L7 MedNeuro2 Sp25 Lecture 7 - Brainstem Motor 2 PDF

Motor Brainstem 2 Hindbrain and Corticobulbar DO-SYS-725 Med Neuro II Lecture 7 - Tony Harper, Ph.D Thursday Jan 23 @10am 1 Learning Objectives I can diagnose lesions to the corticobulbar tract and the GSE and SVE...

Motor Brainstem 2 Hindbrain and Corticobulbar DO-SYS-725 Med Neuro II Lecture 7 - Tony Harper, Ph.D Thursday Jan 23 @10am 1 Learning Objectives I can diagnose lesions to the corticobulbar tract and the GSE and SVE nuclei of cranial nerves 5,6,7, 10, 11, and 12 I understand the association of brainstem parasympathetic and branchiomotor nuclei with the adult distribution of cranial nerves 5,7,9 and 10, and the embryonic pharyngeal arches I can identify the nuclei and tracts mentioned in today’s lecture in whole brain photos and myelin-stained cross sections of the pons and medulla 2  Trigeminal Nerve develops in association with Pharyngeal Arch 1 (both maxillary and mandibular processes) and the Trigeminal Motor Nucleus. Facial Nerve is Associated with Pharyngeal Arch 2, the Facial Motor Nucleus and the Superior Salivatory Nucleus (in chorda tympani and greater petrosal nn) Glossopharyngeal Nerve develops in association with Pharyngeal Arch 3, and the Inferior Salivary Nucleus (in tympanic nerve -> lesser petrosal nerve) Vagus Nerve develops in association with pharyngeal arches 4 and 6 (recurrent branch) and parasympathetic ? Dorsal Motor Nucleus of the Vagus Nerve Nucleus Ambiguus provides branchiomotor innervation to pharyngeal arches 3-6 3  Hindbrain Midbrain forms as “kyphotic” flexure of neural tube Ancient part of brain homologous among all bilaterally symmetric animals Pons forms as “lordotic” flexure. (only very prominent in primates) Rhombomeres 1-3 form metencephalon 4  Pons Pneumotaxic Apneustic Center Center Cerebellum Together with Cerebellum, forms metencephalon Basis(longitudinal and Pons transverse fibers and pontine nuclei) and Fourth tegmentum Ventricle Respiration is Medulla Reticular “viscerosomatic reflex” (not Formation technically autonomic) Olive 5 Pons Nuclei Trigeminal Motor Nucleus – Innervates First pharyngeal arch muscles: Temporalis, Masseter, Medial Pterygoid, Lateral Pterygoid, Tensor Veli Palatini, Tensor Tympani, Anterior Belly of Digastric, and Mylohyoid mm. Only distributed in V3 Facial Motor Nucleus – Innervates Second Pharyngeal Arch Muscles: Muscles of facial expression, Stapedius, Posterior Belly of Digastric, Stylohyoid Locus Coeruleus melanin containing nucleus containing the cell bodies of Pontine Micturition Center noradrenergic neurons in the brain (PMC) Relaxes internal urethral sphincter, allowing micturition Pontine Nuclei contain Pontocerebellar neuron cell bodies – these end as mossy fibers in cerebellum Abducens Nucleus – to ipsilateral Superior Salivatory Nucleus – Lateral Rectus muscle (and Preganglionic parasympathetic cell surrounded by PPRF) bodies, whose axons join with sensory axons to form nervus intermedius of the facial nerve 6 Pons Long Tracts Medial Lemniscus Spinothalamic Corticospinal Spinothalamic Tract Vestibular Nuclei Spinothalamic Tract Medial Longitudinal Medial Longitudinal Medial Longitudinal Fasciculus Fasciculus Fasciculus Spinothalamic Tract Medial Lemniscus Medial Lemniscus Medial Lemniscus Basis Pontis Corticospinal Tract 7 CN V – Trigeminal n. motor The motor trigeminal nucleus lies in the dorsal aspect of the pontine tegmentum. Lower motor neurons enter the mandibular division of the trigeminal nerve (V3). Innervates the muscles of mastication (and a few more). Basic Clinical Neuroscience (3rd ed.) Fig. 5-6C 8 CN V – Trigeminal n. motor injury Lesions to the motor component of the trigeminal nerve may result in ipsilateral paralysis of muscles of mastication. Motor injury may result in deviation of the jaw toward the lesioned side when the mouth is opened due to the unopposed action of the contralateral lateral pterygoid mm. Basic Clinical Neuroscience (3rd ed.) Fig. 5-6 (left) Gohil et al., (2019), A Rare Case of Multi-compartment