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Home , Middle cerebral artery

Neurological Anatomy Debbie Summers RN, MSN, CS

I. Overview of Neuroanatomy A. Divisions of the Nervous System 1. Central Nervous System a. Brain b. Spinal Cord 2. Peripheral Nervous System a. Cranial Nerves – 12 Pairs b. Spinal Nerves – 31 pairs c. Autonomic Nervous System  Sympathetic nervous system - “Fight” or take a “flight”  Parasympathetic nervous system - “Rest” and “digest” B. Cells of Nervous System 1. Neurons - functional cell have specialized projections called dendrites and axons. Dendrites bring information to the cell body and axons take information away from the cell body. 2. Neuroglia cells – supporting structure cells C. Skull 1. 8 Cranial Bones 2. 14 Facial Bones D. Meninges and Spaces 1. Meninges-PAD the brain A. Dura Mater-tough mother, lines the skull and brain folds B. Arachnoid – fibrous elastic layer which reabsorbs CSF C. Pia Mater-delicate vascular layer covering the brain and provides nutrients 2. Spaces A. Epidural D. Subdural E. Subarachnoid

August 1, 2002 E. 1. - conceptualization, abstraction, judgement formation, motor function, write words, and higher level centers for autonomic function.  Pre-frontal area – personality and character  Frontal eye fields – voluntary eye scanning movements; conjugate movements of eye to opposite side of stimuli; voluntary fixation on object  Precentral gryus – motor area – voluntary movement, opposite side of body - Homunculus- “little man”  Motor speech – broca’s area – word formation, articulation, speed and rhythm, pronunciations 2. - highest integrative and coordinating center for perception and interpretation of sensory information, ability to recognize body parts and left versus right.  post-central gyrus located in parietal lobe is sensory 3. - Memory storage, auditory integration, and hearing  Receptive speech - wernicke’s area 4. Occipital lobe- Visual center and understanding of written material

Functional Divisions of the Responsible for many “higher order” functions like language and information processing. Language centers are usually found only in the left . Cortical Area Function Problem Solving, Emotion, Complex Thought Motor Association Cortex Coordination of complex movement Initiation of voluntary movement Primary Somatosensory Cortex Receives tactile information from the body Sensory Association Area Processing of multisensory information Visual Association Area Complex processing of visual information Visual Cortex Detection of simple visual stimuli Wernicke's Area Language comprehension Auditory Association Area Complex processing of auditory information Auditory Cortex Detection of sound quality (loudness, tone) Speech Center Speech production and articulation (Broca's Area)

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5. Subcortical areas

a. fibers connecting subdivisions of the brain and spinal cord. Shape of an open fan. b. Limbic system- short term memory, learning, and emotional behavior. c. - diffuse network deep in cerebral hemispheres. Exhibits regulating and controlling influences on motor integration major center of the extrapyramidal motor system d. Thalamus- relay station e. Hypothalamus- most intricate connection between endocrine and neurosystem - Temperature regulation - Water regulation - Control hormonal secretion of pituitary gland - Control BP (autonomic nervous system) f. Pituitary Gland  Anterior – TSH, TSH, ACTH, Prolactin, LH, FSH  Posterior – ADH, Oxytocin

F. Brainstem 1. Midbrain- Motor movement, relay of impulses, postural reflex patterns, auditory reflexes, righting reflex, some control of vision and origin of cranial nerves III and IV. 2. Pons- Pneumotaxic center (rhythm of respiration), connection between medulla, midbrain, and cerebellum, and origin of cranial nerves V, VI, VII, and VIII. 3. Medulla oblongata- cardiac, vasomotor, and respiratory center, center for cough, swallowing, and hiccuping, role in reticular activating system, and origin of cranial nerves IX, X, XI, and XII.

