Chapter 6 Outline - Brainstem Organization PDF

Chapter 6: Overview and Organization of the Brainstem Introduction to the Brainstem Definition: The brainstem is the portion of the central nervous system that connects the cerebral hemispheres with the spinal cord. Location: Situated in the posterior cranial fo...

Chapter 6: Overview and Organization of the Brainstem Introduction to the Brainstem Definition: The brainstem is the portion of the central nervous system that connects the cerebral hemispheres with the spinal cord. Location: Situated in the posterior cranial fossa, below the cerebrum and anterior to the cerebellum. Importance: Houses vital control centers for consciousness, cardiovascular function, and respiration. Serves as a conduit for ascending and descending pathways. Contains nuclei of cranial nerves III to XII. Major Divisions of the Brainstem Region Position Key Structures Functions Cranial Nerves Tectum: Superior colliculi, Inferior colliculi Tegmentum: Most superior Visual processing Midbrain Periaqueductal gray matter, CN III (Oculomotor) portion of the Auditory processing (Mesencephalon) Red nucleus CN IV (Trochlear) brainstem Motor control Cerebral peduncles: Contain descending cortical fibers Basilar part: Contains CN V (Trigeminal) pontine nuclei Relay station between CN VI (Abducens) Middle portion of cerebral cortex and Pons CN VII (Facial) the brainstem Pontine tegmentum: cerebellum CN VIII Houses nuclei and fiber Respiratory control (Vestibulocochlear) tracts  Region Position Key Structures Functions Cranial Nerves Open part: Superior portion with visible fourth ventricle CN IX Cardiovascular control (Glossopharyngeal) Most inferior Closed part: Inferior Respiratory control CN X (Vagus) Medulla Oblongata portion of the portion where central canal Relay of sensory and CN XI (Accessory) brainstem begins motor information CN XII (Hypoglossal) Other structures: Pyramids, Olive, Gracile nuclei, Cuneate nuclei Internal Organization of the Brainstem a. Gray Matter Cranial nerve nuclei (III to XII) Reticular formation nuclei Other specialized nuclei (e.g., red nucleus, substantia nigra) b. White Matter Ascending tracts: Spinothalamic, dorsal column-medial lemniscus Descending tracts: Corticospinal, rubrospinal, vestibulospinal, reticulospinal, tectospinal Transverse fibers: Pontocerebellar fibers c. Reticular Formation Diffuse network of neurons extending throughout the brainstem Functions: Arousal, sleep-wake cycle, pain modulation, cardiovascular and respiratory control Cranial Nerves (See PowerPoint for more detail of each CN) CN Type Function Pathway Test Conditions/Syndromes Nasal epithelium → Smell Anosmia, Kallmann I. Olfactory Sensory Sense of smell Olfactory bulb → identification test syndrome Frontal lobe Retina → Optic chiasm → Lateral Visual acuity test, II. Optic Sensory Vision Optic neuritis, Papilledema geniculate nucleus → Visual field test Occipital lobe Eye movement (up, down, Midbrain → Superior Pupillary light Motor, Oculomotor nerve palsy, III. Oculomotor medial), Pupil constriction, orbital fissure → reflex, Eye Parasympathetic Aneurysm compression Lens accommodation Orbit movement test Midbrain → Superior Eye movement Superior oblique muscle (eye Trochlear nerve palsy, IV. Trochlear Motor orbital fissure → test (looking movement down and out) Superior oblique palsy Orbit down and in) Facial sensation Facial sensation, Mastication Pons → Trigeminal Trigeminal neuralgia, V. Trigeminal Sensory, Motor test, Jaw muscles ganglion → Face Trigeminal neuropathy clenching Pons → Superior Lateral rectus muscle (eye Eye movement Abducens nerve palsy, VI. Abducens Motor orbital fissure → movement laterally) test (lateral gaze) Lateral rectus palsy Orbit Facial expression, Taste Pons → Internal Facial muscle Motor, Sensory, Bell's palsy, Ramsay Hunt VII. Facial (anterior 2/3 of tongue), acoustic meatus → movement, Taste Parasympathetic syndrome Lacrimal and salivary glands Face test  CN Type Function Pathway Test Conditions/Syndromes Inner ear → Internal VIII. Audiometry, Ménière's disease, Acoustic Sensory Hearing, Balance acoustic meatus → Vestibulocochlear Caloric test neuroma Pons Taste (posterior 1/3 of Medulla → Jugular IX. Sensory, Motor, Gag reflex, Taste tongue), Swallowing, Parotid foramen → Pharynx, Glossopharyngeal neuralgia Glossopharyngeal Parasympathetic test gland