BRAINSTEM-ANATOMICAL DETAILS WITH EXPLANATIOON.pptx

ANAOTMY OF BRAINSTEM

1. Development of the Brain The brain develops from the cranial part of neural tube* . The cranial part is divided into 3 parts: *recall from embryology the caudal 2/3 forms the spinal cord and the cranial or upper 1/3 forms the brain FOREBRAIN MIDBRAIN HINDBRAIN Cavity 2 lateral ventricles 3rd ventricle cerebral aq u ed uc t 4th ventricle Subdivided into Two cerebral h emisphe r es Diencephalon: thalamus, hypothalamus, epithalamus & subthalamus The midbrain is also called m ese nc e ph alon Pons. Cerebellum. Med ul l a oblongata. Note: the brain stem develops from 2 different parts. The pons and medulla oblongata develop from the hindbrain where as the midbrain develops from the midbrain.

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 o b o ngata

3. 3 PARTS MID BRAIN PONS MEDULLA Present in the Posterior Cranial fossa. Connects narrow spinal cord with the expanded Forebrain.

4. 3 broad functions It serves as a conduit for the ascending tracts and descending tracts connecting the spinal cord to the different parts of the higher centers in the forebrain Inportant reflex centers present - respiration, cvs and control of consiousness Nuclei for CN 3 to 12

5. DORSAL VIEW VENTRAL VIEW LATERAL VIEW

6. Midbra i n Pons Medulla oblong a ta Ventral surface of brain stem

7. Midbrain Cerebral pedun c l e s Pons Basis pontis Medulla V entral – Lateral V iew

8. POSTERIOR SURFACE OF PONS

9. PONS MIDBRAIN MEDULLA PARTS OF THE BRAIN STEM

10. OLIVES D E CUS S A TION OF PYRAMIDS PYRAMIDS MEDULLA

11. THE FOURTH VENTRICLE FOURTH VENTRICLE

12. VENTRAL ASPECT

13. DORSAL ASPECT

14. V erti c al Col u mns of Cranial Nerves

15. Inter n al Col u mns of Nuc l ei

16. Brain Stem Clivus The brainstem is the region of the brain that connects the cerebrum with the spinal cord SITE: It lies on the basilar part of occipital bone ( clivus ). PARTS: From above downwards: Mid brain , pons & medulla oblongata CONNECTIONS WITH CEREBELLUM: Each part of brain stem is connected to cerebellum by cerebellar peduncles (superior, middle & inferior). Superior peduncle connects midbrain with cerebellum Middle peduncle connects pons with cerebellum Inferior peduncle connects medulla oblongata with cerebellum

17. Sagittal Section Of Brain Cere b ell u m Mid brain Pons Medulla Superior cerebellar peduncle T h alamus

18. Functions of the Brain Stem 1. Pathway of tracts between cerebral cortex & spinal cord (ascending and descending tracts) . Site of origin of nuclei of cranial nerves (from 3rd to 12th). Site of emergence of cranial nerves (from 3rd to 12th). Contains groups of nuclei & related fibers known as reticular formation * responsible for: control of level of consciousness , perception of pain , regulation of cardiovascular & respiratory systems . * Complex matrix of nuclei and related fibers/axons 1 2 & 3 4

19. Brain Stem – Ventral Surface Note: the numbers refer to the cranial nerves Outline of the lecture We will discuss the ventral surface of each part (medulla, pons, midbrain) then we will discuss the dorsal. In each side (ventral/dorsal) we will see the general feature and the nerves coming out.

20. Medulla – Ventral Surface Ventral median fissure: Continuation of ventral median fissure of spinal cord. Divides the medulla into 2 halves Its lower part is marked by decussation of most of pyramida l (corticospinal) fibers (75%-90%). Pyramid : An elevation, lies on either (lateral ) side of ventral median fissure Produced by corticospinal tract .

