1. Brain stem
DR N SATYANARAYANA

2. Brain stem
Objectives of this lecture are to –
Discuss the external features & blood supply of mid brain, pons & medulla oblongata.
Explain the internal features of mid brain, pons & medulla oblongata (by cross section of these structures)

3. Outcomes
4.1. compare the external features of midbrain, pons and medulla
4.2. Describe the internal structure of the midbrain at superior and inferior colliculi levels
4.3. Describe the internal features of pons at the level of facial colliculus
4.4.Distinguish the internal structure of medulla at vatious levels:lemniscal decussation, pyramidal decussation and olivary nucleus
4.5. Discuss the blood supply of midbrain,pons and medulla

4. Definition Brain stem – the “stem” of the brain,
-connects spinal cord to cerebrum
-connects nerves of the peripheral nervous system to the brain
-Important for basic functions of life-vasomotor
center and respiratory centers
(diencephalon is the part of the forebrain that includes the thalamus and hypothalamus)
Alertness
Arousal
Breathing
Blood Pressure
Contains Most of the Cranial Nerves
Digestion
Heart Rate
Other Autonomic Functions 4

5. 3 Main Parts
Midbrain
Pons
Medulla oblongata

6. Brain stem It contains the nuclei of the cranial nerves.
The cerebellum is connected to the brain stem by 3 pairs of peduncles-
the inferior cerebellar peduncles with medulla,
the middle cerebellar peduncle with pons,
the superior cerebellar peduncle with midbrain.
MID BRAIN
PONS
MEDULLA OBLONGATA

7. Brain stem
- contains C.N III to C.N. XII ( except the spinal part of C.N. XI)
MID-BRAIN… 3rd & 4th C.N.
PONS … 5th , 6th ,7th & 8th C.N.
MEDULLA OBLONGATA … 9th , 10th , 11th & 12th C.N.
All these cranial nerves come out from ventral aspect,
except the 4th C.N.
4th C.N. comes out dorsally and then winds around to reach the ventral aspect.

8. MID-BRAIN
3rd & 4th C.N.
3rd C.N.
4th C.N.

9. PONS
5th , 6th ,7th & 8th C.N.
5th C.N.
6th C.N.
7th C.N.
8th C.N.

10. MEDULLA OBLONGATA 9th , 10th , 11th & 12th C.N. 9th C.N. 10th C.N.P
9th C.N. O
10th C.N.
11th C.N.
12th C.N.

11. MID BRAIN

12. MIDBRAIN - mesencephalon -connects hindbrain to forebrain
Cavity- cerebral aqueduct
Passes through tentorial notch
Relations
anterior-: interpeduncular structures
Posterior: splenum of corpus callosum, great cerebral vein
Pineal body
Thalamus
Eitherside: parahippocampal gyri
Optic tract
Posterior cerebral artery
Basilar vein, trochlear nerve ,geniculate bodies

13. Length – 2.5 cm
External features
Two cerebellar peduncles anteriorly - Superior .C.P.
Corpora quadrigemina posterioly…
- Rt. & Lt. superior colliculi.
- Rt. & Lt. inferior colliculi.
3. Medial & Lateral genicuate bodies – are present on postero-lateral aspect of mid-brain.
4. Superior colliculus is attached to Lateral geniculate body by Superior brachium.
5. Inferior colliculus is attached to Medial geniculate body by Inferior brachium.

14. Midbrain 3rd CN Cerebral crus Sup. colliculus Inf. colliculus pons
Posterior surface
Anterior surface

15. Midbrain - Internal features
Sections of Mid-brain
Sup. colliculus
Inf. colliculus

16. Midbrain - Internal features
Mid- brain is divided into… (1) Tectum - behind line drawn through cerebral aqueduct. It consists of the Superior and Inferior colliculi. (2)Cerebral peduncles- part lying in front of transverse line. - consists of 3 parts : Tegmentum Substantia nigra Crus cerebri

17. C.S. at superior colliculus level of Mid-brain

18. C.S. at superior colliculus level of Mid-brain

19. C.S. at superior colliculus level of Mid-brain
Crus cerebri –
- ventral part of section.
- divides into 3 parts ….
Medial 1/5 – fronto-pontine fibres.
Middle 3/5 - corticospinal & cortico-nuclear fibres.
Lateral 1/5 - tempero-pontine
- parieto-pontine
- occipito-pontine fibres.
Above continuous with corona radiata & below with longitudinal fibres of basilar part of pons.

