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Spinal Cord Anatomy

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Spinal Cord Anatomy

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    1. Spinal Cord Anatomy AP 150 Chapter 12

    3. Meninges Connective tissue membranes Dura mater: outermost layer; continuous with epineurium of the spinal nerves Arachnoid mater: thin and wispy Pia mater: bound tightly to surface Forms the filum terminale anchors spinal cord to coccyx Forms the denticulate ligaments that attach the spinal cord to the dura Spaces Epidural: external to the dura Anesthestics injected here Fat-fill Subdural space: serous fluid Subarachnoid: between pia and arachnoid Filled with CSF

    4. Cross Section of Spinal Cord Anterior median fissure and posterior median sulcus deep clefts partially separating left and right halves Gray matter: neuron cell bodies, dendrites, axons Divided into horns Posterior (dorsal) horn Anterior (ventral) horn Lateral horn White matter Myelinated axons Divided into three columns (funiculi) Ventral Dorsal lateral Each of these divided into sensory or motor tracts

    5. Cross section of Spinal Cord Commissures: connections between left and right halves Gray with central canal in the center White Roots Spinal nerves arise as rootlets then combine to form dorsal and ventral roots Dorsal and ventral roots merge laterally and form the spinal nerve

    6. Organization of Spinal Cord Gray Matter Recall, it is divided into horns Dorsal, lateral (only in thoracic region), and ventral Dorsal half sensory roots and ganglia Ventral half motor roots Based on the type of neurons/cell bodies located in each horn, it is specialized further into 4 regions Somatic sensory (SS) - axons of somatic sensory neurons Visceral sensory (VS) - neurons of visceral sensory neur. Visceral motor (VM) - cell bodies of visceral motor neurons Somatic motor (SM) - cell bodies of somatic motor neurons

    7. Gray Matter: Organization

    8. White Matter in the Spinal Cord Divided into three funiculi (columns) posterior, lateral, and anterior Columns contain 3 different types of fibers (Ascend., Descend., Trans.) Fibers run in three directions Ascending fibers - compose the sensory tracts Descending fibers - compose the motor tracts Commissural (transverse) fibers - connect opposite sides of cord

    9. White Matter Fiber Tract Generalizations Pathways decussate (most) Most consist of a chain of two or three neurons Most exhibit somatotopy (precise spatial relationships) All pathways are paired one on each side of the spinal cord

    10. White Matter: Pathway Generalizations

    11. Descending (Motor) Pathways Descending tracts deliver motor instructions from the brain to the spinal cord Divided into two groups Pyramidal, or corticospinal, tracts Indirect pathways, essentially all others Motor pathways involve two neurons Upper motor neuron (UMN) Lower motor neuron (LMN) aka anterior horn motor neuron (also, final common pathway)

    12. Pyramidal (Corticospinal) Tracts Originate in the precentral gyrus of brain (aka, primary motor area) I.e., cell body of the UMN located in precentral gyrus Pyramidal neuron is the UMN Its axon forms the corticospinal tract UMN synapses in the anterior horn with LMN Some UMN decussate in pyramids = Lateral corticospinal tracts Others decussate at other levels of s.c. = Anterior corticospinal tracts LMN (anterior horn motor neurons) Exits spinal cord via anterior root Activates skeletal muscles Regulates fast and fine (skilled) movements

    13. Corticospinal tracts

    14. Extrapyramidal Motor Tracts Includes all motor pathways not part of the pyramidal system Upper motor neuron (UMN) originates in nuclei deep in cerebrum (not in cerebral cortex) UMN does not pass through the pyramids! LMN is an anterior horn motor neuron This system includes Rubrospinal Vestibulospinal Reticulospinal Tectospinal tracts Regulate: Axial muscles that maintain balance and posture Muscles controlling coarse movements of the proximal portions of limbs Head, neck, and eye movement

    15. Extrapyramidal Tract

    16. Extrapyramidal (Multineuronal) Pathways Reticulospinal tracts originates at reticular formation of brain; maintain balance Rubrospinal tracts originate in red nucleus of midbrain; control flexor muscles Tectospinal tracts - originate in superior colliculi and mediate head and eye movements towards visual targets (flash of light)

    17. Main Ascending Pathways The central processes of first-order neurons branch diffusely as they enter the spinal cord and medulla Some branches take part in spinal cord reflexes Others synapse with second-order neurons in the cord and medullary nuclei

    18. Three Ascending Pathways The nonspecific and specific ascending pathways send impulses to the sensory cortex These pathways are responsible for discriminative touch (2 pt. discrimination) and conscious proprioception (body position sense). The spinocerebellar tracts send impulses to the cerebellum and do not contribute to sensory perception

    19. Nonspecific Ascending Pathway Include the lateral and anterior spinothalamic tracts Lateral: transmits impulses concerned with pain and temp. to opposite side of brain Anterior: transmits impulses concerned with crude touch and pressure to opposite side of brain 1st order neuron: sensory neuron 2nd order neuron: interneurons of dorsal horn; synapse with 3rd order neuron in thalamus 3rd order neuron: carry impulse from thalamus to postcentral gyrus

    20. Specific and Posterior Spinocerebellar Tracts

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