3 G. Cerebellum Coordination of fine motor movement, balance, rapid repetitive movements. H. Ventricles-400-600 cc CSF daily, reabsorption. Clear fluid with high glucose

1. Cerebral Spinal Fluid (CSF) a. Formed: Choroid Plexus b. Circulates: c. Lateral ventricles d. Intraventricular foremen (Foramen of Monroe - this is the sight for zero referencing ventricular drains. it is located midway between the lateral aspect of the eyebrow and the tragus of the ear.) i 3rd Ventricle ii Aqueduct of Sylvius iii 4th Ventricle iv Cisterna & Subarachnoid space v Foramen of Luscka & Magendie e. Absorbed: Arachnoid Villi (determined by hydrostatic pressure)

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Circle of Willis: Brings the system intact to provide collateral flow, but also area that most cerebral aneurysms are found (i.e. at the base of the anterior, middle, or post cerebral )

5 ABBR Name of ACA Anterior Cerebral Artery AComA Anterior Communicating Artery AICA Anterior Inferior ASA BA Basilary Artery ICA MCA Middle Cerebral Artery PCA Posterior Cerebral Artery PComA Posterior Communicating Artery PICA Posterior Inferior Cerebellar Artery SCA Superior Cerebellar Artery VA

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Abbr Name of Artery Distribution Ascends through base of skull to give rise to the anterior and Internal Carotid ICA middle , and connect with posterior half of circle Artery of Willis via posterior communicating artery Anterior Cerebral Supplies most medial portions of frontal lobes and superior ACA Artery medial parietal lobes Middle Cerebral Trifurcates into temporal, frontal, and parietal branches that MCA Artery supply most of the parenchyma of these lobes Anterior AComA Communicating Connects the anterior cerebral arteries at their closest juncture Artery The vertebrals emerge from the posterior base of skull and merge VA Vertebral Artery to form the basilar artery Formed by the junction of the two vertebral arteries, it terminates BA Basilar Artery as a bifurcation into the posterior cerebral arteries Posterior Cerebral Supplies the occipital lobe and the inferior portion of temporal PCA Artery lobe. A branch supplies the choroid plexus. Posterior Connects the anterior circle of Willis with the posterior cerebral PComA Communicating artery of vertebral-basilar circulation posteriorly Artery Superior SCA Supplies the dorsal cerebellum, pons, and midbrain Cerebellar Artery Anterior Inferior AICA Supplies the inferior cerebellum and portions of pons and medulla Cerebellar Artery Posterior Inferior Supplies the posterior cerebellum, choroid plexus in 4th ventricle, PICA Cerebellar Artery and portions of medulla Anterior Spinal ASA Descends along the anterior (ventral) aspect of the spinal cord Artery

Venous Circulation

a) External Jugular - venous blood from the skin and muscles of the head b) Internal Jugular - drains the dural sinuses of the brain c) Dural Sinuses - large within the dura mater of the brain i) Superior Sagittal ii) Inferior Sagittal iii) Straight iv) Transverse v) Sigmoid vi) Cavernous vii) Petrosal d) Superficial Veins i) Drain cortex into the dural sinuses

7 e) Deep veins - drain the white matter, thalamostriate, septal, internal cerebral and the great cerebral (Vein of Galen) into the Internal Jugular vein

Cranial Nerve Function

I. Olfactory Sense of smell II. Optic Vision III. Oculomotor Elevation of upper eyelid Responsible for EOM IV. Troclear Responsible for EOM V. Trigeminal Sensory- Facial Motor- Jaw, chewing VI. Abducens Responsible for EOM VII. Facial Sensory- Taste anterior 2/3 of tongue Motor- Facial movement VIII. Acoustic Hearing and balance IX. Glossopharyngeal Uvula movement - swallowing X. Vagus Carotid sinus reflex XI. Spinal accessory Shoulder movement XII. Hypoglossal Tongue movement

