- •Preface
- •Contents
- •1 Elements of the Nervous System
- •2 Somatosensory System
- •3 Motor System
- •4 Brainstem
- •5 Cerebellum
- •6 Diencephalon and Autonomic Nervous System
- •7 Limbic System
- •8 Basal Ganglia
- •9 Cerebrum
- •10 Coverings of the Brain and Spinal Cord; Cerebrospinal Fluid and Ventricular System
- •Further Reading
- •Index
- •Abbreviations
- •1 Elements of the Nervous System
- •Elements of the Nervous System
- •Information Flow in the Nervous System
- •Synapses
- •Neurotransmitters and Receptors
- •Functional Groups of Neurons
- •Glial Cells
- •Development of the Nervous System
- •2 Somatosensory System
- •Peripheral Nerve, Dorsal Root Ganglion, Posterior Root
- •Peripheral Regulatory Circuits
- •Central Components of the Somatosensory System
- •Posterior and Anterior Spinocerebellar Tracts
- •Posterior Columns
- •Anterior Spinothalamic Tract
- •Lateral Spinothalamic Tract
- •Other Afferent Tracts of the Spinal Cord
- •Central Processing of Somatosensory Information
- •Somatosensory Deficits due to Lesions at Specific Sites along the Somatosensory Pathways
- •3 Motor System
- •Central Components of the Motor System and Clinical Syndromes of Lesions Affecting Them
- •Motor Cortical Areas
- •Corticospinal Tract (Pyramidal Tract)
- •Corticonuclear (Corticobulbar) Tract
- •Other Central Components of the Motor System
- •Lesions of Central Motor Pathways
- •Peripheral Components of the Motor System and Clinical Syndromes of Lesions Affecting Them
- •Clinical Syndromes of Motor Unit Lesions
- •Complex Clinical Syndromes due to Lesions of Specific Components of the Nervous System
- •Spinal Cord Syndromes
- •Vascular Spinal Cord Syndromes
- •Nerve Root Syndromes (Radicular Syndromes)
- •Plexus Syndromes
- •Peripheral Nerve Syndromes
- •Syndromes of the Neuromuscular Junction and Muscle
- •4 Brainstem
- •Surface Anatomy of the Brainstem
- •Medulla
- •Pons
- •Midbrain
- •Olfactory System (CN I)
- •Visual System (CN II)
- •Eye Movements (CN III, IV, and VI)
- •Trigeminal Nerve (CN V)
- •Facial Nerve (CN VII) and Nervus Intermedius
- •Vagal System (CN IX, X, and the Cranial Portion of XI)
- •Hypoglossal Nerve (CN XII)
- •Topographical Anatomy of the Brainstem
- •Internal Structure of the Brainstem
- •5 Cerebellum
- •Surface Anatomy
- •Internal Structure
- •Cerebellar Cortex
- •Cerebellar Nuclei
- •Connections of the Cerebellum with Other Parts of the Nervous System
- •Cerebellar Function and Cerebellar Syndromes
- •Vestibulocerebellum
- •Spinocerebellum
- •Cerebrocerebellum
- •Cerebellar Tumors
- •6 Diencephalon and Autonomic Nervous System
- •Location and Components of the Diencephalon
- •Functions of the Thalamus
- •Syndromes of Thalamic Lesions
- •Thalamic Vascular Syndromes
- •Epithalamus
- •Subthalamus
- •Hypothalamic Nuclei
- •Afferent and Efferent Projections of the Hypothalamus
- •Functions of the Hypothalamus
- •Sympathetic Nervous System
- •Parasympathetic Nervous System
- •Visceral and Referred Pain
- •7 Limbic System
- •Anatomical Overview
- •Internal and External Connections
- •Microanatomy of the Hippocampal Formation
- •Amygdala
- •Functions of the Limbic System
- •Types of Memory
- •8 Basal Ganglia
- •Preliminary Remarks on Terminology
- •The Role of the Basal Ganglia in the Motor System: Phylogenetic Aspects
- •Connections of the Basal Ganglia
- •Function and Dysfunction of the Basal Ganglia
- •Clinical Syndromes of Basal Ganglia Lesions
- •9 Cerebrum
- •Development
- •Gross Anatomy and Subdivision of the Cerebrum
- •Gyri and Sulci
- •Histological Organization of the Cerebral Cortex
- •Laminar Architecture
- •Cerebral White Matter
- •Projection Fibers
- •Association Fibers
- •Commissural Fibers
- •Functional Localization in the Cerebral Cortex
- •Primary Cortical Fields
- •Association Areas
- •Frontal Lobe
- •Coverings of the Brain and Spinal Cord
- •Dura Mater
- •Arachnoid
- •Pia Mater
- •Cerebrospinal Fluid Circulation and Resorption
- •Arteries of the Anterior and Middle Cranial Fossae
- •Arteries of the Posterior Fossa
