Copyright © 2011 Pearson Education, Inc. All rights reserved. Systems, Structures, and Cells That Make Up Your Nervous System Topic 2 The Anatomy of the Brain (Nervous System)

Outline of topic 1. General layout of the Nervous system 2. Cells of the Nervous system: Anatomy of Neuron 3. Spinal Cord 4. Major structure of the Brain 5. Central Nervous System Copyright © 2011 Pearson Education, Inc. All rights reserved.

General layout of the Nervous System COPYRIGHT © ALLYN & BACON The brain is a large mass of neurons, glia, and other supporting cells. It is the most protected organ of the body, encased in a tough, bony skull and floating in a pool of cerebrospinal fluid. The brain receives a copious supply of blood and is chemically guarded by the blood–brain barrier. The brain receives approximately 20 percent of the blood flow from the heart, and it receives it continuously. Other parts of the body, such as the skeletal muscles or digestive system, receive varying quantities of blood, depending on their needs (relative to those of other regions). But the brain always receives its share.

Copyright © 2011 Pearson Education, Inc. All rights reserved. 1) General Layout of the Nervous System a) Central Nervous System (CNS) Brain (in the skull) Spinal Cord (in the spine) b) Peripheral Nervous System (PNS) Located outside of the skull and spine Connects the central nervous system to all other parts of the body Serves to bring information into the CNS and carry signals out of the CNS

How do you differentiate CNS and PNS? COPYRIGHT © ALLYN & BACON

Copyright © 2011 Pearson Education, Inc. All rights reserved. General Layout of the Nervous System Continued b) Peripheral Nervous System i) Somatic Nervous System  Afferent nerves (sensory)  Efferent nerves (motor) ii) Autonomic Nervous System  Sympathetic and parasympathetic nerves  Both are efferent

Copyright © 2011 Pearson Education, Inc. All rights reserved. ii) Autonomic Nervous System All nerves are efferent Sympathetic and parasympathetic nerves generally have opposite effects Two-stage neural paths, neuron exiting the CNS synapses on a second-stage neuron before the target organ

Copyright © 2011 Pearson Education, Inc. All rights reserved. Autonomic Nervous System Continued Sympathetic Thoracic and lumbar “Fight or flight” Second stage neurons are far from the target organ Parasympathetic Cranial and sacral “Rest and restore” Second stage neurons are near the target organ

Copyright © 2011 Pearson Education, Inc. All rights reserved. FIGURE 3.2 The major divisions of the nervous system.

Copyright © 2011 Pearson Education, Inc. All rights reserved. Meninges, Ventricles, and Cerebrospinal Fluid (CSF) CNS encased in bone and covered by three meninges Dura mater – tough outer membrane Arachnoid membrane – web-like Pia mater – adheres to CNS surface Cerebrospinal fluid (CSF) Fluid serves as cushion

Copyright © 2011 Pearson Education, Inc. All rights reserved. FIGURE 3.3 The cerebral ventricles.

Copyright © 2011 Pearson Education, Inc. All rights reserved. Protecting the Brain Chemical protection The blood-brain barrier – tightly-packed cells of blood vessel walls prevent entry of many molecules Physical protection Skull Meninges Cerebrospinal fluid (CSF)

Copyright © 2011 Pearson Education, Inc. All rights reserved. 2) Cells of the Nervous System: Anatomy of Neurons Neurons Specialized cells for the reception, conduction, and transmission of electrochemical signals Many sizes and shapes

Copyright © 2011 Pearson Education, Inc. All rights reserved. FIGURE 3.5 The major external features of a typical neuron.

Copyright © 2011 Pearson Education, Inc. All rights reserved. FIGURE 3.6 The major internal features of a typical neuron.

Copyright © 2011 Pearson Education, Inc. All rights reserved. FIGURE 3.7 The cell membrane is a lipid bilayer with signal proteins and channel proteins embedded in it.

Copyright © 2011 Pearson Education, Inc. All rights reserved. FIGURE 3.8 A unipolar neuron, a bipolar neuron, a multipolar neuron, and an interneuron.

Copyright © 2011 Pearson Education, Inc. All rights reserved. Glial Cells: The Forgotten Cells Glial cells Outnumber neurons 10:1 Support neurons Recent evidence for glial communication and modulatory effects of glia on neuronal communication Four classes of Glial cells: Oligodendrocytes – extensions rich in myelin create myelin sheaths in CNS Schwann cells – similar to function of oligodendrocytes but in PNS, can guide axonal regeneration Astrocytes – largest glia, star-shaped, many functions Microglia – involved in response to injury or disease

Copyright © 2011 Pearson Education, Inc. All rights reserved. FIGURE 3.9 The myelination of CNS axons by an oligodendrocyte and the myelination of PNS axons by Schwann cells.