Epidermoid Presenting with Pure Motor Trigeminal Neuropathy, Case Report and Review of the Literature (right) 9 CN VI – Abducens n. Abducens nucleus is located in the caudal pons close to the fourth ventricle. Surrounded by PPRF Abducens nerve fibers emerge from the brainstem at the pontomedullary junction. Innervates the lateral rectus m. in the orbit. If lesioned near corticospinal tract, can produce “wrong-way eyes” syndrome Basic Clinical Neuroscience (3rd ed.) Fig. 5-7 10 CN VI – Abducens n. Neuroanatomy through Clinical Cases (2 ed ed), Blumenfeld, Fig 12-11 11 CN VI – Abducens Nerve Injury Abducens nerve injury are associated with esotropia (medial strabismus). Diplopia worsens when attempting to abduct the affected eye. Duane retraction Syndrome – is a rare congenital disorder caused by a lack of a functional abducens nucleus (usually left side, more common in females). L eye affected Basic Clinical Neuroscience (3rd ed.) Fig. 5-7 (left) Carneiro Jr. et al., (2011), Orbitoethmoidal impacted injury by kitchen knife causing abducens nerve palsy, Oral and Maxillofacial Surgery (right middle) http://www.neuroophthalmology.ca/textbook/disorders-of-eye-movements/iv-neuropathies-and-nuclear-palsies/v-abducens-vi-nerve-palsy (right top & bottom) 12 CN VII – Facial n. motor The facial motor nucleus lies in the lateral pons. It is divided into two smaller subdivisions. Facial motor fascicles initially course dorsally within the pontine tegmentum before wrapping around the facial nucleus and exiting ventrally. Innervates the muscles of facial expression (and a few more). Basic Clinical Neuroscience (3rd ed.) Fig. 5-8 13  PNS Lesion – Facial Nerve Lesion Other symptoms of facial weakness include: Lagophthalmos – inability to blink, Drooling Hard to pronounce labial sounds like “pa pa” and “ma Long term facial paralysis can result in ma” atrophy of facial muscles and surrounding soft tissues. As in Progressive Hemifacial Atrophy (Perry-Romberg Syndrome) Paralysis of CN7 14 CN VII – Facial n. motor injury Lesions or conditions like Bell’s Palsy may result in ipsilateral paralysis of the motor component of the facial nerve (especially the muscles of facial expression). Hyperacusis (sounds are perceived as too loud) may result if lesion happens proximal to the nerve to the stapedius R side affected Basic Clinical Neuroscience (3rd ed.) Fig. 5-8 (left) Naolabial Fold (from Lev. Labii. https://entsho.com/facial-nerve-palsy (middle) https://en.wikipedia.org/wiki/Bell%27s_palsy (left) Sup. Ala. Nasi ) 15 CN VII – Facial n. motor injury Similar to palate with vagus nerve, the lips of people with facial UMN lesion tend to divert contralateral to injury Facial nerve lesions which affect the forehead are suggestive of a LMN lesion, a characteristic finding of Bell’s palsy and suggestive of a peripheral lesion. Lower face UMNs only contralateral Facial paralysis which spares the forehead is suggestive of a UMN lesion, a characteristic of lesions to the contralateral cortex or genu of internal capsule. Neuroanatomy through Clinical Cases (2 ed ed), Blumenfeld, Fig 12.3 16 Diagnosing Facial Upper Motor Neuron Injury Check to see if forehead wrinkling muscles are functional (e.g. frontalis) If not, it is a Facial Nerve of Nucleus injury However, some patients Patient showing Bells Phenomenon just have wrinkly (Palpebral Oculogyric Reflex) foreheads, and it is hard to tell if upper facial Bells Phenomenon is a protective reflex causing the cornea to roll dorsally whenever we blink muscles are functional However, if the orbicularis oculi is denervated, the reflex will still occur even though the patient can no longer close eyelids Can use Bell’s Phenomenon to diagnose facial UMN injury by spreading open patient’s orbicularis oculi with palms of hands If patient’s orbicularis oculi is still functional they should still be bale to close eye tightly during blinking and you will not be able to see Bell’s Phenomenon Only in a patient with facial weakness (paresis) or paralysis of upper facial