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How do BRAINSTEM LESIONS affect the brain? - NEET PG Anatomy

Mar 30, 2023

How do BRAINSTEM LESIONS affect the brain - NEET PG Anatomy

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Midbrain: Transverse Sections

  • Showing the anterior aspect of the midbrain
  • The topmost part is called the Crust Cerebri.
    • The pyramidal tract passes through them.
    • Corticospinal Tract and the corticonuclear tract.
  • There is substantial nigra.
    • This is part of the basal ganglia.
    • It will show the deposition of melanin.
    • Due to this deposition, it will be of dark color.
  • There is an Aqueduct of the midbrain, which is surrounded by gray matter.
    • This gray matter is called the Periaqueductal brain.
    • There will be the presence of 2 nuclei, the 3rd nerve nucleus and the 4th nerve nucleus.
    • In the case of the 3rd nerve nucleus, the section is taken at the level of the superior colliculus.
    • In the case of the 4th nerve nucleus, the section is taken at the level of the inferior colliculus.
  • There is the red nucleus, which is present in the upper portion of the midbrain.
    • As it is present in the upper portion of the midbrain, it is at the superior colliculus level.

Read this blog further to get a quick overview of this important anatomy topic for NEET PG exam preparation.

Pons: Transverse section

Consider putting a patient in the CT Scan machine and looking at the transverse section from the anterior angle and the right side angle.

  • The corticospinal and corticobulbar tract passes through the anterior near the midline.
    • It is known as the pyramidal system
    • They control the skeletal muscles of the body.
    • Right-sided Spastic palsy is caused due to injury in the pyramidal system.
  • Pons will have 5, 6, 7, and 8 nerves. 
    • The 6th nerve nucleus is present at the posterior area.
    • The 7th nerve nucleus is present in the anterior area.
      • It makes a bend around the 6th nerve nucleus before it exists. 
      • This bend causes an elevation, which is called the facial colliculus.
      • The facial colliculus is on the floor of the 4th ventricle.  
        • The 4th ventricle is present in the brainstem behind the cerebellum.
      • Moreover, it exists at the Pontomedullary junction along with the 6th and the 8th nerve nucleus. 
    • The nucleus of the 8th nerve is called the vestibulo-cochlear nucleus.

Medulla oblongata: Transverse section

CT Scan; Inferior view

  • The top part is the Pyramidal system.
  • The 12th nerve comes from the medulla.
  • The nucleus ambiguous is giving the 9th, 10th, and 11th nerves.

Medial brainstem lesions

Medial Md-brain Syndrome (Right-sided Weber syndrome)

  • The 3rd nerve lesion
  • Down & out eye
  • Partial ptosis
  • Contralateral spastic paralysis
  • If pons region: lateral rectus will be compromised → squint
  • If medial Medullary syndrome: hypoglossal nucleus is near the mid-line →  tongue palsy
  • Body has contra-lateral involvement while face has ipsilateral involvement: referred as alternating hemiplegia 
  • The lateral rectus is more powerful, causing the outing of the eye, and the superior oblique is more powerful, causing the downing of the eye
  • This will cause an Oculomotor lesion on the same side - Ipsilateral oculomotor paralysis with wide, fixed pupils
  • There will be contra-lateral spastic hemiplegia in the corticospinal tract
  • Corticobulbar contra-lateral facial and hypoglossal paralysis will also be seen, which will be caused due to the 5th, 7th, and 12th nerves associated
  • In the case of the substantia nigra getting injured, there will be contra-lateral Parkinsonism

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Lateral brainstem lesions (Wallenberg Syndrome)

  • The major affected area is the pons and the lateral medulla region.
    • If it is a right-sided lesion, it will affect nerve number 5, number 7, and the Nucleus ambiguous will be compromised on the same side of face & contralateral side of body.
    • Some insight into the right-sided Wallenberg syndrome:
      • It is the cause of the injury of the spinothalamic tract.
      • There will be ipsilateral Horner's syndrome because the Hypothalamo spinal pathway is compromised.
      • Spinal Sensory nucleus of the trigeminal is compromised there will be an Ipsilateral sensory alteration of pain and temperature.
      • Due to the spinothalamic tract compromise, the body will experience a contralateral alteration of pain and temperature.
      • In the right-sided Wallenberg syndrome, the right side of the face will be affected, and the left side of the body will be affected.
      • Therefore it is called alternating hemi-anesthesia.
      • They will also be ipsilateral cerebellar ataxia.
  • There is right-sided thalamus and the left-sided thalamus
  • Under them, there is a hypothalamus on both the side(1st order neuron)
  •  Below them, there will be the brainstem
  •  Under the brainstem, there is the spinal cord
  •  An H-shaped gray matter called the Posterior Horn cell.
  • The pain and temperature of the body are controlled by the free nerve ending.
    • The first-order neuron will be in the dorsal ganglion.
    • The second-order neuron will be in the posterior horn cell.
    • These neurons transfer the nerve fibers through the Contra-lateral pathway passing the spinal cord and the lateral medulla up-to the lateral thalamus (Ventroposterior lateral nucleus of Thalamus)
  • There will be ischemia in the lateral medulla.
    • It is also called the Spinal lemniscus
    • In the case of an injury to this area, there will be a Contralateral effect on the body.
    • The Spinal sensory nucleus of the trigeminal nucleus that enters the spinal cord carries the pain and temperature of the body on the same side. Therefore, there will be an Ipsilateral alteration of pain and temperature on the same side of the face.
    • There will be an experience of the right-sided Horner syndrome.
      • It is associated with the hypothalamus pathway.
      • The T1 spinal segment of the spinal cord connecting the hypothalamus on the right side is injured.
      • It is also called the lateral horn cell of the spinal cord.
      • Moreover, it will cause an injury to the nucleus. This will cause ipsilateral paralysis, causing difficulty in speech and swallowing.
      • The nucleus tractus solitarius will be injured, which will cause the loss of taste on the same half of the tongue.
      • In the case of vestibular nucleus injury, the patient will suffer from Vertigo.
      • In the case of the 12th nerve nucleus, there will be partial tongue palsy. The medial lemniscus is also involved.
      • The inferior olive is present in the medulla and gives out crossing Olivocerebellar fibers.

Related: Best Notes for NEET PG


Right sided wallenberg syndrome
Injury to right sided spino-thalamic tract

Contra-lateral loss of pain & temperature
Injury to spino-thalamic tractFall on the same sideHeel shin test positive on same side of lesionCerebellar ataxia
Injury to right sided spino-thalamic tract(descending sympathetic tract)Right sided horner syndrome
Nucleus ambiguous involvement(nerve 9th & 10thRight sided palate, larynx & pharynx muscles weakness
Spinal sensory nucleus of trigeminalIpsilateral loss of pain & temperature on face
Nucleus tractus solitarius involvedLoss of sensation on the same half of the tongue
Vestibular nucleusvertigo
12th nerve injuryPartial tongue palsy in medial medullary syndrome
Pyramidal tract injuryContra-lateral spastic paralysis(medial medullary syndrome)

Q. The position of nucleus ambiguous is?

  1. Anteromedial to olive
  2. Anterolateral to olive
  3. Posteromedial to olive
  4. Posterolateral to olive

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