Anatomy of the Nervous System
Anatomy of the Nervous System PS 235
Popular in Biological Bases of Behavior
Popular in Psychology (PSYC)
This 13 page Class Notes was uploaded by Marissa Tawadros on Sunday September 18, 2016. The Class Notes belongs to PS 235 at Butler University taught by Dr. Jennifer Berry in Fall 2016. Since its upload, it has received 4 views. For similar materials see Biological Bases of Behavior in Psychology (PSYC) at Butler University.
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Date Created: 09/18/16
Chapter 3 General Layout of the Nervous System Divisions of the Nervous System The vertebrate system is composed of two divisions: o Central Nervous System Division of the nervous system located within the skull and spine o Peripheral Nervous System Division of the nervous system located outside the skull and spine Composed of two divisions Somatic Nervous System o The part of the PNS that interacts with the external environment Afferent Nerves Carry sensory signals from the skin, skeletal muscles, joints, eyes, ears, and so on to the CNS Efferent Nerves Carry motor signals from the CNS to the skeletal muscles Autonomic Nervous System o Part of the PNS that regulates the body’s internal environment Sympathetic Nerves Autonomic motor nerves that project from the CNS in the lumbar (small of the back) and thoracic (chest) regions of the spinal cord Neurons that project from the CNS synapse on the second- stage neurons at a substantial distance from their target organs Stimulate, organize, and mobilize energy resources in threatening situations Changes are indicative of psychological arousal Parasympathetic Autonomic motor nerves that project from the brain and sacral (lower back) region of the spinal cord Neurons that project from the CNS synapse near their target organs on a very short second-stage neurons Conserves energy Changes are indicative of psychological relaxation The 12 pairs of nerves extending from the brain o Olfactory Nerves Sensory nerves o Optic Nerves Contain sensory and motor fibers o Vagus Nerves Longest Contain motor and sensory fibers that travel to and from the gut Meninges, Ventricles, and Cerebrospinal Fluid The CNS is the most protected organ in the body. o Meninges The 3 protective membranes that cover the CNS Dura Mater (tough mother) o The tough outer meninx Arachnoid Membrane o The meninx between the dura mater and the pia mater and has the appearance of a gauzelike spiderweb o Subarachnoid Space Beneath the arachnoid membrane Contains many blood vessles and the cerebrospinal fluid Pia Mater o Innermost meninx Cerebrospinal Fluid o The colorless fluid that fills the subarachnoid space, central canal, and the cerebral ventricles o Protects the CNS o Central Canal Small central channel that runs the length of the spinal cord o Cerebral Ventricles Four large internal chambers of the brain: Two lateral ventricles Third ventricle Fourth ventricle o Choroid Plexuses Network of capillaries or small blood vessels that protrude into the ventricles from the pia mater Thought that the cerebrospinal fluid is produced by this Blood-Brain Barrier The mechanism that keeps certain toxic substances in the blood from passing into the brain tissue Cells of the Nervous System Anatomy of Neurons External Anatomy of Neurons Cell Body o The metabolic center of the neuron (soma) Cell Membrane o The semipermeable membrane that encloses the neuron Dendrites o The processes emanating from the cell body, which receive most of the synaptic contacts from other neurons Axon Hillock o The cone-shape region at the junction between the axon and the cell body Axon o The long, narrow process that projects from the cell body Myelin o The fatty insulation around many axons Nodes of Ranvier o The gaps between the sections of myelin Buttons o The buttonlike endings of the axon branches, which release chemicals into the synapses Synapses o The gaps between the adjacent neurons across which chemical signals are transmitted Internal Anatomy of Neurons Endoplasmic Reticulum o A system of folded membranes in the cell body Rough portions (with ribosomes) play a role in the synthesis of proteins Smooth portions (without ribosomes) play a role in the synthesis of fats Nucleus o The DNA-containing structure of the cell body Mitochondria o Sites of oxygen-consuming energy release Cytoplasm o The clear internal fluid of the cell Ribosomes o Internal cellular structures on which proteins are synthesized Golgi Complex o A connected system of membranes that packages molecules in vesicles Microtubules o Tubules responsible for the rapid transport of material throughout neurons Synaptic Neurons o Spherical membrane packages that store neurotransmitter molecules ready for release near the synapses Neurotransmitters o Molecules that are released from active neurons and influence the activity of other cells Neuron Cell Membrane The neuron cell membrane is composed of a lipid bilayer, or two layers of fat molecules o Embedded in there are protein molecules that are the basis of many of the cell membrane’s functions o Channel proteins; certain molecules can pass o Single proteins; transfer a signal to the inside of the neuron when particular molecules bind to them on the outside of the membrane Classes of Neurons Multipolar Neuron o A neuron with more that two processes extending from its cell body