L6 MedNeuro2 Sp25 Lec6 BrainstemMotor1 PDF

Still Important Motor Brainstem 1 Introduction, Midbrain and eye movements DO-SYS-725 Med Neuro II Lecture 6 - Tony Harper, Ph.D Thursday Jan 23 @9am 1 Learning Objectives 1) I can recognize/predict the symp...

Still Important Motor Brainstem 1 Introduction, Midbrain and eye movements DO-SYS-725 Med Neuro II Lecture 6 - Tony Harper, Ph.D Thursday Jan 23 @9am 1 Learning Objectives 1) I can recognize/predict the symptoms produced by lesions to primary motor nuclei and long white matter tracts in the midbrain 2) I can explain functional components and peripheral distribution of the three main motor columns in the brainstem 3) I understand which eye movements are produced by each extraocular muscle, and the CNS regions associated with conjugate eye movements 4)I can identify the nerves, nuclei and tracts mentioned in the lecture in preserved brain photographs and stained cross sections of the midbrain 2  Cranial Fossae Anterior fossa Middle fossa Lateral fissure Superior Petrosal Sinus and Tentorium Cerebelli Posterior fossa Cerebellum Brainstem Vertebrobasilar arteries 3  Brainstem Only ~ 1 Billion neurons (~1% total Midbrain in brain) (Mesencephalon) Extends from pyramidal decussation (caudally) to posterior commissure (cranially) Includes the Medulla, Pons and Midbrain Located within the posterior cranial fossa Supplied by vertebrobasilar arterial group Hindbrain Core of brainstem is composed of (Rhombencephalon) ancient Reticular Formation structure Contains many serotonergic “raphe nuclei” at all levels 4  Gray Matter White Matter Primary Other Nuclei Reticular Nuclei Long Tracts Formation “Other” Tracts Dorsal Column- Spinothalamic Corticospinal Medial Primary Medial Lemniscus Cerebellar Primary Tract (Pyramidal) Peduncles Longitudinal Motor Sensory (Anterolateral Fasciculus Nuclei Tract Nuclei System) 5  Brainstem White Matter Tracts America Colors are used to display somatotopy in contralateral half of body Long tracks: throughout Dorsal Column – Medial Lemniscus Pathway (DCML) brainstem Spinothalamic Tract (part of “Anterolateral Tract”) lectures and Corticospinal (Pyramidal) Tract lab “Not long” tracts Medial Longitudinal Fasciculus (MLF) Cerebellar peduncles Spinal Trigeminal Tract 6  Brainstem Nuclei Primary motor nuclei: Locations where cell bodies of somatic and autonomic Lower Motor Neurons (LMNs) are located. Primary sensory nuclei: Locations of first synapse of peripheral sensory neurons (first-order neurons) Neurons with cell bodies in primary nuclei sometimes called First Order Multipolar neurons (FOMs – which is confusing because they are second-order sensory neurons) Many, many, other nuclei and “centers” of functionally related neurons 7 Primary Motor Nuclei (memorize these) 8  = Sulcus Limitans GSE – General Somatic Efferent LMNs to skeletal muscles In brainstem, innervates things that wiggle inside of head (tongue, extraocular muscles) SVE – “Special” Visceral Efferent AKA “Branchiomotor” or “Branchiomeric” Only in hindbrain LMNs to skeletal muscles of pharyngeal arches GVE – General Visceral Efferent AKA “Visceral Efferent” or Autonomic In brainstem, contains parasympathetic preganglionic cell bodies + sensory components (not gonna talk about today) 9  New Special Visceral Efferent cell column develops just in hindbrain 10 Primary Sensory Nuclei Diagram from Haines Atlas (pg Special Somatic Afferent 97 in 10th edition) Cochlear nuclei You should Vestibular Nuclei become very Somatosensory familiar with this Spinal Trigeminal Nucleus whole diagram Main Trigeminal Nucleus (Mesencephalic Trigeminal Nucleus is special) Viscerosensory and Taste Nucleus Solitarius Some Miscellaneous Nuclei Red Nucleus Substantia Nigra Corpora quadrigemina Pontine Nuclei Inferior Olivary Nucleus 11 Primary Motor Nuclei Branchiomotor Trigeminal Motor Nucleus Facial Nucleus Nucleus Ambiguus Autonomic Edinger-Westphal Nucleus Superior Salivary Nucleus Inferior Salivary Nucleus Dorsal Motor Nucleus of Vagus Somatomotor Oculomotor Nucleus Trochlear Nucleus Abducens Nucleus Hypoglossal Nucleus 12 13  General Visceral Efferent Column GVE column contains cell bodies of autonomic neurons. In the brainstem these are all Preganglionic Parasympathetic neurons projecting to Parasympathetic ganglia (e.g. COPS) 14 GSE is one of the two columns that innervates typical skeletal muscles within the head. Can think of GSE as innervating things that “wiggle inside the head” e.g. tongue and eyes General Somatic Efferent Column 15  SVE column not present in midbrain Branches of the Vagus Nerve CN10 provide To Stylopharyngeus Special