GROSS ANATOMY AND CLINICAL PROBLEMS OF CNS BLOOD SUPPLY AND GLOSSOPHARYNGEAL NERVE © 2019zillmusom I. OVERVIEW - Branches to CNS are described as arising from two sources: Vertebral and Internal Carotid arteries. A. Spinal Cord - Anterior Arteries and Posterior Spinal Arteries form as branches of Vertebral Arteries; however, most blood supply to the spinal cord is derived from Radicular arteries (branches of segmental arteries that enter via Intervertebral Foramina) B. Brain - Common Carotid arteries bifurcate to Internal and External Carotid arteries; Internal Carotid arteries supply 80% of brain; 15% of strokes are associated with stenosis (narrowing) of Internal Carotid artery at or near bifurcation. II. GROSS ANATOMY OF BLOOD SUPPLY OF SPINAL CORD A. Arterial supply 1. Anterior Spinal artery - single artery formed from branches of both Vertebral arteries; courses on anterior surface of cord. 2. Posterior Spinal arteries - paired arteries dorsolateral to spinal cord; arise (75%) from Posterior Inferior Cerebellar arteries (branch of Vertebral Artery) or directly from Vertebral arteries (25%). 3. Radicular (root) arteries - Most of blood supply to spinal cord is provided by Radicular (root) arteries; most these arteries arise from the Aorta and enter the spinal canal through Intervertebral foramina; one particularly large artery (Great Radicular Artery of Adamkiewicz, usually unpaired) arises from T9-T12 and provides major blood supply to lumbar and sacral spinal cord. Clinical Note: Obstruction of Radicular Artery (of Adamkiewicz) - Can occur during clamping for heart surgery or by a dissecting Aortic aneurysm; causes infarction (tissue death in spinal cord) similar to an Anterior Spinal Artery syndrome (symptoms include paraplegia (Corticospinal tracts, bilateral voluntary paralysis of legs and lower body), loss of pain and temperature sense (Spinothalamc tract, loss of sphincter control) with sparing of vibration and position sense (Dorsal Columns, sensory). B. Venous drainage - venous blood drains to venous plexuses with extensive anastomoses. 1. Venous plexus in Pia Mater - drains spinal cord and Anterior and Posterior spinal veins. 2. Internal Vertebral Venous Plexus - lies in Epidural Space inside vertebral canal; drains venous plexus of Pia mater and veins of vertebrae; drains to External venous plexus by Intervertebral veins. 3. Intervertebral veins - pass through Intervertebral foramina; drain to other veins in body. 3. External Vertebral Venous Plexus - outside of vertebrae; connects to other veins of body. 1 Clinical Note: Metastasis to vertebral column and spinal cord - Veins and venous plexuses of spinal cord have no valves; direction of flow depends on pressure which is low in venous system; disease processes can spread to spinal cord and vertebra from other regions of body by External and Internal Vertebral venous plexuses and intervertebral veins (ex. carcinoma of prostate in pelvis can metastasize to vertebral column). III. BIFURCATION OF COMMON CAROTID ARTERIES IN NECK - Common Carotid arteries arise from Brachiocephalic trunk on right, Arch of Aorta on left; ascend in Carotid sheath and bifurcate at upper border of Thyroid cartilage to External and Internal Carotid arteries. A.. Design of Anatomical Bifurcation vs Repeated Branching - Arterial bifurcation maintains high rate of flow in vessels. Repeated branching from a single vessel would not be as effective, because flow (velocity) decreases when the total cross- sectional diameter of vessels increases (i.e., more blood is brought to brain by single bifurcation). B. Formation of Arterial Plaque - Bifurcations of large vessels create regions of local changes in pressure and flow (potential turbulence). This is thought to contribute to formation of arterial plaque. Note: Carotid artery disease - Accumulation of plaque at Carotid bifurcation is common; narrowing of artery (Carotid stenosis) can compromise blood supply to brain; stenosis can be asymptomatic but also give rise to emboli that can course in Internal Carotid artery and produce