20. (2) Substantia nigra
-a pigmented layer of gray matter (extrapyramidal system)
Contains nerve cells with melanin pigments.
Dorsal compact part & ventral reticular parts
afferent fibres -- motor cortex, corpus striatum
efferent fibres - spinal cord & red nucleus
Function – control of muscle tone

21. - ovoid mass of gray matter.
(3) Tegmentum
(a) Red Nucleus.
- ovoid mass of gray matter.
- afferents - from cerebellum (dentate nucleus) & also from corpus striatum & sub-thalamic nucleus, substantia nigra.
- sends efferents to spinal cord as Rubro-spinal tract, which cross to opposite side , forming Ventral tegmetal decussation.

22. (b) Dorsal tegmental decussation –tectospinal tract
(c) Ventral tegmental decussation - Rubrospinal tract.
(d) Medial , trigeminal & spinal lemnisci.
(e) Fibres of lateral lemniscus - entered MGB & IC
(f) Medial Longitudinal Bundle

23. (4) In Central gray matter -
(a) Nucleus of 3rd C.N…(motor nu) ventral to cerebral aqueduct.
(b) Mesencephalic nucleus …lateral to cerebral aqueduct.
(c) Edinger – Westphal Nucleus …
- lies medial to rostral half of 3rd C.N. nucleus.
- gives off general visceral efferent fibres to Ciliary ganglion for intrinsic muscles of the eye.

24. (5) Gray matter of Superior colliculus
- dorsal part of the mid-brain.
- receives afferent fibres from spinal cord, optic tract & cerebral cortex.
- sends efferent fibres to spinal cord & nuclei of brain stem.
- efferent fibres form Dorsal tegmental decussation.
- for reflex movement of eye, head &neck , in response to visual stimuli.

25. C.S. at inferior colliculus level of Mid-brain

26. C.S. at inferior colliculus level of Mid-brain
tectum
4th nerve decussation
Inferior collculus
tegmentum
Cerebral aqueduct
Substantia nigra
Crus cerebri

27. C.S. at inferior colliculus level of Mid-brain

28. C.S. at inferior colliculus level of Mid-brain
(1) Crus cerebri.
- ventral part of section.
- divides into 3 parts ….
Medial 1/5 – fronto-pontine fibres.
Middle 3/5 - corticospinal & cortico-nuclear fibres.
Lateral 1/5 - tempero-pontine
- parieto-pontine
- occipito-pontine fibres.
Above continuous with corona radiata & below with longitudinal fibres of basilar part of pons.
1/5

29. C.S. at inferior colliculus level of Mid-brain
(2) Substantia nigra
-a pigmented layer of gray matter (extrapyramidal system)
Contains nerve cells with melanin pigments.
Dorsal compact part & ventral reticular parts
afferent fibres -- motor cortex, corpus striatum
efferent fibres - spinal cord & red nucleus
Function – control of muscle tone
Substantia nigra
Lesion leads to Parkinson’s disease

30. C.S. at inferior colliculus level of Mid-brain
(3) Tegmentum
Trochlear nucleus —gives fibres of trochlear nerve-Emerges from dorsal aspect.
Mesencephalic nucleus of 5th nerve-receives proprioceptive fibres of 5th nerve. (face& scalp)
Decussation of fibres of superior cerebellar peduncle.
Medial, trigeminal, spinal & lateral lemnisci
Cerebral aqueduct & periaqueductal grey matter
Medial Longitudinal Bundle, Tectospinal tract

31. C.S. at inferior colliculus level of Mid-brain
(4) Gray matter of Inferior colliculus - Reflex auditory centre& relay station on the auditory pathway - receives afferent fibres from Lateral lemniscus. - sends efferent fibres to medial geniculate body and superior colliculus. - it concerns with auditory reflex movements.