- •Collateral Circulation in the Brain
- •Dural Sinuses
- •Venous Drainage
- •Cerebral Ischemia
- •Arterial Hypoperfusion
- •Particular Cerebrovascular Syndromes
- •Impaired Venous Drainage from the Brain
- •Intracranial Hemorrhage
- •Intracerebral Hemorrhage (Nontraumatic)
- •Subarachnoid Hemorrhage
- •Subdural and Epidural Hematoma
- •Impaired Venous Drainage
- •Spinal Cord Hemorrhage and Hematoma
- •Further Reading
- •Index
1 1
1Elements of the Nervous System
Information Flow
in the Nervous System . . . . . . . . . 2
Neurons and Synapses . . . . . . . . . 3
Neurotransmitters
and Receptors . . . . . . . . . . . . . . . . 10
Functional Groups of Neurons . . . 12
Glial Cells . . . . . . . . . . . . . . . . . . . . 13
Development of the Nervous
System . . . . . . . . . . . . . . . . . . . . . . 13
Baehr, Duus' Topical Diagnosis in Neurology © 2005 Thieme
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1 2
1 Elements of the Nervous System
The nervous system is composed of cells, called neurons, that are specialized for information processing and transmission. Neurons make contact with each other at junctions called synapses, at which information is transferred from one neuron to the next by means of chemical messenger substances called neurotransmitters. In general, neurons can be divided into two classes: excitatory and inhibitory. The organization of the nervous system is easier to understand after a brief consideration of its (ontogenetic) development.
Information Flow in the Nervous System
Information flow in the nervous system can be broken down schematically into three steps (Fig. 1.1): an external or internal stimulus impinging on the sense organs induces the generation of nerve impulses that travel toward the central nervous system (CNS) (afferent impulses); complex processing occurs within the CNS (information processing); and, as the product of this processing, the CNS generates impulses that travel toward the periphery (efferent impulses) and effect the (motor) response of the organism to the stimulus. Thus, when a pedestrian sees a green traffic light, afferent impulses are generated in the optic nerves and visual system that convey information about the specific color present. Then, at higher levels in the CNS, the stimulus is interpreted and assigned a meaning (green light = go). Efferent impulses to the legs then effect the motor response (crossing the street).
In the simplest case, information can be transferred directly from the afferent to the efferent arm, without any intervening complex processing in the CNS; this is what happens, for example, in an intrinsic muscle reflex such as the knee-jerk (patellar) reflex.
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Neurons and Synapses · 3 |
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Neurons and Synapses
Neurons
The neurons and their processes (see below) and the synapses (see p. 7) are responsible for the flow of information in the nervous system. At the synapses, information is transferred from one neuron to the next by means of chemical substances called neurotransmitters.
Dendrites and axons. Neurons transfer information in one direction only because they are bipolar: they receive information from other neurons at one end, and transmit information to other neurons at the other end.
The receptive structures of a nerve cell, called dendrites, are branched processes attached to the cell body. Neurons vary considerably with regard to the number and branching pattern of their dendrites. The forward conducting structure is the axon, which in humans can be up to a meter in length. In contrast to the variable number of dendrites, each neuron possesses only a single axon. “Axis cylinder” is an older and now little-used term for “axon” that refers to its long, cylindrical shape. At its distal end, the axon splits into a number of terminal branches, each of which ends in a so-called terminal bouton that makes contact with the next neuron (Fig. 1.2).
