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Pons & Midbrain Neuroanatomy

these lectures will cover some of the objects of the Central Nervous System ...
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Pons and Midbrain

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Pons & Midbrain Neuroanatomy

  1. 1. Pons and Midbrain Neuroanatomy lecture 5 Abbas A. A. Shawka Medical student 2nd grade
  2. 2. Subjects • Pons  General overview  Gross anatomy  Internal organization • Midbrain
  3. 3. Pons • lies inferior to the midbrain, superior to the medulla oblongata and anterior to the cerebellum • Ventral ( basilar ) part - Rests upon a bony depression posterior to sella turica called “ the “clivus “ - Sulcus basilaris in medline for basilar artery. - Trigeminal nerves exit from the upper border • Dorsal part - Form the upper part of rhomboid fossa hindbrain pons Medulla oblongata Cerebellum 4th vemtricle
  4. 4. Cerebellar peduncle 1- superior cerebellar peduncle 2- middle cerebellar peduncle 3- inferior cerebellar peduncle - Superior cerebellar peduncle emerges from the superior surface of pons - On each side, there is the attachment of middle cerebellar peduncle 1 2 3
  5. 5. Cerebellopontine angle • The cerebellopontine angle is a structure at the margin of the cerebellum and pons. Cerebello- pontine angle is the area of lateral cistern containing CSF, arachnoid tissue, cranial nerves, and associate vessels. • contents : 1. Facial nerve (CN VII) 2. Vestibulocochlear nerve (CN VIII) 3. Flocculus of the cerebellum 4. Lateral recess of the 4th ventricle 1 2 3 4
  6. 6. Pons – Dorsal view • The dorsal surface of the pons is concealed by the attached cerebellum. • The aqueduct ( arrow ) of the midbrain opens out at the upper border of the pons into the cavity of the fourth ventricle, which is mostly pontine but medullary at its lower end. • The pontine part of the roof of the ventricle consists only of a thin sheet of white matter, the superior medullary velum (1) , upon which lies the lingula of the cerebellum (2) . The velum is attached at each side to the superior cerebellar peduncles. 1 2
  7. 7. Internal organization of Pons
  8. 8. Internal structure • Generally the pons contain the following :- 1. Nuclei of 4 cranial nerves (V, VI, VII & VIII) 2. Respiratory center nuclei (apneustic & pneumotaxic nuclei / work with MO) 3. Nuclei & tracts in connection with the cerebellum 4. Other tracts in connection with other parts of the CNS
  9. 9. Pons Basilar part Dorsal part White materGray mater Pontine n. White mater Gray mater Cortico-ponto- cerebellar corticonuclear corticospinal Superior olivary complex ( trapezoid nuclei) Trapezoid body Cranial nerve nuclei ?
  10. 10. Basilar part • Grey mater :- - Pontine nuclei - Continous with the arcuate nuclei in medulla - Afferent :- corticopontine fibers of the same side - Efferent :- cortico-ponto- cerebellar fibers ( thorough the middle cerebellar peduncle ) - WILL BE STUDIED WITH CEREBELLUM !!
  11. 11. Basilar part • Wite mater :- • Cerebral cortex  internal capsule  crus cerebri  dividing to 3 parts !! 1. Cortico-ponto-cerebellar fibers synapse with pontine nuclei then go to the cerebellum through middle cerebellar peduncle 2. Corticonuclear fibers :- to motor nuclei of cranial nerve 3. Corticospinal fibers :- to form the pyramids • Most of cortical fibers end in pontine nuclei ! • Middle cerebellar peduncle contains cortico-ponto-cerebellar fibers of the opposite side only.
