20.10
La moelle épinière
La moelle spinale est la principale région nerveuse du système nerveux central du corps, communiquant des informations sensorielles afférentes de la p…
- [Instructrice] La moelle épinière est un cylindre épaisde tissu nerveux qui comprendune partie du système nerveux central,transmettant des informations sensorielles afférentesde la périphérie au cerveauet des informations motrices efférentesdu cerveau à la périphérie. En coupe transversale,la matière grise à l'intérieur de la moelle épinièreest en forme de papillon. La corne ventrale de la matière grisecontient les neurones moteurs.
Il est entouré de matière blanche avec des groupes d'axonesdes voies à la fois ascendantes et descendantes. Au centre se trouve un canal centralcontenant le liquide céphalo-rachidienqui nourrit le tissu nerveux. Le cordon lui-même est entouré de membranes,les méninges rachidiennes, qui incluent les pachyméninges.
Connectée au tronc cérébral,la moelle épinière traverse le trou occipitalet la série d'os de la colonne vertébralejusqu'à la terminaison du niveau lombaire L1, deux,et forme un long faisceau de nerfsappelé queue-de-cheval. Elle est subdivisée en niveaux ou régions,déterminés par la position des vertèbres,avec des nerfs spinaux appariés. Par exemple, la colonne cervicale, région C2 à C7,correspond aux nerfs innervant le cou,les épaules, les bras et les mains.
Dans chaque vertèbre, des paires de racines nerveusessortent par le trou vertébral en branches distinctes. La racine du nerf ventral aiguille les musclesdans le contrôle du mouvement,tandis que la racine du nerf dorsal innerve la peaudans la transmission de la sensation. Chaque zone de la peau innervée parun nerf spinal spécifique est appelée dermatomeet représentée par les cartes de dermatome.
Ces cartes permettent aux cliniciens d'identifierl'origine d'une douleur ou affection cutanée quelconque.
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Q1: What are the main structural components of the spinal cord?
The spinal cord contains gray matter in the center, appearing butterfly-shaped in cross-section, surrounded by white matter. The gray matter includes dorsal horns that relay sensory information and ventral horns containing motor neurons. A central canal runs through the middle, containing cerebrospinal fluid that nourishes nervous tissue. Three protective membranes, the spinal meninges, surround the entire cord.
Q2: How does the spinal cord transmit information between the brain and body?
The spinal cord communicates afferent sensory information from the periphery to the brain and efferent motor information from the brain to the periphery. Dorsal nerve roots convey sensation to the spinal cord, while ventral nerve roots target skeletal muscle to control movement. This bidirectional communication allows the central nervous system to receive sensory input and send motor commands throughout the body.
Q3: Where does the spinal cord begin and end in the vertebral column?
The spinal cord connects at the brain stem and runs through the foramen magnum at the base of the skull. It extends downward through the vertebral column and terminates at the lumbar level between L1 and L2 vertebrae. Below this termination point, a bundle of nerves called the cauda equina continues downward through the vertebral canal.
Q4: What are dermatomes and why are they clinically important?
Dermatomes are areas of skin supplied by a peripheral nerve from a single dorsal root ganglion. Each spinal cord segment innervates a specific body region represented as a dermatome on dermatome maps. Clinicians use these maps to identify the origin of pain or skin conditions and to localize spinal cord lesions or peripheral nerve root damage, though adjacent dermatomes overlap considerably.
Q5: How is the spinal cord organized into regions and nerve pairs?
The spinal cord is divided into four regions and segmentally organized with 31 pairs of spinal nerves: eight cervical, 12 thoracic, five lumbar, five sacral, and one coccygeal. Each region corresponds to vertebral levels. For example, cervical regions C2 to C7 innervate the neck, shoulders, arms, and hands. Paired spinal nerves exit through vertebral foramina at each level.
Q6: What is the function of white matter in the spinal cord?
White matter surrounds the gray matter and contains large numbers of myelinated axon fibers arranged into longitudinal bundles called dorsal, lateral, and ventral columns. These columns form ascending and descending tracts that carry sensory and motor information between the brain and peripheral nervous system, enabling communication throughout the central nervous system.
Q7: How do ventral and dorsal nerve roots differ in function?
Ventral nerve roots contain motor axons that target skeletal muscles to control movement and motor function. Dorsal nerve roots contain sensory axons that innervate the skin to convey sensation and sensory information. This functional separation allows the spinal cord to simultaneously process motor commands and sensory input from different body regions.