Chapter 1 - Introduction

An understanding of functional neuroanatomy is critical to understanding the symptoms of nervous system damage. Most disorders of the nervous system either target particular brain structures or target components of functional systems. Therefore, knowing these structures and their basic functions permits localization of the nervous system damage. This chapter will consider the important elements of clinical neuroanatomy. There are several good texts that provide greater detail on these systems (1-3).

An atlas of brain structures is essential to the study of neuroanatomy. There are many good atlases (4-6) and some can be found on the Web. One such atlas is located at: www.dartmouth.edu/~rswenson/Atlas.

This review will discuss the cellular components of the nervous system first and then will consider the peripheral nervous system (PNS) before discussing the Central nervous system (CNS). In the CNS we will first consider the sensory systems and then motor systems before discussing limbic and higher cortical functions.

References:

1. Purves D, ed. Neuroscience, 3rd Ed. Sinauer, 2004. Excellent text of basic neuroscience. It is somewhat deficient in neuroanatomy, but it is very clear and easy to follow. There are interesting digressions that are provided as separate short articles that are set off in boxes from the rest of the text.


2. Nolte J. The Human Brain: An Introduction to Its Functional Anatomy, 5th edition, Mosby, 2002. Standard text of neuroscience utilized in many medical schools. It is comprehensive but not overly detailed.


3. Kandel ER, Schwartz JH, Jessell TM. Principles of Neural Science. McGraw-Hill, 2000. This is the "bible" of neuroscience texts. Well-organized but quite heavy in sections. It extensively references primary sources and introduces methodology. This is a wonderful text for the graduate or the advanced student of neuroscience. Each section can be studied on its own by the student with a background in neuroscience.


4. Haines DE. Neuroanatomy: An Atlas of Structures, Sections, and Systems (Book with CD-ROM). 5th ed. Lippincott Williams & Wilkins, 2002.

Comprehensive atlas: includes a large number of schematic drawings of functional systems of the brain.

5. Nolte J and Angevine JB. The Human Brain: In Photographs and Diagrams, 2nd ed. Mosby, 2000. This atlas includes many illustrations that provide a 3-dimentional feel for brain structures.


6. Martin JH, Leonard ME, Radzyner HJ. Neuroanatomy: Text and Atlas, 3rd ed. McGraw-Hill, 2002. Atlas is incorporated in a text with more description than is found in most atlases.

List of Figures

Figure 1. A. Nernst equation. At body temperature, the potassium equilibrium potential (which represents the great majority of resting membrane potential) is a constant times the logarithm of the ratio of concentrations of potassium outside and inside the cell. B. Goldman-Hodgkins-Katz equation. This is similar to the Nernst equation except that it adds a factor for permeability. If an ion is impermeable, its contribution to the membrane potential (V) is nil. The higher the relative permeability, the closer the membrane will be to the equilibrium potential for that ion.


Figure 2. Action potential. Depolarization is a graded phenomenon until threshold is reached. At that point, voltage-gated sodium channels are opened and the movement of sodium rapidly depolarizes the neuron. The voltage-gated sodium channels are then rapidly inactivated and voltage gated potassium channels are opened, which drives the cell back toward the potassium equilibrium potential (near -90 mV). Until the cell repolarizes, the voltage-gated sodium channels are inactivated and another action potential cannot be generated (absolute refractory period). Until the voltage gated potassium channels are inactivated it is harder (but not impossible) to generate an action potential (relative refractory period).


Figure 3. A myelomere of the spinal cord, and one of its two associated spinal nerves. In A: A, anterior median fissure; P, posterior median sulcus. B shows the arterial supply to the cord. C depicts a sensory axon in the dorsal nerve root and a somatic motor axon in the ventral nerve root. Additionally, there is a sympathetic preganglionic axon arising from a neuron in the spinal cord lateral horn and this is traversing the white ramus communicans to the sympathetic gangliated chain where it is synapsing on a small postganglionic neuron. A and B by permission of R. O'Rahilly, "Basic Human Anatomy."