Visceral Efferent (SVE) motor innervation to all pharynx Column muscles except To All Other Pharyngeal and Stylopharyngeus Laryngeal Muscles 16 Hypoglossal Nucleus Nucleus Ambiguus Facial Abducens Nucleus Nucleus 17 General Regional Terms A few terms related to features of the all parts of the brainstem: Ø Tectum – located in the dorsal midbrain, comprised of the superior colliculi and the inferior colliculi. Ø Tegmentum – area ventral to the cerebral aqueduct in the midbrain and ventral to the 4th ventricle in the pons and medulla. Contains cranial nerve nuclei and most of the reticular formation. Ø Basis – most ventral region, containing corticospinal and corticobulbar tracts. Neuroanatomy through Clinical Cases (2 ed ed), Blumenfeld, Fig 14.2 18 Midbrain (aka Mesencephalon) Normal Sagittal T1 MRI Sagittal T2 MRI with Hummingbird Sign Earliest region of brain to reach adult form (has no subdivisions like forebrain and hindbrain) Earliest forming part of midbrain is the Mesencephalic Trigeminal Nucleus (which is actually a displaced peripheral sensory ganglion of unipolar neurons) The midbrain contains cerebral aqueduct, cerebral peduncles, and corpora quadrigemina and cell bodies of most dopaminergic neurons Atrophied midbrain creates Hummingbird Sign, a symptom of disease such as Progressive Supranuclear Palsy (PSP) 19 Midbrain Lesion “Panda Sign” Panda Sign is caused by inflammation of tegmentum around the red nuclei and substantia nigra visible on T2-MRI (also a smaller panda in pons) Characteristic of Wilson’s Disease – A congenital copper toxicity syndrome 20  Red Nucleus – contains fibers of the Vertical Gaze Center Midbrain Nuclei (cranial tip of MLF) contralateral superior cerebellar peduncle and CN3. Results in ataxia and reduced tone in contralateral limb Substantia Nigra Superior Colliculus Inferior Colliculus (caudal to red nucleus) Periaqueductal Grey Decussation of superior cerebellar peduncles (Somatic) Oculomotor Nucleus – to ipsilateral extraocular Edinger-Westphal Nucleus (Accessory Oculomotor mm. Nucleus) – preganglionic parasympathetic to ipsilateral ciliary ganglion Trochlear Nucleus – to contralateral superior oblique m. (the only LMNs that decussate) 21 Midbrain Long Tracts Medial Lemniscus Spinothalamic Corticospinal Spinotectal Fibers Spinothalamic Tract Superior Colliculus Spinothalamic Tract Medial Lemniscus Periaqueductal Gray Medial Lemniscus Spinothalamic Tract Red Nucleus Medial Lemniscus Substantia Nigra Red Nucleus Red Nucleus Crus Cerebri Substantia Nigra 22 CN III – Oculomotor n. Oculomotor nerve arises from the midbrain at the level of the superior colliculus. Innervates most extraocular muscles - superior rectus m., medial rectus m., inferior rectus m., inferior oblique m., levator palpebrae superioris m. (technically not extra-ocular). Nearby Edinger Westphal nuc. provides pupillary constriction and accommodation. Basic Clinical Neuroscience (3rd ed.) Fig. 5-4 23 CN III – Oculomotor n. Neuroanatomy through Clinical Cases (2 ed ed), Blumenfeld, Fig 13-2 24 CN III – Oculomotor n. injury Oculomotor nerve injury may result in three signs: Ø Ptosis – due to loss of levator palpebrae superioris m. Ø Exotropia (lateral strabismus) – due to loss of extraocular mm. Ø Mydriasis – due to loss of parasympathetic function. Basic Clinical Neuroscience (3rd ed.) Fig. 5-4 (left) Radia et al. (2017), Evaluation of Third Nerve Palsy, British Journal of Hospital Medicine (top right) 25 CN III – Oculomotor n. injury Compressive or tensile lesions may affect the superficial autonomic fibers of CN III first, resulting in an isolated “blown pupil”. (e.g. blown pupil ipsilateral to uncal herniation) Internal diseases of the nerve / vascular disorders will spare the pupillary fibers but may damage the deeper motor fibers, resulting in a “pupil-sparing” ophthalmoplegia. Woodruff and Edlow (2008), Evaluation of Third Nerve Palsy in the Emergency Department, Journal of Emergency Medicine (top) Practical Neuroophthamology (2013) Right Pupil-Sparing Third Nerve Palsy (bottom right) Clinical Neurology and Neuroanatomy (1st ed.), Fig. 11-4 (left) 26 CN IV – Trochlear n. Trochlear nerve nucleus is located in the midbrain at the level of the inferior colliculus. The trochlear nerve fascicles exit dorsal brainstem. Lower motor neurons for the trochlear nerve decussate to enter the contralateral superior oblique muscle. Basic Clinical Neuroscience (3rd ed.) Fig. 5-5 27 CN IV – Trochlear n. Neuroanatomy through Clinical Cases (2 ed ed), Blumenfeld, Fig 13-4 28 CN IV – Trochlear n. injury R eye affected Trochlear nerve damage may cause hypertropia and