  12. 12. Dorsal ( tegmental ) part • Trapezoid body and trapezoid nuclei - Lie in the lower part of the pons & represent part of the acoustic pathway - Consist of transverse fibers coming from the cochlear nuclei bilaterally (especially from the opposite side) - These fibers end in grey matter nuclei called nuclei of trapezoid body (superior olivary complex) - From these nuclei fibers ascend as the lateral lemniscus to higher centers
  13. 13. Trigeminal nerve Nerve Modality Nucleus location Distribution Trigeminal nerve GSA Main Sensory nucleus of V nerve Pons ( posterior part ) Touch and pressure Spinal nucleus of V nerve Pons – C2 level Pain and temperature Mesencephalic nucleus of V nerve Pons – midbrain level Proprioception SVE Motor nucleus of V nerve Pons ( medial to main sensory nucleus ) Motor to muscles of mastication, mylohyoid, anterior belly of digastric, tensor veli palatini, and tensor tympani
  14. 14. Nuclei of trigeminal nerve V Mainmotor
  15. 15. Trigeminal lemniscus pathway Crossed or Uncrosses ?!
  16. 16. Abducent nerve Nerve Modality Nucleus Location Distribution Abducent nerve GSE Abducent nucleus Pons ( dorsal part ) Motor to lateral rectus to direct gaze laterally
  17. 17. Fascial nerve Nerve Modality Nucleus Location Distribution Fascial nerve SVE Motor nucleus of VII nerve Pons ( lower part ) Motor to muscles of facial expression and scalp; also supplie stapedius of middle ear, stylohyoid, and posterior belly of digastric GVE Superior salivatory nucleus Posteriolater al to motor nucleus Parasympathetic innervation to submandibular and sublingual salivary glands, lacrimal gland, and glands of nose and palate GSA Spinal nucleus of V nerve Pons – c2 Sensation from skin of external acoustic meatus SVA Solitary tract nucleus Lower pons Taste from anterior two thirds of tongue, and palate.
  18. 18. Nuclei of fascial nerve VII 1. Motor nucleus of fascial nerve VII 2. Superior salivatory nucleus 3. Spinal nucleus of V nerve 4. Sloitary tract nucleus 1 2 3 4
  19. 19. UMNL and LMNL of fascial nerve ?
  20. 20. Note : Vestibulocochlear nerve VIII will be studied in the sense of hearing and equilibrium and in cranial nerves lecture !
  21. 21. Unilateral pontine paralysis • Similar to lateral medullary syndrome but involves the nuclei of CNs in pons !! 1. UMN Paralysis of the opposite side of the body ( corticospinal tract damage ) 2. Internal squint of the same side ( abducent nucleus damage ) 3. Ipsilateral LMN fascial paralysis ( damage to fascial motor nucleus ) 4. Ipsilateral loss of fascial sensation and mastication muscles ( Trigeminal nerve nuclei damage ) 5. Distributed consciousness ( due to reticular formation damage )
  22. 22. Midbrain
  23. 23. Midbrain • The midbrain or mesencephalon is a portion of the central nervous system associated with vision, hearing, motor control, sleep/wake, arousal (alertness), and temperature regulation. Forebrain midbrain hindbrain 2 Cerebral hemisphere+ 2 lateral cavity Deep portion (thalamus & hypothalamus ) with their cavity ( the 3rd ventricle ) Connect the forebrain with the hindbrain Adequate cerebellum pons Medulla oblongata Cerebellum 4th vemtricle
  24. 24. Midbrain • connects the pons and cerebellum with the diencephalon ( structures lateral to the 3rd ventricle ). • Specifically, the midbrain consists of :  Tectum“Corpora quadrigemina” 1. inferior colliculi 2. superior colliculi  cerebral peduncle 1. midbrain tegmentum 2. crus cerebri 3. substantia nigra  Cerebral aqueduct : connect the 3rd and 4th ventricles
  25. 25. Cerebral peduncle - Two cylindrical masses situated at the base of the brain largely hidden by the temporal lobes - They emerge from the upper surface of the pons & diverge as they pass upward to disappear into the substance of the cerebral hemispheres - The interpeduncular fossa between them is occupied by the posterior perforated substance - They are surrounded by the parahippocampal gyrus & optic tracts
  26. 26. Cerebral peduncles • The cerebral peduncles are structures at the front of the midbrain which arise from the front of the pons and contain the large ascending (sensory) and descending (motor) nerve tracts that run to and from the cerebrum from the pons. • Mainly, the three common areas that give rise to the cerebral peduncles are the cerebral cortex, the spinal cord and the cerebellum. • The cerebral peduncle, by most classifications, is everything in the midbrain except the tectum.  Cerebral peduncles include the 1. Crus cerebri 2. Substantia nigra 3. Tegentum 1 2 3
  27. 27. Crus cerebri • The cerebral crus (crus cerebri) is the anterior portion of the cerebral peduncle which contains the motor tracts • In some older texts this is called the cerebral peduncle but presently it is usually limited to just the anterior white matter portion of it. • So, cerebral crus composed of nerve fibers ( It is a white mater ) ! 1. Cortico-ponto-cerebellar fibers 2. Corticonuclear fibers 3. Corticospinal fibers • PART OF THE MOTOR PATHWAY !!!