Figure 4. The sensory distribution of peripheral nerves. With permission of R. O'Rahilly, "Basic Human Anatomy."


Figure 5. The approximate sensory distribution of dorsal roots (after Forster). Note that there is near complete overlap between adjacent nerve roots with the exception of a small distal portion of the distribution (so-called "autonomous zones"). With permission from R. O'Rahilly, "Basic human Anatomy."


Figure 6. Sympathetic pathway to the head. Note the descending connection from the hypothalamus through the brain stem and cervical spinal cord to the pregangilionic neuron in the upper thoracic cord. The axon from the preganglionic neuron exits the cord and joins the sympathetic gangliated chain. Those destined for the head ascend the cervical sympathetic chain to reach the superior cervical ganglion, where they synapse with postganglionic neurons. The axons from the postganglionic neurons join blood vessels to the head (those to the orbit are depicted in the figure as following the internal carotid to the ophthalmic artery. With permission from A.G. Reeves, "Disorders of the Nervous System."


Figure 7. Progressive stages of development of the neural tube. The black represents the location of neural crest cells. The light gray circle (directly below the neural tube) is the notocord.


Figure 8. A. A view of the dorsal aspect of the embryo showing the location of the neural epithelium and the successive stages of closure of the neural tube. Note that the anterior and posterior neuropore are open at each end in the lower figure. B. The neural tube in the region that will be the spinal cord (left) and brain stem (right). Note how the alar plates have separated from one another in the view at the left. The motor cranial nerve nuclei are ventromedial to the sulcus limitans and the sensory nuclei are dorsolateral. GSE = general somatic efferent (somatic motor to eyes and tongue); GVE = general visceral efferent (parasympathetic); SVE = special visceral efferent (branchial motor to larynx, pharynx and jaw muscles); GVA = general visceral afferent (visceral sensory); GSA = general somatic afferent (somatic sensory); SSA = special somatic afferent (hearing and vestibular function). Special visceral affterent (SVA; taste fibers) terminate in nuclei in the same general region as GVA.


Figure 9. Efferent connections from the raphe nuclei (serotonin; A) and from the locus ceruleus and medullary reticular formation (norepinephrine; B). RN = raphe nuclei; BS = brain stem; Th = thalamus; S = septal nuclei; HC = hippocampus; Amy = amygdala; H = hypothalamus; LC = locus ceruleus; RF = reticular formation.

Figure 10. Spinothalmic tract. Spinal cord at the bottom and cerebral cortex at the top. Note that the sections are not to scale.


Figure 11. Descending pathways modifying pain perception. Regions that are cross-hatched contain enkephalinergic interneurons. EAA = excitatory amino acids; NE = norepinephrine; 5-HT = serotonin.


Figure 12. Dorsal columns pathways, medial lemniscus pathway. A. Fasciculus gracilis (from lower limb). B. Fasciculus cuneatus (from upper limb).


Figure 13. Spinocerebellar pathways. A. Dorsal (posterior) spinocerebellar tract. B. Cuneocerebellar tract.


Figure 14. Location of ascending and descending tracts of the spinal cord. Ascending tracts on the right and descending on the left.


Figure 15. Ventral view of the brain stem including the locations of the cranial nerves. By permission of R. O'Rahilly, "Basic Human Anatomy."


Figure 16. Trigeminal sensory systems. Trigeminal tracts and nuclei are superimposed over a dorsal view of the brain stem with the caudal medulla at the lower aspect of the figure and the midbrain at the upper. Note that the mesencephalic tract and nucleus are not shown.


Figure 17. Structure of the ear. Note that the inner ear consists of a cavity in the bone (bony labyrinth) containing a sac. This sac consists of the coiled cochlear duct (hearing) and vestibular elements that include three semicircular ducts that are oriented at right angels to one another.


Figure 18. A. Location of the semicircular ducts in the head. Note that the anterior semicircular duct of one ear is in the same plane as the posterior canal from the other ear. AC = anterior semicircular canal; PC = posterior semicircular canal; LC = lateral semicircular canal. B. The structure of hair cells. Note that the kinocilium is longer and is attached to the tip of the other cilia by a filament. Tension on this filament will open ion channels and result in an increase in action potentials in the nerve (below). C. Structure of a christae. Note that all of the hair cells are polarized in the same direction. D. Structure of a macula. Note that the hair cells have different polarization.


