Nigra and Red nucleus (Intrinsic) Crus cerebri with nerve fibres Cranial Nerve III (Oculomotor) Reticular formation
Midbrain: Internal features at level of inferior colliculus Component parts & contents Tectum/Colliculi Tegmentum Substantia Nigra (Intrinsic) Crus cerebri with nerve fibres Superior cerebellar peduncles & decussation (central) Cranial Nerve IV (Trochlear) Reticular formation Note absence of red nucleus!!!
Swellings Pontomedullary junction Cranial Nerves Middle cerebellar peduncle Floor of 4 th ventricle (Pontine part) Pons External Features
PONS - COMPONENTS 2 main parts: Ventral & Dorsal (Tegmentum) A) Dorsal sensory/motor tegmental portion B) Ventral pontine nuclei with pontocerebellar fibres Cranial Nerve Nuclei V, VI, VII, VIII Tracts E.g. Medial (ML), Spinal (SL) & Lateral (LL) lemnisci Reticular Formation
1) Sulcus (ventral median, ventrolateral, dorsal median & dsorsolateral) 2) Swellings: pyramid & olive (ventral) 2) Cranial Nerves 4) Inferior cerebellar peduncle 5) Floor of 4 th ventricle (Medullary part) Medulla External Features
Medulla Oblongata: Components 1) Composed mostly of continuations of fibre tracts of spinal cord 2) Decussations of Internal arcuate fibres to form medial lemniscus 3) Decussation of Corticospinal tract 4) Cranial nerve nuclei (VIII XII) 5) Gracile, Cuneate & Olivary Nuclei 6) Nucleus of spinal tract of trigeminal N
MRI OF BRAINSTEM A- Medulla B- Pons C- Midbrain
Questions List the external features of the midbrain (pons or medulla) What are the five basic internal features in a crosssection of the brainstem? With a well labelled diagram, describe the boundaries and contents of the interpeduncular fossa Draw a well labelled cross-section of the midbrain at the level of the superior colliculus. List any three internal differences with cross-section at level of inferior colliculus.