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Brain stem

Introduction:

It is part of central nervous system connecting spinal cord with the forebrain.

Location:

Posterior cranial fossa on basilar part of occipital bone.

Parts: (From Above downwards) (****Viva)

Midbrain

Pons

Medulla oblongata

Anterior surface of Brainstem Posterior surface of Brainstem

Midbrain

Pons

Medulla oblongata

Pons

Midbrain

Medulla oblongata

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Midbrain: Upper most part of brain stem.

It connects brainstem to diencephalon and cerebrum.

External Features: (Midbrain) (***viva)

Anterior surface of Brainstem Posterior surface of Brainstem

Features on Anterior surface:

Cerebral peduncles (Crus cerebri): Diverging peduncles are bundle of fibers seen on anterior surface.

Features on Posterior surface:

Colliculi: (All four colliculi together also known as Corpora Quadrigemina or tectum of midbrain)

1. Two superior colliculi: (Concerned with Visuospinal reflex)

2. Two inferior colliculi: (Relay station of Auditory pathway)

Cerebral peduncle

Occulomotor nerve Trochlear nerve

Inferior colliculus Superior colliculus

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Nerves emerging from Midbrain: (***Viva)

Occulomotor nerve (III cranial nerve): emerging from medial aspect of cerebral peduncles on anterior surface supplies all muscles of eyeball except Superior oblique and Lateral rectus.

Trochlear nerve (IV cranial nerve): emerging from posterior surface of midbrain below inferior colliculus. (ONLY CRANIAL NERVE EMERGING FROM POSTERIOR SURFACE)

Internal Features: Internal features studied by two sections of midbrain:

1. Transverse Section (T.S.) at level of superior colliculus

2. Transverse Section (T.S.) at level of inferior colliculus

Transverse Section (T.S.) at level of superior colliculus:

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Gray matter seen in the section: (Nuclei seen at this level) (***viva)

1. Occulomotor nucleus: in the periaqueductal region supplies all muscles of eyeball except superior oblique and lateral rectus. It is also contain fibers of Edinger Westphal nucleus (Parasympathetic nucleus) for light reflex and accommodation reflex.

2. Red nucleus: red colous nucleus in tegmentum of midbrain concerned with motor activity.

3. Substantia Nigra: Purple colour nucleus between crus cerebri and tegmentum. They are dopaminergic neurons and damage to this neurons leads to Parkinson’s disease.

4. Nucleus of superior colliculs: Center for Visuospinal reflex (Movement of eyeball, head and neck and trunk while following a moving object for example looking at the flying objects like plane).

White matter seen in the section: (***viva)

1. Crus cerebri: containing corticopontine fibers from cortex to pontine nuclei and corticonuclear and corticospinal tracts.

2. Spinal lemniscus: Bundle of fibers containing spinothalamic tracts to thalamus.

3. Trigeminal lemniscus: Bundle of fibers containing sensory fibers from trigeminal nerve to thalamus.

4. Medial lemniscus: Bundle of fibers containing posterior column fibers from spinal cord to thalamus.

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Transverse Section (T.S.) at level of inferior colliculus:

Gray matter seen in the section: (Nuclei seen at this level) (***viva)

1. Troclear nucleus: in the periaqueductal region supplies superior oblique muscle of eye

2. Substantia Nigra: Purple colour nucleus between crus cerebri and tegmentum. They are dopaminergic neurons and damage to this neurons leads to Parkinson’s disease.

3. Nucleus of inferior colliculs: Relay station of Auditory pathway of hearing.

White matter seen in the section: (***viva)

1. Crus cerebri: containing corticopontine fibers from cortex to pontine nuclei and corticonuclear and corticospinal tracts.

2. Superior cerebellar peduncle: Fibers from cerebellum cross in midbrain at this level.

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3. Spinal lemniscus, Trigeminal lemniscus and Medial lemniscus same as section at level of superior colliculus).

4. Lateral lemniscus: Bundle of fibers containing auditory pathway to inferior colliculus for relay.

Applied anatomy of Midbrain: (***viva)

Trauma to midbrain: due to sharpe edge of tentorium cerebelli.

Ipsilateral paralysis of muscles of eye

Dilated pupil and loss of accommodation reflex and light reflex

Blockage of cerebral aqueduct:

It leads to Hydrocephalus.

Weber’s Syndrome:

Occlusion of Posterior cerebral artery

Involve Occulomotor nerve and crus cerebri.

