1. Brain Stem: Internal Organization & Connections Med 6573: Nervous System University of Minnesota Medical School Duluth Donna J. Forbes, Ph.D. 18 & 19 February 2008

2. Learning Objectives (See pages 1 & 2 of.doc file for details) You need to know: the identity & function of brain stem structures. where they are located relative to one another. their blood supply. what happens if there is a lesion in a particular area.

3. Nolte 11 - 4 Nolte 11 - 5 pyramid tegmentum Basal or basilar pons tegmentum tectum substantia nigra crus cerebri inf. olivary nucleus 11-14 11-13 11-12 11-11 11-10 11-9 11-7 & 8 MedullaPons Midbrain 11-14 11-12 11-9

4. Nolte fig. 15-2 Caudal MedullaRostral Medulla Caudal Pons Rostral Pons Rostral Midbrain Caudal Midbrain Key to Abbreviations Oc = oculomotor nucleus Ab = abducens nucleus Tr = trochlear nucleus Hy = hypoglossal nucleus dV = dorsal motor nucleus of vagus EW = Edinger Westphal nucleus mT = trigeminal motor nucleus Fa = facial nucleus Am = nucleus ambiguus spT = tract of spinal trigeminal nucleus sT = main trigeminal sensory nucleus Sol = solitary nucleus Ves = vestibular nuclei DSCP = decussation of sup. cerebellar peduncle IC = inferior colliculus RF = reticular formation RN = red nucleus SC = superior colliculus SCP = superior cerebellar peduncle SN = substantia nigra GSE GVE SVE GSA SVA & GVA SSA Cranial Nerve Nuclei Note: Not all Cranial Nerve Nuclei are illustrated. RF (RF)

5. Reticular Formation Long tracts Cranial nerves (and nuclei) Cerebellar connex Reticular formationReticular formation = Central core region of the brain stem= Central core region of the brain stem Widespread connections (afferents & efferents)Widespread connections (afferents & efferents) Pg. 3

6. Rostral Reticular Formation: midbrain + rostral pons Caudal Reticular Formation: caudal pons + medulla midbrain pons medulla spinal cord Reticular Formation Pg. 3

7. Functional Organization of the Reticular Formation Ascending Reticular Activating System (ARAS) Control of Somatic Motor Functions Regulation of Visceral Functions Analgesic Effect of Raphe Nuclei Alert, conscious state of the forebrain Motor, reflex & autonomic functions Modulation of pain Rostral RF + Diencephalon Raphe Nuclei + Periaqueductal Gray Caudal RF + Cranial Nerve Nuclei + Spinal Cord Pg. 3

8. Cerebral Cortex Control of Somatic Motor Functions Motor Neurons in Brain Stem & Spinal Cord Reticulospinal (& reticulobulbar) tr. Corticospinal tract Corticobulbar tract Reticular Formation Vestibular Nuclei Brain Stem Vestibulospinal (& vestibulobulbar) tr. Cerebellum Inferior Cerebellar Peduncle Pyramidal system Extrapyramidal system Pg. 3

9. Regulation of Visceral Function Hypothalamus & Amygdala Reticular Formation Preganglionic Sympathetic & Parasympathetic Neurons Reticulospinal & Reticulobulbar tracts Damage to this descending autonomic pathway in the brain stem and spinal cord can produce: Horner’s syndrome Urinary incontinence Disruption of respiratory & cardiovascular function “descending autonomic pathway” Pg. 4

10. Regulation of Visceral Function: Autonomic Centers in the caudal RF Cardiovascular Centers: regulate heart rate and blood pressure. Pg. 4 Depressor area in medullary RF Pressor area in pontine and medullary RF Respiratory Centers: regulate inspiration, expiration and normal breathing rhythms. Inspiratory area in medullary RF Expiratory area in medullary RF Pneumotaxic area in pontine RF

