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PSY 335: Biological Psychology Chapter 7: Movement The Control of Movement Muscles and Their Movements Vertebrate muscles fall into three categories • Smooth muscles control internal organs • Skeletal or striated muscles control movement of body in relation to the environment • Cardiac muscles have properties intermediate between those of the smooth and skeletal muscles The Control of Movement Muscles and Their Movements • Neuromuscular junction: synapse of motor neuron with muscle fiber Axons release acetylcholine at synapse Each muscle moves in one direction and in absence of acetlycholine it relaxes Movement in two directions requires antagonistic muscles: flexor to raise arm and extensor to lower arm A pair of antagonistic muscles Fast & Slow Muscles Fast twitch fibers • Fast contractions, easily fatigued, increased by sprinting; anaerobic Slow twitch fibers • Slow contractions resistant to fatigue, increased by long-distance running; aerobic • However, body appears to have adaptive mechanism that will eventually lead us to fatigue in endurance activities Muscle Control by Proprioceptors Proprioceptors • Receptor that is sensitive to the position or movement of a part of the body • Muscle spindle: senses stretch of muscle and sends negative feedback to motor neuron to contract Golgi tendon organ • Senses increase in muscle tension and sends message to inhibit motor neuron and brake contraction Units of Movement Voluntary and Involuntary Movements • Reflexes such as the stretch reflex or constriction of pupil to light are involuntary • Most movements, e.g., walking, are a combination of voluntary and involuntary muscle control Sensitivity to Feedback Ballistic Movements • Once started cannot be altered • Reflexes Sequences of Behaviors Central pattern generators • Neural mechanisms in spinal cord and elsewhere that generate rhythmic patterns • Started by stimulus but motor program sets frequency of movement, e.g., cats scratch themselves 3-4 times/sec Sequences of Behaviors Motor program is a fixed sequence of movements • Ex: cat washing face, gymnast with complex movements, yawn • Automatic patterns may be disrupted when thinking about them, e.g., typing or playing piano • Evolutionary holdover: chicken still flaps wings when dropped even though can’t fly Brain Mechanisms of Movement Role of Cerebral Cortex • Important for complex actions such as writing • Stimulation of primary motor cortex elicits certain outcome movements in corresponding body area ▫ 500 msec stimulation of arm region of monkey results in grasping movement and moving hand toward head ▫ Finger area of cortex active when pianist hears music Role of Cerebral Cortex Planning a Movement Posterior parietal cortex • Keeps track of position of body relative to environment • If damaged we can describe what we see but can’t walk toward it, pick it up, or step over object Primary somatosensory cortex • Main receiving area for touch and other body information • Responds to shape of object and grasping, lifting or lowering Role of Cerebral Cortex Planning a Movement Premotor cortex • Active during preparations for a movement ▫ receives information about target and body location Supplementary motor cortex • Active during preparations for a rapid series of movements; typing, dancing, speaking, playing musical instrument Prefrontal cortex • Active when planning and calculating possible outcomes of a movement • Damage results in badly planned movements, showering with clothes on, salting tea instead of food, etc. • Inactive during dreaming and dreams are usually haphazard Mirror Neurons Rizzolatti (2002) • A neural basis for observational learning • Neurons fire in motor cortex not only when monkey was eating ice cream and peanuts but also when viewing other monkeys or humans doing the same Click on pictures for videos Giacomo Rizzolatti 78 years old Mirror Neurons Mirror neurons respond to a particular “kind” of action (e.g., grasping) and when observing someone doing the action The activity of a particular neuron in the premotor area of a monkey Built-in Mirror Neurons? Meltzoff & Moore (1977) • Posit that we have a built-in mechanism • Some newborns imitate a few facial movements • These neurons connect the sight of the movement to the movement itself Tongue protrusion is most common Connections From Brain to Spinal Cord Messages from the brain must eventually reach the medulla and spinal cord, which control the muscles Corticospinal tracts • These are paths from the cerebral cortex to the spinal cord • Two paths: lateral and medial corticospinal tracts • Nearly all movements rely on a combination of both tracts, but a movement may rely on one tract more than the other Connections From Brain to Spinal Cord Lateral Corticospinal Tract • Originate from primary motor cortex, surrounding areas and red nucleus • In pyramids of medulla, axons cross over to opposite side of spinal cord but contralateral control develops gradually • Primarily responsible for controlling the arm muscles • Controls movement in hands, fingers, toes • Damage here means loss of fine movements Connections From Brain to Spinal Cord Medial Corticospinal Tract • Includes axons from the primary and supplementary motor cortex, midbrain tectum, reticular formation and vestibular nucleus ▫ Do not cross to lateral side because axons control bilateral movement of the neck, shoulders, and trunk ▫ Damage here impairs walking, turning, bending, standing up and sitting down Role of Cerebellum • Important for motor control and has more neurons than rest of brain • Enhances new motor programs and skills • Processes information about guiding movement, not the movement itself ▫ active when weighing objects with hands or when objects rub hands Role of Cerebellum Damage causes difficulty with: • Rapid, ballistic movements, sequences that require accurate