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The Spinal Cord • the Brain • Brain Function

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The Spinal Cord • the Brain • Brain Function About This Chapter • Emergent properties of neural networks • Evolution of nervous system • Anatomy of the central nervous system • The spinal cord • The brain • Brain function © 2016 Pearson Education, Inc. Emergent Properties of Neural Networks • Plasticity is the restructure of the brain networks in response to sensory input and experience. • Affective behaviors are related to feeling and emotion • Cognitive behaviors link to thinking © 2016 Pearson Education, Inc. CNS: Gray and White Matter • The CNS consists of the brain and the spinal cord. • Gray matter – Unmyelinated nerve cell bodies – Clusters of cell bodies in the CNS are nuclei – Dendrites – Axon terminals • White matter – Myelinated axons – Axon bundles connecting CNS regions are tracts • Contain very few cell bodies © 2016 Pearson Education, Inc. Figure 9.3c The Central Nervous System Posterior View of Spinal Cord and Vertebra Central canal Gray matter White matter Spinal nerve Pia mater Spinal Arachnoid Meninges cord membrane Dura mater Body of Autonomic vertebra ganglion Spinal nerve © 2016 Pearson Education, Inc. CNS: Bone and Connective Tissue • Brain is encased in bony skull, or cranium • Spinal cord runs through vertebral column • Meninges lie between bone and tissues to stabilize neural tissue and protect from bruising – Dura mater – Arachnoid membrane – Subarachnoid space contains cerebrospinal fluid secreted by choroid plexus – Pia mater • The brain floats in cerebrospinal fluid (CSF) secreted by the choroid plexus in the ventricles. © 2016 Pearson Education, Inc. Figure 9.3a The Central Nervous System Posterior View of the CNS Cranium Cerebral hemispheres Cerebellum Cervical spinal nerves Thoracic spinal nerves Sectioned vertebrae Lumbar spinal nerves Sacral spinal nerves Coccygeal nerve © 2016 Pearson Education, Inc. Figure 9.3b The Central Nervous System Sectional View of the Meninges The meninges and extracellular fluid cushion the delicate brain tissue. Venous sinus Cranium Dura mater Subdural space Arachnoid membrane Pia mater Brain Subarachnoid space © 2016 Pearson Education, Inc. Figure 9.4a Cerebrospinal Fluid Ventricles of the Brain Lateral ventricles The lateral ventricles consist of the first and second ventricles. The third and fourth ventricles Third ventricle extend through the brain stem and connect to the central canal that runs through the spinal cord. Compare the frontal view to the Fourth ventricle cross section in Fig. 9.10a. Cerebellum Central canal Spinal cord Lateral view Frontal view © 2016 Pearson Education, Inc. Figure 9.4b Cerebrospinal Fluid Cerebrospinal Fluid Secretion Cerebrospinal fluid is secreted into the ventricles and flows throughout the subarachnoid space, where it cushions the central nervous system. Arachnoid villi Choroid plexus of third ventricle Pia mater Arachnoid membrane Sinus Choroid plexus of fourth ventricle Spinal cord Central canal Subarachnoid space Arachnoid membrane Dura mater © 2016 Pearson Education, Inc. Figure 9.4c Cerebrospinal Fluid Choroid Plexus The choroid plexus transports ions and nutrients from the blood into the cerebrospinal fluid. Capillary Ependymal cells Water Ions, vitamins, nutrients Cerebrospinal fluid in third ventricle © 2016 Pearson Education, Inc. Figure 9.4d Cerebrospinal Fluid Cerebrospinal Fluid Reabsorption Cerebrospinal fluid is reabsorbed into the blood at fingerlike projections of the arachnoid membrane called villi. Cerebrospinal fluid Bone of skull Dura mater Endothelial lining Blood in venous sinus Fluid movement Arachnoid Cerebral cortex villus Dura mater (inner layer) Pia Subarachnoid Arachnoid Subdural mater space membrane space © 2016 Pearson Education, Inc. The Blood-Brain Barrier • Highly selective permeability of brain capillaries • Astrocytes foot processes promote tight junctions between endothelial cells • Protects brain from toxic water soluble compounds and pathogens • Small lipid-soluble molecules cross the blood-brain barrier © 2016 Pearson Education, Inc. Figure 9.5 The blood-brain barrier This cerebral angiogram shows the extensive blood supply Neurons are to the brain, which has about 400 miles of capillaries. protected from harmful substances in the blood because brain capillaries are not leaky. Astrocyte Anterior cerebral artery Astrocyte foot Posterior Tight junctions secrete cerebral processes prevent solute paracrines that artery movement between promote tight endothelial cells. Middle junction formation. cerebral artery Circle of Willis Internal Capillary carotid lumen artery Basal lamina © 2016 Pearson Education, Inc. CNS: Neural Tissue – Metabolic Needs • Oxygen – Passes freely across blood–brain barrier – Brain receives 15% of blood pumped by heart • Glucose – Membrane transporters move glucose from plasma into the brain interstitial fluid – Brain responsible for about half of body’s glucose consumption – Progressive hypoglycemia leads to confusion, unconsciousness, and death. © 2016 Pearson Education, Inc. The Spinal Cord • Segments associated with spinal nerves • Dorsal root neurons carry sensory information. • The cell bodies of afferent neurons are located in the dorsal root ganglia. • Ventral roots carry information from the CNS to muscles and glands. • Afferent neurons connect with interneurons in the dorsal horns. © 2016 Pearson Education, Inc. The Spinal Cord • Ventral horns contain cell bodies of afferent neurons. • Ascending tracts take sensory information to the brain and descending tracts carry signals from the brain. • Propriospinal tracts stay in the cord • Spinal reflexes are integrated in the spinal cord. © 2016 Pearson Education, Inc. Figure 9.7 Spinal reflexes © 2016 Pearson Education, Inc. The Brain: The Brain Stem • Oldest region of the brain • 11 of 12 cranial nerves originate from the brain stem • Cranial nerves can include sensory fibers, efferent fibers, or both (mixed nerves). – Many nuclei are associated with reticular formation • Controls wakefulness, sleep, muscle tone, pain modulation © 2016 Pearson Education, Inc. The Brain: The Brain Stem • Medulla – Somatosensory and corticospinal tracts – Pyramids – Controls involuntary functions: blood pressure, breathing, swallowing, vomiting © 2016 Pearson Education, Inc. The Brain: The Brain Stem • Pons – Relay station, coordinates control of breathing • Midbrain – Eye movement, relay signals for hearing and seeing reflexes © 2016 Pearson Education, Inc. Table 9.1 The Cranial Nerves © 2016 Pearson Education, Inc. Figure 9.8f Anatomy Summary Lateral View of Brain Stem Thalamus Cut edge of ascending Optic tract tracts to cerebrum Midbrain Pons Cut edges of tracts leading to Cranial cerebellum nerves Medulla oblongata Functions of the Brain Stem Midbrain Spinal cord • Eye movement Pons • Relay station between cerebrum and cerebellum • Coordination of breathing [Fig. 18.14] Medulla oblongata • Control of involuntary functions [Fig. 11.3] Reticular formation (not shown) See Figure 9.16. • Arousal • Sleep • Muscle tone • Pain modulation © 2016 Pearson Education, Inc..
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