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Functional Brain Systems • Networks of neurons that work together and span wide areas of the brain • Limbic system • Reticular formation Copyright © 2010 Pearson Education, Inc. Limbic System • Structures on the medial aspects of cerebral hemispheres and diencephalon • Includes parts of the diencephalon and some cerebral structures that encircle the brain stem Copyright © 2010 Pearson Education, Inc. Limbic System Diencephalic structures of the limbic system Corpus callosum Fiber tracts connecting limbic system structures Cerebral structures of the limbic system Copyright © 2010 Pearson Education, Inc. Figure 12.18 Limbic System • Emotional or affective brain • Amygdala—recognizes angry or fearful facial expressions, assesses danger, and elicits the fear response • Cingulate gyrus—plays a role in expressing emotions via gestures, and resolves mental conflict • Puts emotional responses to odors • Example: skunks smell bad Copyright © 2010 Pearson Education, Inc. Limbic System: Emotion and Cognition • The limbic system interacts with the prefrontal lobes, therefore: • We can react emotionally to things we consciously understand to be happening • We are consciously aware of emotional richness in our lives • Hippocampus and amygdala—play a role in memory Copyright © 2010 Pearson Education, Inc. Reticular Formation • Runs through brainstem (medulla, pons, midbrain) • Has far-flung axonal connections with hypothalamus, thalamus, cerebral cortex, cerebellum, and spinal cord Copyright © 2010 Pearson Education, Inc. Reticular Formation: RAS and Motor Function • Reticular Activating System (RAS) • Sends impulses to the cerebral cortex to keep it conscious and alert • Filters out repetitive and weak stimuli (~99% of all stimuli!) • Severe injury results in permanent unconsciousness (coma) Copyright © 2010 Pearson Education, Inc. Reticular activating system Radiations to cerebral cortex Visual impulses Auditory impulses Reticular formation Ascending general sensory tracts (touch, pain, temperature) Copyright © 2010 Pearson Education, Inc. Descending motor projections to spinal cord Figure 12.19 Consciousness • Conscious perception of sensation • Voluntary initiation and control of movement • Capabilities associated with higher mental processing (memory, logic, judgment, etc.) • Loss of consciousness (e.g., fainting or syncopy) is a signal that brain function is impaired Copyright © 2010 Pearson Education, Inc. Consciousness • Clinically defined on a continuum that grades behavior in response to stimuli • Alertness • Drowsiness (lethargy) • Stupor • Coma Copyright © 2010 Pearson Education, Inc. Protection of the Brain • Bone (skull) • Membranes (meninges) • Watery cushion (cerebrospinal fluid) • Blood-brain barrier Copyright © 2010 Pearson Education, Inc. Meninges • Cover and protect the CNS • Protect blood vessels and enclose venous sinuses • Contain cerebrospinal fluid (CSF) • Form partitions in the skull Copyright © 2010 Pearson Education, Inc. Meninges • Three layers • Dura mater • Arachnoid mater • Pia mater Copyright © 2010 Pearson Education, Inc. Superior sagittal sinus Subdural space Subarachnoid space Copyright © 2010 Pearson Education, Inc. Skin of scalp Periosteum Bone of skull Periosteal Dura Meningeal mater Arachnoid mater Pia mater Arachnoid villus Blood vessel Falx cerebri (in longitudinal fissure only) Figure 12.24 Dura Mater • Strongest meninx • Two layers of fibrous connective tissue (around the brain) separate to form dural sinuses Copyright © 2010 Pearson Education, Inc. Dura Mater • Dural septa limit excessive movement of the brain • Falx cerebri—in the longitudinal fissure; attached to crista galli • Falx cerebelli—along the vermis of the cerebellum • Tentorium cerebelli—horizontal dural fold over cerebellum and in the transverse