Flashcards in Brainstem Deck (12):
Locate and identify the attachment points of all the brainstem cranial nerves
(CNIII – CNXII)
Olfactory (I): Olfactory bulb – not brainstem
Optic (II): Ventral diencephalon – not brainstem
Occulomotor (III): Ventral midbrain
Trochlear (IV): Dorsal midbrain – only nerve to exit posteriorly and innervate muscle exclusively on contralateral side
Trigeminal (V): Ventro-lateral pons
Abducens (VI): Ventrally at the pons-medulla junction
Facial (VII): Laterally at the pons-medulla junction
Vestibulocochlear/Auditory (VIII): Laterally at the pons-medulla junction , more caudal than Facial Nerve
Glossopharyngeal (IX): Lateral medulla, caudo-vetral to VIII
Vagus (X): Lateral medulla, caudal to IX
Accessory (XI): Lateral medulla-spinal cord junction
Hypoglossal (XII): Ventro-lateral, caudal medulla
Locate and identify the following features on the intact brainstem: approximate dividing lines between medulla, pons and midbrain; optic chiasm, mammillary body, superior and inferior colliculi; crus cerebri (cerebral peduncle), basal pons, superior, middle and inferior cerebellar peduncles, pyramid and olive.
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Even sadder face
Starting at the receptor endorgan and ending in cortex, identify the components of and trace the pathways taken by systems serving somatosensory functions for the body and head, including: I) pain & temperature for the body, ii) pain and temperature for the face, iii) touch and vibration sensation for the arms and for the legs, and iv) touch and vibration sensation for the face
Starting from auditory receptors and ending in cortex, identify the components of and trace the pathways taken by the auditory system including: cochlear nuclei,
superior olive, trapezoid nuc., lateral lemniscus, inferior colliculus, medial geniculate and auditory cortex.
Describe the role of the MLF in the circuitry of the vestibuloocular reflex
The VOR allows you to move your eyes separately from your head motion, so eyes may remain focused on the same place while the head moves. The vestibulocochlear nerve (CN VIII) conveys information about how you're moving your head to cranial nerves III, IV and VI (occulomotor, trochlear and abducens).
Stimulation of the lateral semicircular canals results in transmission of info in the ipsilateral CN VIII to the vestibular nucleus. Projections from this nucleus extend to innervate the CN VI (abducens) which stimulates the lateral rectus muscle (relax on one side and tense on the other). Abducens interneurons then project to the contralateral MLF, where they innervate the occulomotor nucleus, which stimulates the contralateral medial rectus. This allows one eye to move in a medial direction to the exact same degree that the first eye is tracking laterally in response to head movement.
Name the cranial nerve nuclei that give rise to preganglionic parasympathetic fibers and give their function.
Edinger-Westphal Nucleus: CN III – occulomotor to ciliary muscle muscles via ciliary ganglion
Superior Salivatory Nucleus: CN VII – facial to lacrimal and submandibular glands via pterygopalatine ganglion and submandibular ganglion respectively
Inferior Salivatory Nucleus: CN IX – glossopharyngeal to parotid gland via otic ganglion
Dorsal Motor Nucleus of the vagus: innervate heart, lungs and GI tract and other thoracic/abdominal vagal innervations
Define Corticonuclear (corticobulbar) fiber systems and describe how their distribution to ipsilateral and contralateral motoneurons is different for the upper and lower parts of the face
Axons that are homologous to corticospinal fibers, but terminate in the motor nuclei of cranial nerves in the brain stem (e.g., nuclei V, VII, IX, X, XI and XII) form the corticobulbar tract. Thus, they are the axons of the upper motor neurons that synapse on the lower motor neurons of the cranial nerves.
The corticobulbar fibers accompany the corticospinal axons through the internal capsule and cerebral peduncle, and then gradually leave the corticospinal tract to enter the tegmentum of the pons and medulla to terminate in the different nuclei.
•Facial nucleus (VII): The neurons that innervate the muscles of the lower face (below the forehead) receive mainly crossed input from the opposite motor cortex.
•Hypoglossal nucleus (XII): The neurons that innervate the genioglossus muscle receive mainly crossed input from the opposite motor cortex.
Therefore a lesion involving all of the corticospinal and corticobulbar fibers from the left cerebral cortex produces
1. Right hemiparesis (weakness of the right upper and lower limbs).
2. Weakness of the right face below the forehead.
3. Deviation of the tongue to the right upon protrusion (transient).
Trace corticospinal fibers through all levels of the brainstem and identify whether they arise from ipsilateral or contralateral motor cortex for all levels of the brainstem and spinal cord.
Corticospinal fibers arise in the primary motor cortex (Broadman’s Area 4) and descend through the internal capsule, the crus cerebri, and the basilar pons. They are still ipsilateral at the level of the inferior olive. They remain ipsilateral until the pyramidal decussation in the medulla. By C7-C8, the majority of the corticospinal fibers cross over to the contralateral side and form the lateral corticospinal tract. However, remember that some do stay ipsilateral and descend in the anterior corticospinal tract, innervating the axial muscles that control posture.
Trace the pathways of the pupillary light reflex
Photosensitive retinal ganglion cells detect light → optic nerve via optic disc → decussate at optic chiasm → pretectal nucleus (upper midbrain) → Edinger-Westphal Nucleus → oculomotor nerve → ciliary gangion neurons → constrictor muscle of the iris.
Trace the arterial blood supply from the vertebral arteries to the Circle of Willis including the major brainstem branches: Posterior Inferior Cerebellar A.(PICA), Anterior Inferior Cerebellar A. (AICA), Superior Cerebellar A. (SCA) and Posterior Cerebral Artery
•Midbrain = posterior cerebral artery, posterior communicating artery, superior cerebellar artery
Medial basal pons (corticospinal tract & medial lemniscus) = paramedian branches of basilar artery
Lateral pons (spinothalamic tract & spinal tract + nuc. of trigeminal nerve) = superior cerebellar artery rostrally and AICA caudally
Medial medulla (corticospinal tract & medial lemniscus) = vertebral artery
•Lower medullary levels = anterior spinal artery
Lateral medulla (spinothalamic tract & spinal tract + nuc. of trigeminal nerve) = vertebral artery or PICA