aiming and timing • Finger-to-nose task: initial rapid movement may strike face or hold segment of task may waver, as when intoxicated • Judging differences in delay in pairs of tones Role of Cerebellum Park et al. (2009) • Study on college basketball players found an enlargement of part of the cerebellum • Possibly related to gifted athletic prowess; however, has not be determined if this was the cause or the result of the participants athletic skill Role of Cerebellum Damage in Cerebellum: • Does not effect controlling force of movement or judging loudness of tones • Does not cause problems completing tasks requiring continuous motor activity Cellular Organization in Cerebellum • Receives input from the spinal cord, sensory systems through the cranial nerve nuclei, and from the cerebral cortex • Cells are arranged in precise, repeating geometrical patterns ▫ Purkinje cells are very flat and exist in sequential planes ▫ parallel fibers are perpendicular to the planes of the Purkinje cells ▫ parallel fibers excite Purkinje cell the more excited, the longer the duration of the Purkinje output which may control either a movement or a cognitive process Role of Basal Ganglia A group of large subcortical structures in the forebrain • Caudate nucleus and putamen receive input from thalamus and cortex • Globus pallidus sends information to the thalamus where it goes on to the motor and premotor cortices • Stores sensory information to guide movements, learn rules and organize sequences of movements into a smooth, automatic whole Role of Basal Ganglia The basal ganglia select a movement by ceasing to inhibit it Turner & Anderson (2005) Procedure • Monkeys were trained to move one hand to the left or right to receive food • A signal indicated exactly when to move Results • On trials when it heard a signal indicating exactly when to move, the basal ganglia showed little activity • On trials that required a delay in movement, the basal ganglia were highly active Conscious Decisions & Movements Libet, Gleason, Wright, & Pearl (1983) Procedure • Electrodes attached to participants scalp to record brain activity in motor cortex • Participants looked at a clocklike device where light moved around a circle in 2.56 seconds • They were asked to flex there wrist whenever they choose as the clock was ticking • When they decide to move, they were required to remember that specific time on the clock for selfreport later Readiness Potential Libet, Gleason, Wright, & Pearl (1983) Results • On average, participants report their decision to move occurred about 200 ms before the actual movement • However, brain activity showed brain activity 300 ms before that • The motor cortex produces a kind of activity before any voluntary movement • This readiness potential begins about 500 ms before the movement Readiness Potential Libet, Gleason, Wright, & Pearl (1983) Interpretation • Brain activity responsible for the movement began before the person’s conscious decision • Researchers posit that conscious decision does not cause a person’s action Readiness Potential Limitations • People may not be accurate when reporting the time they become conscious of something Movement Disorders Parkinson’s Disease • About 1-2% of people over 65 • Gradual progressive death of neurons especially in substantia nigra • Decrease in dopamine results in decreased excitation of cerebral cortex Movement Disorders Parkinson’s Disease • Symptoms begin when neurons decrease 20%-30% ▫ The main symptoms are rigidity, muscle tremors, slow movements, and difficulty initiating physical and mental activity ▫ Slow on cognitive tasks ▫ Some depression and memory loss Click on picture for video Parkinson’s Disease Risk Factors • Genetics ▫ ▫ Early onset in identical twin good predictor for other twin but less so after 50 years of age 5 genes more common in patients but no specific gene for disease • Exposure to Toxins ▫ ▫ Chronic exposure to hazardous chemicals; herbicides and pesticides MPTP designer drug which destroys dopamine releasing neurons Parkinson’s Disease Intriguing link • People who smoke cigarettes or drink coffee have less chance to develop Parkinson’s disease • Smoking actually has the greater effect See next slide Parkinson’s Disease Wirdefeldt, Gatz, Pawitan, & Pederson (2005) Procedure • Questionnaire filled out by over 1000 participants (young adult twins) • Decades later they looked at the medical records of these individuals Results • Never smoked: 18.4% • Moderate smokers: 13.8% • Heavy smokers: 11.6% L-Dopa Treatment • Most common treatment for Parkinson’s disease • Precursor for dopamine that crosses blood-brain barrier ▫ Effective in early to intermediate stages but some patients do not benefit at all ▫ Does not stop progression of the disease, may do harm ▫ Side effects: nausea, restlessness, sleep problems, low blood pressure, hallucinations, and delusions Other Therapies One or more of following usually combined with LDopa • Drugs ▫ Antioxidants, dopamine receptor stimulants, glutamate blockers, drugs that decrease apoptosis, electrical stimulation of globus pallidus, or surgery • Stem Cell Transplants ▫ ▫ Most successful with substantia nigra cells transplanted from fetuses into young rats Some benefits with fetal brain transplants to patients; difficult and expensive Huntington’s Disease Severe neurological disorder striking 1 in 10,000 • Extensive damage to caudate nucleus, putamen, and globus pallidus, and some in the cerebral cortex • Symptoms most often appear in those 30-50 years old ▫ Begin with jerky arm movements, then facial twitch, later tremors spread and develop into writhing ▫ Cannot learn new or improve movements ▫ Includes depression, memory impairment, anxiety, hallucination Click on picture for video Credits Some slides prepared with the help of the following websites: • http://streaming.missioncollege.org/dguich/media/Movement.ppt