21. Medulla – Ventral Surface Olive : An elevation, lies lateral to the pyramid. Produced by inferior olivary nucleus* (important in control of movement). Nerves emerging from Medulla (4 nerves): Hypoglossal (12th): from sulcus between pyramid & olive Glossopharyngeal (9th), vagus (10th) & Extra Extra cranial part of accessory (11th): from sulcus dorsolateral to olive (from above downwards) *Convoluted mass of grey matter

22. Pons – Ventral Surface o Basilar sulcus : Divides the pons into 2 halves, occupied by basilar artery . o Transverse pontine (pontocerebellar) fibers : Originate from pontine nuclei , They cross the midline & pass through the contralateral middle cerebellar peduncle to enter the opposite cerebellar hemisphere. * * Extra Extra

23. Pons – Ventral Surface Nerves emerging from Pons (4 nerves): Trigeminal ( 5th ): from the middle of ventrolateral aspect of pons, as 2 roots: a small medial motor root & a large lateral sensory root*. Abducent ( 6th ): from sulcus/junction between pons & pyramid. Facial ( 7th ) & Vestibulocochlear ( 8th ): at cerebellopontine angle ( junction between medulla, pons & cerebellum ). Both nerves emerge as 2 roots: from medial to lateral : motor root of 7th, sensory root of 7th vestibular part of 8th & cochlear part of 8 th . Vestibulo 1 st since its first in the name then cochlear *to remember small m edial m otor root & a l arge l ateral sensory root

24. Extra Midbrain – Ventral Surface It is formed of a large column of descending fibers ( crus cerebri or basis pedunculi ), on either side. The 2 crura cerebri are separated by a depression called the interpeduncular fossa . Nerve emerging from Midbrain (one): Occulomotor ( 3rd ): from medial aspect of crus cerebri. * Crus Cerebri

25. Medulla – Dorsal Surface open medulla closed medulla o The features differ in the caudal part ( closed medulla ) and the cranial part ( open medulla ). E xt r a The caudal part closes around the fourth ventricle forming the central canal so it is called closed medulla .

26. Dorsal median sulcus : divides the closed medulla into 2 halves. Fasciculus gracilis : on either side of dorsal median sulcus. Gracile tubercle : an elevation produced at the upper part of fasciculus gracilis, marks the site of gracile nucleus . Fasciculus cuneatus : on either side of fasciculus gracilis. Cuneate tubercle : an elevation produced at the upper part of fasciculus cuneatus, marks the site of cuneate nucleus . Medulla – Dorsal Surface Closed Medulla Cavity : central canal . Composed of : Recall : Fasciculus gracilis and fasciculus cuneatus are ascending tracts in the dorsal white column which terminate on their respective nuclei: gracile nucleus and cuneate nucleus.

27. Cavity: 4th ventricle On either side, an inverted V-shaped sulcus divides the area into 3 parts (from medial to lateral) : Hypoglossal triangle : overlies hypoglossal nucleus. Vagal triangle : overlies dorsal vagal nucleus. V estibular area : overlies vestibular nuclei. Medulla – Dorsal Surface Open Medulla E xt r a

28. Pons – Dorsal Surface Separated from open medulla by an imaginary line passing between the caudal margins of middle cerebellar peduncle . On either side of median sulcus , it divides into 2 parts (from medial to lateral ) : Medial eminence & facial colliculus : overlies abducent nucleus The abducent nucleus lies medially, and below it is the fiber of the facial nerve which goes above and around it and forms the facial colliculus . V estibular area : overlies vestibular nuclei. * * Ex t r a

29. o The dorsal surfaces of open medulla and pons lie in the caudal 1/3rd and the rostral 2/3rd of the floor of the 4th ventricle respectively. Dorsal surface of pons  rostral or cranial 2/3 rd of 4 th ventricle Dorsal surface of open medulla  caudal 1/3 rd of 4 th ventricle P MO pons

30. Midbrain – Dorsal Surface Marked by 4 elevations/ colliculi : T wo superior colliculi : concerned with visual reflexes*. T wo inferior colliculi : forms part of auditory pathway. Nerve emerging from Midbrain (one) : Trochlear ( 4th ): just caudal to inferior colliculus (The only cranial nerve emerging from dorsal surface of brain stem, the rest were from the ventral). To remember: The trochlear is the only cranial nerve that emerges from the dorsal / posterior surface . *To remember: he superior colliculi is concerned with the eyes (auditory) & the eyes are at the top of the face (superior).