Ipsilateral ophthalmopegia

Contralateral paralysis of lower part of face, tongue, arm and leg

Eyeball deviated laterally (Paralysis of medial rectus)

Drooping of eyelid (ptosis)

Pupil is dilated and fixedto light and accomodation reflex

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Benedict’s Syndrome:

Occlusion of Posterior cerebral artery

Similar to Weber’s syndrome with following differences:

Involve Medial lemniscus and Red nucleus

Contralateral hemianesthesia

Involuntary movements of limbs on opposite side.

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Pons: Middle and widest part of brain stem.

It is between medulla oblongata and midbrain.

Anterior surface of Brainstem Posterior surface of Brainstem

External Features: (***viva)

Features on Anterior surface:

Basilar sulcus: Midline sulcus which is occupied by Basilar Artery.

Transverse running fibres on the surface: Pontocerebellar fibres which continues as Mddle cerebellar peduncle

Trigeminal nerve emerge at lateral part of pons

Basilar Sulcus

Trigeminal nerve

Facial colliculus

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Features on Posterior surface: (***viva)

Median sulcus in the midline

Facial colliculus: Paramedian elevation raised by underlying abducent nucleus covered by winding fibres of facial nerve

Nerves emerging from Pons: (***viva)

Trigeminal nerve (V cranial nerve): emerging from lateral part. It demarcates between pons and middle cerebellar peduncle.

Internal Features: Internal features studied by two sections of Pons:

It is divided into two parts by transversely running fibers known as Trapezoid body:

Basilar part: Anterior part

Tegmentum: Posterior part

Basilar part is same at both level of sections:

Basilar part contains: Pontocerebellar tract (transversely running) & Corticospinal tract (Vertically running) and dispersed Pontine nuclei

1. Transverse Section (T.S.) at level of Trigeminal nuclei

2. Transverse Section (T.S.) at level of Facial colliculus

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Transverse Section (T.S.) at level of Trigeminal nuclei:

Gray matter seen in the section: (Nuclei seen at this level) (**viva)

1. Motor nucleus of trigeminal nerve: supply muscles of mastication.

2. Principal sensory nucleus of trigeminal nerve: Lateral to motor nucleus (Touch and Pressure sensations from Face) (**viva)

White matter seen in the section:

1. Trapezoid body (Fibers derived from cochlear nuclei and run transversely)

2. Medial lemniscus: Continuation of posterior column fibers

3. Spinal lemniscus: Spinothalamic tracts

4. Lateral Lemniscus: Continuation of auditory pathway

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Transverse Section (T.S.) at level of Facial colliculus:

Gray matter seen in the section: (Nuclei seen at this level) (****Viva)

1. Facial nucleus: Supply muscles of facial expression. Facial nerve from facial nucleus winds around the abducent nucleus.(Neurobiotaxis)

2. Abducent nucleus: supply Lateral rectus muscle of eye.

3. Vestibular and cochlear nuclei

White matter seen in the section:

1. Trapezoid body

2. Medial longitudinal fasciculus

3. Spinal lemniscus, Medial Lemniscus and Lateral Lemniscus: (Same as above section )

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Applied Anatomy of Pons

Tumors of pons:

Occuring in childhood

Weakness of facial muscles, Lateral rectus paralysis (Medial squint of eye) and contralateral hemiparesis is characteristic of involvement of Pons.

Nystagmus

Impairment of hearing

Weakness of jaw muscles

Pontine hemorrhage: (****viva)

Hemorrhage from basilar artery

“Pinpoint” pupil

Facial paralysis same side

Paralysis of muscles of opposite side

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Medulla Oblongata: Lower part of brain stem

Continues as Spinal cord at foramen magnum

Pyramidal in shape

Anterior surface of Brainstem Posterior surface of Brainstem

External Features: (Medulla Oblongata) (****Very important –Short note and viva)

Features on Anterior surface: (***viva)

Anterior Median fissure-same like spinal cord

Pyramidal dicussation-crossing over of corticospinal tract

Pyramid-an paramedian elevation raised by corticospinal tract

Olive- An oval shaped elevation lateral to pyramid

Inferior Cerebellar peduncle: Bundle of fibres lateral to olive

Pyramid

VII

Vagal triangle

Hypoglossal triangle VI

Olive Gracile and cuneate tubercles

SCP

ICP MCP

VIII

X IX

XI XII

Pyramidal decussation

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Features on Posterior surface: (***viva)

Closed Part: lower part with posterior median sulcus, tractus gracilis & cuneatus, Gracile & cuneate tubercles

