Neuroanatomy 5 In Person Cerebellum and Intro to CNs PDF

Cerebellum (In-Person Class) Presented By: Dr. L. Terzic; [email protected] (Toronto Campus) Dr. M. Doroudi; [email protected] (Boucher Campus) BMS Neuroanatomy Lecture 5 Cerebellum and Introduction to Cranial Nerves (In-Person Class) Presented By: Dr. K. Lumsden; [email protected] (Toronto Campus) D...

Cerebellum (In-Person Class) Presented By: Dr. L. Terzic; [email protected] (Toronto Campus) Dr. M. Doroudi; [email protected] (Boucher Campus) BMS Neuroanatomy Lecture 5 Cerebellum and Introduction to Cranial Nerves (In-Person Class) Presented By: Dr. K. Lumsden; [email protected] (Toronto Campus) Dr. M. Doroudi; [email protected] Boucher Campus) Cerebellum: The Big Picture r Functions: 1. Affects ipsilateral motor function 2. Balance and posture 3. Fine tuning of skilled motor functions Via feedback: compares what cortex said to do with what joints/muscles really did and corrects 4. Initiation, termination, coordination, and timing of movements: Allows you to start and stop without overshooting. Allows you simultaneously perform multi joint tasks (ie bring arm over head: not first bend elbow, then shoulder etc) 5. Planning of motor movements - Should I bunt or swing at the ball? 6. Motor learning - ie golf swing based on previous trials: too fast for fine tuning How does the cerebellum exert motor influence? Via: 1.Rubrospinal (skeletal muscle control, tone, posture) 2.Vestibulospinal (balance in response to head movements) 3.Reticulospinal tract (influences reflexes and voluntary and autonomic 4.Connections to the cerebral cortex, which can then influence the corticospinal tracts Cerebellum: Anatomy Lobes: – Anterior & posterior lobes; Provide subconscious movements – Floculonodular lobe; Regulates equilibrium Vermis: “worm-like” part that separates the 2 hemispheres Foli: gyri-like convolutions on the surface of the cerebellum Internal anatomy of cerebellum White matter – arbor vitae Gray matter (cortex) – peripherally arranged around arbor vitae 6 Cerebellum: Anatomy (Review) Deep nuclei: ü Dentate, Interposed (consists of emboliform and globose nuclei): both voluntary movements ü Fastigial: balance Cerebellum: Anatomy (Review) Peduncles: superior, middle, and inferior (“highways” into and out of cerebellum) SCP: Mostly output MCP & ICP: Mostly input r Functional Divisions of the Cerebellum x Vestibulocerebellum (Corresponds to Floculo-nodular lobe) 1. Functions: Balance Coordination of eye movements 2. Major Inputs: Vestibular fibers from vestibulocochlear nerve and vestibular nuclei 3. Major Outputs: (via fastigial nucleus) Vestibulospinal tract (motor balance) Reticulospinal tracts (motor influences) Medial longitudinal fasciculus üRuns from vestibular nuclei to interconnect occulomotor, trochlear and abducens nuclei in brainstem (eye movements) r Common problem with lesion: Nystagmus archicerebellum: Greek archi = first, hence the oldest part of the cerebellum Nystagmus rapid involuntary movements of the eyes that may be: 1.Side to side (horizontal nystagmus) 2.Up and down (vertical nystagmus) 3.Rotary x Spinocerebellum (Corresponds to the majority of the vermis) Functions: - Adjusts movements as they are occurring - Corrective feedback to fine-tune motor skills Major Inputs: - Spinocerebellar, cuneocerebellar tracts (proprioception from periphery) - Corticopontocerebellar fibers (primary motor: copy from cortex) Major Outputs: (via Interposed nuclei) Rubrospinal, corticospinal r Common problems with lesion: Gait is affected: Because of Loss of motor coordination. paleo: Greek palaios = old; hence, paleocerebellum, the earliest stage in the evolution of the cerebellum. x Cerebrocerebellum (also called neocerebellum or pontocerebellum) (Corresponds to the majority of the cerebellar hemispheres) neo- (neos-): Greek = new 1. Functions: Planning movements Rapid alternating movements Fine dexterity (Quickness) Initiation, termination, coordination and timing of movements Motor learning 2. Major inputs: Corticopontocerebellar (premotor and association areas) Olivocerebellar 3. Major outputs: (via Dentate nucleus) Corticospinal, rubrospinal r Common lesions problems include dysmetria, dysdiadochokinesia, asynergia Cerebellar Lesions 1. Ataxia: “without order” (motor coordination is lost) Dysarythria: ataxia of laryngeal muscles. ü jerky articulation, separation of syllables, changing sound intensities (https://www.youtube.com/watch?v=kYP7ICsFyV4) Cerebellar Nystagmus: ataxia of ocular muscles ü tremor of eyeballs that usually occurs when patient attempts to fixes eyes on an object off to the side. Truncal ataxia: inability to maintain an upright position (affects gait). ü Unstable, wide gait with irregular steps and lateral bending Ataxia: An inability to coordinate muscle activity during voluntary movement; most often due to disorders of the cerebellum or the posterior columns of the spinal cord; may involve the limbs, head, or trunk. Syn: ataxy, incoordination. 