Anatomy of brainstem

1. Brainstem By Dr Manah Chandra Changmai IMS

2. Located between the cerebrum and the spinal cord  Provides a pathway for tracts running between higher and lower neural centers. Consists of the midbrain, pons , and medulla oblongata . Each region is about an inch in length. Microscopically , it consists of deep gray matter surrounded by white matter fiber tracts. Produce automatic behaviors necessary for survival. Brainstem Midbrain Pons Medulla obongata

3. Midbrain Pons Medulla oblongata Ventral surface of brain stem

4. Midbrain Cerebral peduncles Pons Basis pontis Medulla Ventral – Lateral View

5. Vertical Columns of Cranial Nerves

6. Internal Columns of Nuclei

7. Motor nuclei Somatic motor closest to midline eyes, tongue CN III, IV, VI, XII Branchial motor Lateral position Branchial arches: chewing, expression, middle ear, pharynx, larynx, sternomastoic , trapezius CN V, VII, XI N. ambiguus (IX, X) Visceral motor ventral / ventrolateral Parasympathetic: glands, smooth muscle, heart, lungs, GI above splenic flexure Edinger -Westfall (III) Sup. & Inf. salivatory Sensory nuclei General sensory lateral to branchial motor Face, sinuses, meninges All modalities CN V mainly Also CN VII, IX, X Visceral sensory lateral to visceral motor Taste; cardiorespiratory , GI info N. of the solitary tract (CN VII, IX, X) Special sensory furthest lateral Balance; hearing CN VIII (vestibular) CN VIII (cochlear) Subdivisions of Vertical Columns

8. Midbrain

9. Shortest brain stem,not more than 2cm in length,lies in the posterior cranial Fossa . For descriptive purpose,divided into Dorsal tectum and right and left cerebral Peduncles. Each cerebral peduncles divide further into ventral crus cerebri and a dorsal Tegmentum by a pigmented lamina “ Substantia nigra ” Cerebral peduncles contains: -Descending fibers that go to the cerebellum via the pons -Descending pyramidal tracts Running through the midbrain is the hollow cerebral aqueduct which connects the 3 rd and 4 th ventricles of the brain. Connects pons and cerebrum with forebra in Midbrain Crus cerebri

10. Basis Tegmentum Tectum Ventral – Dorsal Organization

11. Patterning of the Midbrain

12. The roof of the aqueduct ( the tectum ) contains the corpora quadrigemina 2 superior colliculi that control reflex movements of the eyes, head and neck in response to visual stimuli 2 inferior colliculi that control reflex movements of the head, neck, and trunk in response to auditory stimuli Corpora quadregemina Superior colliculi larger and darker than inferior colliculi,the difference In colour due to superficial neurons in Superior colliculi Superior and inferior colliculi seperated by cruciform sulcus Superior colliculi Inferior colliculi

13. Internal Structure of Midbrain Cross section at two levels Level of inferior colliculus Level of superior colliculus

14. Internal structure Transverse section of midbrain Common to both at inferior and superior colliculus : Crus cerebri (or basis pedunculi ) : - Consists of fibres descending from cerebral cortex. - Its medial one-sixth is occupied by coticopontine fibres from frontal lobe,lateral one-sixth fibres from temporal,occipital and parietal lobes,the intermediate two third by corticospinal and cortico - nuclear fibres . Substantia nigra : - Present immediately behind and medial to basis pedunculi . - It appears dark as neuron within it contain pigment. ( neuromelanin )

15. Crus cerebri Substantia nigra

16. Basis pedunculi Substantia nigra Crus cerebri (cerebral peduncle) Cerebral aqueduct

17. Cross section at inferior colliculus Internal Structure of Midbrain

18. Section at the level of inferior colliculus Inferior colliculus - large mass of grey matter lying in the tectum - Forms cell station in auditory pathway. Trochlear nucleus: - Lies in the ventral part of central grey matter Mesencephalic nucleus of trigeminal nerve: - Lies in lateral part of the central grey matter Medial leminiscus : - Fibres of ventral spinothalamic tract Spinal leminiscus : - Fibres of lateral spinothalamic and spinotectal tract. Trigeminal leminiscus Inferior colliculus

19. Inferior colliculus Mesencephalic nucleus of V cranial nerve Trochlear nerve(N) Medial longitudinal fasciculus

20. Cross section at Level of superior colliculus

21. Section at the level of superior colliculus Two large masses of grey matter seen at this level Superior colliculus in the tectum – Receives visual input from retina and frontal and occipital eye fields – Receives auditor input from inferior colliculus – Mediates audiovisual refflexes Commissure of superior colliculus – Connects two superior colliculus Brachium of superior colliculus – Pathway for fibres from superior colliculus to Cortex

22. Red nucleus in the tegmentum - Lies in the anterior part of the tegmentum , dorsomedial to the substantia nigra - It is called because of reddish colour which is due to the presence of iron pigment in its neurons. Oculomotor nucleus - Related to the ventral part of central grey matter Cerebral aqueduct and periaqueductal gray matter Medial longitundinal fasciculus – Vestibular fibres that coordinate eye movements – Interconnects ocular motor CN 3, 4, 6 Central tegmental tract Section at the level of superior colliculus ……contd.