o Most neurons are this Unipolar o A neuron with one process extending from its cell body Bipolar o A neuron with two processes extending from its cell body Interneuron o Neurons with short axons or no axons at all, whose function is to integrate neural activity within one single brain structure Neurons and Neuroanatomical Structure In general, there are two kinds of gross neural structures in the nervous system: o Those composed primarily of cell bodies o Those composed primarily of axons In the CNS o Nuclei Clusters of cell bodies o Tracts Bundles of axons In the PNS o Ganglia Clusters of cell bodies o Nerves Bundles of axons Glia: The Forgotten Cells Glia o Several classes of noneural cells of the nervous system, whose important contributions to the nervous system function are just starting to be understood o Oligodendrocytes Glia cells that myelinate CNS axons o Schwann Cells The glia cells that compose the myelin sheaths of PNS axons and promote their regeneration o Microglia Glia cells that respond to injury or disease by engulfing cellular debris and triggering inflammatory responses o Astrocytes Large, star-shaped glia cells that play a role in the passage of chemicals from the blood into CNS neurons and preform several other important functions that are not yet well understood Neuroanatomical Techniques and Directions Neuroanatomical Techniques The major problem in visualizing neurons is that they are so tightly packed and their axons and dendrites so intricately intertwine that looking through a microscope at unprepared neural tissue reveals almost nothing about them o The key to the study of neuroanatomy lies in preparing neural tissue in a variety of ways Permitting a clear view of a different aspect of neural structure and then combining the knowledge obtained from each of the preparations Golgi Stain Golgi Stain o A neural stain that completely darkens a few of the neurons in each slice of tissue, thereby revealing their silhouettes Used when the overall shape of the neuron is of interest Provides no indication of the number of neurons in an area or the nature of their inner structure Nissl Stain Nissl Stain o A neural stain that has an affinity for structures in neuron cell bodies Electron Microscopy Electron Microscopy o A neuroanatomical technique used to study the fine details of cellular structure Neuroanatomical Tracing Techniques Anterograde tracing methods o Used when the investigator wants to trace the paths of axons projecting away from cell bodies located in a particular area Injects into the area one of several chemicals that are taken up by cell bodies and then transported forward along their axons to their terminal buttons After a few days the brain is removed and sliced Slices are treated to reveal the locations of the injected chemical Retrograde tracing methods o Used when the investigator wants to trace the paths of axons projecting into a particular area Injects into the area one of several chemicals that are taken up by terminal buttons and then transported backward along their axons to their cell bodies After a few days the brain is removed and sliced Slices are treated to reveal the locations of the injected chemical Directions in the Vertebrate Nervous System The vertebrate nervous system has 3 axes: o Anterior-posterior o Dorsal-ventral o Medial-lateral o Anterior Toward the nose end of a vertebrate o Posterior Toward the tail end of a vertebrate o Dorsal Toward the surface of the back or the top of the head o Ventral Toward the surface of the chest or the bottom of the head o Medial Toward the midline of the body o Lateral Away from the midline of the body o Superior Toward the top of the primate head or brain o Inferior Toward the bottom of the primate head or brain o Proximal Nearer the central core of the body The elbows are proximal to the wrists o Distal Farther from the central core of the body The wrists are distal to the elbows o Horizontal Sections Any slices of brain tissue cut in a plane that is parallel to the top of the brain o Frontal Sections Any slices of brain tissue cut in a plane that is parallel to the face o Sagittal Sections Any slices of brain tissue cut in a plane that is parallel to the side of the brain o Midsagittal Section A section cut down the center of the brain, between the two hemispheres o Cross Section A section cut at a right angle to any long, narrow structure such as the spinal cord or a nerve Spinal Cord In cross section, it is apparent that the spinal cord comprises two different areas: o An inner H-shaped core of grey matter o A surrounding area of white matter Grey Matter Composed largely of cell bodies and unmyelinated interneurons o Dorsal Horns The tow dorsal arms of the spinal grey matter o Ventral Horns The two ventral horns of the spinal grey matter White Matter Composed largely of myelinated axons Spinal Nerves are attached to the spinal cord o One on the left one on the right At 31 different levels of the spine Each of the spinal nerves divides as it nears the cord and its axons are joined to the cord via one of two roots o Dorsal root Sensory (afferent) unipolar neurons with their cell bodies grouped together right outside the cord o Ventral root Motor (efferent) multipolar neurons with their cell bodies in the ventral horns Five Major Divisions of the Brain Forebrain Midbrain Hindbrain Telencephalon o