Neuro Study Guide Ch. 3 PDF

3.1 Motor System: Spinal Region cell bodies: in ventral horn (motor) signals: in dorsal horn (sensory) what is a motor unit? • alpha motor neurons and muscle fibers that activate it • regionalized according to muscles in that area • distal muscles: lateral • proximal muscles: medial • extenso...

3.1 Motor System: Spinal Region cell bodies: in ventral horn (motor) signals: in dorsal horn (sensory) what is a motor unit? • alpha motor neurons and muscle fibers that activate it • regionalized according to muscles in that area • distal muscles: lateral • proximal muscles: medial • extensors: anterior • flexors: posterior * motor signals travel up & down spinal levels to communicate w/ muscle groups myotome : group of muscles innervated by a single spinal nerve • spinal level is important for assigned movement of a joint * movement controlled by stimuli in periphery or CNS C5 lets go for a drive C5-C6 look at the rips C6 flick of the wrist C7 welcome to heaven C8 pick me up mate TI for my rum L2 Raise my knee to the moon L3 i gotta pee L4 kick down the door L5 give my big toe a high five SI to the sun why is communication of sensory, motor & interneurons important? reciprocal inhibition • one muscle contracts (shortening of spindles) -> sensing change (rate of change) -> feedback sent to spinal cord (ventral horn) -> interneurons activated -> signal to inhibit contraction of anatogonist muscle to not fight activity & prevent injury muscle synergies (conductor • ) synergy: muscles activated TOGETHER in a healthy normal system coordinates timing, degree, inhibition of muscle action ex: walking (knee extensors, flexors, & combined hip extensors for fluid motion) How? Type 2 afferent signaling from periphery, interneurons, motor neurons proprioception • know where body is in time & space golgi tendon organ: tells us about lengthening or tension w/in tendon signal from GTO -> spinal interneurons -> facilitate or inhibit muscle activation ex: walking, sense different stretches during gait to inhibit or allow muscle contraction • rudimentary stepping pattern highway of interneurons connecting sensory & motor signals being coordinated @ or near the spinal level activate motor neurons that elicit alternating flexion & extension @ hip/knee ex: w/ E-stim can mimic movements w/o CNS Reflexes phasic stretch: force applied to tendon providing quick stretch ex: reflex hammer stretch to patellar tendon (deep tendon reflex) • detected by peripheral receptors @ tendon in muscle spindles • activates 1a afferent nerves -> spinal cord -> dorsal horn -> interacts w/ alpha motor neuron in ventral horn -> initiating efferent signal to same muscle withdrawal / crossed extension reflex: coordination of muscle activation in response to noxious/ pain stimulus ex: sharp tack • signal sensed @ multiple levels (L2, 3, 4 ipsi & contra) -> signals flexor withdrawal response on side w/ pain -> crossed extension activation on opposite • • • summary: brain/cortical control not necessary for base level coordination to occur, motor signaling is. for protection & conserving muscle energy afferent pain signal occurs in multiple spinal levels w/o cortical input local response to withdraw • contra response for muscle support 3.2 Motor System: Nerve Assessment motor nerve conduction velocity test: locate are of problem along muscle activation • damage can be in motor nerve, neuromuscular junction, w/in muscle testing process • electrode on nerve • stimulus given • measure time to depolarize • test repeat on another site (proximal vs distal) • amplitude & conduction velocity = dist/time abnormal= abnormal = neuromuscular nerve problem junction or within muscle electromyography: measurement of electric activity in a muscle fxn: understand where lesion in motor nervous sytem is ex: motor neuron lesion, motor tract lesion, myopathy how to • use surface electrodes on target muscle • more invasive & precise w/ needle electrodes in muscle motor neuron lesion: damage ro nerve or neural body that directly activates the muscle being tested ex: post polio syndrome • less motor neurons on ant horn • make branches to compensate -> denervated muscle how do muscles present w/ motor lesion? • heightened muscle activity (EMG) w/ needle • mini involuntary muscle contractions • giant firing rates w/ minimal muscle contraction • low firing rates bc decrease motor neurons during request for max muscle contraction motor tract lesion: along motor tracts of spinal cord ex: lack of butterfly in cross section ask somebody if motor lesion tracts present w/ normal or giant firing rather w/ min contraction • degeneration in lateral corticospinal tract, rubrospinal tract, medial motor tracts • can’t convey proper messages for muscle activation how do motor tract lesions present? • normal insertional activity • normal fxn w/ minimal muscle contraction • low firing rates w/ max muscle contraction request myopathy: damage to muscle itself • normal insertional activity • smaller response during minimal voluntary contraction • normal recruitment of motor units • low amplitude of muscle activation • same # of motor units activated: sufficient nerve/ neuromuscular junction fxn • poor muscle response summary: nerve conduction studies/EMG provide info on differential diagnosis to identify where injury is at 3.3 Motor System: Over Tracts Vertical tracts Motor signals being sent through the spinal cord into the peripheruy Regions of motor tracts Medial motor tracts located in the medial anterior part of the spinal cord, white