23. Medial lemniscus – Spinal afferent tract Spinal lemniscus – Spinal afferent tract Substantia nigra – Receives GAGAergic input from caudate putamen – Projects dopaminergic fibres to caudate putamen – Projects nondopminergic fibres to thalamus Crus cerebri Section at the level of superior colliculus ……contd. Superior colliculus

24. Edinger westfal nucleus Red nucleus Occulomotor nucleus Superior colliculus – relay from cortex and cerebellum to spinal cord, inferior olive, reticular formation, cerebellum Controls arm movement

25. Corticobulbar Fibers – Arise from precentral and postcentral Gyri – May synapse directly on motor neurons or indirectly via interneurons ( corticoreticular fibers) – Innervate sensory relay nuclei – Innervate cranial nerve motor nuclei bilaterally, with the exception of upper face division of the facial nucleus – Innervates the ipsilateral spinal nucleus of CN 11, which supplies the sternocleidomastoid muscle and the contralateral spinal nucleus of CN 11, which innervates the trapezius muscle

26. Pons

27. Pons The pons shows a convex anterior surface with prominent transversely running fibres . These fibres collect to form bundles,the middle cerebellar peduncles. Trigeminal nerve emerges from the anterior surface,at the junction between pons and middle cerebellar peduncle. The anterior surface of pons is marked in the midline by a shallow groove,the sulcus basilaris which lodges the basilar artery. Pons s Sulcus basilaris

28. Subdivided into ventral and dorsal part Ventral part of the pons contains Pontine nuclei: Recieves corticopontine fibres from frontal, temporal,parietal and occipital lobes of cerebrum The efferent fibres form the transverse fibres of pons . It has been estimated that there are about twenty million neurons in pontine nuclei.Most of them are glutaminergic . Vertically running corticospinal and corticopontine fibres . Transversely running fibres arising in pontine nucle i Pontine nuclei

29. The dorsal part of the pons may be regarded as continuation of the part of the medulla behind the pyramids. Superiorly continous with the tegmentum of the midbrain. Occupied predominately by reticular formation Posterior surface help to form floor of fourth ventricle The dorsal part is bounded laterally by inferior cerebellar peduncle in the lower part of the pons and superior cerebellar peduncle in upper part. Dorsal part of pons DORSAL PART Midpons Upper pons

30. 4 Lateral lemniscus » Auditory pathway that conducts most contralateral cochlear input 5 Medial lemniscus » Spinal afferent pathway 6 Spinal lemniscus » Spinal afferent pathway 1 Dorsal and ventral cochlear nuclei – Receives auditory input from the cochlea through CN 8 2 Trapezoid body – Formed by decussating fibres of the ventral cochlear nuclei 3 Superior olivary nucleus – Auditory relay nucleus that receives input from the cochlear nuclei and contributes to lateral lemniscus Six ascending tract Dorsal surface of pons

31. Medial lemniscus Ascending 2 nd order sensory neurons Descending upper motor neurons Middle cerebellar peduncle Restiform body (inf. cerebellar peduncle ) Connection of pons to cerebellum 4 th Ventricle

32. Section through lower part of the pons Abducent nucleus of CN 6 • Lateral gaze Dorsal and ventral cochlear nuclei of CN8 Medial, lateral and superior vestibular nuclei of CN 8 • Receive proprioceptive input from vestibular systems and cerebellum • Projects to cerebellum and medial longitudinal fasciculus Spinal trigeminal tract of CN 5 Facial nucleus of CN 7 • Gives rise to fibres that innervate the muscles of facial expression Superior olivary nucleus – Auditory relay nucleus that receives input from the cochlear nuclei and contributes to lateral lemniscus

33. Vestibular Nuclei Pure sensory  lateral location Balance Cranial Nerves of Lower Pons

34. Abducens N. nucleus Facial N. nucleus Abduction of eye Longest, most vulnerable CN Muscles of face At a slightly higher level Cranial Nerves of Lower Pons

35. Mid Pons Middle cerebellar peduncle 4 th Ventricle Corticospinal tract , corticobulbar tract, corticopontine fibers Descending fibers

