CHAPTER 1
Overview of the nervous system

Learning objectives

1. Describe the basic subdivisions of the human nervous system.
2. Understand basic neuroanatomical terminology.
3. Identify the major structures on the external surface of the gross brain.
4. Identify the major structures on the midsagittal surface of the brain.
5. Identify the cranial nerves.

Divisions of the nervous system

Anatomic

1. Central nervous system (CNS)
   1. Brain and spinal cord
   2. Collection of nerve cell bodies = nucleus
2. Peripheral nervous system (PNS)
   1. Peripheral nerves
   2. Collection of nerve cell bodies = ganglia

Functional

1. Sensory (afferent)
   1. General - touch
   2. Special senses - sight, sound, taste, smell, balance
2. Motor (efferent)
   1. Voluntary (somatic) - skeletal muscle
   2. Involuntary (autonomic) - smooth and cardiac muscle
      1. Parasympathetic - craniosacral (III, VII, IX, X, S2-S4)
      2. Sympathetic - thoracolumbar (T1-L2)
3. Integrative - interneurons within the CNS

Components of the nervous system

Neurons

1. Highly specialized, excitable cells
2. Morphologic diversity

Glia - supporting cells

1. Schwann cells (neurolemmocytes) - myelin producing
2. Oligodendrocytes - myelin producing
3. Astrocytes - nutritional support
4. Microglia - macrophages (immune support)

Neurons

Cellular structure

1. Dendrites
2. Axon
   1. Axon hillock
   2. Terminal arborization/terminal boutons
   3. Synapse/synaptic vesicles
   4. Anterograde/retrograde flow
3. Soma (perikaryon, cell body)
   1. Nucleus/nucleolus
   2. Nissl bodies (rough endoplasmic reticulum and polyribosomes)
   3. Lipofuscin
4. Cell membrane (plasmalemma, neurolemma)
5. Types: unipolar, bipolar, multipolar, pseudounipolar

Glia - central nervous system

Oligodendrocytes - myelin production; one oligodendrocyte for many axons

Astrocytes - support cells, glial fibrillary acid protein (GFAP), end feet

1. Fibrous astrocytes - white matter
2. Protoplasmic astrocytes - gray matter

Microglia - macrophage-like, scavenging cells

Ependymal cells - columnar, ciliated cells lining the ventricles

Central nervous system

Gray matter

1. Nerve cell bodies (nuclei)
2. Dendrites and axons
3. Glia

White matter

1. Nerve fibers (axons) - myelinated
2. Glia

Brain neuroanatomy

Orientation of the brain - 90 degree rotation at midbrain flexure

1. Superior - inferior
2. Anterior - posterior
3. Dorsal - ventral
4. Rostral - caudal

Planes of the brain

1. Sagittal plane
   1. Midsagittal
   2. Parasagittal
2. Horizontal plane (transverse, axial)
3. Frontal plane (coronal)

Views of the brain

1. Superior
   1. Interhemispheric fissure (sagittal)
   2. Precentral gyrus (primary motor)
   3. Central sulcus
   4. Postcentral gyrus (primary somatosensory)
2. Inferior
   1. Interhemispheric fissure (sagittal)
   2. Lateral fissure (Sylvian)
   3. Midbrain - cerebral peduncles
   4. Pons
   5. Medulla oblongata - pyramids, inferior olives
   6. Cerebellum
   7. Olfactory bulb and tract
   8. Optic chiasm and tract
   9. Infundibulum (pituitary stalk)
   10. Mammillary bodies
   11. Cranial nerves (12)
       1. Olfactory nerve (I)
       2. Optic nerve (II)
       3. Occulomotor nerve (III)
       4. Trochlear nerve (IV)
       5. Trigeminal nerve (V)
       6. Abducens nerve (VI)
       7. Facial nerve (VII)
       8. Vestibulocochlear nerve (VIII)
       9. Glossopharyngeal nerve (IX)
       10. Vagus nerve (X)
       11. Spinal accessory nerve (XI)
       12. Hypoglossal nerve (XII)
3. Lateral
   1. Lateral fissure (Sylvian)
   2. Brain stem (midbrain, pons, and medulla)
   3. Cerebellum
   4. Central sulcus
   5. Precentral gyrus (primary motor)
   6. Postcentral gyrus (primary sensory)
   7. Lobes of the brain
      1. Frontal lobe
      2. Parietal lobe
      3. Occipital lobe (vision)
      4. Temporal lobe (auditory)
   8. Insular cortex
   9. Superior temporal gyrus (auditory)
4. Midsagittal
   1. Frontal cortex
   2. Parietal cortex
   3. Occipital cortex
   4. Cerebellum
   5. Corpus callosum
   6. Hypothalamus
   7. Thalamus
   8. Pineal gland
   9. Midbrain
   10. Pons
   11. Medulla oblongata
   12. Cingulate gyrus
   13. Fornix
   14. Amygdala
   15. Hippocampus

Subdivisions of the brain and spinal cord

1. Spinal cord
   1. Central grey matter
      1. Posterior (dorsal) horn - sensory (afferent)
      2. Lateral horn - autonomic
      3. Anterior (ventral) horn - motor (efferent) - alpha motor neurons
   2. Peripheral white matter
   3. Reflexes and basic integration
   4. Cervical (8 nerves)
   5. Thoracic (12 nerves)
   6. Lumbar (5 nerves)
   7. Sacral (5 nerves)
   8. Coccygeal (1 nerve)
2. Brain stem
   1. Midbrain
   2. Pons
   3. Medulla oblongata
3. Diencephalon
   1. Thalamus
   2. Hypothalamus
   3. Epithalamus - pineal gland
4. Cerebrum - cerebral hemispheres - telencephalon
   1. Frontal lobe
   2. Parietal lobe
   3. Temporal lobe
   4. Occipital lobe
   5. Six histological layers
   6. Integration of afferent and efferent information
5. Cerebellum
   1. Three histological layers
      1. Molecular layer
      2. Purkinje cell layer
      3. Granule cell layer
   2. Coordinates balance and muscle tone
6. Cranial nerves (12)
   1. Olfactory nerve (I)
   2. Optic nerve (II)
   3. Occulomotor nerve (III)
   4. Trochlear nerve (IV)
   5. Trigeminal nerve (V)
   6. Abducens nerve (VI)
   7. Facial nerve (VII)
   8. Vestibulocochlear nerve (VIII)
   9. Glossopharyngeal nerve (IX)
   10. Vagus nerve (X)
   11. Spinal accessory nerve (XI)
   12. Hypoglossal nerve (XII)

Clinical considerations

Caveats

1. Anterior (ventral) and posterior (dorsal)
2. Ipsilateral and contralateral
3. Anatomical axial view versus clinical axial view

Lesions

Neighborhood effects

Case studies

Multiple sclerosis

Age-related cognitive decline

Study questions

Introduction

The nervous system is a remarkable communication system that can send a message from one part of the body to the brain, react to that message, and produce a response within seconds. The goal of this chapter is to introduce the components and organization of the nervous system. This may be a review for some, but it will set a foundation on which the remainder of the text can be built.

Nervous system organization

The nervous system can be described in two ways: anatomically or functionally. Anatomically, the nervous system is divided into a central component (brain and spinal cord) and a peripheral component (cranial nerves...