Copyright © 2011 Pearson Education, Inc. All rights reserved. Terminology Note CNSPNS Myelin-providing glia Oligodendrocytes Schwann cells Clusters of cell bodies Nuclei (singular nucleus) Ganglia (singular ganglion) Bundles of axonsTracts Nerves

Copyright © 2011 Pearson Education, Inc. All rights reserved. Neuroanatomical Techniques and Directions Golgi stain – allows for visualization of individual neurons Nissl stain – selectively stains cell bodies Electron microscopy – provides information about the details of neuronal structure

Copyright © 2011 Pearson Education, Inc. All rights reserved. FIGURE 3.11 Neural tissue that has been stained by the Golgi method. (Ed Reschke © Peter Arnold, Inc.)

Copyright © 2011 Pearson Education, Inc. All rights reserved. FIGURE 3.12 The Nissl stain. (Courtesy of Carl Ernst and Brian Christie, Department of Psychology, University of British Columbia.)

Copyright © 2011 Pearson Education, Inc. All rights reserved. FIGURE 3.13 A color-enhanced scanning electron micrograph of a neuron cell body (green) studded with terminal buttons (orange). Courtesy of Jerold J. M. Chun, M.D., Ph.D.

Copyright © 2011 Pearson Education, Inc. All rights reserved. Neuroanatomical Tracing Techniques Anterograde (forward) tracing to where axons project away from an area Retrograde (backward) tracing from where axons are projecting into an area

Copyright © 2011 Pearson Education, Inc. All rights reserved. FIGURE 3.14 Anatomical directions in a representative vertebrate (cat).

Copyright © 2011 Pearson Education, Inc. All rights reserved. FIGURE 3.15 Anatomical directions in a human.

Copyright © 2011 Pearson Education, Inc. All rights reserved. Directions in the Vertebrate Nervous System Continued Anatomical directions ignore the fact that humans walk upright. Therefore, top of the head is both “dorsal” (back) and “superior” (top) Other directions: Medial – toward the middle Lateral – toward the side Proximal – close Distal – far

Copyright © 2011 Pearson Education, Inc. All rights reserved. Sections of the Brain How can you examine a brain? Cross Section - with respect to the central nervous system, a slice taken at right angles to the neuraxis Horizontal – a slice parallel to the ground Frontal (coronal) – slicing bread or salami Sagittal – a midsagittal section separates the left and right halves See figure 3.16 & 3.2.

Copyright © 2011 Pearson Education, Inc. All rights reserved. FIGURE 3.16 Horizontal, frontal (coronal), and sagittal planes in the human brain and a cross section of the human spinal cord.

Copyright © 2011 Pearson Education, Inc. All rights reserved.

Midsagittal view Copyright © 2011 Pearson Education, Inc. All rights reserved.

3) Spinal Cord Gray matter – inner component, primarily cell bodies White matter – outer area, mainly myelinated axons Dorsal – afferent, sensory Ventral – efferent, motor

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The Spinal Cord COPYRIGHT © ALLYN & BACON The spinal cord is a long, conical structure, approximately as thick as one’s little finger. The principal function of the spinal cord is to distribute motor fibers to the effector organs of the body (glands and muscles) and to collect somatosensory information to be passed on to the brain. The spinal cord also has a certain degree of autonomy from the brain; various reflexive control circuits.

The Spinal Cord COPYRIGHT © ALLYN & BACON Spinal Cord the cord of nervous tissue that extends caudally from the medulla Spinal Root a bundle of axons surrounded by connective tissue that occurs in pairs, which fuse and form a spinal nerve

The Spinal Cord COPYRIGHT © ALLYN & BACON Cauda Equina (ee kwye na) a bundle of spinal roots located caudal to the end of the spinal cord Caudal Block the anesthesia and paralysis of the lower part of the body produced by injection of a local anesthetic into the cerebrospinal fluid surrounding the cauda equina.

Figure 3.21, page 91 COPYRIGHT © ALLYN & BACON

The Spinal Cord COPYRIGHT © ALLYN & BACON Dorsal Root the spinal root that contains incoming (afferent) sensory fibers Ventral Root the spinal root that contains outgoing (efferent) motor fibers Spinal Nerve a peripheral nerve attached to the spinal cord

The Spinal Cord COPYRIGHT © ALLYN & BACON Afferent Axon an axon directed toward the central nervous system, conveying sensory information Dorsal Root Ganglion a nodule on a dorsal root that contains cell bodies of afferent spinal nerve neurons Efferent Axon (eff ur ent) an axon directed away from the central nervous system, conveying motor commands to muscles and glands

Copyright © 2011 Pearson Education, Inc. All rights reserved. FIGURE 3.17 The dorsal and ventral roots of the spinal cord. FIGURE 3.18 A schematic cross section of the spinal cord.

Section Summary The outer part of the spinal cord consists of white matter: axons conveying information up or down. The central gray matter contains cell bodies. Copyright © 2011 Pearson Education, Inc. All rights reserved.

