Physiology 1.04 - Neurophysiology-Cortical Functions (Part 2)

November 1, 2017 | Author: Jessica Compuesto | Category: Cerebrospinal Fluid, Prefrontal Cortex, Cerebral Cortex, Neuroanatomy, Brain
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Neurophysiology-Cortical Functions (Part 2)...



1.04 JULY 9, 2013


Katherine Munarriz, M.D. Prefrontal Association Area functions in close association with the motor cortex to plan complex patterns and sequences of motor movements receives strong input through a massive subcortical bundle of nerve fibers connecting the parietooccipitotemporal association area with the prefrontal association area subcortical bundle of nerve fibers  PFC receives preanalyzed sensory information, especially information on the spatial coordinates of the body that is necessary for planning effective movements Dorsolateral  Executive Functions Makes one give attention to tasks at hand despite million sensory stimuli  Planning, Sequencing, Elaboration of thought, Judgment Lesions: ↓ attention  ADHD (attention deficit hyperactive disorder) ↓ storage of information into short term memory  easily distracted; they cannot hold thoughts long enough for storage in STM ↓ planning, organizing, anticipate needs & problems ↓working towards goal ↓ initiative to do work ↓mental capacity for sustained intellectual effort ↓abstract thought, insight, depth Ventral Orbital  Emotional Integration Related to limbic system Establishment and conditioning of emotional reactions Lesions: ↓ ability to differentiate among conflicting thoughts ↓ ability to determine good and bad, better and best ↓ social and moral control Hemispherical Specialization Figure 1 The right PTO specializes in the spatial representation of objects by sight, touch or sound. The left PTO specializes in language: the sound of words, written words (sight) or Braille.

Cerebral Dominance: Dominant Hemisphere language functions (LEFT) Non-Dominant Hemisphere  non-verbal skills (RIGHT)

Which lobe is affected by disorders? -

Planning & Initiation of motor – Primary motor area Auditory perception – Area 41 Speech perception & comprehension – Wernicke’s area Music perception – Area 22 (right) Visual object & face recognition – Fusiform gyrus Retrograde & Anterograde; Verbal & Non-verbal – Inferolateral temporal lobe

TRANSCRIBERS: Maja, Von, Catie, Kenan, Eli, Rissa, Trisha, Eunika

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Cerebral Blood Flow -

supplied by four large arteries: two carotid and two vertebral arteries, which merge to form the circle of Willis at the base of the brain arteries arising from the circle of Willis travel along the brain surface and give rise to pial arteries, which branch out into smaller vessels called penetrating arteries and arterioles penetrating vessels are separated slightly from the brain tissue by an extension of the subarachnoid space called the Virchow-Robin space

Normal CBF = 50 – 65 (55mL)/100gm brain tissue/min; for entire brain, this amounts to 750 – 900 mL/min. Brain comprises only 2% of TBW but receives 15% CO. If 25m/100 gm brain tissue/min  Cerebral ischemia If 12m/100 gm brain tissue/min  Cerebral infarction CBF = CPP/CVR Q = Δ Pressure OHM’S LAW CVR Q = CBF Mechanisms that influence CVR: 1. Pressure auto-regulation 2. Chemical control 3. Neural control 4. Metabolic auto-regulation

1. PRESSURE AUTO-REGULATION BP  vessel wall is stretched  vascular smooth muscle responds by CONTRACTING  vessel diameter  resistance  Blood flow returns to normal *BP falls  Blood flow initially falls  Mechanisms activated that cause vasodilation  Increased blood flow

resistance 

CBF is auto-regulated between MAP = 60-140 mmHg in non-hypertensives and MAP = 60-180 mmHg in hypertensives MAP = DBP + 1/3 PP (SBP – DBP) Ex. BP 120/80 MAP = 80 + 1/3 (120-80) = 93.33 2. CHEMICAL CONTROL PaCO2; [H+] VD (vasodilation)  CBF Cerebral tissue O2 < 30 mmHg VD (vasodilation)  CBF

TRANSCRIBERS: Maja, Von, Catie, Kenan, Eli, Rissa, Trisha, Eunika

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3. NEURAL CONTROL Exercise  vessels

CBF  SNS Vasoconstriction (VC)  prevent high pressures from reaching smaller blood

