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12 Cards in this Set
- Front
- Back
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Structure of the spinal cord |
• Spinal Cord- a cylinder of nervous tissue that arises from the brainstem at the foreman magnum of the skull • 31 pairs of spinal cord • Anterior and posterior grooves (anterior median fissure/posterior median sulcus) • Cervical region / 7 vertebrae • Thoracic region/ 12 vertebrae • Lumbar region/ 5 vertebrae • Sacral region(Cord ends at saccrum) • In two places the cord is a little thicker than everywhere else: o Inferior cervical region, a cervical enlargement gives rise to nerves of the upper limbs. o In the lumbosacral region, there is a similar lumbar enlargement that issues nerves to the pelvic region and lower limbs. • Medullary cone (Conus medullaris): Area inferior to the lumbar enlargement, the cord tapers to a point. • Cauda Equina: arises from the lumbar enlargement and medullary cone, a bundle of nerve roots that occupy the vertebral canal from L2-L5; named for resemblance to horse tail; innervates the pelvic organs and lower limbs. • Meninges: three fiberous membranes that enclose the spinal cord and brain. o Membranes separate the soft tissue of the nervous system from the bones of the vertebrae and skull. o Superficial-Deep: Dura Mater/Arachnoid Mater/ Pia Mater • Dura Mater forms dural sheath ▪ Dural sheath: Loose-fitting sleeve o Tough, Collagenous, bout as thick as rubber kitchen glove o Epidural Space: space between the sheath and the vertebral bones; occupied by blood vessels, adipose tissue, and loose connective tissue. • Arachnoid Mater : o Simple Squamous epithelium o Arachnoid membrane o Adhering to the inside of the dura o Loose mesh of collagenous and elastic fibers spanning the gap between the arachnoid membrane and the Pia Mater ▪ Subarachnoid Space: filled with cerebrospinal fluid (CSF) (The Gap mentioned above) • Inferior to the medullary cone; called the Lumbar Cistern; occupied by the cauda equina and CSF • Pia Mater o Delicate, transparent membrane that closely follows the contours of the spinal cord. Continues beyond the medullary cone as a fibrous strand, the Terminal Filum, within the Lumber cistern. o At the vertebra S2, it exits the lower end of the cistern and fuses with the Dura mater and the two forms a coccygeal ligament that anchors the cord and menegies to vertebra col. o At regular intervals along the cord, extensions of the pia called denticulate ligaments extend through the arachnoid to the dura, anchoring the cord and limiting side-to-side movements. • The Spinal Cord consists of TWO kinds of nervous tissue. o Gray Matter ▪ Relatively dull color because it contains very little myelin. ▪ Contains: Somas, Dendrites, and Proximal parts of the axons of neurons. ▪ Site of the synaptic contact between neurons, and therefore the site of all neutral integration in the spinal cord. o White Matter ▪ Bright, pearly white appearance due to an abundance of myelin. ▪ Composed of: bundles of axons, called tracts, that carry signals from one level of the CNS to another. o Both gray and white matters also have an abundance of glial cells. • Nervous tissue is often histologically stained with silver compounds, which give the gray matter a brown or golden color; white matter a lighter to tan to amber color. |
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Pathway of information in gray matter of the spinal cord |
• Near its attachment to the spinal cord, a spinal nerve branches into a posterior (dorsal) root and anterior (ventral) root. The posterior root carries sensory nerve fibers, which enter the posterior horn of the cord and sometimes synapse with an interneuron there. Such interneurons are especially numerous in the cervical and lumbar enlargements and are quite evident in histological sections at these levels. The anterior horns contain the large somas o the somatic motor neurons. Axons from these neurons exit by way of the anterior root of the spinal nerve and lead to the skeletal muscles. • An additional lateral horn is visible on both sides of gray matter. o Contains neurons of the sympathetic nervous system, which send their axons out of the cord by way of the anterior root along with the somatic efferent fibers. |
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Possible pathway of information in white matter |
• Consists of bundles of axons that course up and down the cord and provide avenues of communication between different levels of CNS. These bundles are arranged in three pairs called columns or funiculi, a posterior (dorsal), lateral, and anterior (ventral) column. • Each column consists of subdivisions called tracts or fasciculi |
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Gracile fascilus |
• Gracile Fasciculus: • Carries signals from the midthoracic and lower parts of the body • Consists of: first order of nerve fibers that travel up the ipsilateral side of the spinal cord and terminate at the gracile nucleus in the medulla oblongata of the brain stem. • These fibers carry signals for: vibration, visceral pain, deep and in the medulla oblongata of the brain stem. • These fibers carry signals for: vibration, visceral pain, deep and discriminative touch (touch whose location one can precisely identify), and especially proprioception from the lower limbs and lower trunk. • Decussation: In Medulla • Functions: Sensations of the limb and trunk position and movement, deep touch, visceral pain, and vibration, below level T6 • Ascending tract • Contralateral • If damaged: trouble with functioning the lower body. |
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Cortospinal |
• Carry motor signals from the cerebral cortex for precise, finely coordinated limb movements. The fibers of the system form ridges called pyramids on the anterior surface of the medulla oblongata, so these tracts were once called pyramidal tracts. • Lateral Corticospinal; contralateral side i. Decussation: In Medulla ii. Functions: Fine control of limbs • Anterior Corticospinal ;ipsilateral side i. Fibers of the anterior side decussate lower in the cord, they even control contralateral muscles. ii. Decussation: In Spinal Cord iii. Functions: Fine control of limbs • Contralateral • If damaged: trouble with fine motor functioning |
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Lateral reticulospinal |
• Originate in the reticular formation is the brainstem. They control muscles of the upper and lower limbs, especially to maintain posture and balance. They also contain descending analgesic pathways that reduce the transmission of pain signals to the brain. • Ipsilateral • Functions: Balance, posture; regulation of awareness and pain |
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Spinothalamic |
• Decussation: In the Spinal Cord • Functions: Sensations of light touch, tickle, itch, temperature, pain and pressure. • Contralateral • Along with other smaller tracts for the anterolateral system, this passes up the anterior and lateral columns of the spinal cord. The Spinothamalic tract carries signals: • Pain, temperature, pressure, tickle, itch, and light or crude touch • Light touch: the sensation produced by stroking hairless skin with a feather or cotton wisp, without indenting the skin. • Crude touch is touch whose location one can only vaguely identify. |
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5. A survivor of a car accident can move her limbs and feel when they are moving, but she can’t feel temperature or tell if someone is touching her. Which tract might be affected? |
Spinothalamic |
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What is a nerve |
A cord like organ composed of numerous axons bound together by connective tissue |
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Anterior root |
Motor |
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Anterior root |
Motor |
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Posterior |
Sensory |