Open part: Vagal triangle & Hypoglossal triangle

Nerves emerging from Medulla oblongata: (***viva)

Abducent nerve (VI cranial nerve): at ponto-medullary junction near pyramid

Facial nerve (VII Cranial nerve) & Vestibulocochlear nerve (VIII Cranial nerve): at pontomedullary junction laterally

Glossopharyngeal (IX cranial nerve) , Vagus (X cranial nerve)and cranial part of Accessory nerve (XI cranial nerve): Behind the olive

Hypoglossal nerve XII Cranial nerve): Between the pyramid & olive

Internal Features: Internal features studied by three sections of Pons:

1. Transverse Section (T.S.) at level of Pyramidal decussation

2. Transverse Section (T.S.) at level of Sensory decussation

3. Transverse Section (T.S.) at the level of Open part of Medulla oblongata

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Transverse Section (T.S.) at level of Pyramidal decussation:

Gray matter seen in the section:

1. Supraspinal nucleus continuation of Substantia gelatinosa (Nucleus for 1st cervical nerve)

2. Spinal Accessory Nucleus (Supply Sternocleidomastoid and trapezius)

White matter seen in the section:

1. Pyramidal Tracts

2. Pyamidal deccussation where 75 % fibres of Pyramidal tract (Corticospinal teract) crosses to opposite side (Motor tract) and form lateral corticospinal tract. (***viva)

3. Other ascending tracts

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Transverse Section (T.S.) at level of Sensory decussation:

Gray matter seen in the section: (Nuclei at this level) (**viva)

1. Nucleus Gracilis & Cuneatus (Relay station for tectile descriminations, vibration and conscious joint sensation)

2. Nucleus of Spinal Tract of trigeminal nerve (Pain and temperature from face)

White matter seen in the section:

1. Pyramidal Tracts

2. Sensory deccussation where fibres of Gracile & Cuneate tract crosses to opposite side by internal arcuate fibres and forms Medial Lemniscus (Posterior column fibers) (***viva)

3. Lateral and Anterior spinothalamic tract combine to form Spinal Lemniscus

4. Other ascending tracts

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Transverse Section (T.S.) at level of Open part of Medulla oblongata (At the level of Olive):

(****Very important Section)

Gray matter seen in the section: (Nuclei seen at this level) (***viva)

1. Hypoglossal Nucleus (Supply muscles of tongue)

2. Dorsal Vagal Nucleus (Parasympathetic to heart, lung and abdomen)

3. Vestibular nuclei(Balance) & Cochlear Nuclei (Hearing)

4. Inferior Olivary Nucleus (extrapyramidal motor)

5. Nucleus Ambiguus (Combine nucleus of 9th ,10th and Cranial accessory nerve-Pharynx, soft palate Larynx)

6. Nucleus of tractus solitarius (Taste sensation)

7. Nucleus of Spinal Tract of trigeminal nerve

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8. Arcuate nuclei: Displaced pontine nuclei

White matter seen in the section:

1. Pyramidal Tracts

2. Medial Lemniscus

3. Tectospinal tract

4. Medial Longitudinal Fasciculus (Paramedian bundle- coordinate activities of different nuclei)

5. Inferior cerebellar peduncle

6. Spinal lemniscus

7. Other ascending tracts

Applied Anatomy (Medulla oblongata):

Medulla oblongata contain dorsal vagal nucleus which is cardiorespiratory centre and damage to this leads to Death. Hence it is also known as vital center.

Arnold-Chiari Malformation is congenital anomaly.

1. Herniation of tonsil of cerebellum and Medulla oblongata through Foramen magnum.

2. Blockage of roof of fourth ventricle.

3. Internal Hydrocephalus.

4. Associated other anomalies like spina bifida.

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Lateral Medullary Syndrome: (PICA Syndrome) (**viva)

Blockage of Posterior Inferior Cerebellar Artery

Damage to lateral part of Medulla

Paralysis of palatal and laryngeal muscle

Loss of balance

Vertigo, nausea, vomiting, Nystagmus

Dysphagia-difficulty in swallowing

Dysarthria-difficulty in speech

Loss of pain (Analgesia) and temperature sensations on face

Ipsilateral Horner’s syndrome

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Medial Medullary Syndrome:

Blockage of Vertebral artery

Damage to Medial part

Contralateral hemiplegia

Ipsilateral Paralysis of muscles of tongue-tip pf tungue deviates to the paralysed side.

Contralateral loss of vibration, joint position and tectile discrimination sensations

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