Brainstem anatomy

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vickrum
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303388
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Brainstem anatomy
Updated:
2015-10-10 04:53:21
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MICN301
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  1. Name the parts of the brainstem
  2. Describe the features through this section at the superior colliculus
    What cranial nerves and nuclei come from this region?
    • Transverse section at level of the midbrain (through the superior colliculi)
    • Superior colliculus
    • Cerebral aqueduct
    • Cerebral peduncles: anchor the brain to the brainstem. Includes;
    • - Substantia nigra
    • - Crus cerebri/ cerebral crus or base
    • Occulomotor Nucleus: and from it the CN III nerve
    • Medial longitudinal fasciculus
    • Spinothalamic tracts
    • Medial Lemniscus
    • Cranial nerve 3 = Occulomotor nerve shoots out anteriorly
  3. Describe the features through this section at the inferior colliculus
    What cranial nerves and nuclei come from this region?
    • Transverse section at level of the midbrain (through the inferior colliculi)
    • Inferior colliculus
    • Cerebral aqueduct
    • Cerebral peduncles: anchor the brain to the brainstem. Includes;
    • - Substantia nigra
    • - Crus cerebri/ cerebral crus or base
    • Trochlear nucleus: and from it the CN IV nerve
    • Medial longitudinal fasciculus
    • Spinothalamic tracts
    • Medial Lemniscus
    • Cranial nerve 4 = Trochlear nerves come out posteriorly and crosses over, wraps around brainstem and comes out the front
  4. Describe the features through this section of the Mid-Pons
    What cranial nerves and nuclei come from this region?
    • Floor of the fourth ventricle
    • Middle cerebellar peduncles
    • Basilar region; containing
    • - Descending pyramidal (corticospinal) fibres: cross-sectioned pyramidal tract fibres
    • - Ponto-cerebellar fibres: running transversely
    • Superior cerebellar peduncles
    • Motor and Sensory nuclei of the Trigeminal Nerve
    • Spinothalamic tract
    • Medial Lemniscus pathway
    • Motor and Sensory Nuclei of the Trigeminal nerve: Come through anteriorly, motor = medial
  5. Describe the features through this section of the Caudal-Pons
    What cranial nerves and nuclei come from this region? 
    • Facial Colliculus: formed by fibers from the motor nucleus of the facial nerve as they loop over the abducens nucleus
    • Abducens nucleus; and
    • - Abducens Cranial Nerve (VI CN)
    • Facial nucleus; and the indirect path of the
    • - Facial nerve
    • Medial Longitudinal Fasiculus
    • Vesibulocochlear nucleus: with fibres moving anteriorly and direct
    • Medial Lemniscus pathway; Head medial → arms and legs lateral
    • Spinothalamic tract
    • Corticosponal tracts: descending
    • Nerves of Abducens (VI), Facial (VII) and Vestibulocochlear (VIII) come out at this level
    • - Green, Yellow and Brown
  6. Describe the features through this section of the Open Medulla
    What cranial nerves and nuclei come from this region?

