bio125_lecture2 - 7 basic parts of the CNS • • • •...

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Unformatted text preview: 7 basic parts of the CNS • • • • • • • Spinal cord medulla pons brainstem midbrain cerebellum diencephalon forebrain cerebral hemishperes • PN01101.JPG The Subdivisions and Components of the Central Nervous System Spinal cord • Extends from the base of the skull to the first lumbar vertebra. • Receives sensory info from skin, joints, and muscles of trunk and limbs, and contains motor neurons responsible for both voluntary and reflex movements. • Nerve fibers bundled in 31 pairs of spinal nerves, a sensory division (dorsal root ganglia) and a motor division (ventral root). • Is thicker in regions that innervate the limbs. Internal anatomy of the spinal cord Internal anatomy of the spinal cord • Contains both white and grey matter. • Grey matter shaped like an “H”. Dorsal horns and ventral horns. • Dorsal horns contain sensory relay neurons, receives input from periphery • Ventral horns contains motor nuclei that innervate muscles-send output • White matter contains longitudinal tracts of ascending and descending axons grouped together by function. Spinal cord tracts • Dorsal column-sensory info travels up it to the brain. • Lateral columns-also called the corticospinal tracts. Take info from brain and send it to the muscles. • Ventral columns (sometimes called anterolateral column)- carry pain info up and motor info down. Internal Structure of the Spinal Cord • PN01112.JPG General rules of spinal cord organization • neurons and axons that process and relay sensory information are found dorsally • preganglionic visceral motor neurons are found in an intermediate/lateral region • somatic motor neurons and axons are found in the ventral portion of the cord. Brainstem • medulla-regulates blood pressure and respiration • pons-ventral- pontine nuclei, relay info from cortex to cerebellum, dorsal-respiration taste and sleep • midbrain- auditory and visual systems, substantia nigra (dopanergic neurons). Deteriorates in Parkinson’s disease. Close up of the brain stem Brain stem • Target or source for all cranial nerves that deal with sensory and motor function in the head and neck. • Nuclei within brainstem are the targets and sources of these nerves. • Also is a throughway which all info going up and down must pass. • Because of its small area and restricted blood supply-it is very susceptible to damage. Parkinson’s- loss of dopamine making neurons in the midbrain The brainstem is all you need to live Mike, as everyone knows, was the arguably lucky fowl who survived a beheading by a Colorado farmer in 1945, thriving for 18 months with only a brain stem. Fed on corn dropped directly into his gullet, Mike choked to death during a sideshow tour in 1947, when the farmer — after forging a new and profitable relationship with Mike — was unable to clear his esophagus, having forgotten to bring along the eyedropper he used for that purpose. Cerebellum • two hemispheres, several lobes divided by fissures • neurons in sheets, called cortex. • receives sensory input from spinal cord, motor info from cerebral cortex, balance info from inner ear and vestibular organs • primarily used motor control, particularly in making postural adjustments and in fine-tuning movements. • essential for the coordination, planning of movements, learning motor tasks and storing this information. • also used for higher cognitive functions, including language. cerebellum Diencephalon • Contains the thalamus and hypothalamus • Thalamus- “relay station to the cerebral cortex”- an essential link in the transfer of most sensory information from periphery to cerebral cortex. Also plays a role in filtering information from the periphery. • hypothalamus - lies ventral to thalamus. Controls a variety of functions, growth, eating, drinking, maternal behavior by regulating hormonal secretions of the pituitary gland. Connects to virtually every part of brain. Important in initiating and maintaining behaviors that the organism finds rewarding Thalamus-gateway to the cortex The thalamus • pair of ovoid structures. • incoming sensory information relays in the thalamus before entering the cerebral cortex. many sensory, motor, and cognitive functions • highly organized connections with cortex • connections are mostly reciprocal Hypothalamus thalamus hypothalamus Midsagittal View of the Human Brain • PN01143.JPG Cerebrum • two hemispheres which sit atop and surround the diencephalon and much of the brain stem. • Seat of cognition, but it doesn't work alone! • two major parts – cortex – subcortex Cerebral Hemispheres • cerebral cortex-cognitive functioning • basal ganglia-control of fine movement • amygdala-social behavior and expression of emotion • hippocampus-memory Cerebral cortex • highly convoluted shape-grooves (sulci) and elevated regions (gyri). If sulci are especially deep called fissures. • About 2 to 4 mm thick, 100K neurons/mm2 • Segregated into left and right hemispheres connected to each other at the corpus callosum • Anatomically divided into four lobes • functionally distinct regions • Organized into layers • Greatly expanded in humans Subcortex • white matter • subcortical nuclei • ventricles. White matter • three classes of white matter pathways: – descending pathways – ascending pathways – cortico-cortical pathways cortico-cortical pathways • within hemisphere – short vs. long (fasciculi) • between hemisphere – mostly homologous connections – commissures – corpus callosum ventricles • are a system of inter-connected fluid-filled cavities in the brain. • cerebral-spinal fluid (CSF) The Cerebral Cortex • Sulci (fissures) and Gyri • Lobar Anatomy – – – – frontal parietal temporal occipital Primary versus Non-Primary Cortex • Primary cortex – cortical areas that are the primary projection fields targeted by the sensory input pathways – cortical areas that are the principal fields which have neurons that project down into the spinal cord – Primary visual (calcarine sulcus) – Primary auditory (Heschl's) – Primary somato (post-central gyrus) – Primary motor (pre-central gyrus) • Non-primary cortex – everything in between – referred to collectively as association cortex 4 lobes of the cerebral cortex • frontal-planning responses to stimuli, contains: motor cortex (precentral gyrus) • parietal-somatic sensory cortex-(postcentral gyrus) • temporal-audition and insular cortex (taste) • occipital-vision Primary somatosensory cortex Primary motor cortex The cerebral cortex is a layered structure. 