cerebrovascular occlusion (Stroke); studies indicate that ~15% of strokes are associated with stenosis (narrowing) of Internal Carotid arteries (outside the cranial cavity). Note: Preliminary Diagnostic indicators of Carotid Stenosis - Carotid pulse - Pulse of Common Carotid artery is taken at the Carotid bifurcation, lateral to upper border of Thyroid Cartilage. Carotid auscultation - stethoscope placed below angle of mandible. Note: Carotid Endarterectomy - surgical intervention to remove plaque from Carotid arteries/open occluded vessels; performed through incision in neck, anterior to Sternocleidomastoid muscle; artery is clamped and incised; a filter and bypass are inserted and plaque is removed; care must be taken to avoid damage to cranial nerves (6% complication rate) and to sensory branches to Carotid sinus and Carotid body (see below). IV. CAROTID SINUS AND CAROTID BODY - sensory endings for baroreception (pressure) and chemoreception; innervation: Glossopharyngeal nerve CN IX. A. Carotid Sinus - dilated region at base of Internal Carotid Artery above Bifurcation - sensory endings (Visceral sensory) of Glossopharyngeal N. (CN IX) monitor blood pressure (baroreception); stimulation of Carotid Sinus produces decreased blood pressure and slowing of heart rate (bradycardia). B. Carotid Body - small (~4 mm.), reddish-brown body, posterior to Bifurcation; visceral chemoreceptive sensory endings (CN IX) mainly monitor blood oxygen, etc.; stimulation of produces increased blood pressure and hyperventilation. 2 Note: Bilateral damage to Carotid sinus and Carotid body can occur during carotid endarterectomy or after neck irradiation or trauma; Increased variability of blood pressure and heart rate. 3 REFERENCE HANDOUT: DO NOT MEMORIZE V. GLOSSOPHARYNGEAL NERVE BRANCHES/ CLINICAL CORRELATES NERVE ANATOMY/CONTAINS INNERVATES CLINICAL Tympanic Nerve, Visceral Sensory (GVA), Visceral sensory to Poor localization of pain Visceral Sensory Passes back into middle Middle Ear in Otitis Media - ('whole (GVA) [and Somatic ear, forms Tympanic (Tympanic cavity), side of my head hurts) Sensory (GSA) Plexus; [Somatic Auditory tube, sensory fibers to outer Mastoid sinus ear (GSA)] Somatic sensory to outer ear Lesser Petrosal Nerve, Parasympathetic Parotid Salivary Damage to IX produces Parasympathetic Visceral motor (GVE) to Gland decreased salivation Visceral motor (GVE) Parotid, synapse in Otic Ganglion Carotid Sinus - Carotid branches, Visceral Sensory (GVA) Damage during carotid baroreception (blood Visceral Sensory fibers that monitor endarterectomy or neck pressure) (GVA) pressure and oxygen in trauma produces Carotid Body - blood blood chemoreception impaired cardiovascular reflexes (primarily PO2) Nerve to Branchiomotor (SVE) - Stylopharyngeus Stylopharyngeus acts to Stylopharyngeus, Embryologically derived raise pharynx in Branchiomotor (SVE) from Branchial arch III swallowing Pharyngeal branches, Visceral sensory (GVA) mucosa of Decreased or absent Gag Visceral sensory (GVA) to Oropharynx Oropharynx Reflex - IX to X Tonsillar branches Visceral sensory (GVA) Mucosa overlying Glossopharyngeal nerve (Visceral sensory, to mucosa overlying Palatine tonsils can be damaged in GVA) palatine tonsils Tonsillectomy Lingual branches Visceral sensory (GVA) Tongue (posterior Loss of taste and (Visceral sensory, GVA and Taste (SVA) 1/3) sensation to posterior 1/3 and Taste, SVA) of tongue GLOSSOPHARYNGEAL NERVE PALSY - Glossopharyngeal nerve lesions produce difficulty in swallowing, an absent gag reflex, impaired cardiovascular reflexes and decreased secretions of the parotid gland; loss of taste and impaired sensation over the posterior one-third of the tongue; impaired sensation in oropharynx. Note: Glossopharyngeal nerve damage rarely occurs in isolation and often affects Vagus nerve - Vagus nerve lesions produce palatal and pharyngeal paralysis; laryngeal paralysis; and effects in Thorax including abnormalities of esophageal motility, gastric acid secretion, gallbladder emptying, and heart rate; and other autonomic dysfunction. 4.