31. SUMMARY The brain stem is composed (from above downwards) of: midbrain , pons & medulla oblongata which are continuous with each other, and with diencephalon above & with spinal cord below . The brain stem is connected with cerebellum through three pair of cerebellar peduncles . The brain stem is the site of (1) cranial nuclei, (2) the pathway of important ascending & descending tracts & (3) the site of emergence of cranial nerves (from 3 rd to 12 th ). Cranial nerves ( with the exception of 4 th ) emerge from ventral surface of brain stem.

32. MIDBRAIN 0.8 inch in length Connects Pons and cerebellum with the forebrain The midbrain is traversed by NARROW CHANNEL, THE CEREBRAL AQUEDUCT, filled with CSF Posterior surface- 4 colliculi- Corpora Quadrigemina Superior colliculi- Visual Inferior colliculi- auditory In the midline below the Inferior colliculus- trochlear nerves emerge When the midbrain is viewed from the anterior aspect, we see two large bundles of fibres, one on each side of the middle line. These are the crura of the midbrain

33. For convenience of description, the midbrain may be divided as follows The part lying behind a transverse line drawn through the cerebral aqueduct is called the tectum. It consists of the superior and inferior colliculi of the two sides. The part lying in front of the transverse line is made up of right and left halves called the cerebral peduncles. Each peduncle consists of three parts. From anterior to posterior side these are the crus cerebri (or basis pedunculi), the substantia nigra and the tegmentum.

34. Connects pons and cerebrum with forebra in 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. Midbrain Crus cerebri

35. Basis T egm e n tum T ectum V e n tral – Dors a l Org a nizat i on

36. Patterning of the Midbrain

37. 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 and inferior colliculi seperated by cruciform sulcus Superior colliculi larger and darker than inferior colliculi,the difference In colour due to superficial neurons in Superior colliculi Superior colliculi Inferior collicu l i

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

39. 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 )

40. The main features to be seen through a section of upper part of the Midbrain

41. The main features to be seen through a section of lower part of the Midbrain

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

43. PONS The Pons is anterior to the cerebellum and connects the medulla with the midbrain. 1 inch Anterior surface has basilar groove which lodges the basilar artery. Connected to cerebellum via Middle cerebellar peduncle.

44. On either side of the lower part of the Pons there is a region called the cerebello-pontine angle. This region lies near the lateral aperture of the fourth ventricle. The facial, vestibulocochlear and Glossopharyngeal nerves, the nervus intermedius, and sometimes the labyrinthine arteries lie in this region. The pons is divisible into a ventral part and a dorsal part The ventral (or basilar) part contains numerous transverse and vertical fibres. Amongst the fibres are groups of cells that constitute the pontine nuclei. When traced laterally the transverse fibres form the middle cerebellar peduncle. The vertical fibres are of two types. Some of them descend from the cerebral cortex to end in the pontine nuclei. Others are corticospinal fibres that descend through the pons into the medulla where they form the pyramids .

45. 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. P o ns s Sulcus basilaris

46. POSTERIOR SURFACE OF PONS

47. INTERNAL STRUCTURE OF PONS Divided into Studied at two levels : At level of facial colliculus(caudal part) At level of trigeminal nuclei(cranial part) Trapezoid body (anterior) Tegmentum (posterior)

48. 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 t wenty 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

49. Transverse section through cranial part

50. Transverse section through caudal part

51. INTERNAL STRUCTURE OF THE MEDULLA Considered at 4 levels Level of decussation of Pyramids Level of decussation of lemnisci Level of the olives Level just inferior to the Pons

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

53. Level of decussation of Pyramids

54. Pyramidal tract Lateral corticospinal tract 75 – 90% spinal nucleus of V From pons to C4 Gracile nucleus Anterior corticospinal tract innervate muscles of trunk -- fibers to Le v el of P y ram i dal Decussation

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

56. Sensory decussation / level of lemnisci

57. Medial lemniscus Carries 2 nd order sensory neurons to VPL thalamus Internal arcuate fibers Cuneate nucleus Gracile nucleus Medial longitudinal fasciculus Le v el of Lemn i scal Decussation

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

59. Level of the olives

60. 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 Medi a l Inferior Le v el of I nfer i or O l i ves