32. Lesion of mid – brain.
Weber’s syndrome.
Involves 3rd C.N. & Pyramidal tract.
result in hemiplegia of opposite side with 3rd C.N. paralysis.

33. PONS

34. Pons Function Connects the medulla & midbrain
Transmit information between spinal cord & higher brain regions via neural circuits
Relay motor information between cerebral cortex & cerebellum

35. PONS Length – 2.5 cm External features .. Dorsal & ventral surfaces…
convex in all directions-transveresly striated
2.Vertical basilar sulcus (vertical) .. lodges Basilar Artery.
3. Dorsal surface is hidden by cerebellum.
4. Dorsal surface forms upper part of floor of 4th Ventricle.
5. Laterally .. Continuous with Middle Cerebellar Peduncle- trigeminal nerve
6. Superior border- 3rd ,4th
7. Inferior border .. With 6th, 7th & 8th C.N.
PONS
MCP
BASILAR GROOVE

36. PONS 5th C.N. 6th C.N. 7th C.N. 8th C.N. MID BRAIN PONS 4th ventricle
Posterior surface
Anterior surface

37. PONS The pons is divisible into - ventral part (basilar) &
dorsal part (Tegmentum).
Ventral (basilar) part
- The basilar (ventral) part has a uniform structure throughout length of pons.
- contains transverse and vertical fibres & Pontine nuclei.
(i) Transverse fibres are the pontocerebellar fibres- cross the midline to enter the opposite middle cerebellar peduncle.
(ii) The vertical fibres -
- Some of them descend from cerebral cortex to end in the pontine nuclei. (corticopontine)
- Corticospinal fibres that descend through the pons in to the medulla .
- Corticonuclear fibres end in the motor nuclei of cranial nerves mainly of opposite side.

38. Pons - Internal features
Sections of Pons.
Upper part
Lower part
The basilar (ventral) part has a uniform structure throughout
length.
However, the structure of tegmentum (dorsal) part differs
in upper & lower part of pons.

39. PONS
(Dorsal)
(ventral)

40. C.S. of lower part of Pons.

41. C.S. of upper part of Pons.

42. Ventral (basilar) part

43. Ventral (basilar) part pons
GREY MATTER
(iii) Pontine nuclei
Scattered groups of cells separated by nerve fibres.
Afferents - Corticopontine fibres of the same side.
Efferents - Pontocerebellar fibres that cross the midline & pass through the middle cerebellar peduncle to enter the cerebellum. (Cortico-ponto-cerebellar pathway)
WHITE MATTER
CONTAIN-
Longitudinal fibres- 1. corticospinal and corticonuclear (pyramidal) tracts.
Corticopontine fibres ends in pontine nuclei.
Transverse fibres are pontocerebellar fibres begning in the pontine nuclei and going to opposite half of cerebellum through inferior cerebellar peduncle.

44. Tegmentum of pons (dorsal part)
- However, the structure of tegmentum (dorsal) part differs in upper & lower part of pons.

45. Tegmentum of pons (dorsal part)
Ventral & dorsal cochler nuclei
- Receive (afferents) fibres of the cochlear nerve.
- Efferents of the ventral cochlear nuclei cross the midline in the ventral part of tegmentum & end in the superior olivary nucleus & dorsal nucleus of trapezoid body of opposite side.
- These crossing & decussating fibres form the trapezoid body (bundle of secondary auditory fibres)
- Most of the fibres of the dorsal cochlear nuclei also end in the superior olivary nucleus & dorsal nucleus of trapezoid body of opposite side.
- Some fibres of cochlear nuclei are uncrossed.