  28. 28. Substantia nigra • Main afferent : corpus striatum ( basal ganglia ) • Main efferent : thalamus • Functionally to the extrapyramidal system .. • WILL BE STUDIED WITH THE EXTRAPYRAMIDAL SYSTEM !!
  29. 29. Tegmentum 1. Red nuclei 2. White mater
  30. 30. Red nucleus • structure in the rostral midbrain involved in motor coordination • It is pale pink in color; the color is believed to be due to iron, which is present in the red nucleus in at least two different forms: hemoglobin and ferritin • It comprises a caudal magnocellular and a rostral parvocellular part. • It is located in the tegmentum of the midbrain next to the substantia nigra. • • The red nucleus and substantia nigra are subcortical centers of the extrapyramidal motor system.
  31. 31. Red nucleus connections • The red nucleus receives many inputs from the cerebellum of the opposite side and an input from the motor cortex of the same side. • The red nucleus has two sets of efferents:- 1. In humans, the majority of the output goes to the bundle of fibers continues through the medial tegmental field toward the inferior olive of the same side, to form part of a pathway that ultimately influence the cerebellum. 2. The other output (the rubrospinal projection) goes to the rhombencephalic reticular formation and spinal cord of the opposite side, making up the rubrospinal tract • because of the well-developed cerebral cortex, the corticospinal tract has taken over the role of the rubrospinal.
  32. 32. Red nucleus functions • where the corticospinal tract is dominant (as in primates), the rubrospinal tract may be considered to be vestigial. Therefore, here the red nucleus is less important in motor functions than in many other mammals. However, the crawling of babies is controlled by the red nucleus, as is arm swinging in typical walking. The red nucleus may play an additional role in controlling muscles of the shoulder and upper arm via projections of its magnocellular part. In humans, the red nucleus also has sparse control over hands, as the rubrospinal tract is more involved in large muscle movement such as that for arms (but not the legs, as the tract terminates in the superior thoracic region of the spinal cord). Fine control of the fingers is not modified by the functioning of the red nucleus (rather it relies on the corticospinal tract)
  33. 33. Tegmentum white mater 1. The superior cerebellar peduncle : • Enter the midbrain tegmentum • decussate at the level of the inferior colliculi on their way to the red nuclei 2. The medial longitudinal fasciculus: • In the mid-brain it is situated on the ventral aspect of the cerebral aqueduct • It consists largely of fibers which connect the nuclei of the hind- brain and mid-brain to each other • MLF is the main central connection for the oculomotor nerve, trochlear nerve, and abducens nerve.
  34. 34. Tegmentum white mater 3. The medial lemniscus: • -Arise in the gracile & cuneate nuclei of the medulla ( of opposite site ) & decussate there as internal arcuate fibres. • -In the midbrain it attains dorsolateral position 4. The lateral lemniscus: • From trapezoid body • terminates, on cells of the inferior colliculus and medial geniculate body for auditory reflexes • Both the trapezoid body and lateral lemniscus contain cell stations which make connexions with the extraocular nuclei via the medial longitudinal bundle.