8 Cerebral Circulation Anterior Circulation - Internal Carotid Artery 1. Middle Cerebral Artery (MCA) a. Superior branches of MCA supply these key functional areas:  Primary motor cortex for face and arm, and axons originating in the leg as well as face and arm areas that are headed for the internal capsule as part of the corticobulbar or corticospinal tracts  Broca's area and other related gray and white matter important for language expression--in the language-dominant (usually left) hemisphere  Frontal eye fields (important for 'looking at' eye movements to the opposite side)  Primary somatosensory cortex for face and arm  Parts of lateral frontal and parietal lobes important for 3-D visuospatial perceptions of one's own body and of the outside world, and for ability to interpret and express emotions--in the nondominant (usually right) hemisphere b. Inferior branches of MCA supply these key functional areas:  Wernicke's and other related areas important for language comprehension in the language-dominant (usually left) hemisphere  Parts of the posterior parietal lobe important for 3-D visuospatial perceptions of one's own body and of the outside world, and for the ability to interpret emotions--in the nondominant (usually right) hemisphere  Optic radiations, particularly fibers that represent information from the contralateral superior quadrants and loop forward into the temporal lobe (they are located anterior and lateral to the temporal horn of the lateral ventricle) as they travel from the lateral geniculate body to the striate cortex, located in the occipital lobe 2. Anterior Cerebral Artery (ACA)  septal area  primary motor cortex for the leg and foot areas, and the urinary bladder  additional motor planning areas in the medial frontal lobe, anterior to the  primary somatosensory cortex for the leg and foot  most of the corpus callosum except its posterior part; these callosal fibers enable the language- dominant hemisphere to find out what the other hemisphere is doing, and to direct its activities

Posterior Circulation - Vertebral-Basilar 1. Posterior Cerebral Artery (PCA) 2. Vertebral-Basilar Artery Penetrating branches of PCA participate in supplying the following key functional areas:  Diencephalon including thalamus, subthalamic nucleus, and hypothalamus  Midbrain including cerebral peduncle, third nerve and nucleus, red nucleus and its connections, superior cerebellar peduncle, reticular formation Cortical branches of PCA participate in supplying the following key functional areas: Posterior branches to the parietal and occipital lobe  Optic radiations and striate cortex (the primary visual cortex may be entirely supplied by PCA, or the tip of the occipital may be located in the border zone shared by PCA and MCA)  splenium of the corpus callosum (these crossing fibers participate in the transfer of visual information to the language-dominant hemisphere) Anterior branches to the medial temporal lobe  Hippocampal formation and the posterior fornix (these structures are critical for laying down new declarative memories

9 Anterior Circulation Deficits Patterns of Blocked Vessel or Branch Possible Deficits Extracranial Deficits depend on the extent of collateral supply and how quickly Internal occlusion occurred. As many as 30-40% of carotid occlusions near the Carotid bifurcation are clinically silent. MCA-main stem (M1) • Contralateral hemiplegia and hemisensory loss • Contralateral hemianopsia • Global aphasia (L)* or denial, neglect, and disturbed spatial perception perhaps with emotional 'flatness' (R)* • Eye and head deviation toward lesion in acute stage MCA-superior • Contralateral Hemiparesis and hemisensory loss (face and arm more cortical division than leg; often motor more than sensory) • Expressive (Broca's) aphasia (L)* or neglect and disturbed spatial perception (R)* • Eye and head deviation toward lesion in acute stage MCA- inferior cortical division • Receptive (Wernicke's) aphasia (L) or denial, neglect and disturbed spatial perception (R)* • Contralateral hemianopsia-usually upper quadrants are most affected MCA-lenticulostriate branch "Pure motor" stroke often, but not necessarily, involving lower face, arm and leg equally but sparing sensation Posterior Circulation Stroke Deficits Blocked Vessel/ Branch Deficit Pattern One vertebral -termed "Wallenberg's syndrome" artery in the rostral medulla in some cases, -sensation loss on ipsilateral side of face but contralateral trunk and PICA branch limbs -ipsilateral ataxia -ipsilateral Horner's syndrome -ipsilateral vocal cord paralysis -hoarseness -impaired swallowing -vertigo, nausea, vomiting Penetrating paramedian basilar branch in pons -pure motor stroke -contralateral hemiplegia -involvement of face depends on infarction location Basilar occlusion affecting the rostral pons -termed "locked-in syndrome" bilaterally -complete bilateral paralysis rendering patient motionless and mute yet capable of perceiving sensory stimuli -vertical components of 3rd and 4th nerve function may be spared Penetrating PCA branch supplying thalamus -pure sensory loss -involves face, arm, trunk and leg -initially hemianesthesia but may eventually develop into thalamic pain syndrome with painful dysesthesias in affected parts

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