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Neuroanatomy Overview: Key Concepts

Jul 16, 2024

Neuroanatomy Overview: Key Concepts

Basics of Neuroanatomy

  • Gray Matter: Group of cell bodies. Found in the CNS as nuclei and in the PNS as ganglia.
  • White Matter: Group of axons surrounded by myelin sheath, giving a white color. Found in CNS as tracts and in PNS as nerves.
  • Neurons: Composed of cell bodies (pericarya), axons, and dendrites.
    • Types of neurons based on poles: multipolar, bipolar, pseudo-unipolar, anaxonic, and apolar neurons.
  • Supporting Cells:
    • CNS: Oligodendrocytes (myelination), astrocytes, microglia, ependymal cells.
    • PNS: Schwann cells (myelination), satellite cells.
  • Myelination Cells: CNS (Oligodendrocytes) and PNS (Schwann cells).

Brain Vesicles

  • Development begins at week 4.
  • Three primary vesicles: prosencephalon (forebrain), mesencephalon (midbrain), rhombencephalon (hindbrain).
  • Prosencephalon develops into telencephalon (cerebral hemispheres, lateral ventricles) and diencephalon (thalamus, hypothalamus, third ventricle).
  • Rhombencephalon develops into metencephalon (pons, cerebellum) and myelencephalon (medulla oblongata).

Nervous Tissue Structures

  • Neuronal Tissue Proper: Contains neurons.
  • Specialized Connective Tissue: Glial cells such as astrocytes, oligodendrocytes.
  • Ordinary Connective Tissue: Meninges (dura mater, arachnoid mater, pia mater).

Neuronal Classifications

  • Based on Poles:
    • Unipolar
    • Bipolar
    • Pseudo-unipolar
    • Multipolar
  • Based on Functions:
    • Sensory neurons
    • Motor neurons
    • Interneurons
    • Autonomic neurons

Synaptic Organization of White Matter Fibers

  • Association Fibers: Connect cortical regions within the same hemisphere.
  • Projection Fibers: Connect higher to lower centers and vice versa (e.g., corticospinal tract, internal capsule).
  • Commissural Fibers: Connect identical structures on both sides (e.g., corpus callosum).

Blood Supply to the Brain

  • Primarily through two systems: vertebrobasilar and internal carotid systems.
  • Circle of Willis: Formed by the union of the vertebrobasilar and internal carotid systems, located at the base of the brain.
  • Key arteries: anterior cerebral, middle cerebral, posterior cerebral, anterior communicating, and posterior communicating arteries.

Basal Ganglia

  • Key structures: corpus striatum (caudate nucleus, lentiform nucleus), claustrum, substantia nigra, subthalamus.
  • Lentiform Nucleus: Divided into putamen and globus pallidus (external and internal).
  • Associated disorders:
    • Caudate Nucleus: Chorea
    • Globus Pallidus: Athetosis
    • Subthalamic Nucleus: Hemiballismus
    • Hepatolenticular Degeneration: Wilson's Disease (copper deposition).

Thalamus and Hypothalamus

  • Thalamus: Sensory relay station, involved in motor and sensory signal transmission.
  • Hypothalamus: Autonomic control, links the nervous system to the endocrine system via the pituitary gland.
  • Walls of the Third Ventricle:
    • Anterior Wall: Rostrum, anterior commissure, lamina terminalis.
    • Floor: Optic chiasma, tuber cinereum, mammillary bodies, posterior perforated substance.
    • Roof: Fornix, choroid plexus.
    • Posterior Wall: Habenular commissure, pineal recess, posterior commissure.

Midbrain

  • External Features: Contains superior and inferior colliculi (dorsal), cerebral peduncles (ventral).
  • Internal Features: Divided into tectum (colliculi), tegmentum (contains red nucleus, substantia nigra), and basis pedunculi (crus cerebri).

Pons

  • External Features: Ventral median sulcus, dorsal contains nuclei of cranial nerves V, VI, VII, VIII.
  • Posterior Features: Facial colliculi, striae medullares.

Medulla Oblongata

  • External Features: Pyramids (ventral), olives (lateral).
  • Dorsal Features: Gracile and cuneate tubercles.

Cerebellum

  • Anatomy: Two hemispheres and a central vermis; divided into anterior, posterior, and flocculonodular lobes. Connected to the brainstem via the superior, middle, and inferior cerebellar peduncles.
  • Functions: Coordination, precision, and accurate timing of movements; maintains balance and posture.

Cranial Nerves

  • Total: 12 pairs, numbered I-XII.
    • I: Olfactory (smell)
    • II: Optic (vision)
    • III: Oculomotor (eye movements, pupil constriction)
    • IV: Trochlear (eye movements)
    • V: Trigeminal (facial sensation, mastication)
    • VI: Abducens (eye movements)
    • VII: Facial (facial expression, taste)
    • VIII: Vestibulocochlear (hearing, balance)
    • IX: Glossopharyngeal (taste, swallowing)
    • X: Vagus (autonomic functions, taste)
    • XI: Accessory (shoulder and neck muscles)
    • XII: Hypoglossal (tongue movements)

Spinal Cord

  • Length: Approximately 45 cm in adults (ends at L1-L2); longer in children (ends at L3).
  • Segments: 31 pairs of spinal nerves: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal.
  • Enlargements: Cervical, lumbar, and conus medullaris (lower end, gives rise to cauda equina).
  • Pathways/Tracts:
    • Ascending (sensory):
      • Dorsal Columns (Gracile and Cuneate): Fine touch, vibration, proprioception.
      • Spinothalamic: Pain, temperature, crude touch, pressure.
      • Spinocerebellar: Proprioception.
    • Descending (motor):
      • Corticospinal (lateral and anterior): Voluntary motor control.
      • Extrapyramidal tracts: Involuntary control (reticulospinal, rubrospinal, vestibulospinal, olivospinal).

These notes serve as a comprehensive overview of critical concepts in neuroanatomy, useful for preparing for exams and understanding the structural and functional organization of the nervous system.

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