  35. 35. Tegmentum white mater 5. The vestibulospinal tract: -Arise in the vestibular nuclei -Some of them descend in the spinal cord & some ascend in the tegmentum of the midbrain 6. The tectospinal tract: -Arise in the superior colliculi -Decussate & descend near the midline 7. The rubrospinal tract: -Arise in the red nucleus -Cross the midline & descends into the lateral funiculus of the spinal cord
  36. 36. Corpora quadrigemina ( tectum ) • Tecum is region of the brain, specifically the dorsal part of the midbrain • Corpora quadrigemina are the four colliculi—two inferior, two superior—located on the tectum of the dorsal aspect of the midbrain. • The corpora quadrigemina are reflex centers involving vision and hearing Pulvinir
  37. 37. Superior colliculi • The brachium of superior colliculus (or superior brachium) extends laterally from the superior colliculus, and, passing between the pulvinar ( not shown ) and medial geniculate body (1) , is partly continued into an eminence called the lateral geniculate body (2) , and partly into the optic tract (3) . 1 2 3
  38. 38. Inferior colliculi • principal midbrain nucleus of the auditory pathway and receives input from several peripheral brainstem nuclei in the auditory pathway, as well as inputs from the auditory cortex. • Its bimodal neurons are implied in auditory-somatosensory interaction, receiving projections from somatosensory nuclei. This multisensory integration may underlie a filtering of self- effected sounds from vocalization, chewing, or respiration activities • Inferior brachium pass to the medial geniculate body
  39. 39. Note • Lateral geniculate and medial geniculate bodies are part of the diencephalon ( Forebrain ) !!
  40. 40. Cerebral aqueduct • 1.8 cm long • Traverses the midbrain • Surrounded by a layer of gray matter called the central (periaqueductal) gray • Contains no choroid plexus • Transmits CSF from the third to the fourth ventricle
  41. 41. Nuclei in periaqueductal grey mater • 1) The nuclei of oculomotor nerve (level with the superior colliculi) • 2) The nucleus of the trochlear nerve (level with the inferior colliculi • ( 1 & 2 lie in the ventral part of the gray ) • 3- The mesencephalic nucleus of the trigeminal nerve extends along the entire length of the aqueduct in the lateral part of the gray 1 2 3
  42. 42. Oculomotor nerve Nerve Modality Nuclei Location Distribution Oculomotor nerve SVE Edinger- wesphal nucleus Midbrain Parasympathetic innervation to sphincter pupillae and ciliary muscles that constrict pupil and accommodate lens of eye GSE Nucleus of oculomotor nerve Midbrain To eye muscles except lateral rectus ( abducens ) and superior oblique ( trochlear
  43. 43. Oculomotor nerve nuclei 1- E-W nuclei 2- motor nucleus 1 2
  44. 44. Trochlear nerve Nerve Modality Nucleus Lcation Distribution Trochlear nerve GSE Nucleus of trochlear nerve Midbrain To superior oblique muscle
  45. 45. Reticular formation • Gray and white mater • More in the tegmentum ( midbrain ) • Upward connection  thalamus and cortex. • Downward connection  to spinal cord. • RF is filter for stimuli !! - Prevent repetitive stimuli - Enhance infrequent stimuli - Allow important repetitive stimuli for example the pain stimuli • Sleep  RF • RF diseases  Grades of coma !? • GA ( general anesthesia ) drugs act on RF ! • Analgesic drugs have one of its mechanism action through the RF
  46. 46. Reticular formation connections • Afferent from :- 1. Various sensory pathways and systems 2. Other parts of CNS 3. Factors infleucing the activity of RF ( e.g. drugs and hormones ) • Efferent to :- 1. Autonomic and locomotor control centres of brainstem and spinal cord. 2. Cranial nerve nuclei, e.g. dorsal nucleus of vagus. 3. Cerebral cortex—indirectly through diencephalic nuclei. 4. Red nucleus, substantia nigra and tectum of midbrain.
  47. 47. Thank you

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