11. Centers respond to input from sensory receptors: Baroreceptors (pressure sensors) in carotid & aortic sinuses Chemoreceptors in carotid & aortic bodies Stretch receptors in the lungs Glossopharyngeal & Vagal nerves convey the input from these receptors to the Caudal Solitary Nucleus. Caudal Solitary Nucleus communicates with the Autonomic Centers in the RF; in turn, they communicate via Reticulobulbar & Reticulospinal fibers with preganglionic parasympathetic & sympathetic neurons. Regulation of Visceral Function: Autonomic Centers in the caudal RF Pg. 4

12. Increased BP stimulates aortic & carotid baroreceptors Cardiovascular Depressor Center in RF Decrease HR & BP (GVE) X (GVA) Caudal solitary nucleus IX, X Regulation of Visceral Function: Autonomic Centers in the caudal RF Pg. 4 Example: Baroreceptor Reflex Increase in Blood Pressure will invoke a Parasympathetic response to decrease Heart Rate and Blood Pressure while inhibiting the Sympathetic system. Decrease in Blood Pressure (hemorrhage or when one stands up from lying down) will invoke a Sympathetic response to increase Heart Rate and Blood Pressure while inhibiting the Parasympathetic system. RB = Reticulobulbar Nucleus Ambiguus RB tr. + RS = Reticulospinal (GVE) Pre-ganglionic sympathetics in lateral horn of T1 - T5 RS tr. Increase HR & BP PostGang symp -

13. Respiratory Centers in the RF Overlap the location of the cardiovascular centers. Respond to blood levels of oxygen and carbon dioxide. Inspiratory area in medullary RF produces an inspiratory response when stimulated. Expiratory area in medullary RF produces an expiratory response when stimulated. Pneumotaxic area in pontine RF regulates the normal respiratory rhythm. Regulation of Visceral Function: Autonomic Centers Pg. 4

14. Protect the brainstem since damage to the cardiovascular and respiratory centers is incompatible with life. Regulation of Visceral Function: Autonomic Centers Pg. 4

15. Analgesic Effect of the Raphe System Nuclei RF Raphe Nuclei in rostral medulla & caudal pons Raphe Spinal Tract projects from the Reticular Formation to the Spinal Cord.Raphe Spinal Tract projects from the Reticular Formation to the Spinal Cord. Stimulation of these nuclei modulates pain. Pg. 5

16. Hypothalamus & Limbic System Cerebral Cortex Raphe Spinal Tract Ouch! Periaqueductal gray of midbrain Nucleus Raphe Magnus of Medulla Opiates (such as morphine) activate opiate receptors in periaqueductal gray, raphe magnus nucleus and dorsal horn. Dorsal horn of spinal cord Enkephalinergic interneurons in substantia gelatinosa (dorsal horn of spinal cord) Primary afferent pain fiber 1° Thalamus 3° Spinothalamic tract cell 2° Pg. 5 serotonin

17. Now we will put together all the components of the brain stem in a series of cross sections from cervical cord to midbrain: Long tracts Cranial nerve nuclei Additional nuclei: inferior olivary nucleus, red nucleus, etc. Connections with cerebellum & elsewhere

18. Remember our goals or objectives: You need to know: the identity & function of brain stem structures. where they are located relative to one another. their blood supply. what happens if there is a lesion in a particular area.

19. Cervical Spinal Cord: C3 Nolte 10 - 6 FG FC LCST STT Accessory nucleus DSCT VSCT Substantia gelatinosa

20. Caudal Medulla near Spino-Medullary Junction = Most Caudal Aspect of the Pyramidal Decussation Nolte 11 - 7 DSCT VSCT Spinal trigeminal tract & nucleus Spinothalamic tr. Pyramidal Decussation Accessory Nucl. in ventral horn Fasc. & Nucl. Gracilis Fasc. & Nucl. Cuneatus Pg. 6

