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Kin 1080b - Part 2.docx

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Western University
Kinesiology 1080A/B
Matthew Heath

Lecture Notes Apraxia and CK ­ Following a stroke after the first few weeks usually leads to apraxia (either short term or long term) ­ Stroke to right parietal lobe, patient could preform tasks flawlessly. But as soon as there was an object in her hand, her movements become impaired (jerky and uncontrolled) o Due to stroke, her somatosensory cortex is too highly tuned and amplifies the signals o Called a somatosensory form of apraxia o Chronic impairment ­ Dyspraxia o Seen in young children but gradually grow out of it as their cortex becomes more sophisticated o Developmental in nature (soft issue) o Developmental coordinative disorder o Delay in sophisticated praxia system o Character deficit with timing of a movement o Difficulty speaking Cerebral Asymmetries in Down Syndrome ­ Persons with Down’s syndrome “perceive” speech with their right cerebral hemisphere ­ Probably not a good thing because that hemisphere is not optimized for speech perception ­ Trisomy 21 ­ Cerebellum and brain are smaller ­ 90% of the population are right hand dominate ­ Of the 90%, 99% are left hemisphere dominate for speech and language ­ 90% of left hand dominate have speech and language lateralized to the left hemisphere as well ­ 50% of people with Down Syndrome are left handed ­ fMRI activates Broca’s Area (left hemisphere) in the general population ­ fMRI of people with Down Syndrome activate right hemisphere for the perception of speech ­ Model of Reverse Cerebral Specialization o People with Down Syndrome have everything lateralized to the opposite side ­ Just like in the general population, speech production in people with Down Syndrome are also lateralized to the left hemisphere ­ Therefore, only perception of speech was atypical for a person with Down Syndrome ­ Model of Biological Disassociation o People with Down Syndrome have a particular deficit in motor behaviors because of their functional separation between their right hemisphere speech perception and their left hemisphere speech perception and praxis systems o Explains difficulty in learning new motor tasks verbally  Optimal learning strategies = Visually (overdeveloped mirror neuron system) ­ Corpus callosum in people with Down Syndrome is rounded and Rostral Fifth is very thin and doesn’t contain many axons o Rostral Fifth is critically involved for the between hemisphere communication of verbal information Spinal Cord Connections ­ Information leaves spinal cord via the ventral root ganglion, travels via alpha motor neuron to extrafusal muscle fibre ­ Information from intrafusal muscle fibres enter spinal cord via the dorsal root ganglion and synapses back onto the alpha motor neuron ­ Fusimotor neuron (or gamma motor neuron) synapses onto an intrafusal muscle fibre ­ Golgi Tendon Organ detects tension or force acting on a muscle, and sends signal back via the dorsal root ganglion and synapses onto an interneuron and interneuron synapses onto an alpha motor unit (oligosynaptic) ­ Interneuron allows for the connection of one synapse with another synapse at the same level segment (or area) within the spinal cord ­ Propriospinal neurons allow connections between different segments of the spinal cord Pyramidal Tract ­ is composed of a million fibres and allows for descending motor control ­ Information from M1, SMA, PMA and parietal cortex enter the spinal cord via the pyramidal tract ­ Comprised of the corticalspinal tract and corticobulbar tract ­ Corticobulbar Tract ­ Corticobulbar fibres extend from the motor cortex to the “bulb” (the brain stem) ­ Motor neuron activity organized by cerebral cortex ­ Control facial musculature and muscles of mastication ­ Contains upper and lower motorneurons (neuron on M1 and alpha motor neuron) ­ Unilateral impairment contralateral to the lesion ­ Terminates at the brain stem (monosynaptic connection) ­ Facial nucleus is divided into rostral (innervates forehead) and caudal (innervates mouth) parts ­ Rostral part innervated bilaterally ­ Caudal part innervated from contralateral cortex ­ Tumor on left upper motor neurons leads to asymmetrical innervation of lower facial musculature (paralysis on contralesional side) ­ Lower motor neuronal injury (injury to alpha motor neuron) leads to complete paralysis on one full side of the face ­ _muscles.html Corticospinal Tract Ventral Corticospinal Tract ­ Originates from M1 (and SMA and PMA) ­ Long axons descend “uncrossed” (ipsilateral connection) in ventral columns of the spinal cord, forming ventral corticospinal tract ­ Innervates axial musculature (muscles involved in gross body movements or truck muscles) ­ Make connections with propriospinal neurons (allow for communication of neural signals between segments of the spinal cord) o Send its projections to multiple alpha motor neurons at different levels in the spinal cord and they might go on to innervate different truck muscles ­ Designed to allow for communication and coordination of multiple muscles ­ Example: Bending at the hips Lateral Corticospinal Tract ­ Originate from M1 (also from SMA, PMA, and the Parietal Cortex) ­ 75% of fibres cross at pyramidal decussation ­ Monosynaptic connections (which is needed for precision grips) ­ Goal-directed actions which allow for precise, single digit control ­ Injury to head representation of hand region in M1 lose ability to perform precision grip since they lose the ability to control single digits (can still perform power grip) ­ Humans have the most descending motor neurons and they synapse on a single alpha motor neuron Important Differences Between Both Tracts ­ Lateral corticospinal tract connects (synapses) with a motor neuron ­ Ventral corticospinal tract connects to propriospinal neurons, which ultimately synapse with motor neurons o Propriospinal neurons allow coordination between multiple motor neurons Ablation Study ­ Selectively impairs the lateral corticospinal tract which in turn impairs fine coordination of individual fingers ­ People with stroke often have difficulty performing daily living activities such as buttoning a shirt – they can only make a fist when manipulating objects ­ Monkey takes 5 minutes to finally get a food reward item since it can only use a power grip ­ This type of study in monkeys is a