Intro to Neuroanatomy

NERVOUS SYSTEM ORGANIZATION

A. NEUROANATOMICAL TERMS

  • Structure of a Typical Neuron   - Nerve Cell (Neuron): Main excitable cell of the nervous tissue     - Cell Body (Soma): The location of the neuron is dependent on this structure.     - Axon: Processes carrying impulses away from the soma; can be myelinated or unmyelinated.     - Dendrites: Processes carrying impulses toward the soma.   - Glial Cells: Supporting cells of the nervous system     - PNS: Schwann cells     - CNS: Oligodendrocytes   - Synapse (Synaptic Gap): Site of communication between neurons, where chemical neurotransmitters are released.   - Myelin: Lipoprotein produced by glial cells that forms a sheath around the axon; myelin sheath acts as an electrical insulator, increasing nerve conduction velocity.

B. DIVISIONS OF THE NERVOUS SYSTEM

  • Central Nervous System (CNS): Composed of the brain and spinal cord; integrates information passing to and from the periphery.

  • Peripheral Nervous System (PNS): All nervous system parts except the CNS.

COMPONENTS OF THE PNS

  • Divisions:   - Cranial Nerves: Emanate from the brain.   - Spinal Nerves: Emanate from the spinal cord.   - Associated Ganglia: Collections of nerve cell bodies.

C. AUTONOMIC NERVOUS SYSTEM

  • Components: Arises from both CNS and PNS; regulates the internal environment outside conscious control.   - Divisions: Sympathetic and Parasympathetic.

D. WHITE VS. GRAY MATTER

  • White Matter: Composed predominantly of myelinated axons, giving it a lighter appearance. White matter structures include:\   - Examples:     - Corona Radiata: Fan-like sheet connecting to/from the cerebral cortex.     - Peduncle: Connects different CNS areas (e.g., Cerebellar peduncles connect cerebrum to the brainstem).     - Funiculus: Bundle of nerve fibers for spinal cord divisions.     - Tracts: Nerve fiber bundles with common origins and terminations.

  • Gray Matter: Composed of unmyelinated somas, denser and darker appearance; localized primarily in the brain and spinal cord regions.

E. ASCENDING AND DESCENDING TRACTS

  • Naming Convention: First part indicates origin, second indicates termination (e.g., Lateral corticospinal tract: origin – cerebral cortex, termination – spinal cord).   - Ascending tracts carry impulses to the brain (e.g., Lateral spinothalamic tract for pain).   - Descending tracts carry impulses from the brain (e.g., Lateral corticospinal tract for motor function).

CNS: BRAIN

A. BRAIN DIVISIONS

  • Three Major Divisions:   - Forebrain: Cerebrum (Outer cerebral cortex, inner white matter, basal nuclei) and Diencephalon (Thalamus, Hypothalamus, Epithalamus).   - Midbrain: Connects forebrain and hindbrain.   - Hindbrain: Composes of the Pons, Cerebellum, and Medulla Oblongata.   - Development from the embryonic neural tube.

B. FUNCTIONAL & BRODMANN AREAS

  • Brodmann's Areas: 47 distinct areas based on cytoarchitecture; each area tied to specific neurological functions.   - Examples of Functional Areas:     - Motor (Area 4): Primary motor cortex on the precentral gyrus.     - Somatosensory (Areas 3,1,2): Primary somatosensory cortex on the postcentral gyrus.     - Visual (Area 17): Located around the calcarine fissure.     - Auditory Areas (Areas 41,42): Located in the anterior transverse temporal gyrus.

CNS: BRAINSTEM

A. DIVISION OF BRAINSTEM

  • Composed of:   - Midbrain: Contains colliculi.   - Pons: Connects with the cerebellum.   - Medulla Oblongata: The lowest part, containing the 4th ventricle.

B. NEURAL TUBE DEVELOPMENT

  • Development involves a split into dorsal (sensory nuclei) and ventral (motor nuclei) plates.

C. BRAINSTEM REGIONS

  • Divided into:   - Tectum: Roof of the midbrain.   - Tegmentum: Covering with cranial nerve nuclei.   - Base: Contains the basis with various tracts.

D. PARTS OF BRAINSTEM (CROSS-SECTIONAL)

  • Cross-sectional anatomy identified through notable frameworks involving white tracts and nuclei located in each region, which are visualized by staining mechanisms of myelin.

E. RETICULAR FORMATION

  • Consists of a complex network of nuclei that manage crucial autonomic and reflexive functions, regulating essential life-sustaining functions.

F. BRAINSTEM RULE OF “4”

  • A mnemonic aiding in localization of brainstem lesions:   - 4 Medial Structures (Motor pathways, Medial lemniscus, Motor nuclei)   - 4 Side Structures (Spinothalamic pathway, Sensory nuclei)   - 4 CNs above, at, and below the pons.

CNS: SPINAL CORD

A. EXTERNAL FEATURES

  • Extends from the foramen magnum to lower border of L1 vertebra; contains cervical and lumbar enlargements.

B. DEVELOPMENTAL CHANGES

  • Spinal cord growth differs from vertebral column, leading to termination levels moving over a lifetime (L2-L3 at birth, L1-L2 in adults).

C. SPINAL NERVES

  • Includes all pairs that exit intervertebral foramina, differentiating cervical nerves as emerging above corresponding vertebrae, with the notable exception of C8.

D. CROSS-SECTIONAL ANATOMY

  • White Matter: Surrounds gray matter; composed of nerve fibers organized into tracts.

  • Gray Matter: Centralized regions categorized into dorsal and ventral horns with additional lateral horns.

E. REXED LAMINAE

  • Gray matter organized into distinct laminae identified by function and structure.

NEUROANATOMICAL LOCALIZATION

A. STEPS IN CLINICAL NEUROLOGIC DIAGNOSIS

  1. Recognition of impairment.

  2. Identification of affected nervous systems site.

  3. Etiology evaluation with differential diagnoses.

  4. Use ancillary diagnostic procedures for confirmation.

B. RECOGNITION OF IMPAIRED FUNCTION

  • Relies on comprehensive history taking and physical neurological examination.

C. THE KEY TO LOCALIZATION

  • Understanding structure morphology and functional representation.

D. ASCENDING AND DESCENDING TRACTS

  • Lesion presentations correlating with affected structures and nearby pathways of sensory and motor functions.

E. SYSTEMS, PATHWAYS, & FIBER TRACTS

  • Different systems can exhibit overlapping symptoms depending on their pathways.

REVIEW QUESTIONS

  1. Identify the type of tract for the lateral corticospinal tract. (Answer: Descending)

  2. Which structure controls the autonomic nervous system? (Answer: Hypothalamus)

  3. What is the largest part of the human brain? (Answer: Cerebrum)

  4. Where is the trigeminal ganglion located? (Answer: Peripheral nervous system)

  5. In which division does the Thalamus belong? (Answer: Forebrain)

  6. Which structure separates the frontal and parietal lobes? (Answer: Central Sulcus)

  7. Where is the Red Nuclei found? (Answer: Rostral Midbrain)

REFERENCES

  • Splittgerber, R. et al (2019). Snell's Clinical Neuroanatomy.

  • Haines, D. E. (2015). Neuroanatomy in Clinical Context.

  • Gilman, S. and Newman, S. W. (2003). Essentials of Clinical Neuroanatomy.

  • Brazis, P.W. et al. (2016). Localization in Clinical Neurology.