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UWL BIO 312 - Nervous system V: spinal cord

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Lecture 12 Lecture Outline:I Spinal corda. Anatomyb. Physiologyc. 4 main ascending somatosensory pathwaysi. Dorsal column (fasciculis cuneatus, fasciculis gracilis)ii. Lateral spinothalamic tractiii. Anterior spinothalamic tractiv. Spinocerebellar tractd. Descending tractsi. Pyramidal systemii. Extrapyramidal systeme. Referred painCurrent Lecture:Spinal Cord Anatomy:- White Matter: consists of myelinated axons forming ascending and descending tractso Horns of gray matter divides white matter into dorsal and ventral columns/funiculio Each column consists of distinct bundles of axons called tracts Each tract is composed of axons having similar origin, destination, and functiono Ascending tracts: composed of axons either 1st or 2nd order neurons carrying sensory info up the spinal cord High degree of segregation of modalities into specific tractso Descending tracts: composed of axons of motor neurons that carry signals from brain down spinal cord Synapse on motor neurons in lateral and ventral hornso Decussation: the crossing over of sensory reception from one side of the body to the opposite side of the braino Ipsilateral: same side of the body relative to the stimulus energyo Contralateral: opposite side of the body relative to the stimulus energySpinal cord physiology:Ascending tracts:- White matter consists of 5 or 6 major ascending tracts on each side of the SC (4 carry somatosensory info)- Dorsal column pathway: consists of tracts focused on high resolution touch, pressure, vibration, proprioceptiono Fasciculis cuneatus: focuses on fine touch/pressure from dermatomes at T6 and above (upper chest and upper extremities)o Fasciculis gracilis: focuses on fine touch/pressure from below T6o 1st order neuron enters spinal cord and travels ipsilaterally up to the medulla oblongata through the fasciculis cuneatus or gracilis depending on where the stimulus energy originatedo 2nd order neuron synapses with the 1st and decussates before traveling contralaterally through the mid-braino 3rd order neurons synapse with the second at the ventral nuclei in thalamus and travel to the appropriate area of the somatosensory cortexBio 312- Lateral Spinothalamic tract: focused on temperature and paino Sensory info travels to the spinal cord and enters through the dorsal root and immediately synapses with the second order neurono 2nd order neuron immediately decussates and ascends through the contralateral lateral spinothalamic tracto 3rd order neuron synapses with the 2nd order neuron in the thalamus where it branches and travels to the appropriate area of the somatosensory cortex- Anterior Spinothalamic tract: focused on crude/low resolution touch and pressureo Synapses follow same pattern of lateral spinothalamic tract- Spinocerebellar tracts: focused on subconscious proprioception, composed of posterior and anterior tractso Travels to cerebellum and helps us perform smooth coordinated movementsDescending tracts: - Pyramidal system = Corticospinal tracts- Extrapyramidal system: all other spinal tracts, involuntary muscle control- Corticospinal tracts: involved in voluntary skeletal muscle contractiono Left side muscles are controlled by right side somatosensory cortex- Spastic paralysis: occurs from damage to coricospinal tracts (upper motor neurons), cannot voluntarily contract muscle (can reflexively)- Flaccid paralysis: occurs form damage to motor neuron outside of spinal cord (lower motor neurons), muscle cannot contract at all- Suppose right side of cord at level T10 is severed:o Would lose fine touch and pressure sensation from right leg (does not decussate until medulla)o Would lose pain, temperature, and crude touch and pressure from left leg (immediately decussates)Referred Pain: pain sensed in a region of body inappropriate to actual nociceptive stimulus- Classic example is right shoulder and arm pain felt during cardiac arrest- Most commonly sensed in skin when internal organ being affected- Dermatome rule: area of skin to which pain is referred is innervated by same spinal segments as is the affected organo Convergence theory: brain gets used to sensory information coming from a certain location and automatically assigns the same response from that dermatome (regardless of specific location)- Projected Pain: (phantom limb pain) pain or sensation felt in a missing limb or area of the bodyo Explained by law of projection, doctrine of specific nerve energieso More common following losing limb in trauma than surgical amputationo Stimulus energy being perceived further up the nerve but brain assumes sensation is coming from the distal portion of the


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UWL BIO 312 - Nervous system V: spinal cord

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