Motor System 11 29 2013 Motor system is very simple divided into two divisions o Pyramidal extra pyramidal Neurons look like pyramids Extra pyramidal Motor System Helps you move smoother and better o Can survive without it o Aka rest of motor cortex Basal ganglia o control movement o control singing in birds Huntington s Disease o When caudate nucleus degenerates Early state symptoms Includes basal ganglia cerebellum thalamus pre motor Neocortex caudate nucleus putamen and Globus Pallidus Slight uncontrollable muscle movements Stumbling clumsiness Mood changes depression Aggressive antisocial behavior Progression symptoms Difficulty in speech swallowing Emotional changes Stubbornness Mood swings Frustration Impaired concentration Parkinson s disease o Degeneration of dopamine neurons Dopamine released in basal ganglia from neurons originating in substantia nigra w in brainstem Degeneration of dopamine neurons is accelerated severe in Parkinson s disease Dr James Parkinson o Documented the disease s progression with accuracy still used today o Symptoms Difficult of initiate normal movements or stop movements once initiated Lack of facial expressions pill rolling time slowed movement resting tremor of hands feet that worsens over o REM sleep behavior disorder may be initial manifestation of PD o Therapeutic approaches to compensate for loss of DA cells Pyramidal Motor System One you always think about when think about movements o Simply stated you can move all you want to move with pyramidal motor system Two synapses Can survive with only this system if needed Upper MN s motor neurons o originate in precentral gyrus starts in primary motor cortex motor homunculus controls movement of face hands fingers etc crosses central body plane to make synapse in spinal o descend into spinal cord to make synaptic connection with the cord Lower MN s LMN then connects directly to a muscle Reason why we move so fast o big neurons deep in cortex that look like pyramids BIG neurons o Upper MN Loss Spasticity rigidity Resistance to passive movements Increased spinal reflexes Weakness Appearance of spinal reflexes present prior to CNS development AKA reflexes when we were babies Ex Babinski Reflex o Produced by scraping sharp object across bottom ball of foot o Look at where big toe goes Stroke Muscle rigidity Makes major reflexes more intense Lower MN s constantly firing Inhereted disorder o ALS Bodies make toxic proteins that attack both neurons Causes upper MN s and or lower MN s to degenerate Have both symptoms Lower MN s o Originate in anterior spinal column o Innervate individual muscles of body Innervation happens via MN s to acetylcholine receptors Live in folds of muscles Folds allow us to have more ACE receptors o Distal muscles Control fine motor movements Located in lateral aspect of spinal cord Fingers neurons Fine motor control requires additional Ratio of MN fibers to innervated muscle fibers is proportional to degree of fine motor control o Few MN s vs large group of muscle fibers is associated w o Many MN s vs small of motor fibers associated w excellent limited motor control Ex back muscles find motor control Ex fingers face Homunculus o Muscarinic Mostly in brain o Nicotinic Two types of acetylcholine receptors exist Located in neuromuscular junction as well as brain Nicotine makes our muscles contract Fingers get cold if you re a smoker b c they contract blood vessels Ligand gated sodium channel Nicotine receptors live in folds of muscle ACE binds to these receptors Fast ionic channels that allow sodium ions to rush in Membrane potential approx same as neuron Negative inside Depolarizes outer membrane of muscle fibers o Depolarization wave quickly spreads outward BOTH directions away from o Whole muscle depolarizes and synapse contracts o Lower MN Loss Flaccid paralysis No ability to contract muscle Decreased or absent spinal reflexes Muscle atrophy Fasciculations Small muscle fibers contracting twitching Myasthenia gravis o Autoimmune disease o Attacks acetylcholine nicotinic receptors Nicotine receptors disappear Impairs ability of neuromuscular junction to work Motor system fatigue worsens as day progresses Trouble keeping eyelids open Walking up stairs is exhausting Drugs that reduce metabolism of acetylcholine help patients overcome loss of nicotinic receptors Modified nerve gases attack Acetylcholinesterase which job is to destroy ACE Allows for more ACE in system helping these patients More ACE allows these people to use the little receptors they have Peripheral Motor System Reflexes o Spinal cord mostly only controls reflexes Evolutionary less control over body with the development of our brains Lower MN often called an Alpha MN o causes muscle to contract when activated Separate innervation to muscle comes from Gamma MN o Innervates a specialized regions called Muscle Spindle Muscle spindles contains stretch detectors Live throughout muscles Relay stretch info back to brain via sensory neurons Allow knee jerk response and other reflexes 1 Add weight to muscles 2 Muscles stretch activating muscle spindles 3 Spindles tell motor neurons to fire Muscle spindle alpha MN allow us to compensate our muscles to maintain steady level of contraction Produce inhibition of antagonist muscle group in order to allow movement to occur Ex biceps on triceps off o If this malfunctions people tense up can t move Losing upper MN will do this o Parkinson s Huntington s Input from brain sets tone of spindles o Ex If we are stressed muscles are tense Flexor Reflux to painful stimuli is organized by small interneurons at multiple levels of spinal cord 1 Step on tack 2 Info up to brain 3 Muscles contract and pull away from pain source Hard wired never have to think about doing it During pain flexor movement there is a contralateral extensor reflex that straightens opposite leg for stability o This simple pain withdrawal reflex is basis of walking Golgi Tendon Organ o Attach muscle to bone o Provide feedback on muscle FORCE not stretch Spindles don t tell you force so we need Golgi tendons o GTO can both excite inhibit muscle activity Helps apply correct amount of force to life either egg or heavy weight o If GTO has too much pressure it gives up Ex jump off building GTO saves muscles instead of brain Central Control of Movement Sensory motor cortex work together to control movement Voluntary action o Originate in frontal love Decide plan what to do b c it s voluntary Intentional actions Premotor