21. Spinothalamic tr. Caudal (Closed) Medulla just caudal to the Obex Nolte 11-8 & 15-4 XII X Sol Amb Spinal trigeminal tract & nucleus Nucl. Gracilis Fasc. & Nucl. Cuneatus Pyramid (CST/CBT) Internal Arcuate Fibers of the decussation of the Medial Lemniscus Medial Longitudinal fasc. Medial Lemniscus Lateral Cuneate Nucl. Cerebellum CCT Pg. 7 VSCT DSCT

22. Nolte 11-9 & 15-5 Rostral (Open) Medulla just rostral to the Obex X Vest CN X DSCT cerebellum Amb Sol CN XII XII Medial longitudinal fasc. Spinal Trigeminal tr. & nucl. Lateral Cuneate Nucl. CCT Inferior cerebellar peduncle Pyramid (CST/CBT) Spinothalamic tr Inferior Olivary Nucl. OCT M L DSCT VSCT Pg. 8 Tracts in the Inferior Cerebellar Peduncle: Dorsal Spinocerebellar (DSCT) Cuneocerebellar (CCT) Olivocerebellar (OCT) Vestibulocerebellar Trigeminocerebellar Reticulocerebellar Cerebello-vestibular Cerebello-reticular Afferents Efferents

23. Caudal Pons at the level of the Facial Colliculus Nolte 11-10 & 15-6 VI VII Vest V Lateral lemniscus Superior olivary nucl. Trapezoid body Fourth Ventricle Superior Cerebellar Peduncle Medial Longitudinal Fasciculus Inferior Cerebellar Peduncle Middle Cerebellar Peduncle Central Tegmental Tract Deep Cerebellar Nuclei Pontine Nuclei Pontocerebellar fibers Cerebellum Corticospinal Corticobulbar Corticopontine Pg. 9

24. Mid-Pons at the level of the Trigeminal Nerve Nolte 11-11 & 15-7 Tracts in the SCP  Cerebello-rubro-thalamic  Ventral (anterior) spinocerebellar  Trigeminocerebellar 2 1 Pg. 10

25. Rostral Pons near the Pons-Midbrain Junction Nolte 11 - 12 IV Pg. 11 ?

26. Caudal midbrain at the level of Inferior Colliculus Nolte 11-13 & 15-8 Pg. 12 Motor thalamus Inferior Olivary Nucleus Cerebellum Cortico-rubral tr. in crus cerebri Cerebral Cortex Central Tegmental tr. Olivocerebellar tr. SCP Rubrospinal tr. RED NUCLEUS LMN’s in Spinal Cord

27. Rostral Midbrain at level of Superior Colliculus Nolte 11-14 & 15-9 SUPERIOR COLLICULUS Occipital Cortex Retina CST & CBT Oculomotor nucl. & nerve. Pg. 13

28. Nolte 11-26 Pg. 14 Blood Supply to the Brain Stem Basilar a. Sup. Cerebellar a. PICA Vertebral a. (PICA) Ant. Inf. Cerebellar a. Post. Cerebral a. Ant. Spinal a. Post. Communicating a.

29. Nolte 12-29 & 12-30 Pg. 14 Lesions in the Paramedian Region affect: Descending motor pathways Medial lemniscus Nuclei of cranial nerves III, IV, VI & XII Lesions in the Lateral Region affect: Pathways to & from cerebellum Descending sympathetic pathways (reticulospinal) Spinothalamic tract Nuclei of cranial nerves V, VII, VIII, IX or X

30. Recognize the following syndromes and identify the specific structures which are involved and why you think so. Medial medullary syndrome or inferior alternating hemiplegia Lateral medullary, PICA or Wallenberg's syndrome Abducens or middle alternating hemiplegia Weber's syndrome or superior alternating hemiplegia Horner's syndrome See the “VascularSyndromes.doc file

31. See Brain Stem Practice Quiz on the WebSite See BrStemPractice.ppt for these Nolte brain stem cross sections without labels.