secretion tongue Medulla → Jugular Motor, Sensory, Pharynx and larynx muscles, Gag reflex, Voice Vocal cord paralysis, Vagus X. Vagus foramen → Neck, Parasympathetic Heart rate, Digestion quality nerve dysfunction thorax, abdomen Medulla and upper Head turning, Sternocleidomastoid and spinal cord → XI. Accessory Motor Shoulder Accessory nerve palsy trapezius muscles Jugular foramen → shrugging Neck muscles Medulla → Tongue XII. Hypoglossal Motor Tongue movements Hypoglossal canal → movement and Hypoglossal nerve palsy Tongue strength Cranial Nerves: Functional Classification - Clarifies types of information each nerve carries Breaks down each nerve by modalities Functional - Distinguishes between sensory, motor, and mixed nerves (GSE, GVE, GSA, SVE, SVA, SSA, Classification - Differentiates general vs. special, somatic vs. visceral GVA) functions Cranial Nerve Origin Modality Function Motor to levator palpebrae superioris, superior rectus, inferior CN III—oculomotor Midbrain GSE rectus, medial rectus, and inferior oblique  Parasympathetic: motor to sphincter pupillae, ciliary muscles GVE for accommodation CN IV—trochlear Midbrain GSE Motor to superior oblique muscle CN V—trigeminal Pons GSA Proprioception from muscles of mastication GSA Discriminative touch and vibration from the head GSA Pain and temperature from the head SVE Motor to muscles of mastication CN VI—abducens Pons GSE Motor to lateral rectus CN VII—facial Pons SVE Motor to muscles of facial expression Sensory from external acoustic meatus and skin posterior to GSA the ear Parasympathetic motor to lacrimal, sublingual, and GVE submandibular glands SVA Taste from anterior two-thirds of the tongue CN VIII— Pons SSA Balance vestibulocochlear SSA Hearing General sensation from posterior third of the tongue, tonsil, CN IX— Medulla GSA skin of external ear, internal surface of tympanic membrane, glossopharyngeus pharynx  Chemoreceptors and baroreceptors in the carotid body, GVA visceral afferent information from the tongue and pharynx (gag reflex) SVA Taste from the posterior third of the tongue SVE Motor to stylopharyngeus GVE Parasympathetic to parotid gland Sensory from posterior meninges, external acoustic meatus, CN X—vagus Medulla GSA and skin posterior to the ear Sensory from the larynx, trachea, esophagus, thoracic and GVA abdominal viscera, stretch receptors in aortic arch, chemoreceptors in aortic bodies adjacent to the arch SVA Sensory from taste buds in the epiglottis Motor to pharyngeal muscles and intrinsic muscles of the SVE larynx Parasympathetic to smooth muscles and glands of the GVE pharynx, larynx, and thoracic and abdominal viscera GVE Cardiac muscle CN XI—accessory Medulla SVE Sternocleidomastoid and trapezius CN XII— Hyoglossus, genioglossus, styloglossus, and all intrinsic Medulla GSE hypoglossal muscles of the tongue Review for Chapters 2-4  Category Abbreviation Full Term Description Somatic GSE General Somatic Efferent Motor fibers to skeletal muscles derived from somites GSA General Somatic Afferent Sensory fibers for general sensations from the skin and deep structures SSA Special Somatic Afferent Sensory fibers for special senses (vision, hearing, balance) Visceral GVE General Visceral Efferent Parasympathetic motor fibers to smooth muscles and glands SVE Special Visceral Efferent Motor fibers to muscles derived from branchial arches SVA Special Visceral Afferent Sensory fibers for special sensations (taste) GVA General Visceral Afferent Sensory fibers from internal organs and blood vessels Functional Components a. Cranial Nerve Nuclei Midbrain: Oculomotor (III), Trochlear (IV) Pons: Trigeminal (V), Abducens (VI), Facial (VII), Vestibulocochlear (VIII) Medulla: Glossopharyngeal (IX), Vagus (X), Accessory (XI), Hypoglossal (XII) b. Ascending and Descending Tracts Corticospinal tract: Major motor pathway Spinothalamic tract: Pain and temperature sensation Dorsal column-medial lemniscus: Fine touch and proprioception Rubrospinal tract: Motor coordination c. Integrative Centers Respiratory centers: Dorsal and ventral respiratory groups in medulla Cardiovascular centers: Vasomotor center in medulla Sleep-wake centers: Reticular activating system Vascular Supply of the Brainstem  a. Arterial Supply Vertebral arteries: Supply medulla and inferior pons Basilar artery: Supplies pons and midbrain Circle of Willis: Contributes to