fissure Copyright © 2010 Pearson Education, Inc. Superior sagittal sinus Straight sinus Crista galli of the ethmoid bone Pituitary gland Falx cerebri Tentorium cerebelli Falx cerebelli (a) Dural septa Copyright © 2010 Pearson Education, Inc. Figure 12.25a Arachnoid Mater • Middle layer with weblike extensions • Separated from the dura mater by the subdural space • Subarachnoid space contains CSF and blood vessels • Arachnoid villi protrude into the superior sagittal sinus and permit CSF reabsorption Copyright © 2010 Pearson Education, Inc. Superior sagittal sinus Subdural space Subarachnoid space Copyright © 2010 Pearson Education, Inc. Skin of scalp Periosteum Bone of skull Periosteal Dura Meningeal mater Arachnoid mater Pia mater Arachnoid villus Blood vessel Falx cerebri (in longitudinal fissure only) Figure 12.24 Pia Mater • Layer of delicate vascularized connective tissue that clings tightly to the brain Copyright © 2010 Pearson Education, Inc. Cerebrospinal Fluid (CSF) • Composition • Watery solution • Less protein and different ion concentrations than plasma • Constant volume Copyright © 2010 Pearson Education, Inc. Cerebrospinal Fluid (CSF) • Functions • Gives buoyancy to the CNS organs • Protects the CNS from blows and other trauma • Nourishes the brain and carries chemical signals Copyright © 2010 Pearson Education, Inc. Superior sagittal sinus 4 Choroid plexus Arachnoid villus Interventricular foramen Subarachnoid space Arachnoid mater Meningeal dura mater Periosteal dura mater 1 Right lateral ventricle (deep to cut) Choroid plexus of fourth ventricle 3 Third ventricle 1 CSF is produced by the Cerebral aqueduct Lateral aperture Fourth ventricle Median aperture Central canal of spinal cord (a) CSF circulation Copyright © 2010 Pearson Education, Inc. 2 choroid plexus of each ventricle. 2 CSF flows through the ventricles and into the subarachnoid space via the median and lateral apertures. Some CSF flows through the central canal of the spinal cord. 3 CSF flows through the subarachnoid space. 4 CSF is absorbed into the dural venous sinuses via the arachnoid villi. Figure 12.26a Choroid Plexuses • Produce CSF at a constant rate • Hang from the roof of each ventricle • Clusters of capillaries enclosed by pia mater and a layer of ependymal cells • Ependymal cells use ion pumps to control the composition of the CSF and help cleanse CSF by removing wastes Copyright © 2010 Pearson Education, Inc. Ependymal cells Capillary Section of choroid plexus Connective tissue of pia mater Wastes and unnecessary solutes absorbed CSF forms as a filtrate containing glucose, oxygen, vitamins, and ions (Na+, Cl–, Mg2+, etc.) (b) CSF formation by choroid plexuses Copyright © 2010 Pearson Education, Inc. Cavity of ventricle Figure 12.26b Blood-Brain Barrier • Helps maintain a stable environment for the brain • Separates neurons from some bloodborne substances Copyright © 2010 Pearson Education, Inc. Blood-Brain Barrier Selective barrier • Allows nutrients to move by facilitated diffusion • Allows any fat-soluble substances to pass, including alcohol, nicotine, and anesthetics Formed by • Continuous endothelium of capillary walls • Basal lamina • Feet of astrocytes Absent in brain areas that “need to know” about blood composition (vomiting center, etc.) Copyright © 2010 Pearson Education, Inc. Blood brain barrier Notice feet of astrocytes wrapping around capillaries Capillary Neuron Astrocyte Copyright © 2010 Pearson Education, Inc. Figure 11.3a Traumatic brain injuries • Concussion—temporary alteration in function • Contusion—permanent damage • Subdural or subarachnoid hemorrhage—may force brain stem through the foramen magnum, resulting in death • Cerebral edema—swelling of the brain associated with traumatic head injury • Contrecoup injury (to opposite side) Copyright © 2010 Pearson Education, Inc.