matter, central to the anterior horns These signals come from the cerebral cortex • tracts in the medial system are reticulospinal, medial, and lateral vestibulospinal and the medial corticospinal tracts - these tracts are grossly responsible for controlling postural Lateral motor tracts located laterally bw the anterior and posterior horn on each side of the spinal cord -signals come from cerebral cortex and red nucleus in the midbrain • includes the lateral corticospinal tract and rubrospinal tract - together are responsible for innervating appendicular muscles for limb movement Nonspecific motor tracts carry signals from the brainstem region, at the midbrain and pons but NOT the cortical level Two Nonspecfic Motor Tracts 1. ceruleospinal 2. Raphespinal tracts -together they form the emotional motor system Fxn to impact the quality and coordination of movement in response to an emotion, such as fear and anxiety this is done by altering the activity of interneurons and motor neurons throughout the spinal levels Vertical corticobrainstem tracts convey signals from the cortex to the cranial nerves within the brainstem region Summary: there are multiple motor tracts within the spinal cord conveying signals for movement or muscle activation in different parts of the body. Motor tracts can be grouped by location: medial and lateral spinal cord, brainstem and more expansive emotional motor system 🦵💪 ✅ 3.4 Motor System: Medial Tracts 4 tracts form the medial motor vertical tracts w/in spinal cord 1. Reticulospinal 2. Medial vestibulospinal 3. Lateral vestibulospinal 4. Medial corticospinal -these primarily innervated axial and girdle musculature facilitating posture and core strength Cell bodies for these tracts are located in the medial anterior horn of the gray area of the spinal cord they all convey information for posture and gross movements that can occur without mulch • conscious thought Movements are automatic and respond to some sort of sensory feedback before a person actually • consciously senses the feedback Automatic motor control primarily is coordinated at the brainstem level which is where these 3 tracts derive Medial Corticospinal tract a single tract starting from the cortex Reticulospinal Tract begins w/in the reticular formation of the brainstem and projects downward through the spinal cord, sending signals to both ipsilateral and contralateral motor neurons at the spinal level • • these motor neurons are responsible for activating postural and gross mvmnts for all 4 limbs this subconscious motor pathway is responsible for anticipatory postural adjustments like coordinated muscle activation during reaching, walking, or directing gaze or attention toward a stimulus like a noise or light Reticulospinal neurons DO receive signals from the cortex, cerebellum and sensory feedback to modulate responses Lateral Vestibulospinal Tract derived from the lateral vestibular nucleus within the pons -responds to signals coming from the inner ear or the vestibular apparatus, that helps orient the body towards gravity Pathway helps the body maintain balance over its base of support in line w the pull of gravity -signal goes from the lateral vestibular nucleus down to the end of the SC, along the medial anterior SC for posture and balance, by facilitating extensors muscles to counteract gravity Medial Vestibulospinal Tract derived from the medial vestibular nuclei w/in the rosteral medulla. This is inferior to the location of the lateral vestibular nucleus, but still located w/in the brainstem -responds to signals also coming from the vestibular apparatus, but this time to signals specifically regarding head movement and position -signal goes from the medial vestibular nucleus, down the SC but only to the cervical or thoracic regions -primary purpose is to activate and coordinate muscle activity in the neck and upper back Medial Motor Tracts aka Medial CorticalSpinal Tract arises in the primary motor cortex and supplementary motor area within the cortex, through the anterior aspect of the brainstem, and terminated in the upper thoracic region of the SC -similar to medial motor tracts, the projections are sent ipsilaterally and contralaterally, providing signals for bilateral control of axial and upper girdle muscles 3.5 Motor System: Lateral Tracts Two major motor tracts in the lateral aspect of the SC 1. Rubrospinal 2. Lateral Corticospinal -systems are responsible for distal limb movement and fractionation Fractionation of Movements ability to isolate one active muscle from another or group of muscles -almost the opposite of synergy ex: how we can flex one finger but extend the others or flex at the elbow but extend at the wrist -muscles that can only function in synergy lose capacity for fractioned movements Lateral Corticospinal Tract starts at the cortex level, specifically at the premotor cortex -the premotor cortex then descends donwards through the SC King of voluntary mvmnt Rubrospinal Tracts begins at the red nucleus The red nucleus is located w/in the midbrain and descends down through the entire SC -rubrospinal plays a much smaller role than the lateral corticospinal tract Pathway: Begins at red nucleus w/in midbrain V Decussate or crosses midline (in ventral tegmental decussation) W Descends through the pons and SC contralterally -tract is responsible for the distal upper extremity extensors muscles, primarily innervating the wrist and finger extensions Lateral Corticospinal Tract is the king of voluntary movement and the fractionation of movement -at level of the