The Spinal Cord Spinal Nerves Together with brain
The Spinal Cord & Spinal Nerves • Together with brain forms the CNS • Functions – spinal cord reflexes – integration (summation of inhibitory and excitatory) nerve impulses – highway for upward and downward travel of sensory and motor information
Spinal Cord Protection By the vertebral column, meninges, cerebrospinal fluid, and vertebral ligaments.
Structures Covering the Spinal Cord • Vertebrae • Epidural space filled with fat • Dura mater – dense irregular CT tube • Subdural space filled with interstitial fluid • Arachnoid = spider web of collagen fibers • Subarachnoid space = CSF • Pia mater
External Anatomy of Spinal Cord • Flattened cylinder • 16 -18 Inches long & 3/4 inch diameter • In adult ends at L 2 • In newborn ends at L 4 • Growth of cord stops at age 5 • Cervical enlargement – upper limbs • Lumbar enlargement – lower limbs
Inferior End of Spinal Cord • Conus medullaris – cone-shaped end of spinal cord • Caudae equinae (horse’s tail) – dorsal & ventral roots of lowest spinal nerves
Spinal Cord & Spinal Nerves • Spinal nerves begin as roots • Dorsal or posterior root is incoming sensory fibers – dorsal root ganglion (swelling) = cell bodies of sensory nerves • Ventral or anterior root is outgoing motor fibers
Spinal tap or Lumbar Puncture • Technique – long needle into subarachnoid space – safe from L 3 to L 5 • Purpose – sampling CSF for diagnosis – injection of antibiotics, anesthetics or chemotherapy – measurement of CSF pressure
Gray Matter of the Spinal Cord Note: colors in reverse due to staining of tissue • Gray matter is shaped like the letter H or a butterfly – contains neuron cell bodies, unmyelinated axons & dendrites – paired dorsal and ventral gray horns – gray commissure crosses the midline • Central canal continuous with 4 th ventricle of brain
White Matter of the Spinal Cord • White matter covers gray matter • Contains axons that form ascending & descending tracts
Tracts of the Spinal Cord • Function of tracts – highway for sensory & motor information – sensory tracts ascend – motor tracts descend • Naming of tracts – indicates position & direction of signal – example = anterior spinothalamic tract • impulses travel from spinal cord towards brain (thalamus) • found in anterior part of spinal cord
Spinal Nerves • 31 Pairs of spinal nerves • Named & numbered by the cord level of their origin – 8 pairs of cervical nerves (C 1 to C 8) – 12 pairs of thoracic nerves (T 1 to T 12) – 5 pairs of lumbar nerves (L 1 to L 5) – 5 pairs of sacral nerves (S 1 to S 5) – 1 pair of coccygeal nerves • Mixed sensory & motor nerves
Connective Tissue Coverings • Endoneurium = wrapping of each nerve fibers • Perineurium = surrounds group of nerve fibers forming a fascicle • Epineurium = covering of entire nerve
Endoneurium Perineurium Epineurium
Dermatomes & Myotomes • Each spinal nerve contains both sensory & motor nerve fibers • Dermatome – area of skin supplied by one spinal nerve – overlap prevents loss of sensation if one damaged – sensory anesthesia requires 3 spinal nerves to be blocked • Skin on face supplied by Cranial Nerve V
Dermatomes • Damaged regions of the spinal cord can be distinguished by patterns of numbness over a dermatome region • Spinal cord transection – injury that severs the cord loss of sensation & motor control below the injury
Disorders • Neuritis – inflammation of nerves – caused by injury, vitamin deficiency or poison • Shingles – infection of peripheral nerve by chicken pox virus – causes pain, skin discoloration, line of skin blisters • Poliomyelitis – viral infection causing motor neuron death and possible death from cardiac failure or respiratory arrest
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