muscles will you https://www.aafp.org/afp/2014/0215/p283.html (left) https://www.jems.com/patient-care/differentiating-facial-weakness-caused-b/ (right) be able to see Bell’s Phenomenon while spreading open their orbicularis oculi 17  Aka osmotic demyelination syndrome (because can affect areas besides pons) Caused by too rapid correction for sodium deficiency (hyponatremia), usually in comatose/unresponsive patients Myelinated axons in pons are especially susceptible to damage from hypertonic extracellular fluids, and permanent damage to corticospinal tract may be caused by rapid IV saline administration 18 Medulla Oblongata AKA Myelencephalon Inferior Not just stump between Olivary Cardiovascular spinal cord and rest of brain, Nucleus Centers contains more nuclei that the Respiratory Rhythmicity other sections of brainstem Center Cuneate Separated into cranial “open Nucleus medulla” and caudal “closed Gracile medulla” Nucleus Not associated with anger (or football) per se Reticular Formation 19 20  Inferior Olivary Nucleus– contains Olivocerebellar neuron cell bodies – these end as climbing fibers in the cerebellar cortex Inferior Salivatory Nucleus – Preganglionic parasympathetic cell bodies, whose axons join to form the Glossopharyngeal Nerve’s Tympanic Branch, and Lesser Petrosal Nerve. Stimulate postganglionic neurons which innervate the Parotid Salivatory Gland Nucleus Ambiguus– Innervates all Dorsal Motor Nucleus of Vagus Hypoglossal Nucleus – Innervates Nerve – Contains all preganglionic Pharyngeal and Laryngeal Muscles all Tongue Muscles through the through the Vagus (mostly) and parasympathetic cell bodies for the Hypoglossal Nerve except Glossopharyngeal (Stylopharyngeus) entire Vagus Nerve Palatoglossus Nerves. Also innervates Palatoglossus, Levator Veli palatini and Musculus Uvulae (CNX), and has some autonomic cell bodies. 21 Medulla Long Tracts Medial Lemniscus Spinothalamic Corticospinal Medial Longitudinal Medial Medial Fasciculus Longitudinal Longitudinal Spinothalamic Fasciculus Fasciculus Tract Spinothalamic Spinothalamic Tract Tract Medial Inferior Medial Olivary Medial Inferior Lemniscus Lemniscus Nucleus Lemniscus Olivary Pyramid Pyramid Nucleus Gracile Nucleus Cuneate Nucleus Medial Lemniscus Internal Arcuate Fibers 22 Nucleus ambiguus (CN IX, X, XI*) *along with accessory nucleus Nucleus ambiguus is located in the ventrolateral medulla. It is a column of lower motor neuron cell bodies which provide motor innervation to the glossopharyngeal n., vagus n., and the cranial component of the spinal accessory n. Innervates palatal muscles, muscles of the pharynx, and muscles of the larynx. Preganglionic parasympathetic “cardioinhibitory” neurons Basic Clinical Neuroscience (3rd ed.) Fig. 5-9A&B 23 Nucleus ambiguus injury Damage to nucleus ambiguus may result in: Sagging of the palatal arch and deviation of the uvula away from the affected side. Vocal muscle paralysis with a “hoarse” or “breathy” voice. Dysarthria – abnormal motor articulation of speech (distinct from aphasia, which involves higher cognitive function). Dysphagia – impaired swallowing Persistent hiccupping(singultus) Basic Clinical Neuroscience (3rd ed.) Fig. 5-9C (left) https://nnjournal.net/article/view/1120 (right) 24 CN XI – Accessory n. The accessory nerve nucleus has two parts: Ø Cranial portion – a component of nucleus ambiguus. Ø Cervical portion – a column of cells in the ventral horn from C1-C5. The cervical portion innervates the trapezius m. and sternocleidomastoid m. http://wiki.ahuman.org/index.php/HumanNervesCranial 25 CN XI – Accessory n. injury Damage to the accessory nerve may lead to sagging of the scapula due to denervation of the upper trapezius. Weakness in contralateral head rotation may be seen due to denervation of the sternocleidomastoid muscle. https://www.semanticscholar.org/paper/Injuries-to-the-spinal-accessory-nerve%3A-a-lesson-to-Camp-Birch/22254a87f9ec42d1fb550425685341965d35cb5c/figure/0 (right