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Brain stem Medulla oblongata Directional terms – brainstem & spinal cord rostral superior ventral anterior dorsal posterior caudal inferior CNS divisions Medulla oblongata – boundaries & size Extends from the lower pontine margin to a transverse plane, above the first pair of cervical spinal nerves Intersects the upper border of the atlas (v.1) dorsally and the centre of the dens of axis (v.2) ventrally ~3 cm in length and ~2 cm in diameter at its widest Brainstem divisions Midbrain Mesencephalon Pons Cerebellum Metencephalon Medulla Myelencephalon Ventral brainstem cerebral peduncle middle cerebellar peduncle pyramid Dorsal medulla oblongata Vagal Trigone Hypoglossal Trigone Obex Gracile Tubercle Cuneate Tubercle Ventral medulla oblongata Cranial Nerve IX Cranial Nerve X Cranial Nerve XI Ventral medulla oblongata Pyramid Cranial Nerve XII Olive Brainstem – macroscopic overview Dorsal view posterolateral sulcus median sulcus Ventral view anterolateral sulcus CNS derives from the ectoderm Ectoderm Neurulation Differentiation of a subset of neuroectodermal cells into neural precursor cells Neural plate Neural fold Neural tube Key consequences of neurulation formation of neural tube – central nervous system formation of neural crest - all neurons outside of the brain and spinal cord + numerous dispersed cell types Neural tube folding Day 21 → → day 26 Neural tube closure → end of neurulation Cranial neuropore closes on day 25 Caudal neuropore closes on day 27 Human Brain Development - Overview Origin of CNS subdivisions Primary vesicles Encephalic subdivisions (~7 weeks, CS21) Purves, et al, Neuroscience, 3rd ed. http://www.visembryo.com Secondary vesicles Neural tube (& embryo) folding Neural tube folding (5th -8th wk) Embryo folding (4th wk) The neural tube is divided into three layers Ventricular zone Mantle zone (layer) Basal plate Alar plate Marginal zone (layer) mantle layer divides into Ventricular zone Sulcus Limitans Ventricular zone Groove dividing alar from basal plate along the walls of the ventricular system Remains in the adult tissue in the brainstem (4th ventricle) and diencephalon (3rd ventricle--hypothalamic sulcus, which divides the thalamus from the hypothalamus) Separates the cranial nerves into motor (basal) and sensory (alar) nuclei Nuclear columns in the brain stem are further differentiated from those in the spinal cord alar plate sulcus limitans basal plate sulcus limitans sulcus limitans Additional motor & sensory columns The primitive central canal widens into a four-sided pyramid shape with a rhomboid floor → 4th ventricle (extends over the future pons and the medulla As in the spinal cord, the embryonic brain stem has a central gray core with an alar plate (consisting mostly of sensory components) and a basal plate (composed primarily of motor components) Alar vs. Basal plate derivatives dorsal Alar plate = afferent = sensory Basal plate = efferent = motor infeior olivary nucleus ventral somatic visceral visceral somatic Alar vs. Basal plate derivatives somatic dorsal special - hearing general - pain visceral special - taste general – int. organs Alar plate = afferent = sensory Basal plate = efferent = motor visceral infeior olivary nucleus ventral special general somatic special = branchial - pharynx, larynx general - skeletal Alar vs. Basal plate derivatives Estimated time of development of various brain regions Modified from Bayer SA et al. Neurotoxicology 14:83–144, 1993 Longitudinal zones in the brain stem cranial Structures in Medulla oblongata: Nuclei = gray matter → neuronal bodies Reticular formation → neuronal bodies Tracts = white matter → neuronal axons caudal tracts from cortex to medulla or spinal cord tracts from medulla or spinal cord to cortex Medulla oblongata – upper/open alar basal Medulla oblongata – lower/closed (by the 4th ventricle) alar basal Level of CN VIII, IXMedulla Inferior Cerebellar Peduncle Pyramids Inferior Olivary Nucleus Level of CN X, XIIMedulla Inferior Cerebellar Peduncle Pyramids Inferior Olivary Nucleus Inferior olivary nuclei Convoluted laminae of gray matter dorsal to the pyramids Consists of 3 nuclear groups: principal olive (the largest) dorsal accessory olive medial accessory olive Surrounded by a mass of fibers - amiculum olivae Estimated to contain 0.5 million neurons Inferior olivary complex is a relay station between the cortex, subcortical structures, the spinal cord, and the cerebellum The major output of the inferior olivary complex is to the cerebellum (olivocerebellar tract) The medulla is connected