    • This section is of the open medulla. Starting with non-cranial nerve/nuclei structures;
    • - Floor of the 4th ventricle
    • - Olive
    • - Corticospinal tract
    • - Medial Lemniscus pathway
    • - Spinothalamic Pathway
    • - Medial Longitudinal fasiculus
    • *Blacked out = Pre and post olivary sulci
    • #
    • Cranial nerve features;
    • Hypoglossal nucleus (CN XII)
    • - Hypoglossal nerve
    • The below 3 nuclei contribute to a common/indistinguishable nerve for CN IX and X
    • - Dorsal Motor Nucleus of Vagus (CN X only)
    • - Nucleus of the Solitary Tract (CN X and IX)
    • - Nucleus Ambiguus (CN X and IX)
    • Trigeminal nucleus (sensory)
  7. *Think about what sections are affected by whatever blood vessels*
  8. Describe the vasculature supplying the brainstem
    • Superior cerebellar artery:
    • Anterior inferior cerebellar artery (AICA): paramedian branches and long circumferential branches
    • Posterior inferior cerebellar artery (PICA):
    • If there are signs of both a lateral and a medial (paramedian) brainstem syndrome, then one needs to consider a basilar artery problem, possibly an occlusion.
  9. What four rules are there in the rule of 4?:
    • 1.) There are 4 structures in the ‘midline’ beginning with M
    • 2.) There are 4 structures to the side beginning with S.
    • 3.) There are 4 cranial nerves in the medulla, 4 in the pons and 4 above the pons (2 in the midbrain).
    • 4.) The 4 motor nuclei that are in the midline are those that divide equally into 12 except for 1 and 2, that is 3, 4, 6 and 12 (5, 7, 9 and 11 are in the lateral brainstem).
  10. What do these things represent?
    • Cross-section of the brainstem (in this case the medulla, but the same rule of 4 applies to the pons) showing the 4 Midline structures and the 4 Lateral (Side) structures aspect of the brainstem.
    • The size of the coloured areas does not represent the actual anatomical size, but are made large enough to see and label.
    • 1.) MN, motor nucleus (3, 4, 6 or 12);
    • 2.) MLF, median longitudinal fasciculus;
    • 3.) ML, medial lemniscus;
    • 4.) MP, motor pathway (corticospinal tract);
    • 5.) SC, spinocerebellar;
    • 6.) SP, spinothalamic;
    • 7.) SY, sympathetic;
    • 8.) SV, sensory nucleus of 5th cranial nerve.
  11. The 4 medial structures and the associated deficit are:
    • 1.) The Motor pathway (or corticospinal tract): contra lateral weakness of the arm and leg.
    • 2.) The Medial Lemniscus: contra lateral loss of vibration and proprioception in the arm and leg.
    • 3.) The Medial longitudinal fasciculus: ipsilateral internuclear ophthalmoplegia (failure of adduction of the ipsilateral eye towards the nose and nystagmus in the opposite eye as it looks laterally).
    • 4.) The Motor nucleus and nerve: ipsilateral loss of the cranial nerve that is affected (3, 4, 6 or 12).
  12. The 4 lateral structures and the associated deficit are:
    • 1.) The Spinocerebellar pathways: ipsilateral ataxia of the arm and leg.
    • 2.) The Spinothalamic pathway: contra lateral alteration of pain and temperature affecting the arm, leg and rarely the trunk.
    • 3.) The Sensory nucleus of the 5th: ipsilateral alteration of pain and temperature on the face in the distribution of the 5th cranial nerve (this nucleus is a long vertical structure that extends in the lateral aspect of the pons down into the medulla).
    • 4.) The Sympathetic pathway: ipsilateral Horner’s syndrome, that is partial ptosis and a small pupil (miosis).
  13. The 4 cranial nerves in the medulla (+ deficits) are:
    • 9 = Glossopharyngeal: ipsilateral loss of pharyngeal sensation.
    • 10 = Vagus: ipsilateral palatal weakness.
    • 11 = Spinal accessory: ipsilateral weakness of the trapezius and sternocleidomastoid muscles.
    • 12 = Hypoglossal: ipsilateral weakness of the tongue.
    • The 12th cranial nerve is the motor nerve in the midline of the medulla. Although the 9th, 10th and 11th cranial nerves have motor components, they do not divide evenly into 12 (using our rule) and are thus not the medial motor nerves.
  14. The 4 cranial nerves in the pons (+ deficits) are:
    • 5 = Trigeminal: ipsilateral alteration of pain, temperature and light touch on the face back as far as the anterior two-thirds of the scalp and sparing the angle of the jaw.
    • 6 = Abducent: ipsilateral weakness of abduction (lateral movement) of the eye. (eye tends to the midline on the affected side)
    • 7 = Facial: ipsilateral facial weakness.
    • 8 = Auditory: ipsilateral deafness.
    • The 6th cranial nerve is the motor nerve in the pons.
    • The 7th is a motor nerve but it also carries pathways of taste, and using the rule of 4 it does not divide equally in to 12 and thus it is not a motor nerve that is in the midline.
    • * The vestibular portion of the 8th nerve is not included in order to keep the concept simple and to avoid confusion. Nausea and vomiting and vertigo are often more common with involvement of the vestibular connections in the lateral medulla.
  15. The 4 cranial nerves above the pons (+ deficits) are:
    • 4 = Olfactory: not in midbrain.
    • 5 = Optic: not in midbrain.
    • 6 = Oculomotor: impaired adduction, supraduction and infraduction of the ipsilateral eye with or without a dilated pupil. The eye is turned out and slightly down.
    • 7 = Trochlear: eye unable to look down when the eye is looking in towards the nose.
    • The 3rd and 4th cranial nerves are the motor nerves in the midbrain.
  16. How does this information help us diagnose the site of a brainstem lesion?
    • These pathways pass through the entire length of the brainstem and can be likened to ‘meridians of longitude’ whereas the various cranial nerves can be regarded as ‘parallels of latitude’. If you establish where the meridians of longitude and parallels of latitude intersect then you have established the site of the lesion.
    • Thus a medial brainstem syndrome will consist of the 4 M’s and the relevant motor cranial nerve,
    • - a lateral brainstem syndrome will consist of the 4 S’s and either the 9–11th cranial nerve if in the medulla, or the 5th, 7th and 8th cranial nerve if in the pons.

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