Undergoes the greatest growth during development Brain Stem o The stem on which the cerebral hemispheres sit o Diencephalon o Mesencephalon o Metencephalon o Myelencephalon Major Structures of the Brain Myelencephalon (medulla) Most posterior division of the brain, composed largely of tracts carrying signals between the rest of the brain and the body o Reticular Formation Complex network of about 100 tiny nuclei that occupies the central core of the brain stem from the posterior boundary of the myelencephalon to the anterior boundary of the midbrain Netlike appearance Reticular activating system-parts seem to play a role in arousal Metencephalon Houses many ascending and descending tracts and part of the reticular formation o Pons The metencephalic structure that creates a bulge on the ventral surface of the brain stem o Cerebellum Large, convoluted structure on the brain stem’s dorsal surface Sensorimotor structure Cerebellar damage eliminates the ability to precisely control’s one movements and to adapt them to changing conditions Mesencephalon Two divisions: o Tectum The dorsal surface of the midbrain In mammals composed of two bumps Inferior Colliculi o Posterior pair o Auditory function Superior Colliculi o Anterior pair o Visual-motor function, specifically to direct the body’s orientation toward or away from a particular visual stimuli In the lower vertebrates, the function of the tectum is entirely visual-motor Referred to as the optic tectum o Tegmentum The division of the mesencephalon ventral to the tectum Contains 3 structures Periaqueductal Gray o Gray matter situated around the cerebral aqueduct Cerebral Aqueduct o The duct connecting the third and fourth ventricles o It is of special interest because of its role in mediating the analgesic (pain- reducing) effects of opiate drugs Substantia Nigra o Component of the sensorimotor system Diencephalon Composed of 2 structures o Thalamus Large, two-lobed structure that constitutes the top of the brain stem One lobe sits on each side of the third ventricle Massa Intermedia The neural structure that is located in the third ventricle and connects the two lobes of the thalamus Visible on the surface, are white lamina (layers) that are composed of myelinated axons The thalamus comprises of many different pairs of nuclei, most of which project to the cortex Sensory Relay Nuclei o Nuclei that receive signals from sensory receptors, process them, and then transmit them to the appropriate areas of sensory cortex o Receive feedback signals o Hypothalamus Located just below the anterior thalamus Plays an important role in the regulation of several motivated behaviors (eating, sleeping, sexual behavior) Exerts its effects in part by regulating the release of hormones from the pituitary gland Pituitary Gland Dangles from the ventral surface of the brain In addition to the pituitary gland, two other structures appear on the inferior surface of the hypothalamus Optic Chiasm o Point at which the optic nerves from each eye come together o The X shape is created because some of the axons of the optic nerve decussate via the o Decussate To cross over to the other side of the brain The decussating fibers are said to be contralateral and the nondecussating fibers are said to be ipsilateral Contralateral Projecting from one side of the brain to the other Ipsilateral Staying on the same side of the brain Mammillary Bodies o Pair of spherical nuclei located on the inferior side of the hypothalamus, just behind the pituitary Telencephalon Longest division of the human brain, mediates the brains most complex functions Initiates voluntary movement, interprets sensory input, and mediates complex cognitive processes such as learning, speaking, and problem solving Cerebral Cortex The layer of neural tissue covering the cerebral hemispheres Made up of small, unmyelinated neurons Deeply convoluted (furrowed) o Have the effect of increasing the amount of cerebral cortex without increasing the overall volume of the brain o Fissures Large furrows in a convoluted cortex Longitudinal Fissure The largest fissure that almost completely separates the cerebral hemispheres Cerebral Commissures The hemisphere-connecting tracts that connect the cerebral hemispheres Corpus Callosum o The largest cerebral commissures o Sulci The small furrows in a convoluted cortex o Gyri The ridges between fissures and sulci The two major landmarks on the lateral surface of each hemisphere: o Central Fissure o Lateral Fissure o Partially divide each hemisphere into 4 lobes: Frontal Precentral gyrus have motor function Performs complex cognitive functions such as planning response sequences, evaluating the outcomes of potential patterns of behavior, and assessing the significance of the behavior of others Parietal Postcentral gyrus analyzes sensations from the body Plays roles in perceiving the location of both objects and our own bodies and in directing our attention Temporal Superior temporal gyrus is involved in hearing and language Inferior temporal identifies complex visual patterns Medial is important for certain kinds of memories Occipital Analysis of visual input Limbic System and the Basal Ganglia Limbic System o A circuit of midline structures that circle the thalamus o Involved in the regulation of motivated behaviors including the 4 F’s of motivation Fleeing Feeding Fighting Sexual Behavior