Figure 19. Central connection of the vestibular nerve. PPRF = paramedian pontine reticular formation (paraabducens nucleus; pontine lateral gaze center). Cranial nerve nuclei noted in Roman numerals; MLF = medial longitudinal fasciculus; VST = vestibulospinal tract.

Figure 20. Schematic of connections of vestibulo-ocular reflex (VOR). See legend of figure 18 for key to abbreviations.

Figure 21. Optic pathways.


Figure 22. Corticospinal and corticobulbar pathways.


Figure 23. Wiring of the cerebellar cortex. Neurons represented by circles (filled = inhibitory neurons; open = excitatory). Synapses represented by triangles (filled = inhibitory neurons; open = excitatory).

Figure 24. Cerebellar efferent connections.


Figure 25. Fundamental wiring of basal gangliar circuitry. D1 and D2 refer to the principal types of dopamine receptors located on striatal neurons participating in the direct and the indirect pathways, respectively.


Figure 26. Organization of the "ventral striatal system". This system is similar in organization to the other portions of the extrapyramidal system and includes a feedback loop involving a striatal element (the nucleus accumbens), a palidal element (the ventral palidum), a thalamic relay nucleus (the dorsomedial nucleus) and a source of dopamine (the ventral tegmental area). Note that dopamine acts on different types of receptors depending on the location.


Figure 27. Six positions of gaze. Note that vertical movements of an adducted or abducted eye are the responsibility of a single muscle and that there are always at least 2 muscles that are active when the eyes are moved vertically.


Figure 28. Circuitry for voluntary conjugate horizontal gaze to the left. Roman numerals indicate cranial nerve nuclei.


Figure 29. Circuitry for voluntary vertical eye movements. Note that there is no single cerebral cortical vertical gaze center.

Figure 30. Circuitry for smooth pursuit eye movements. Note that this uses much of the same circuitry as the vestibuloocular reflex (see fig. 19). Ipsilateral and contralateral are in relation to the preceding element in the system.


Figure 31. Pathways interconnecting elements of the limbic system.


Figure 32. Connections of the amygdala. B = brain stem; T = thalamus; S = septal nuclei; Hip = hippocampus; PHG = parahippocampal gyrus; H = hypothalamus; OF = orbital frontal cortex; CG = cingulate gyrus.


Figure 33. Structure and connections of the thalamus. A. View of the right thalamus from the dorsal aspect (anterior toward the top of the page). The internal medullary lamina divides the thalamus into lateral, medial and anterior regions. B. View of the thalamus from the lateral aspect. C & D. Shows the cerebral cortical regions that are reciprocally connected with the labeled thalamic regions. "C" is a lateral view of the hemisphere while "D" is a view of the hemisphere from the medial aspect. See fig 33 for details on cerebral cortical organization. DM = dorsomedial; VA = ventral anterior; VL = ventral lateral; VPL = ventral posterolateral; Ant = anterior; LD = lateral dorsal; MG = medial geniculate; LG = lateral geniculate; LP = lateral posterior; IL = intralaminar.


Figure 34. Map of the cerebral cortex. Korbinian Brodmann, 1909. The numbers refer to his numbering scheme for cytoarchitectural subdivisions (see text).


Figure 35. Arteries of the brain.


Figure 36. Distribution of penetrating arteries.


Figure 37. Venous dural sinuses. With permission from R. O'Rahilly, "Basic Human Anatomy."


Figure 38. Cerebrospinal fluid pathways. A, cerebral artery; C, cerebral vein; D, diploic vein; E, emissary vein; M, meningeal vein; 3 and 4, third and fourth ventricles. The lowermost part of the figure shows the caudal end of the spinal cord. lumbar puncture (L.P.) is performed in the lumbar cistern (below the termination of the spinal cord). With permission from R. O'Rahilly, "Basic Human Anatomy."

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