46. Tegmentum of pons (dorsal part)
(2) Superior olivary nucleus & Dorsal nucleus of trapezoid body
- Present in the ventral part of tegmentum.
- Receive (Afferents) from cochlear nuclei & give fibres (efferents) to lateral lemniscus.
(3) Vestibular nuclei- Lie deep to vestibular area of floor of 4th ventricle
- Superior, inferior, lateral & medial.
Afferents: Fibres of vestibular nerve From cerebellum
Efferents: Vestibulocerebellar, Vestibulospinal.
- Concerned with balance

47. Origin & termination of Vestibular nerve

48. Tegmentum of pons (dorsal part)
(4) Abducent nucleus
- is motor nucleus (lies deep to facial colliculus).
- Facial nerve fibres curve round Abducent nucleus forming Facial colliculus.. (Neurobiotaxis) - It receives corticonuclear fibres of the opposite side.
- Its efferents form the abducent nerve fibres.
(5) Motor Facial nucleus
- Lies in the ventral part of tegmentum.
- Dorsal part controls the muscles of upper part of face & under the control of corticonuclear fibres of both sides.
- Ventral part of nucleus controls the muscles of lower part of face & under the control of corticonuclear fibres of opposite side only.
In upper motor neuron lesion, muscles of upper face are not affected. Muscles of lower face are affected on the opposite side.
In lower motor neuron lesion, all the muscles of the same side of face are affected.

49. Lesion of
Facial nerve
UMN
Facial Nucleus
LMN

50. Tegmentum of pons (dorsal part)
(6) Corpus trapezium .
- is compact mass of secondary auditory fibres from Cochlear nucleus.
- it later becomes Lateral lemniscus.
(7) Medial lemniscus .
- contains Posterior column tract fibres.
- carries conscious proprioceptive sensation.
(8) Spinal lemniscus .
- contains fibres of Lateral & Anterior Spino-thalamic tracts.
(9) Medial longitudinal bundle – lies immediately deep to floor of 4th Ventricle.

51. Tegmentum of pons (dorsal part)
(10) Trigeminal nuclei
Spinal nucleus----Elongated nucleus presented throughout the medulla & lower part of pons. Continuous with Sustantia gelatinosa & superior sensory nuclei. It receives Pain & temperature sensations.
Superior sensory nucleus—In the Tegmentum of upper part of pons—Receives touch & pressure fibres of 5th nerve.
Efferents from sensory nuclei cross the midline & ascend on opposite side as Trigeminal lemniscus to VPM of thalamus.
Mesencephalic nucleus—In the tegmentum of lower part of midbrain.-Receives proprioceptive fibres of 5th nerve
Motor nucleus of 5th nerve—Gives motor fibres of 5th nerve –form motor root of 5th nerve.

52. PONS
Blood supply .
- pontine branch of
Basilar artery
anterior cerebellar artery
inferior cerebellar artery &
superior cerebellar artery.
- venous drainage into
Inferior petrosal sinus and
Basilar plexus.

53. Millard – Gibler’s syndrome.
Lesion of Pons.
Millard – Gibler’s syndrome.
Partial or complete paralysis of opposite side of body.
- damage to pyramidal tract.
2. Paralysis of Lateral Rectus m/s of same side.
- Damage to 6th C.N.of one side only.
3. Lesion at emerging facial nerve –
Ipsilateral Lower motor neurone type of Facial paralysis.
4. Lesion of emerging 5th CN -- paralysis of muscles of mastication of same side.
6th CN

54. MEDULLA OBLONGATA

55. Medulla oblongata Function Connects the spinal cord & the brain
Center for autonomic functions
Breathing
Digestion
Heart rate
Blood pressure

56. MEDULLA OBLONGATA
Extent – between Spinal cord (emergence of 1st cervical nerve)
and Pons.
Lies in posterior cranial fossa
Shape – piriform.
Length – about 3 cm.
Lower part contains the central canal ,
Upper part is open and forms the caudal part of the floor of the fourth ventricle.

