Chapter3 - Notes.docx

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Konstantine Zakzanis

Chapter 3 Notes Brain Pathology and Psychological Functions - There is no localizable single store for the meaning of a given entity or event within a cortical region - Meaning is achieved by widespread multiregional activation of fragmentary records pertinent to a given stimulus - Any given behaviour is the product of a myriad of complex neurophysiological and biochemical interactions involving the whole brain - Neurobehavioural Syndrome: Cluster of deficits that tend to occur together with some regularity - Lesions: Localized abnormal tissue changes (although localized, still may affect many functions when the damaged neural structure is involved with more of less different functions) - When site of lesion is known, it is possible to predicted what the cognitive deficit outcome is - Localization of Dysfunction: Correlation between damaged neuroanatomical structures and behavioural functions enables neuropsychologists and neurologists to make educated guesses about the site of a lesion on the basis of abnormal patterns of behaviour o Limitations: Lesioned structure is known not to act on its own, but depends on its function on a network of input and output channels, as the equilibrium of the brain will be influenced in many unpredictable ways even in a restricted lesion o Cannot assume a push-button relationship between local brain sites and specific behaviours Brains processing functions take place at multiple levels (e.g. Encoding a single modality of a percept, energizing memory search) within complex, integrated systems Analogy: Car w/o fuel tank = Incapable of moving forward, however we cannot infer that the function of the fuel tank is to propel the car The Cellular Substrate - NS is a dynamic system in that it modifies its performance, its internal relationships, and its capacity to mediate stimuli from the outside - Glia: 10-50 times more numerous than neurons and are supporting brain cells that lack the ability to transmit information o Astrocytes: One major type type of glial cell with an additional role as a component of the blood-brain barrier o Oligodendroglia: Forms myelin for high-speed conduction of nerve impulses o 10 billion cells in the human cortex = 60 trillion synapses o LTP and LDP provide the neural potential for the variability and flexibility of human behaviour o Key transmitters implicated in neurologic and psychiatric diseases are Ach, DA, NE, 5- HT, glutamate, GABA o When nerve cell is injured/diseased, it may stop functioning and the circuits to which it contributed will then be disrupted Some circuits may eventually reactivate as damaged cells resume functioning or alternative patterns involving different cell populations take over o Pruning: Enhancing organization of specific neuronal pathways through killing neurons through development The Structure of the Brain - Three major anatomical divisions of the brain: o 1. Hindbrain o 2. Midbrain o 3. Forebrain - Brain centers that are the lowest are the most simply organized o Brains functional complexity increases from the lower brain stem up through its succeeding parts o Four ventricles: 1. Lateral ventricles: Most prominent, pair of horn-shaped reservoirs situated inside the cerebral hemispheres, running from front to back and curving around into the temporal lobe 2. Third Ventricle: Situated in the midline in the diencephalon 3. Fourth Ventricle: Lies within the brain stem 4. Cerebral Aqueduct o CSF is produced by special tissues within all of the ventricles but mostly in the lateral ventricles o CSF fluid serves as a shock absorber and helps maintain the shape of the soft nervous tissue of the brain Obstruction of CSF flow causes Normal Pressure Hydrocephalus - Elaborate network of blood vessels maintains a rich supply of nutrients to oxygen-dependent brain tissue - Cerebral blood supply comes from three main arterial distributions: o Site of disease/damage to arterial circulation determines the area of the brain cut off from its oxygen supply and its neuropathologic consequences o Anterior and middle cerebral arteries branch from the internal carotid artery o Anterior Division: Supplies anterior frontal lobe and medial regions of the brain o Middle Cerebral Artery: Feeds the lateral temporal, parietal, and posterior frontal lobes and sends branches deep into sub-cortical regions o Posterior Circulation: Originates from the vertebral arteries, which join to form the basilar and provide blood to the brain stem and cerebellum Basilar Artery: Divides into the posterior cerebral arteries and supplies the occipital cortex and medial and inferior regions of the temporal lobe Hindbrain: Medulla Oblongata - Lowest part of the brain stem containing the medulla oblongata - Corticospinal tract which runs down it crosses the midline here so that each cerebral hemisphere has motor control over the opposite side of the body - Hindbrain is site of basic life-maintaining center for nervous control of: o Respiration o Blood pressure o Heartbeat - Injury in the medulla usually results is death - Medulla contains nuclei (clusters of functionally related nerve cells) involved in movements of mouth and throat structures necessary for swallowing, speech, gagging, control of drooling - Damage in lateral medullary results in sensory deficits Reticular Formation - Runs through bulb from the upper cord to the diencephalon - Network of intertwined and interconnecting nerve cell bodies and fibers that enter into or connect with all major neural tracts going to an from the brain - Contains many nuclei and nerve centers that mediate important and complex postural reflexes o Contribute to the smoothness of muscle activity and maintain muscle tone - Is also the site of RAS (reticular activating system) which controls wakefulness and alerting mechanisms that ready the individual to react - RAS modulates attention through its arousal of the cerebral cortex o Brainstem lesions here give rise to sleep disturbances and to global disorders of consciousness and responsivity (e.g. drowsiness, stupor, coma) Pons - High in the hindbrain and contains major pathways for fibers running between the cerebral cortex and the cerebellum which is attached to the brainstem- Pons and cerebellum together correlate postural and kinesthetic (muscle movement sense) information o Refine and regulate motor impulses relayed from the cerebrum at the top of the brain stem o Lesions of the pons may cause motor, sensory, and coordination disorders Cerebellum - At the posterior base of the brain - Contains reciprocal connections with vestibular and brain stem nuclei, hypothalamus, spinal cord, and strong connections with motor cortex - Contributes to motor control through influences on programming and execution of actions - Cerebellar damage: Known to produce problems of fine motor control, coordination, and postural regulation o May also include dizziness (vertigo) and jerky eye movements - Contains non-motor functions involving all aspects of behaviour o Highly organized neural pathways from both lower and higher areas of the brain project through pons to cerebellum o Cerebellum projects through thalamus to the same cortical areas from which it receives input (frontal, parietal, superior, temporal cortices) - Contains connections with both cortical and subcortical sites - Lesions here cause: Disruption in abstract reasoning, verbal fluency, visuospatial abilities, attention, emotional modulation, and planning and time judgment - Cerebellum also involved in linguistic processing, word generation, working memory, memory and
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