The Central Nervous System I The brain A Basic pattern of CNS organization 1 Cerebral hemispheres diencephalon brainstem and the cerebellum 2 In cross section generally a central cavity surrounded by a gray matter core nuclei external to which is white matter myelinated fiber tracts cerebral hemispheres and cerebellum have an outer bark or cortex of gray matter B Ventricles of brain CSF fluid filled cavities within brain continuous with each other and central canal of spinal cord lined with ependymal cells 1 Lateral ventricles c shaped w in cerebral hemispheres 2 Third ventricle in diencephalon communicates with lateral ventricles via interventricular foramen 3 Fourth ventricle lies dorsal to pons and superior medulla continuous with central canal of spinal cord SC three openings lateral apertures 2 and median aperture connect it to subarachnoid space C Cerebral hemispheres CHs most superior part of brain separated from each other by median longitudinal fissure and from cerebellum by transverse fissure have gyri and sulci on surface divided into five lobes frontal parietal temporal occipital and insula lobes central sulcus delineates precentral gyrus and postcentral gyrus 1 Cerebral cortex perception communication memory understanding appreciation initiation of voluntary movements gray matter neuron cell bodies dendrites no fiber tracts contains three kinds of functional areas motor areas sensory areas association areas each hemisphere concerned with sensory motor functions of opposite side of body hemispheres symmetrical in structure but not function no functional area acts alone a Motor areas located in posterior part of frontal lobes control voluntary motor function know function of areas in bold i primary motor cortex PMC in precentral gyrus pyramidal cells giving rise to long axons corticospinal pyramidal tracts allows conscious control of movements of skeletal muscle ii premotor cortex PC anterior to precentral gyrus frontal lobe controls learned motor skills of repetitive nature iii Brocca s area located in one hemisphere special motor speech area iv Frontal eye field controls voluntary movements of the eyes b Sensory areas not confined to a single lobe concerned with conscious awareness of sensation know function of areas in bold i primary somatosensory cortex PSSC in postcentral gyrus neurons receive information from somatic sensory receptors and proprioreceptors to identify the body region being stimulated spatial discrimination ii somatosensory association area SSA posterior to PSSC many connections with it integrates and analyzes somatosensory inputs into comprehensive evaluation of what is being felt iii visual areas primary visual cortex PVC visual association area receives information from retina interprets evaluates visual input in light of past experiences iv auditory areas primary auditory cortex PAC auditory association area input from cochlear receptors of inner ear integration perception of sound stimulus v olfactory cortex OC input from olfactory receptors vi gustatory cortex perception of taste stimuli c Association areas each sensory area as seen has nearby association area with which it communicates these communicate with motor cortex and other association areas to analyze recognize and act on sensory input there are several of these other association areas an example is the pre frontal cortex know function of areas in bold prefrontal cortex PFC intellect cognition personality 2 Cerebral white matter provides for communication between different areas of cerebral cortex and areas of cerebral cortex and lower CNS centers largely composed of myelinated fibers bundled into large tracts a commissural fibers connect corresponding areas of two hemispheres b association fibers connect adjacent gyri within a single hemisphere or adjacent cortical lobes c projection fibers run vertically fibers connecting cortex to lower brain or spinal cord centers 3 Basal nuclei islands or gray matter deep within cerebral hemispheres have extensive inputs from entire cerebral cortex influence motor movements D Diencephalon central core of forebrain surrounded by CHs includes thalamus hypothalamus epithalamus 1 Thalamus composed of masses of gray matter held together by midline commissure the intermediate mass forms superolateral walls of third ventricle w in thalamus sorting out or editing of information occurs impulses having to do with similar functions are relayed to appropriate area of sensory cortex and cortical association areas virtually all impulses ascending to cerebral cortex funneled through thalamus thus thalamus is gateway to cortex 2 Hypothalamus located below thalamus constitutes inferolateral walls of third ventricle extends from optic chiasm to posterior margin of mammary bodies main visceral control center of body has several homeostatic roles center for emotional response behavior body temperature regulation regulation of food intake regulation of water balance and thirst regulation of sleep wake cycles control of endocrine system functioning 3 Epithalamus most dorsal part of diencephalon helps form roof of the third ventricle most noticeable landmark is pineal gland sleep wake cycles E The brain stem includes midbrain pons medulla oblongata general function is to produce the automatic involuntary behaviors necessary for our survival provides pathways for fiber tracts running between higher and lower neural centers 1 Midbrain located between diencephalon superiorly and pons inferiorly note cerebral peduncles containing pyramidal tracts also superior cerebellar peduncles fiber tracts connecting midbrain to cerebellum dorsally cerebral aqueduct in midbrain connects third and fourth ventricles 2 The pons bulging stem region wedged between the midbrain and medulla oblongata dorsally forms part of the walls of the fourth ventricle composed mostly of conduction tracts other features projection fibers middle cerebellar peduncles several cranial nerves originate from pons nuclei trigemminal nerve V facial nerve VII 3 Medulla oblongata most inferior portion of the brainstem features pyramids large ridges on ventral surface inferior cerebellar peduncles olives number of cranial nerves associated with medulla hypoglossal nerve XII glossopharyngeal IX vagus X accessory XI vestibulocochlear VIII plays crucial role as autonomic reflex center contains following important visceral motor nuclei a cardiovascular center cardiac center heart rate force and vasomotor center TPR