57. MEDULLA OBLONGATA External features-
(a) Anterior median fissure – has pyramidal decussation in lower part.
(b) Posterior median sulcus
(c)Anterolateral and posterolateral sulci- divides anterior, posterior and lateral region
(d) Pyramid –in anterior region
(e) Olive – lateral region
(f) Inferior cerebellar peduncle
(g) lower part has Gracile tubercle
medially and Cuneate tubercle
laterally.
pyramid
olive
Anterior
median
fissure
Cuneate tubercle
Gracile tubercle
Posterior median
sulcus

58. Internal features .. By 3 sections.
(1) C.S. at lower closed part of medulla (Pyramidal decussation).
C.S. of medulla at sensory decussation.
C.S at open part of Medulla oblongata-open part of fourth ventricle
(3) Open part
(2)Upper closed part
(1)Lower closed part

59. (I) X.S. at lower closed part of Medulla Oblongata

60. (I) C.S. at lower closed part of Medulla Oblongata.
Central canal
Gracile tubercle
Cuneate tubercle
Spinal / t & Nucleus of 5th C.N.
Spinal root of 11th C.N.
Dorsal spino-cerebellar tract
Ventral-spino-cerebellar tract
Great motor decussation

61. (I) C.S. at lower closed part of Medulla Oblongata

62. (I) X.S. at lower closed part of Medulla Oblongata
Great Motor Decussation.
- Pyramidal fibres (70%- 90%) decussate across the anterior median fissure & descend in lateral white column of spinal cord as Lateral Cortico – spinal tract.
- Those pyramidal fibers which fail to decussate – Ant. Cortico – spinal tract.
2. Gracile & Cuneate tubercles – upper continuation of Fasciculus Gracilis & Fasciculus Cuneatus.
3. Nucleus of the Spinal tract of Trigeminal nerve.
- close to surface and ventro-lateral to Fas. Cuneatus.
- its tract lies on its lateral aspect.
- carries sensation from the face region.

63. (I) X.S. at lower closed part of Medulla Oblongata
4. Ventral -& Dorsal Spino-cerebellar tracts lie close to lateral surface.
- for unconscious proprioception.
5. Area between Nucleus of Spinal tract of Trigeminal and Pyramidal fibres.
– has Spino-thalamic and Rubro-spinal tracts (which are hidden by Cortico-spinal fibres).
6. Detached anterior horn forms supraspinal nucleus & nucleus of spinal part of accessory nerve.
7. Substantia gelatinosa is replaced by spinal nucleus & tract of trigeminal nerve.

64. (I) X.S. at lower closed part of Medulla Oblongata
8. Reticular formation
1.Core of brain stem
2.Has circuit interneurons - generate motor patterns, coordinate reflexes and simple behaviour
3.Input – summary of sensory information that enters the spinal cord and brain stem
4.Controls level of consciousness, cardiovascular system and respiratory system
Reticular formation – a complex n heterogenous matrix of neurons – control level of concsiousness, perception of pain, regulation of cardio n respiratory syndroms
Influences movement, motor and muscle tone 64

65. (II) C.S. at upper closed part of Medulla (above pyramidal decussation)-sensory decussation

66. (II) C.S. at upper closed part of Medulla (above pyramidal decussation)-sensory decussation

67. (II)C.S. at upper closed part of Medulla (above pyramidal decussation)
Pyramids (Rt. & Lt.) (formed by Cortico-spinal fibres).
2. Nucleus Gracilis (medially) & Nucleus Cuneate (laterally).
- are secondary neurones for Posterior column tract.
3. Internal arcuate fibres .
- axons from Nucleus Gracilis & Cuneatus which cross the median plane.
4. Great Sensory Decussation .
- site of crossing / decussation of internal arcuate fibres. - they form Medial lemniscus on reaching the opposite side.
5. Spinal tract & Nucleus of Trigeminal Nerve.
6. Ventral & Dorsal Spino-cerebellar tracts.

68. (III) C.S. of open part of Medulla oblongata

69. (III) C.S. of open part of Medulla oblongata
Superior coliculus
MID BRAIN
Inferior colliculus
PONS
4th ventricle
MEDULLA OBLONGATA

70. (III) C.S. of open part of Medulla oblongata
4th Ventricle.
I.C.P.
Hypoglossal Nucleus
Dorsal Vagal Nucleus
Medial longitudinal bundle
Tecto
spinal tract
Spinal lemniscus
Medial lemniscus
Olive
12th C.N.
Pyramid
Inferior olivary nucleus

71. olive (III) C.S. of open part of Medulla oblongata
pyramid
Inferior cerebellar peduncle

72. (III) C.S. of open part of Medulla oblongata
1. Two pyramids
2. Olivary Nucleus.
- A hollow crenated mass of Grey matter, deep to olive.
- It belongs to extrapyramydal system.
Afferents –1) Spino olivary tract
2) Fibres from cortex, corpus striatum& reticular formation.
Efferents- 1)Olivospinal tracts
2)Olivocerebellar tracts
- Function is for muscle co-ordination.