with the cerebellum via the inferior cerebellar peduncle (=restiform body) Saggital view Dorsal view Composition of the inferior cerebellar peduncle Olivocerebellar tract (the largest component of this peduncle): inferior olive → cerebellum Dorsal spinocerebellar tract: nucleus dorsalis (Clarke's nucleus) → cerebellum Reticulocerebellar tract: reticular formation → cerebellum Cuneocerebellar tract: accessory cuneate nucleus → cerebellum (homologous to the dorsal spinocerebellar tract) Arcuatocerebellar tract from the arcuate nucleus to the cerebellum Brainstem - ascending pathways Saggital view Dorsal view Gracile/cuneate fascicles & spinothalamic tract carry sensory information from body to cortex Gracile/cuneate fascicles → gracile/cuneate nucleus → medial lemniscus – touch & vibration Spinothalamic tract → transit via medulla – pain & temperature Purves, et al, Neuroscience, 3rd ed. Level of Sensory DecussationCaudal Medulla Nucleus Cuneatus (externaltubercle) Nucleus Gracilis (externaltubercle) Spinal nucleus CN V (external- trigeminal eminence) Inferior Olivary Nucleus Pyramids Level of Motor Decussation Caudal Medulla Fasciculus Gracilis Fasciculus Cuneatus Spinal nucleus CN V Pyramidal Decussation The pyramids contain corticospinal & corticobulbar fibers Corticospinal Arm Trunk Leg 90% decussate → lateral corticospinal tract 10% not decussate – ventral corticospinal tract Fibers for neck & upper limb cross first – level of dens axis – somatotopic arrangement Rostral lesion → bilateral upper limb paralysis without lower limb paralysis Caudal lesion → hemiplegia cruciata Corticospinal and corticobulbar tracts Corticobulbar tracts Motor input to: Reticular formations – mesencephalic, pontine, medullary reticular formations Red Nucleus Cranial Nerve motor nuclei – V, VII, Ambiguus, Spinal Accessory & Hypoglosal Nuclei Note – No direct connections from the primary motor cortex to III, IV, and VI; these nuclei get input from frontal and parietal cortex Cranial nerve nuclei in brain stem Name Nerve Nuclei Oculomotor III Oculomotor, Edinger–Westphal Trochlear IV Trochlear Trigeminal V Abducens VI Main sensory, spinal (descending), mesencephalic, motor (masticatory) pons Abducens Facial VII Facial, superior salivatory, gustatory (solitary)** Vestibulocochlear VIII Cochlear (2 nuclei), vestibular (4 nuclei) Glossopharyngeus IX Ambiguus*, inferior salivatory, solitary** Vagus X Dorsal motor, ambiguus**, solitary* Accessory XI Spinal accessory (C1–5), ambiguus** Hypoglossal XII Hypoglossal midbrain medulla ** The solitary nucleus is common for CN VII, IX, and X * The ambiguus nucleus is common for CN IX, X, and XI CN IX: Glossopharyngeal Origin: Course: Termination: Laterality: Nucleus Ambiguus, Salivatory nucleus, glossopharyngeal ganglion CNIX, through jugular foramen Stylopharyngeus muscle, Psym to parotid gland, nucleus solitarius Ipsilateral CN IX: Glossopharyngeal salivatory solitarius ambiguus Motor Portion Origin: CN X: Vagal Course: Termination: Laterality: Nucleus Ambiguus, dorsal motor nucleus CNX, exit jugular foramen Muscles of larynx, pharynx, palate; Psym to esophagus, trachea, digestive organs, heart, etc. Ipsilateral Sensory Portion Origin: Afferent Ganglion of X Course: CNX, exit jugular foramen Termination: Nucleus Solitarius Laterality: Ipsilateral CN X: Vagal Dorsal motor Ambiguus Solitarius CN XI: Accessory Nucleus solitarius → Ambiguus: swallowing reflex eating and drinking ↓ oropharynx stimulation ↓ CN IX ↓ n. solitarius ↓ n. ambiguus ↓ CN X ↓ nasopharynx & larynx are closed Nucleus solitarius is divided into 2 zones Rostral part – taste sensation Caudomedial part – cardiorespiratory centers → nucleus solitarius is coextensive with the physiologically defined medullary respiratory center, which includes the nucleus ambiguus and surrounding portions of the reticular formation CN XII: Hypoglossal Origin: Course: Termination: Laterality: Hypoglossal Nucleus Hypoglossal canal Muscles of the tongue Ipsilateral CN XII: Hypoglossal Hypoglossal lesions CN XII + medial lemniscus medial lemniscus CN XII + pyramid pyramid Right hypoglossal paralysis Brainstem - descending pathways Saggital view Dorsal view Upper Medulla oblongata Motor somatic visceral Sensory visceral somatic Medial longitudinal fasciculus Middle Medulla oblongata Motor somatic visceral Sensory visceral somatic Lower Medulla oblongata Motor somatic visceral Sensory visceral somatic Blood supply of medulla oblongata Vascular territories: Paramedian Olivary Lateral Dorsal Arteries: Vertebral Anterior spinal Posterior spinal Posterior inferior cerebellar (PICA)