excyclotropia. Person will tend to tilt their head away from the side of the affected superior oblique muscle R eye affected Neutral gaze – right eye hypertropic Right eye unable to direct Normal intorsion and extorsion gaze inferiorly from an adducted position Clinical Neurology and Neuroanatomy (1st ed.), Fig. 11-2 (left) Bazan et al., (2011), Trochlear Nerve Palsy Associated with Claude-Bernard Horner Syndrome after Brainstem Stroke, Case Reports in Neurology (right bottom) Neuroanatomy through Clinical Cases (2 ed ed), Blumenfeld, Fig 13-6 (right top) 29  “straight forward” position of eyes is Extraocular Muscle Actions called Primary Gaze Muscles used to achieve the 8 non-resting positions of the eyeball. Medial and Lateral Rectus muscle have simple actions(yay!), which don’t depend on the current angle between the Orbital and Optic Axes (remember MGA orbit lecture?) The actions of the other four extraocular muscles have actions that depend on the current angle between the optical and orbital axes. Depending on mediolateral angle, for these 4 muscles: “Rectus” Muscles have the ability to adduct the eye “Oblique” muscles have the ability to abduct the eye “Superior” muscles can intort the eye “Inferior” Muscles can extort the eye 30  Clinical Correlation: The “H” Test To “H” test is used to isolate the function of individual muscles. The H-Test diagram is different from the muscle actions described in the previous slide Vertical motions used to isolate the test the effectiveness of individual muscles, with all other Lateral Medial muscles contracting maximally and holding the eye in an adducted or abducted position rectus rectus “counterintuitive” motions from extraocular muscles produced by the difference in alignment of the Orbital and Optic Axes, and the relative placement of muscle insertions relative to each eyeball’s center of motion 31 Supranuclear control of eye movements Frontal eye fields are the chief cortical center responsible for generating contralateral saccades. Control of pursuit is achieved in other areas of the cortex, mainly by the posterior aspect of the temporal lobe. Neuroanatomy through Clinical Cases (2 ed ed), Blumenfeld, Fig 13-14 32 Vertical gaze center Vertical Gaze complicated, because which muscles needed to elevate/depress eyes depend on current gaze direction The vertical gaze center is located in the midbrain, in the rostral interstitial nucleus of the MLF and the interstitial nucleus of Cajal. Lesions to the vertical gaze center typically occur in dorsal midbrain syndrome. Common vertical gaze lesions include tumors of the pineal gland or tectum, hydrocephalus with expansion of the 4th ventricle, and progressive supranuclear palsy. Compression of the dorsal midbrain may cause Dorsal Midbrain Syndrome - which is characterized by bilateral paralysis of upward gaze (Piranaud’s Syndrome), bilateral eyelid retraction (Collier's sign). Clinical Findings of Children with Hydrocephalus (2019), Isik and Ozek (left bottom) https://webpath.med.utah.edu/HISTHTML/NEURANAT/CNS229A.html (left top) Buckley and Holgado, Surgical Treatment of Upgaze Palsy in Piranaud’s Syndrome, (2004), JAAPOS (right) 33 Horizontal gaze center Horizontal gaze is conceptually simpler than vertical, because inhibition/excitation of medial/lateral rectus is always involved, and torsion does not need to be compensated for. The horizontal gaze center is located in the pons, in an area called the paramedian pontine reticular formation (PPRF). From the PPRF, interneurons travel to synapse with lower motor neurons in the ipsilateral abducens nucleus (which innervates the ipsilateral lateral rectus muscle). Additionally, longer interneurons from the abducens nucleus decussate and travel in the medial longitudinal fasciculus to the contralateral oculomotor nucleus (which innervates the medial rectus muscle.) Basic Clinical Neuroscience (3rd ed.) Fig. 10-2 34  Left Right When attempting to look right (viewed as though you are looking into the patient’s eyes): LR MR MR LR R eye L eye Normal (no lesion) CN III nucleus Lesion #1 Abducens nerve L#1 L#3 Lesion #2 MLF Abducens Frontal nucleus/PPRF eye field L#4 (left) Lesion #3 MLF CN VI nucleus L#2 PPRF Lesion #4 FEF 35 Internuclear ophthalmoplegia Internuclear ophthalmoplegia (lesion #3 from previous slide) is damage to the medial longitudinal fasciculus. Associated with multiple sclerosis (because MLF is highly myelinated). Results in a contralateral effort nystagmus. Usually has normal convergence. 36 37 Oculomotor nucleus 38 Oculomotor nucleus 39 Trochlear nucleus 40 Trochlear nucleus 41 Recognizing Stroke 42