73. (III) C.S. of open part of Medulla oblongata
3. Accessory Olivary Nuclei (dorsal & medial.)
- small patches of gray matter.
- afferent fibres from Corpus Striatum.
-efferent fibres (par olivo-cerebellar fibres) to Cerebellum.
4. Medial lemniscus.
- on each side of median plane.
- lies dorsal to Pyramid.
- consists fibres from Great Sensory Decussation.
- function .. Conscious proprioception ( Posterior column tract )
5. Tecto-spinal tract – lies dorsal to medial lemniscus.
- connecting tectum of mid-brain & medulla oblongata.

74. (III) C.S. of open part of Medulla oblongata
6. Medial longitudinal bundle
– lies posterior to Tecto-spinal tract.
- contains association fibres of brain stem.
7. Hypoglossal Nucleus - Motor nucleus (somatic efferent)
- lies close to mid-line, deep to floor of 4th Ventricle.
- medial to 10th C.N. Nucleus.
8. Dorsal Vagal Nucleus .
- also lies deep to floor of 4th Ventricle.
- on lateral side of 12th C.N. Nucleus.
- Gives motor fibres to the organs (parasympathetic) supplied by the vagus. Also receives sensory fibres from the organs.
- it is mixed nucleus ,containing G.V.A & G.V.E.cells.
9. Inferior Cerebellar Peduncle.
- lies at dorso-lateral part of section.
- connects Medulla with Cerebellum.

75. (III) C.S. of open part of Medulla oblongata
Nu. of tractus solitarius
Spinal / t & Nucleus of 5th C.N.
Ventral-spino-cerebellar tract
Nu. ambiguus
10. Nucleus of Tractus Solitarius –(7th,9th & 10th )
Sensory nucleus (Special visceral afferent).
Receives taste fibres from 7th,9th & 10th cranial nerves.
Sends fibres to opposite thalamus.
11. Nucleus Ambiguus .-(9th, 10th & 11th )
- Motor nucleus (Special visceral efferent).
consists of 9th, 10th & 11th C.N. fibres (to branchial musculature).

76. (III) C.S. of open part of Medulla oblongata
12. Spinal tract and nucleus of Trigeminal nerve
- lies on ventro-medial part of section.
- is traversed by Vagus nerve.
13.Dorsal Spino-cerebellar tract – becomes smaller as it enters the I.C.P.
14.Ventral Spino-cerebellar tract – same place.
15. Area behind Olivary Nucleus – Spino-thalamic tract & Rubro-spinal tract.

77. MEDULLA OBLONGATA Blood supply . - directly from the Vertebral Artery.
- indirectly from Posterior Inferior Cerebellar arteries.
Clinical importance
Most injuries to Medulla are rapidly fatal, because it has vital centres (ie Respiratory centre, Cardio-vascular centre )
Common vascular lesions of Medulla are –
Lateral medullary syndrome … due to thrombosis of posterior inferior cerebellar artery.
Medial medullary syndrome … due to thrombosis of Vertebral artery.

78. Lateral medullary syndrome (or) Wallenberg’s syndrome.

79. Lateral medullary syndrome

80. Medial medullary syndrome (or) Dejerine’s anterior bulbar syndrome

81. Development of brain stem
Medulla-rhombencephalon- caudal myelencephalic part
Pons- rhombencephalon- cranial mesencephalic part
Midbrain- mesencephalon

82. QUESTIONS MCQ EXTERNAL FEATURES OF PONS,MEDULLA
INTERNAL FEATURES –diagram at different levels