6 layers can be seen when the brain is stained with dyes that highlight cell bodies The layers are generated in an inside-first, outside last sequence during development The layers are generated in an inside-first, outside last sequence during development The layers are generated in an inside-first, outside last sequence during development Defects in cortical development lissencephaly: smooth brain do not have characteristic gyri patterns leads to death, severe epilepsies and mental retardation Due to defects in neural migration during development question • Do specific regions of the brain control specific functions or Does each part of the brain do all functions or Does a specific function come from many parts of the brain? Early 1800’s Franz Joseph Gall • all behavior emanates from the brain • particular regions of the cerebral cortex controlled specific functions, ie the brain does not act as a single organ. • each function grew with use such as a muscle with exercise • this growing causes the skull to budge creating a pattern of bumps “phrenology” Franz Joseph Gall-phrenology Pierre Flourens (French) • Tested Gall’s ideas by removing different parts of the brain (dogs and rabbits) and asked if specific functions were compromised. • showed medulla important for respiration, cerebellum important for movements. • lesions in cortex affected either zero or many behaviors. Concluded that the cortex was one organ and not regionalized. Brodmann • Used subtle anatomical differences in the brain to divide it into discrete areas or regions • based on distinctive nerve structures and characteristic arrangements of layers • 52 discrete areas-many still used today. Laminar Organization • cortex itself has a thickness of only about 3-4mm. • 6 layers (Neocortex) – Layer IV is the primary (but not exclusive) input layer – Layers II and III are cortico-cortical output layers, • II= ipsi • III= contra – Layers V and VI descending output layers • V = basal ganglia/thal/brain stem/spinal cord • VI = thal/claustrum Korbinian Brodmann Paul Broca • believed that functions could be localized. • studied patients with aphasia-language disorders found in patients who have had a stroke. • 1861-had a patient that could understand language but could not speak, problems with the organizational aspects of language-found lesion in posterior frontal lobe• this kind of aphasia is called motor or expressive aphasia • eight patients with similar problems all had similar lesions, always on the left side. “Nous parlons avec l’hemisphere gauche!” Broca and a patient’s brain Carl Wernicke • had a patient that could speak but not understand language. Called receptive aphasia. • damage was to a different area-left side, posterior part of the temporal lobe. Argued that only simple perceptual and motor activities were localized to a specific area and that most functions result from interconnections between areas. idea of “distributive processing”. Characteristics of Broca's and Wernicke's Aphasias • PN27T10.JPG • PN27010.JPG The Major Brain Areas Involved in the Comprehension and Production of Language conduction aphasia • Inability to produce appropriate responses to heard communication, even though the communication is understood. • Often associated with damage in the Arcuate fasiculus -connects wernike and broca areas. Arcuate Fasciculus: Major association fiber tract in CNS connects Broca’s and Wernicke’s areas other evidence of brain regionalization • 1870 Fritsch and Hitzig- discrete limb movements in dogs can be produced by electrical stimulation of the contra-lateral motor cortex. Thus the right hand is controlled by the left hemisphere. Same as language. Dominant hemisphere. • 1950 Wilder Penfield- neurosurgeon, localized motor functions by stimulating specific areas of the brain. The greatest living Canadian. • Split brain studies by Roger Sperry 1960’s Greatest living Canadian Split Brain studies nobel prize 1981 • corpus callosum and anterior commisure is cut sometimes to prevent severe epilepsies. • Each side of the brain works independently • showed that left hemisphere dominates speech, writing, right hand stereognosis, analysis of right visual field • right hemisphere dominates, emotional coloring of language, spatial abilities, left hand stereognosis, analysis of left visual field Brain imaging techniques see box A of book • Computerized tomography (CT) scan-Uses X-rays in 3-dimensions to generate a brain image. Can be digitally sectioned to show internal areas of the brain. Can distinguish between grey matter and white matter, see the ventricles, has resolution of several millimeters. Magnetic resonance imaging (MRI) • • • • • Uses rotating magnets to generate image Non-invasive Can view images from any angle Resolution under 1 mm Can be adapted to do functional MRI imaging. fMRI functional magnetic resonance imaging • Oxy-hemoglobin and deoxy-hemoglobin have different magnetic resonance signals • Brain areas activated by a specific task utilize O2, then a pulse of O2 comes back and creates an influx of oxy-hemoglobin. • non invasive • Can repeat task many times over. • great spatial resolution ( a few millimeters) • good temporal resolution (seconds or less) CAT Brain Imaging: Anatomy Photography PET MRI Source: modified from Posner & Raichle, Images of Mind fMRI for presurgical planning fMRI for prisoner interrogation? ...
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