midbrain supply b. Venous Drainage Primarily via dural venous sinuses Internal cerebral veins and great cerebral vein (of Galen) Clinical Significance of Brainstem Anatomy a. Lesion Effects Cranial nerve deficits: E.g., facial paralysis, diplopia Motor disturbances: Hemiparesis, quadriparesis Sensory disturbances: Hemianesthesia Autonomic dysfunction: Respiratory and cardiovascular issues b. Neurological Examinations Cranial nerve testing: Assessing function of CN III-XII Reflex testing: Pupillary light reflex, corneal reflex Motor and sensory testing: Evaluating pathways passing through the brainstem Common Brainstem Syndromes Syndrome Name Definition Explanation Functional Outcomes Ipsilateral loss of pain and temperature sensation on the face Caused by occlusion of Contralateral loss of pain and temperature Wallenberg Syndrome A stroke in the the posterior inferior sensation on the body (Lateral Medullary lateral part of the cerebellar artery (PICA) Ipsilateral Horner's syndrome Syndrome) medulla oblongata or vertebral artery Ipsilateral ataxia Dysphagia and dysarthria Vertigo and nystagmus  Syndrome Name Definition Explanation Functional Outcomes Quadriplegia A condition where a Usually caused by a Anarthria (inability to articulate speech) patient is aware but stroke in the ventral Preserved consciousness Locked-in Syndrome cannot move or pons, damaging the Preserved vertical eye movements and communicate corticospinal and blinking verbally corticobulbar tracts Communication often limited to eye movements Can be congenital or Need for mechanical ventilation, especially A failure of Ondine's Curse (Central acquired (e.g., from during sleep automatic breathing, Hypoventilation brainstem stroke or Risk of hypoxia and hypercapnia particularly during Syndrome) tumor affecting the Potential cognitive impairment if chronic sleep medulla) Increased risk of sudden death A midbrain stroke Usually caused by Contralateral hemiparesis affecting the occlusion of the Ipsilateral oculomotor nerve palsy (ptosis, Weber's Syndrome cerebral peduncle paramedian branches of outward and downward deviation of the eye) and oculomotor the posterior cerebral Impaired convergence nerve artery Possible contralateral tremor A pontine stroke Lesion in the ventral Ipsilateral facial palsy Millard-Gubler affecting the facial pons involving the facial Contralateral hemiparesis Syndrome nerve and nerve nucleus and Possible ipsilateral lateral gaze palsy (if corticospinal tract corticospinal fibers abducens nerve involved) Impaired horizontal Impaired adduction of the ipsilateral eye Often caused by multiple eye movements due Nystagmus in the abducting eye Preserved Internuclear sclerosis in younger to a lesion in the convergence Ophthalmoplegia (INO) patients, or stroke in medial longitudinal Diplopia older patients fasciculus (MLF) Possible vertigo and imbalance  Syndrome Name Definition Explanation Functional Outcomes A combination of Miosis (constricted pupil) symptoms due to Can be caused by lesions Partial ptosis disruption of the anywhere along the Horner's Syndrome Anhidrosis (decreased sweating) on the sympathetic nerve sympathetic pathway, affected side of the face supply to the eye including the brainstem Possible enophthalmos and face  Region Position Key Structures Functions Cranial Nerves Tectum: Superior colliculi, Inferior colliculi Tegmentum: Most superior Visual processing Midbrain Periaqueductal gray matter, CN III (Oculomotor) portion of the Auditory processing (Mesencephalon) Red nucleus CN IV (Trochlear) brainstem Motor control Cerebral peduncles: Contain descending cortical fibers Basilar part: Contains CN V (Trigeminal) pontine nuclei Relay station between CN VI (Abducens) Pons Middle portion of cerebral cortex and CN VII (Facial) (Latin for bridge) the brainstem Pontine tegmentum: cerebellum CN VIII Houses nuclei and fiber Respiratory control (Vestibulocochlear) tracts Open part: Superior portion with visible fourth CN IX ventricle Cardiovascular control (Glossopharyngeal) Most inferior Respiratory control CN X (Vagus) Medulla Oblongata portion of the Closed part: Inferior Relay of sensory and CN XI (Accessory) brainstem portion where central canal motor information CN XII begins (Hypoglossal) Region Position Key Structures Functions Cranial Nerves Other structures: Pyramids, Olive, Gracile nuclei, Cuneate nuclei