chronic (long term) deficit Important Terms Innervation- the distribution of nerves to a part of the body Innervation Ratio- The number of muscle fibres innervated by a single alpha motor neuron; can vary from a few to over a thousand (also includes intrafusal muscle fibres and gamma motor neurons) o Movements that are more precise have a smaller innervation ratio Extrafusal Fibres- Power producing muscle fibres external with respect to muscle spindles Intrafusal Fibres- Muscle fibres inside the muscle spindles; innervated by a special system of fusi-motor neurons Motor Neurons and Motor Units ­ Alpha motor meurons = a neuron innverating power-producing, extrafusal muscle fibre (Diameter of fibre determines speed of muscle contraction, therefore alpha motor neurons are thicker than gamma motor neurons) ­ Motor Unit = Alpha motorneuron and all of the muscles it innervates; a unit of force production in skeletal muscles ­ Number of muscle fibres associated with a motor unit ranges from 10 (eye) to a thousand (back musculature) ­ Motor unit pool = a bunch of alpha motor neurons and all of the extrafusal muscle fibres that they innervate Fusi-Motor Neurons (Gamma Motor Neurons) ­ Gamma motor neurons are small neurons innervating intrafusal fibres and changing sensitivity of muscle response to dynamic stretch ­ Stretch = Space Recognition (where your limb is) ­ Intrafusal fibres oriented in parallel with extrafusal fibres ­ Polar connections between intrafusal and extrafusal fibres (run the entire length of a muscle, highly sensitive) ­ Without them, we would have no idea where our feet are, for instance Types of Motor Units ­ Fast Twitch, fatigable (FF) (Fast Motor Unit) o Characterized by highest conduction velocity (100m/s) o Large fiber diameter (highly myelinated) o Innervate fast twitch muscle fibers ­ Fast Twitch, fatigue resistant (FR) o Characterized by medium conduction velocity (60m/s) o Medium fiber diameter o Innervates fast and/or slow twitch muscle fibers ­ Slow Twitch, fatigue resistance (SR) (Slow Motor Unit) o Characterized by slow conduction velocity (40m/s) o Small fiber diameter o Innervates slow twitch muscle fibers ­ Sprinter: 80% fast and 20% slow motor units ­ Marathoner: 20% fast and 80% slow motor units ­ Average person: 50% fast motor units and 50% slow motor units ­ Couch potato: 60% fast and 40% slow motor units ­ Spinal injury: 96% fast and 4% slow motor units (unable to sustain long movements) ­ Dark spots in muscle biopsy represents slow twitch muscle fibers (due to oxygen binding to heme, which contains iron) ­ Motor unit types can be altered ­ Older adults: Used to performing slow movements, which prevents their fast motor units from being active, leading to more falls or a reduced postural stability/support ­ Koceja study found that with wobble board training for 6 weeks it lead to an increase in fast twitch (fatigable) motor units, which improved their balance Henneman Principal (Size Principle) ­ The recruitment of motor units within a muscle proceeds from small motor units to large ones ­ Happens as a function of increasing force requirements ­ Low force contraction, nearly all force produced by slowest motor units ­ If contraction force is increased, larger motor neurons start to fire ­ At the highest levels of force (maximal voluntary contraction), the largest motor unites are recruited Concussions ­ Neuropsychological tests evaluate how accurately or how fast you can do something ­ ERP measures of cognitive processing o Event-related potentials (ERPPs) are averaged electrical brain responses to time-locked stimuli (measured using an EEG, which measures electrical activation of the cortex or neuronal activation) o N2pc (event-related brain potential) = ERP component related to the focusing of visuospatial attention o P300 = Measure of stimulus classification processing speed ­ Visuospatial processing could be thrown off due to the first concussion (limiting visuospatial attention), leading to a second concussion ­ OR the athlete could just be very poor at processing visuospatial information, which would lead to a second concussion ­ De Beaumont Study (2007) o Three groups of athletes: Non-concussed, athletes with a single concussion, and athletes with more than one athletes o Athletes who were concussed were 9 months removed from the incident o No groups differed in terms of performance on Impact Battery o No long term consequences due to their concussion and can return to play o Experiment: Classify target and determine where the opening on the target was in order to make an appropriate response (involved visuospatial attention and classification) o The speed at which people processed response where the same for all 3 groups (not showing any limitations) o N2pc = big negative bump in EEG (amplitude was the same across all 3 groups) o P300 amplitude decreased as a function of increasing concussions  Represents first study that shows difference in neurophysiological vs. neuropsychological analysis  Neurons aren’t firing as effectively compared to individuals who have not been concussed, which relates to how they classify stimuli ­ Summary o Equivalent neuropsychological test profiles of non-concussed, concussed, and multiple concussed athletes o No difference in N2pc in non-concussed, concussed and multiple concussed athletes o Suppressed P300 activity in multiple concussed athletes o The specificity of the long-term effect of concussed provides a framework to pinpoint the cognitive system impaired in multiple concussion o Study use a template to pinpoint cortical regions that might be most sensitive to concussive episode Pro-saccades and Anti-saccades Pro-saccades ­ When you look at an object ­ Entail direct spatial overlap between stimulus and response ­ Stimulus driven ­ Often reflexive ­ Takes a very short period of time to initiate a pro-saccade (180 ms) Anti-saccades ­ Looking mirror symmetrical to the location of the stimulus ­ Provide us with a measure of top-down inhibitory control ­ To complete successfully, you have to inhibit the normally reflexive pro- saccades (response suppression), and then do a process known as vector-inversion (perform 180 degree spatial transformation of the target’s location) ­ Might have a reaction time close to 300 ms (much longer to initiate) ­ Increased reaction time is thought to be directly tied to response
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