2. Dysmetria: “wrong distance” can’t judge distance- movements “overshoot”, and then overcompensate - patient can’t touch finger to nose, heel to shin - leads to intention tremor 3. Dysdiadochokinesia: “without ability to make rapidly alternating movements” - loss of ability to predict where a body part will be at a given time, leading to the next movement in a sequence starting too early or too late. - test by asking patient to rapidly turn palm up and down: results in jumbled movements. 4. Hypotonia (low muscle tone) 5. Asynergia Lack of co-ordination between muscles or other body parts which usually work together. (postural abnormalities) Asynergy: Lack of coordination among various muscle groups during the performance of complex movements, resulting in loss of skill and speed. When severe, results in decomposition of movement, wherein complex motor acts are performed in a series of isolated movements; caused by cerebellar disorders. Syn: asynergia. Organization of the Nervous System Central Nervous System: Brain Brainstem Spinal cord Peripheral Nervous System: Spinal nerves (31 pairs) Cranial nerves (12 pairs) Exit off base of brain and brainstem Pass through cranial foramen to reach peripheral target in face/neck ANTERIOR Fossa Frontal, Ethmoid, Sphenoid CN I only MIDDLE Fossa Sphenoid, Temporal CN II – VI POSTERIOR Fossa Temporal, Occipital CN VII – XII 17 Cranial Nerves: 18 All cranial nerves innervate the ipsilateral (same) side. EXCEPT: CN II Therefore, motor fibers will provide efferent innervation to the same side and sensory carry afferent information from the same side. ANTERIOR fibers will SAGITTAL Nuclei of Cranial nerves III – XI originate within brainstem and nerves exit off brainstem EXCEPT: CN I and II which originate in specific locations 19 Nerve Fiber Modalities for Cranial nerves: GSE: (General Somatic Efferent): motor fibers to skeletal musculature (VOLUNTARY) GSA: (General Somatic Afferent): fibers that carry general sensation (touch, pressure, pain, proprioception , temperature changes, tickle and vibration) GVE: (General Visceral Efferent): motor fibers to smooth muscle, glands, and viscera (INVOLUNTARY) GVA: (General Visceral Afferent): fibers that carry visceral sensation (stretch of organ wall, pain, chemical changes, temperature change) SVE: (Branchial Efferent/Special Visceral Efferent): motor fibers to skeletal, voluntary muscles that developed from branchial (pharyngeal) arches SVA: (Special Visceral Afferent): taste & smell SSA: (Special Somatic Afferent): vision, hearing & balance 21 Motor Component of the Cranial Nerves v The UMNs coming from the cortex send mostly (not always!) bilateral innervation to the nuclei of the cranial nerves (i.e. LMNs), which then project to the ipsilateral muscles (with one exception!) v Cortex to cranial nuclei in the brainstem; Corticobulbar or corticonuclear (UMN) v Cranial nerves nuclei to the muscles by LMNs v Exception for C.N. IV The trochlear nucleus sends innervation to the contralateral superior oblique muscle rather than the ipsilateral muscle v Exception for C.N. VII The lower part of the facial motor nucleus that innervates the lower face muscles receives ONLY contralateral innervation from the cortex rather than bilateral v Exception for C.N. XII Those neurons in the hypoglossal nucleus that innervate the genioglossus muscle receive contralateral innervation from the cortex rather than bilateral Sensory Components of the Cranial Nerves v1st neuron is in the sensory ganglion of the cranial nerve. v 2nd neuron in the ipsilateral (mainly) sensory nucleus of the C.N. nerve in the brainstem v 3rd neuron in the thalamus (mainly contralateral) and terminates in the contralateral cortex 26 v Exception for C.N. I and C.N. II § The olfactory nerve (C.N. I); 1st neuron is in the olfactory epithelium, and 2nd nerve is in the olfactory bulb that goes to the olfactory areas of the brain. 