Cerebrospinal Fluid (CSF) entire cerebral cavity enclosing the brain and spinal cord has a capacity of about 1600 to 1700 mL; about 150 mL of this capacity is occupied by cerebrospinal fluid and the remainder by the brain and cord. formed at a rate of about 500 mL each day, which is 3-4 times as much as the total volume of fluid in the entire cerebrospinal fluid system. About two thirds or more of this fluid originates as secretion from the choroid plexuses in the four ventricles, mainly in the two lateral ventricles. fluid secreted in the lateral ventricles passes first into the third ventricle  flows downward along the aqueduct of Sylvius into the fourth ventricle  fluid passes out of the fourth ventricle through three small openings: two lateral foramina of Luschka and a midline foramen of Magendie; entering the cisterna magna (a fluid space that lies behind the medulla and beneath the cerebellum which is continuous with the subarachnoid space that surrounds the entire brain and spinal cord. CSF then flows upward from the cisterna magna through the subarachnoid spaces surrounding the cerebrum. From here, the fluid flows into and through multiple arachnoidal villi that project into the large sagittal venous sinus and other venous sinuses of the cerebrum. Thus, any extra fluid empties into the venous blood through pores of these villi. Normal ICP (intracranial pressure): < 15mmHg Total CSF vol: ~ 150mL Normal CSF pressure average: 13 cm H2O (range 6 – 19 cm H2O) CSF Formation: Choroid plexus of ventricles at 30mL/hr Deleterious effects of LP with ICP  herniation in the foramen magnum (respiratory and cardiac centers) ICP Brain Blood CSF Cerebral edema  Increased fluid Increased ICP: compresses brain tissue  brain dysfunction Compresses blood vessels  CBF CPP = MAP – ICP Signs and Symptoms of ICP: Headache, vomiting, altered LOC: 1) Bilateral cerebral hemispheres 2) Reticular activating system Papilledema  edematous optic disc (1) high CSF pressure pushes fluid first into the optic nerve sheath and then along the spaces between the optic nerve fibers to the interior of the eyeball; (2) high pressure decreases outward fluid flow in the optic nerves, causing accumulation of excess fluid in the optic disc at the center of the retina; (3) pressure in the sheath also impedes flow of blood in the retinal vein, thereby increasing the retinal capillary pressure throughout the eye, which results in still more retinal edema Cerebral edema: Increased ECF or ICF water in brain a. Cytotoxic = increased ICF water in brain cells 1. Hypoxia (decreased PaO2  decreased ATP  Na, K ATPase pump  increase Na 2. Ischemia *Hyperosmotic  Mannitol; 3% (hypertonic) NaCl b. Vasogenic = increased ECF water in brain interstitial fluid (ISF) Tumors  Cytokines  Inflammatory response  increased permeability of tight junctions TRANSCRIBERS: Maja, Von, Catie, Kenan, Eli, Rissa, Trisha, Eunika

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*Anti-inflammatory  Glucocorticoid; dexamethazole Interstitial = increased ECF water in brain CSF *Diuretics

From Guyton: + Once brain edema begins, it often initiates two vicious circles because of the following positive feedbacks: (1) Edema compresses the vasculature. This in turn decreases blood flow and causes brain ischemia. The ischemia in turn causes arteriolar dilation with still further increase in capillary pressure. The increased capillary pressure then causes more edema fluid, so the edema becomes progressively worse. (2) The decreased cerebral blood flow also decreases oxygen delivery. This increases the permeability of the capillaries, allowing still more fluid leakage. It also turns off the sodium pumps of the neuronal tissue cells, thus allowing these cells to swell in addition. ++Obstruction to Flow of Cerebrospinal Fluid Can Cause Hydrocephalus - In communicating hydrocephalus, fluid flows readily from the ventricular system into the subarachnoid space. Usually caused by blockage of fluid flow in the subarachnoid spaces around the basal regions of the brain or by blockage of the arachnoidal villi where the fluid is normally absorbed into the venous sinuses. - In noncommunicating hydrocephalus, fluid flow out of one or more of the ventricles is blocked. Usually caused by a block in the aqueduct of Sylvius, resulting from atresia (closure) before birth in many babies or from blockage by a brain tumor at any age.

TRANSCRIBERS: Maja, Von, Catie, Kenan, Eli, Rissa, Trisha, Eunika

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