top) https://www.researchgate.net/publication/256482117_Reversible_Isolated_Accessory_Nerve_Palsy_due_to_a_Large_Thrombosed_Vertebral_Aneurysm/figures?lo=1 (right bottom) Charopoulas et al, (2010), Journal of Medical Case Reports (left top) 26 CN XII – Hypoglossal n. The hypoglossal nucleus is located in the dorsal aspect of the medulla. LMNs project between the inferior olive and the corticospinal tract and emerge from the ventral medial medulla. Innervates the muscles of the tongue (except one). Basic Clinical Neuroscience (3rd ed.) Fig. 5-10 27 CN XII – Hypoglossal n. injury Damage to the hypoglossal n. (or nucleus) will result in atrophy of the ipsilateral tongue muscles. Upon protrusion, the apex of the tongue will deviate toward the lesioned side. Basic Clinical Neuroscience (3rd ed.) Fig. 5-10C (right) https://www.researchgate.net/publication/334468144_Unilateral_hypoglossal_nerve_palsy_after_the_use_of_laryngeal_mask_airway_LMA_Protector/figures?lo=1 (middle) https://www.nejm.org/doi/full/10.1056/NEJMicm1114751 (left) 28 Corticobulbar(Corticonuclear) Tract The muscles of the face, tongue, pharynx, and larynx(not the eyes) have upper and lower motor neurons similar to the arrangement of the extremities via the corticospinal tract. Upper motor neurons for cranial nerves travel in the corticobulbar tract (adjacent to the corticospinal tract), terminating in their respective cranial nerve nuclei. Corticobulbar fibers travel through the genu of the internal capsule (at least in dorsal half) Neuroanatomy through Clinical Cases (2 ed ed), Blumenfeld, Fig 2.13 (left), Fig. 6.10B (right) 29 Corticobulbar tract Bilateral innervation of corticobulbar targets usually means that unilateral lesion of the corticobulbar tract usually produce no major UMN symptoms EXCEPT for muscles of the lower face (lips and cheek) which only receive LMNs innervated by contralateral corticobulbar UMNs Important Point: Lesions of corticobulbar tract may appear to resemble Bell’s Palsy but can be differentiated because: Forehead muscles will not be paralyzed Autonomic fibers and taste will be unaffected Hyperacusis will not occur because the stapedius is under reflex control (not cortical) Basic Clinical Neuroscience (3rd ed.) Fig. 6-4 30  Pseudobulbar VS Bulbar Palsy “The Bulb” is an antiquated term for Pseudobulbar Bulbar medulla oblongata “-bulbar” generally used to describe Gag Reflex (IX,X) normal or absent cranial nerve dysfunction below 5 and 7 increased Soft Palate (X) sag away from sag away from Lesions to the corticobulbar Lesions directly to lesion side lesion side tract produce pseudobulbar cranial nerve motor palsy because they effect nuclei in the medulla UMNs before they reach (nucleus ambiguous, Speech (X) spastic flaccid cranial nerve nuclei in the spinal accessory, dysarthria dysarthria medulla. hypoglossal, dorsal (labored (nasal twang) Damage to the corticobulbar motor of vagus and speech) tract therefore produces inferior salivary) UMN symptoms of spacticity produce bulbar palsy and hyperreflexia Tongue Motion “tight tongue” Thrown into These motor nuclei (XII) lies on floor of folds due to Damage to the corticobulbar tract (especially bilateral contain LMNs, and so mouth; atrophy, damage) has the potential to LMN symptoms such as protrudes to possible also produce “pseudobulbar atrophy, fasciculations, affect” (emotional lesioned side fasciculations; incontinence) in patients and hyporeflexia can be protrudes to seen in the effected lesioned side regions Jaw Jerk Reflex present absent (V3) 31 Left is The Good Side Because the lower facial muscles only receive contralateral innervation from the corticobulbar tract, muscles of the left lips and cheek are controlled by the right motor cortex In humans because of lateralization of brain function, the right cerebral cortex is more related to the expression and interpretation of emotions People generally think the left sides of faces are better looking too 32 Trigeminal motor nucleus 33  Abducens nucleus Facial motor nucleus 34 Nucleus Ambiguus 35 Hypoglossal nucleus 36 Spinal Accessory Nucleus 37