27 v Exception for C.N. I and C.N. II §The Optic nerve (C.N. II): 1st neuron is in the retina, and 2nd neuron is in the thalamus, and from there, it goes to the visual cortex 28 CN I - Olfactory Nerve Pathway: Receptors originate in the superior parts of the nasal cavity in the mucosal lining Axons enter cranial cavity through the olfactory foramina in the cribriform plate of ethmoid Synapse in olfactory bulbs inferior to frontal lobe within anterior cranial fossa Bulbs sit between frontal lobe and cribriform plate Signals travel into frontal cortex via olfactory bulb Foramina: Olfactory foramina of Ethmoid Function: special sense = smell! Special Visceral Afferent (SVA) 29 CN I - Olfactory Nerve How does this nerve get injured? 1. Nasal trauma 2. Fracture of ethmoid/cribriform plate If fracture is suspected, do not intubate patient via nasal cavity! 3. Tumor in anterior cranial fossa / frontal lobe What is the outcome? Lack of smell “anosmia” CSF rhinorrhea - leakage of CSF from subarachnoid space due to trauma of the associated bones and meningeal layers (not seen with tumor) Testing CN I = performed usually after head trauma 1. Ask the patient to identify commonly known odors such as vanilla, coffee, soap (with their eyes closed!) 31 Olfactory Nerve Central Connection CN II – Optic Nerve Pathway: Receptors found in retina of the eyeball transmit signals via optic nerve to the optic chiasm and then optic tract Travels posteriorly to synapse in: 1. Thalamus Thalamus 2. Occipital lobe Foramina: Optic canal of sphenoid Function: special sense = Vision Special Somatic Afferent (SSA) Testing CN II =test each eye individually 1. Visual acuity test (Snellen eye chart) 2. Pupillary light response (discussed in L21) 34 Muscles of the Eyeball EYE LID EXTRINSIC EYEBALL INTRINSIC EYEBALL LEVATOR PALPEBRAE SUPERIORIS = elevates eyelid Rectus (Sup, Inf, Med, Lat) Oblique (superior and inferior) PUPILLARY CONSTRICTOR PUPILLARY DILATOR 36 Extrinsic Muscles: MUSCLE NERVE ACTION SUPERIOR RECTUS CN III Elevates and adducts eyeball INFERIOR RECTUS CN III Depressesandadductseyeball MEDIAL RECTUS CN III Adduction of eyeball INFERIOR OBLIQUE CN III Abducts and elevates andlaterally rotates eyeball (extorsion) LEVATOR PALPEBRAE CN III Elevatessuperior eyelid SUPERIOR OBLIQUE CN IV Abducts, depressesandmedially rotates eyeball (intorsion) LATERAL RECTUS CN VI Abductseyeball “LR6SO4AO3” 37 CN III = Oculomotor Nerve Pathway: Nerve begins at midbrain and travels anteriorly towards orbit Innervates several muscles of eyeball after passing through superior orbital fissure Foramina: Superior Orbital Fissure of sphenoid (posterior orbit) Function: nerve has 2 axon modalities: General Somatic Efferent (GSE): Voluntary motor to levator palpebrae superioris, and several extraocular eye muscles: superior rectus, medial rectus, inferior rectus, and inferior oblique muscle General Visceral Efferent (GVE): Visceral motor (parasympathetic) innervation to sphincter pupillae for pupil constriction Synapses in ciliary ganglion 38 CN III = Oculomotor Nerve Common causes of injury: Diabetic neuropathy Aneurysm Cerebral trauma Increased intracranial pressure Cavernous sinus syndrome Patient presentation includes: Ptosis – droopy upper eyelid Mydriasis – permanent dilation of pupil Strabismus – “lazy eye” Eye position is “down and out” Due unopposed action of superior oblique and abducens muscle Diplopia – double vision 40 Testing CN III for accommodation CN IV = Trochlear Nerve Pathway: Originates at midbrain, travels toward eyeball, exits superior orbital fissure Foramina: Superior Orbital Fissure (posterior orbit) Function: voluntary motor to superior oblique muscle = normally pulls the eye down and out General Somatic Efferent (GSE) 43 CN VI = Abducens Nerve Pathway: Originates at pons, travels toward eyeball, exits superior orbital fissure (along with ……?) Foramina: Superior Orbital Fissure (posterior orbit) Function: voluntary motor to lateral rectus muscle = normally Abduct the eye away from the midline General Somatic Efferent (GSE) Testing CN III, IV and VI =test each eye individually 1. Eye movement in “H” pattern, observe for differences 45