Central Nervous SystemWednesday, November 28, 201212:42 PMProtective Structures of the Brain:1. Cranium2. Meninges3. Cerebrospinal fluid (CSF)4. Blood-Brain barrier_______________________________________________________________________________________1. Cranium --> Cranial bones forming the cranial vault which is a bony encasement of the brain --> the lobes of the cerebral hemispheres are named for the overlying cranial bones.2. Meninges -->Outermost meninx --> Dura mater (double-layered)oPeriosteal Layer - attached/lines to the internal surface of the cranial bonesoMeningeal Layer - is separated from middle meninx by the subdural space(dura mater surrounding spinal cord is single-layered)Middle meninx --> arachnoid mater, separated form the meningeal layer of the dura mater by the subdural space, the arachnoid is separated from the innermost meninx, the pia mater, by the subarachnoid spaceSubarachnoid space contains CSF --> CSF around the brainInnermost meninx --> pia mater, attached to the surface of the cerebrum --> the cerebral blood vessels enter/ exits the brain pons through the pia mater3. Cerebrospinal Fluid (CSF) --> Hypotonic filtrate of blood --> blood in the choroid plexus is filtered into spaces (subarachnoid space, ventricles in brain, and central canal in spinal cord)CSF provides protection against trauma --> CSF absorbs/dissipates pressureCSF provides buoyancy to the brain --> lighter (appears to weigh less) due to CSF around/inside the brainCSF provides nutrients glucose and oxygen to neurons (neurons use exclusively glucose/O2 for energy production required for function of the brain)CSF removes metabolic wastes from neurons to the venous circulation to be eliminated by the kidneys4. Blood-Brain Barrier Major Regions of the Brain:1. Cerebrum2. Diencephalon3. Brainstem4. Cerebellum_________________________________________________________________________________________1. Cerebrum --> 83% total mass of the brainSurface of the cerebrum --> involuted with 'hills' - elevated ridges, GYRI & 'valleys' - grooves, SULCIand deeper grooves, FISSURESA median fissure called the Longitudinal Fissure partially separates the cerebrum into two cerebralhemispheres Left & RightEach cerebral hemisphere is divided into 5 lobes by the SulcioFrontal Lobe - central sulcusoParietal Lobe - central sulcus, parieto-occipital sulcusoOccipital Lobe - parieto-occipital sulcusoTemporal Lobe - lateral sulcus separates frontal and parietal lobe for the temporal lobeoInsula - deep to the lateral sulcus, cannot be seen externally2 Cerebral hemispheres held together by the corpus callosumCoronal section of the cerebrum --> 3 regions oCerebral Cortex (outer region) - composed of gray matter, gray matter composed of unmyelinated structures (dendrites, cell bodies and unmyelinated axons)oCerebral White Matter (inner region) - composed mainly of myelinated axonsoBasal Nuclei - classes of cell bodies inside the cerebral white matter3 Functional Areas in the Cerebral Cortex (outer gray matter):oMotor Areas - control voluntary movements, all 4 areas are located in frontal lobe of each cerebral hemisphere (except Broca's area - only in Left cerebral hemisphere)-Primary motor cortex - located in the precentral gyrus in each cerebral hemispherePrecentral gyrus contains large neurons, PYRAMIDAL CELLS --> the axons bundle to form the pyramidal tracts --> tracts descend into lower brain regions and the spinal cord (before the pyramidal tracts descend into the spinal cord, the pyramidal tracts DECUSSATE --> The pyramidal tracts from the precentral gyrus:-In the LEFT cerebral hemisphere crossover to the right side to innervate skeletal muscles on the right side of the body-In the RIGHT cerebral hemisphere cross over to the left side to innervate skeletal muscles on the left side of the body Deccussation of the pyramidal tracts (Decussations of the pyramids) explains the control of the cerebral cortex in the cerebral hemispheres of voluntary skeletal musclemovement)-Premotor cortex-Broca's area - only in the LEFT cerebral hemisphere, connected to the Wernicke's which is also in the left cerebral hemisphere called the Arcuate Fasciculate --> example of association tract-Frontal eye field oSensory Areas - located in all the lobes in each cerebral hemisphere-Somatosensory cortex located in the postcentral gyrus --> receives sensory input from the skin and the joints for spatial discrimination. The sensory tracts decussate hence, input fromthe left side is received by the right postcentral gyrus; input from the right side is received by the left postcentral gyrus. Damage to the pre-central & post-central gyrus in the left cerebral hemisphere --> loss of sensation & paralysis on the right side of the body -Gustatory cortex (taste) located in the insula-Visual cortex located in the occipital lobe-Auditory cortex located in the temporal lobes-Olfactory cortex located in both the temporal & frontal lobesoAssociation Areas - associated with the sensory areas to provide quality to the sensory inputCerebral White Matter (2nd Region in Cerebral Hemisphere)Composed of tracts made up of mainly myelinated axons (myelin - 'white' fatty protein)3 types of Cerebral White Matter Tracts:1. Commissural Tracts2. Projection Tractsa. Descending Tracts - Motor output from the cerebral cortex (pyramidal tracts from precentral gyri)b. Ascending Tracts - Sensory input to the cerebral cortex (spinal-thalamic tract from spinal cord to thalamus and then projected to the cerebral cortex)3. Association Tracts - arcuate fasciculate connects the Broca's area to the Wernicke's area in the LEFT cerebral hemisphereBasal Nuclei (3rd region in the cerebrum)Consists of clusters of neuronal cell bodies deep in the cerebral white matter3 Prominent Basal Nuclei:1. Caudate Nucleus2. Globus Pallidus3. PutamenoPutamen + globus pallidus = LENTIFORM NUCLEUSoLentiform nucleus + caudate = CORPUS STRIATUM (basal nuclei)The descending pyramidal tracts course through the basal nuclei to give them a striated appearance hence, the basal nuclei are also referred to as the corpus striatum 2 Lateral Ventricles are located in the cerebral hemispheres (one in each) Diencephalon (2nd region of the adult brain)Contains the 3rd ventricle (connected to the 2 lateral ventricles by the interventricular foramen)-Thalamus-Hypothalamus-Epithalamus Brainstem (3rd region)-MidbrainoCorpora Quadrigemina-2 Superior Nuclei (Superior Colliculi) - Visual Reflex centers ('tracking'
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