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2 Cards in this Set
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Describe the gross and microscopic structure of the spinal cord.
(Ch. 12 Obj. 19) |
Approx. 18” long (ends at lumbar 1-2)
Cervical & lumbar enlargements: Enlargements in cervical and lumbosacral regions where nerves serving upper and lower limbs arise. Conus medullaris: spinal cord terminates in a tapering cone-shaped structure. Cauda equina: (Horses tail) collection of nerve roots at inferior end of vertebral canal. During fetal development, vertebral column grows faster than the spinal cord. Filum terminale: fibrous extention of conus covered by pia mater, extends from conus medullaris to coccyx, where it anchors spinal cord in place. Spinal nerves (roots) (31) Anterior median fissure & posterior median sulcus (Fig. 12.31) Gray matter: Gray commissure: connects horns and encloses central canal. Anterior horns: Somatic motor nuclei lateral horns: in (thoracic and superior lumbar segments) Visceral motor nuclei Posterior horns: Somatic & visceral sensory nuclei From anterior to posterior horns: SS, VS, VM, SM White matter * Anterior, lateral & posterior funiculus (columns) Spinal meninges (Fig. 12.30) Spinal dural (mater) sheath: not attached to bony walls of vertebral column. Outer most layer. Epidural space: Between dural sheath and bony vertebrae is soft padding of fat and network of veins. * Epidural block:Dermatomes: For example, a thoracic epidural may be performed for upper abdominal surgery, but may not have any effect on the perineum (area around the genitals) or bladder.[9] Nonetheless, giving very large volumes into the epidural space may spread the block both higher and lower. Arachnoid * Subdural space: artificial space created by the separation of the arachnoid mater from the dura mater as the result of trauma, pathologic process, or the absence of cerebrospinal fluid as seen in a cadaver. * Subarachnoid space: CSF fills the subarachnoid space between the arachnoid and pia mater meninges. * Lumbar tap: The dural and arachnoid extend to the level of S2 (the cord ends at L1 or L2), There is little or no chance of damage to cord in this area. * Meningitis: inflammation of the protective membranes covering the brain and spinal cord, known collectively as the meninges. Pia mater: spinal cord is secured to the tough dura mater meninx throughout its length by saw-tothed shelves of pia mater called denticulate ligaments |
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List the major spinal cord tracts, and classify each as a motor or sensory tract.
(Ch. 12 Obj. 20) |
Neuronal composition:
1st order neurons: cell bodies in ganglion conduct impulses from cutaneous receptors and proprioceptors to spinal cord or brain stem. 2nd order neurons: cell bodies in dorsal horn of spinal cord or in medularry nuclei, transmit impulses to thalamus or to cerebellum where they synapse. 3rd order neurons: cell bodies in thalamus, conduct impulses to the somatosensory cortex of the cerebrum. Main ascending: Nonspecific ascending pathways: (anterolateral pathways because located in anterior and lateral white area of spinal cord) are formed by lateral and anterior spinothalamic tracts. Most transmit pain, temp, and coarse touch impulses, sensations that we're aware of but have trouble localizing precisely on the body surface. Specific ascending pathways: (medial lemniscal system) mediate precise, straight-through transmission of inputs from a single type of sensory receptor that can be localized precisely on the body surface, such as discriminate touch and vibration. Formed by paired tracts of dorsal white column – fasciculus cuneatus and fasciculus gracilis. Spinocerebellar tracts: (anterior and posterior spinocerebellar tracts) convey info about muscle tone or tendon stretch to cerebellum. Main descending pathways and tracts: Direct (pyramidal) system: Pyramidal (corticospinal) tracts: originate mainly in pyramidal neurons located in precentral gyri. Axons descend w/out synapsing from the pyramidal neurons to the spinal cord. Stimulations of the ventral horn neurons activates the skeletal muscles with which they're accociated. Primarily regulates fast and fine movements like needlework and typing. Indirect (extrapyramidal) system: all other besides pyramidal tracts but some can be influenced by pyramidal tracts, hence calling them indirect. Regulate balance and posture, coarse limb movements, head neck and eye movements that follow objects in visual field. Many activities are heavily dependent on reflex activity. Reticulospinal and vestibulospinal tracts: maintain balance by varying tone of postural muscles. Rubrospinal tracts: control flexor muscles Tectospinal tracts: and the superior colliculi (eye movement) mediate head movements in response to visual stimuli. |