FIGURE 3.19 The early development of the mammalian brain illustrated in schematic horizontal sections.

Copyright © 2011 Pearson Education, Inc. All rights reserved. FIGURE 3.20 The divisions of the adult human brain.

The Central Nervous System – Brain COPYRIGHT © ALLYN & BACON The brain consists of three major divisions, organized around the three chambers of the tube that develops early in embryonic life: the forebrain, the midbrain, and the hindbrain. Although the basic development of the nervous system is genetically controlled, sensory stimulation plays a role in refining the details. In addition, the neural circuitry of even a fully mature brain can be modified through experience.

The Central Nervous System COPYRIGHT © ALLYN & BACON The large size of the human brain, relative to the brains of other primates, appears to be accomplished primarily by lengthening the first and second periods of brain development. The FOREBRAIN, which surrounds the lateral and third ventricles (hollow, interconnected chambers – little bellies), consists of the telencephalon and diencephalon. The telencephalon contains the cerebral cortex (like the bark of a tree), the limbic system, and the basal ganglia.

The Central Nervous System COPYRIGHT © ALLYN & BACON The cerebral cortex is organized into the frontal, parietal, temporal, and occipital lobes. The central sulcus divides the frontal lobe—which deals specifically with movement and the planning of movement—from the other three lobes (p,t,o), which deal primarily with perceiving and learning. The limbic system—which includes the limbic cortex, the hippocampus, and the amygdala—is involved in emotion, motivation, and learning.

The Central Nervous System COPYRIGHT © ALLYN & BACON The basal ganglia in the forebrain participate in the control of movement. The diencephalon consists of the thalamus, which directs information to and from the cerebral cortex, and the hypothalamus, which controls the endocrine system and modulates species-typical behaviors.

MIDBRAIN – also called mesencephalon, contains two main parts: tectum and tegmentum Tectum – involve in the auditory and visual system such as visual reflexes and reactions to moving stimuli. Tegmentum – play a role in sleep, arousal, attention, muscle tonus, movement (specific movements includes fighting & mating). Copyright © 2011 Pearson Education, Inc. All rights reserved.

The Central Nervous System COPYRIGHT © ALLYN & BACON Section Summary The HINDBRAIN surrounds the fourth ventricle— contains the cerebellum, the pons, and the medulla. The cerebellum plays an important role in integrating and coordinating movements. The pons contains some nuclei that are important in sleep and arousal. The medulla oblongata, too, is involved in sleep and arousal, but it also plays a role in control of movement and in control of vital functions such as heart rate, breathing, and blood pressure.

Copyright © 2011 Pearson Education, Inc. All rights reserved. 4) Major Structures of the Brain Major divisions: a) Hindbrain b) Midbrain c) Forebrain

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4) Major Structures of the Brain a) Hindbrain 1) Myelencephalon = medulla Composed largely of tracts Origin of the reticular formation 2) Metencephalon Many tracts Pons – ventral surface Cerebellum – coordination

Copyright © 2011 Pearson Education, Inc. All rights reserved. FIGURE 3.21 Structures of the human myelencephalon (medulla) and metencephalon.

Copyright © 2011 Pearson Education, Inc. All rights reserved. Major Structures of the Brain Continued Mesencephalon = midbrain tectum has inferior and superior colliculi tegmentum has periaqueductal gray, substantia nigra, and red nucleus Diencephalon thalamus hypothalamus

Copyright © 2011 Pearson Education, Inc. All rights reserved. FIGURE 3.22 The human mesencephalon (midbrain).

Copyright © 2011 Pearson Education, Inc. All rights reserved. FIGURE 3.23 The human diencephalon.

Copyright © 2011 Pearson Education, Inc. All rights reserved. Telencephalon – Cerebral Cortex Convolutions serve to increase surface area Longitudinal fissure – a groove that separates right and left hemispheres Corpus callosum – largest hemisphere-connecting tract

Copyright © 2011 Pearson Education, Inc. All rights reserved. FIGURE 3.25 The major fissures of the human cerebral cortex. FIGURE 3.26 The lobes of the cerebral hemishphere.

Copyright © 2011 Pearson Education, Inc. All rights reserved. Telencephalon – Subcortical Structures Limbic system – regulation of motivated behaviors Mammillary bodies, hippocampus, amygdala, fornix, cingulate, septum Basal ganglia motor system Amygdala, striatum (caudate nucleus + putamen), globus pallidus

Copyright © 2011 Pearson Education, Inc. All rights reserved. FIGURE 3.28 The major structures of the limbic system: amygdala, hippocampus, cingulate cortex, fornix, septum, and mammillary body.

Copyright © 2011 Pearson Education, Inc. All rights reserved. FIGURE 3.29 The basal ganglia: amygdala, striatum (caudate plus putamen) and globus pallidus.

Copyright © 2011 Pearson Education, Inc. All rights reserved. FIGURE 3.30 Summary of major brain structures.