The long peripheral processes of the pseudounipolar neurons of the spinal ganglia are an important special case. These are the fibers that relay information regarding touch, pain, and temperature from the body surface to the CNS. Although they are receptive structures, they nonetheless possess the structural characteristics of axons and are designated as such.
The trophic (nutritive) center of the neuron is its cell body (soma or perikaryon), which contains the cell nucleus and various different types of subcellular organelles.
Axonal transport. The neurotransmitters, or the enzymes catalyzing their biosynthesis, are synthesized in the perikaryon and then carried down axonal microtubules to the end of the axon in a process known as axoplasmic transport. The neurotransmitter molecules are stored in synaptic vesicles inside the terminal boutons (each bouton contains many synaptic vesicles). Axoplasmic transport, generally speaking, can be in either direction—from the cell body toward the end of the axon (anterograde transport), or in the reverse direction (retrograde transport). Rapid axoplasmic transport proceeds at a speed of 200 400 mm/day. This is distinct from axoplasmic flow, whose speed is 15 mm/ day. Axoplasmic transport is exploited in the research laboratory by anterograde and retrograde tracer techniques for the anatomical demonstration of neural projections (Fig. 1.3).
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Nucleolus
Perikaryon
Nucleus
Axon hillock
Axon (neurite)
Myelin sheath
Collateral axon
Collateral axon
Axon ending (terminal) with terminal bouton
Fig. 1.2 Structure of a neuron (schematic drawing). From: Kahle W and Frotscher M: Taschenatlas der Anatomie, vol. 3, 8th ed., Thieme, Stuttgart, 2002.
Baehr, Duus' Topical Diagnosis in Neurology © 2005 Thieme
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Neurons and Synapses · 5 |
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Fig. 1.3 Tracing of neuronal projections with retrograde and anterograde tracer substances. Tracer substances, such as fluorescent dyes, are injected either at the site of origin or at the destination of the neuronal pathway in question. The tracer substances are then transported along the neurons, either from the cell bodies to the axon terminals (anterograde transport) or in the reverse direction (retrograde transport). It is thus possible to trace the entire projection from one end to the other.
a Retrograde transport.
b Retrograde transport from multiple projection areas of a single neuron.
c Anterograde transport from a single cell body into multiple projection areas.
From: Kahle W and Frotscher M: Taschenatlas der Anatomie, vol. 3, 8th ed., Thieme, Stuttgart, 2002.
Axon myelination. Axons are surrounded by a sheath of myelin (Fig. 1.4). The myelin sheath, which is formed by oligodendrocytes (a special class of glial cells) in the central nervous system and by Schwann cells in the peripheral nervous system, is a sheetlike continuation of the oligodendrocyte or Schwann cell membrane that wraps itself around the axon multiple times, providing electrical insulation. Many oligodendrocytes or Schwann cells form the myelin surrounding a single axon. The segments of myelin sheath formed by two adjacent cells are separated by an area of uncovered axonal membrane called a node of Ranvier. Because of the insulating property of myelin, an action potential causes depolarization only at the nodes of Ranvier; thus, neural excitation
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16 · 1 Elements of the Nervous System
Fig. 1.4 Nerve fiber in the central nervous system, with oligodendrocyte and myelin sheath
(schematic drawing). 1, Oligodendrocyte. 2, Axon. 3, Myelin sheath. 4, Node of Ranvier. 5, Inner mesaxon. 6, Outer mesaxon. 7, Pockets of cytoplasm. From: Kahle W and Frotscher M: Taschenatlas der Anatomie, vol. 3, 8th ed., Thieme, Stuttgart, 2002.
jumps from one node of Ranvier to the next, a process known as saltatory conduction. It follows that neural conduction is fastest in neurons that have thick insulating myelin with nodes of Ranvier spaced widely apart. On the other hand, in axons that lack a myelin covering, excitation must travel relatively slowly down the entire axonal membrane. Between these two extremes there are axons with myelin of intermediate thickness. Thus, axons are divided into thickly myelinated, thinly myelinated, and unmyelinated axons (nerve fibers);
Baehr, Duus' Topical Diagnosis in Neurology © 2005 Thieme
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