rostral medulla, 88% of the fibers enter the pyramidal decussation and then continues the pathway down the contralateral corticospinal tract to the motor neurons in the lateral aspect of the anterior horn -10 % of the fibers in the initial tract actually DO NOT cross over; instead join the ipsilateral corticospinal tract, while the remaining 2% of fibers from the original tract link up w the medial corticospinal tract * pls someone make this make sense lool* ' 👶 3.6 Motor System Dysfunctions paresis vs paralysis weakness (more severe) motor. neurons in tract inadequately facilitated so can’t activate ex: stroke, TBI, incomplete spinal cord injuries • what type of patterns? • minimal to no voluntary control of muscles sensation & motor fxn lost or altered • 1/2 body weaker • hemiplegia, paraplegia (bi leg), tetraplegia (bi legs & arms) abnormal reflexes babinski’s sign how to fine pressure from heel to great toe • normal response: curling/flexing toes • - response abnormal response: great toe extends & other toes fan up • + response • upper motor neuron lesion • or motor neuron problem in CNS phasic stretch hyperreflexia : excessive muscle contraction in response to muscle spindle stretch • signals from cortex not being reached in spinal cord • loss of inhibition from primary motor cortex • potential increase excitability @ spinal level tonic stretch reflex : muscle stretched & maintained @ length • primary nerves: quick firing bc sense stretch but slows as stretch maintained • secondary nerves; cont firing @ same rate abnormal response: signals from type II fibers not mediated by higher level motor control -> no pre synaptic inhibition & alpha & gamma motor neurons activate muscle contraction normal response: sustained stretch = presynaptic inhibition of alpha & gamma motor neurons preventing muscle contraction clonus: repeated, involuntary, rhythmic contraction of a single muscle group ex: most common in soleus/wrist how to? • apply quick stretch or noxious stimulus, or even trying voluntary movement characterized as continuous or by number of beats before contraction fades out clasp knife response: muscle being slowly stretch with initial resistance then quick give when resistance suddenly drops myoplasticity: change in muscle due to altered neuromuscular activity or prolonged position altered neuromuscular signaling during immobility or post neurological injury changes actin- • myosin bonds = shortened muscle or contracture leading to further weakness How it presents • contracture • disuse atrophy (paresis, paralysis, fractured arm not being used) muscle tone: resistance w/in muscle being stretched (can be normal or abnormal) abnormal resistance can be decreased leading to • hypotonia • spinal shock • flaccidity resistance can be increased leading to • hypertonia velocity dependent hypertonia spasticity/rigidity increased resistance to movement in all amount of resistance to movement limbs related to speed of passive stretch • slower - lower resist • faster - higher resist causes • hyperreflexia due to impaired signal level regulation/ reticulospinal tract overactivity • myoplastic changes can also cause deceberate: complete disconnect b/w midbrain & pons • ext of arms, flexion of wrists decorticate: posturing, complete disconnect b.w corte or upper part of midbrain w/ lower levels of NS • rigid flexion of UE • ext of LE/neck stimulus: sternal rub lesion to lateral corticospinal tract: loss of fractioned movement ex: Hand: OT peg board, can’t maneuver pins well Walking: foot drop, knee staying straight during swing phase lesion affecting motor tracts • cortical input decreased & abnormal muscle synergies presented • @ rest higher muscle tone in UE encouraging elbow flexion/forearm supination ex: stroke • active intention to lift arms = flexors in synergy w/ UE cup down, ppl getting annoyed Memorize definitions! (denervation), no babinski (toes not crazy) lower motor neuron lesion = problem w/ motor neuron directly innervating skeletal muscle presents: • lack of muscle activation • hypotonia, hyporreflexia or areflexia • paralysis causing muscle flaccidity, muscle fasciculations, muscle atrophy upper motor neuron lesion = affects any motor neuron from cortical level down to lower motor neuron cell body in ant horn of spinal cord (CNS) presents: • lack of inhibition of muscle innervation b/c of impaired cortical control • hyperreflexia, hypertonia, rigidity, muscle weakness due to paresis • babinski sign present, clonus, or clasp knife cup up, spastic party, everyone hyper so hyperreflexia, babinski bc feet going crazy decorticate: cross, t-rex hands deceberate: ext w/ backward low five Summary: -injuries to different parts of the motor system can result in specific impairments or presentations this will facilitate a differential diagnosis and intervention design Complete motor neuron lesions typically result in paralysis or lower motor neuron impairment paralysis, hyporeflexia, and hypotonia -upper motor neuron lesions typically result in paresis, hyperreflexia, hypertonia -during an assessment, we would investigate the pattern and type of motor impairment, paired w any sensory finding to help anticipate what issues a person would have to help develop a plan for your assessment this would also help to problem solve through our screening finding and knowledge of pathophysiology to help you come up to a differential diagnosis knowing dif b/w upper/lower for differential diagnosis vest: more medial closer to body, reticular like last chapter we want that person close to us