36. Lateral lemniscus Pontine nuclei Trapezoid body Mid Pons Trapezoid body : transverse fibers in pontine tegmentum Medial leminiscus fibers from dorsal column (position and vibration) fibers from dorsal column (position and vibration)

37. Medial lemniscus fibers from dorsal column (position and vibration) Trigeminal tract pain, temperature, touch from contralateral face Mid Pons Cranial nerve nuclei and Lemniscal sensory system – in tegmentum of the pons Principal trigeminal sensory nucleus Motor trigeminal nucleus

38. Section through upper part of pons Superior cerebellar peduncle Principal sensory nucleus of CN 5 – Receives discriminative tactile and pressure sensation from face, terminates in thalamus Lateral lemniscus » Auditory pathway that conducts most contralateral cochlear input Trapezoid body – Formed by decussating fibres of the ventral cochlear nuclei

39. decussation Superior cerebellar peduncle Transverse ponto-cerebellar fibers Periaqueductal gray matter Medial longitudinal fasciculus Upper Pons

40. Locus ceruleus Parabrachial Nucleus Pediculopontine Nucleus Upper Pons Some neurons release acetylcholine Other neurons release glutamate They assist in learning and voluntary motor control, e.g. locomotion, saccadic e

41. MEDULLA OBLONGATA

42. Medulla is broad above ,joins with pons narrow below, continous with spinal cord Length is about 3cm, width is about 2cm at its upper end Surfaces shows series of fissures Anterior median fissure Posterior median fissure Spinal cord Medulla oblongata Most inferior region of the brain stem. Becomes the spinal cord at the level of the foramen magnum. External structure of medulla

43. Ventral surface of medulla oblongata contains Pyramid elevation between anterior median and anterolateral sulcus Formed due to decussation of corticospinal fibres . Pyramid Olive Olive Oval swelling between anterolateral posterolateral sulcus,half an inch long Produced by large mass of gray matter called inferior olivary nucleus External surface of medulla

44. Anterior median fissure Pyramid Anterolateral fissure Olive

45. The posterior part of medulla contains Fasciculus gracilis medially ending in rounded elevation ,called nucleus gracilis Fasciculus cuneatus laterally ending in rounded elevation,called nucleus cuneatus Posterior part of the medulla forms the floor of the fourth ventricle Tuberculum cinereum , longitudinal elevation in the lower part of medulla lateral to fasciculus cuneatus . Posterior part of medulla oblongata

46. Posterior median sulcus Posterior median fissure Obex Gracile tubercle Cuneate tubercle Floor of fourth ventricle DORSAL SURFACE OF MEDULLA OBLONGATA

47. Cross section at three levels Level of pyramidal decussation Internal Structure of Medulla

48. Pyramidal tract Lateral corticospinal tract 75 – 90% spinal nucleus of V From pons to C4 Gracile nucleus Anterior corticospinal tract -- fibers to innervate muscles of trunk Level of Pyramidal Decussation

49. Cross section at level of lemniscal decussation Internal Structure of Medulla

50. Medial lemniscus Carries 2 nd order sensory neurons to VPL thalamus Internal arcuate fibers Cuneate nucleus Gracile nucleus Medial longitudinal fasciculus Level of Lemniscal Decussation

51. Cross section at level of Level of inferior olivary nuclei

52. Inferior olivary nuclei Relay between cortex, vestibular nuclei, cerebellum, basal ganglia, and dorsal column nuclei Inferior cerebellar peduncle = Restiform body Hypoglossal nucleus CN XII Vestibular nuclei Medial Inferior Level of Inferior Olives

53. Vestibular nuclei N. solitarious Sensory nucleus for CN VII, IX, X Spinal trigeminal tract CN V, VII, IX, X N. ambiguus Motor nucleus for CN IX, X & XI Dorsal motor nucleus of X Sensation behind ear Posterior 1/3 of the tongue Stylopharyngeus (lifts pharynx) Cranial Nerves of the Medulla

54. N. solitarious Sensory nucleus for CN VII, IX, X Posterior 1/3 of the tongue N. ambiguus Motor nucleus for CN IX, X & XI Stylopharyngeus (lifts pharynx) Inf. salivatory nucleus Parotid gland, parasympathetic Spinal trigeminal tract CN V, VII, IX, X Sensation behind ear CN IX: Glossopharyngeal Nerve

55. Dorsal motor nucleus of X Parasympathetic, preganglionic N. solitarious Sensory nucleus for CN VII, IX, X Taste, epiglottis Cardiorespiratory N. ambiguus Motor nucleus for CN IX, X & XI Pharynx Larynx Spinal trigeminal tract CN V, VII, IX, X Ear CN X: Vagus Nerve

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57. The End