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Cerebellum *2 hemispheres *integration, coordination, & execution of multi-joint movements *controls balance, posture maintenance, & complex muscular movements *well protected Brain Stem *located between cerebrum and SC *function is relay station *3 regions of brain stem - midbrain, pons, medulla oblongata Midbrain *relay station between the cerebrum & SC (deep, older area of brain) *important in reflex including righting of head and auditory reflexes - turn eyes and head toward sound, etc.c Pons * means bulge *fibers run between cerebellum and rest of CNS *important for balance, equilibrium, coordination movement Medulla Oblongata *control center for heart and breathing rate *decussation (crossing) of motor & sensory neurons occur here *contains Reticular Activating System - adjusts levels of arousal & sleep/awake cycle Foramen Magnum Large opening at base of skull just below medulla oblongata boundary between brain stem and SC Spinal Column *protects SC *cord extends down to level of L1 (18.5") *early in development SC is same length as column. then lengthens while cord does not lengthen as much *nerve roots leaving the SC at thoracic & lumbar levels must descend 2 levels before exiting the column Spinal Cord 2 enlargements with narrowing in middle SC is larger at top than bottom because nerves join SC as it ascends 1st SC Enlargement C3 - T2 majority of injuries occur here - less stop wider here due to many sensory & motor neurons coming from UE's SC Narrowing Area thoracic area relatively few motor & sensory neurons from this area 2nd SC Enlargement L1 - S3 wider because of sensory & motor neurons from LE's majority of injuries here affecting LE - less "slop" Conus Medullaris at approximately L1 the SC becomes a cone shaped structure *made up of sacral and spinal segments Cauda Equina below Conus Medullaris the SC ends in a mass of spinal nerve roots (means horse's tail) SC Dura (meninges) unlike brain it is only 1 layer *no periostial layer *dura does not adhere to bone - forms a sac if adhere would take away flexibility and would tear SC Arachnoid functionally and anatomically same as in brain pushed against Dura due to CSF pressure but not physically attached SC Pia connected firmly to SC itself Denticulate Ligaments - flaps in pia that attach through arachnoid to dura, anchors SC Filum Terminale pia continues around the Cauda Equina down to coccyx where it forms a strand and attaches to anchor SC External Filum Terminale dural sac eventually joins the Filum Terminale and attaches to coccyx SC White and Gray Matter opposite of brain - white matter is outside and gray matter is on inside SC Gray Matter divided into 3 horns (H shaped) *dorsal (posterior horn), lateral horn, ventral (anterior) horn Dorsal (Posterior) Horn sensory horn *cell bodies of neurons that carry sensory information up into the brain Lateral Horn motor (only located in thoracic area!!!!) *contains cell bodies of preganglionic sympathetic neurons *processes autonomic info *found only between T1-L2 **** know for test Ventral (Anterior) Horn motor - voluntary *cell bodies of alpha motor neurons that drive voluntary muscles SC White Matter divided into 3 columns *dorsal (posterior), lateral, ventral (anterior) columns Dorsal (Posterior) Column sensory fibers running up to brain *these are myelinated axons carrying sensory info for interpretation Lateral Column both motor and sensory fibers *lateral damage results in both sensory & motor damage Ventral (Anterior) Column mostly motor fibers Column is made of several distinct bundles called tracts Tracts are a group of myelinated nerve fibers that have similar origin, destination, and function Cervical Cord Composition large with slightly flattened shape more white matter with large ventral horn Thoracic Cord Composition ventral horn is narrow - few muscles in this area small dorsal horn - little sensation coming from this area has lateral horn - ANS Lumbar Cord Composition broadens with large dorsal and ventral horns due to lots of motor and sensory activity from area less white matter Sacral Cord Composition lots of gray matter wiht very little white matter tracts mostly enter or leave the SC at levels above this region Spinal Nerves SC has 31 segments with a pair of spinal nerves coming from each segment all have motor & sensory components EXCEPT C1 - only has motor each spinal nerve made of 2 roots - dorsal and ventral Dorsal Root *made of afferent (sensory) fibers dorsal root ganglion * enlargement of dorsal root that contains cell bodies of sensory neurons (cell bodies are outside SC) Ventral Root *made of efferent (motor) neurons cell bodies of neurons forming the ventral root are located in SC Lateral Corticospinal Tract (in spinal cord itself) *voluntary motor system * Motor tracts are a 2 neuron system - upper &lower motor neuron *Upper Motor Neuron begins in the cortex, runs through the internal capsule to the medulla oblongata *In the medulla, 85% of the fibers cross and descend through the SC as the Lateral Corticospinal Tract *The axon exits the SC through the Ventral horn where it synapses onto an interneuron or directly onto the Lower Motor Neuron *The lower motor neuron is generally an Alpha Motor Neuron - it then travels thru ventral root to innervate muscle Upper Motor Neuron Damage *effects seen on opposite side *paralysis, hypertonic, hyperreflexia, spastic paralysis *minimal atrophy Lower Motor Neuron Damage *effects on same side *paralysis, flaccid, atonia (no ton), no reflexes, flaccid paralysis *significant atrophy *may see twitching/jumping of muscle fibers - involuntary Upper & Lower Motor Neuron Damage see characteristics of lower motor neuron lesion - flaccid atonic paralysis with no reflexes Dorsal Column System **Cant be called a tract cuz originates outside CNS*** *Carries vibration and light touch, *Large myelinated fibers (fast), *3 neuron system *Sensory neuron #1 enters through the dorsal root into the SC on the same side *Travels up the SC on the same side into the medulla where it synapses with neuron #2 *Neuron #2 crosses to the opposite side as it goes through the brainstem and into the thalamus (relay station) *Neuron #2 synapses with neuron #3 in the Thalamus and goes to area 3, 1, and 2 of the sensory cortex Lateral Spinothalmic Tract *Carries pain, temp, some touch *Vary small unmyelinated fibers - slow conduction *3 neuron system *Neuron #1 enters through the dorsal root into the dorsal horn and synapses immediately *Neuron #2 crosses in the lateral column of the SC to the opposite side before it ascends up the SC *Neuron #2 ends and synapses with neuron #3 in Thalamus (relay station) *Neuron #3 runs up to area 3, 1, and 2 in the sensory cortex for interpretation *Gate theory