B55_LECTURE_7___MOTOR_CONTROL.pdf (1).pdf

Lec 7 - Motor Control Joint articulation - Use of electromyography (EMG) - Measures muscle contractions - when muscles relax and contract - Antagonistic muscles - act against each other; One muscle contracts and the other relaxes. - Bicep contract -> tricep relax, vice versa. Neuromuscular junction...

Lec 7 - Motor Control Joint articulation - Use of electromyography (EMG) - Measures muscle contractions - when muscles relax and contract - Antagonistic muscles - act against each other; One muscle contracts and the other relaxes. - Bicep contract -> tricep relax, vice versa. Neuromuscular junction -> where nerve meets muscle when info is given. - The alpha motor neurons have significant connections to the muscle fibers, this connection is called the neuromuscular junction. The alpha motor neurons communicate with the muscle using the neurotransmitter – Acetylcholine (ACh). The motor neuron dumps ACh into the synapse of the neuromuscular junction, ACh binds to ACh muscle receptors which triggers muscle contraction. - When Botox a weakened version of botulism is administered it suppresses the release of ACh which causes the muscles to relax; black widow venom causes increases release of ACh which causes uncontrollable spasms, curare competes with ACh for ACh receptors and paralyzes ppl. - Myasthenia Gravis (grave muscle weakness) is an autoimmune neuromuscular disease, causing weakness in skeletal muscles. Those who have this have a diminished ability to use ACh and have it bind to the receptors. They have fewer ACh receptors which makes it more difficult to contract muscles. Signaling between body and spinal cord - When the doctor hits the knee to check reflexes, an afferent signal (touch signal) carried by the sensory neuron goes to the spinal cord through the dorsal root and then a motor neuron from the spinal cord carries an efferent signal This study source was downloaded by 100000845920345 from CourseHero.com on 12-08-2023 10:27:37 GMT -06:00 https://www.coursehero.com/file/182603146/B55-LECTURE-7-MOTOR-CONTROLpdf/ - (motor signal) thru the ventral root to the leg to give an immediate kick. There is an important segregation of information from the spinal cord; body -> spinal cord = touch signals; spinal cord -> body = motor signals. Major motor pathways from the brain - Corticospinal pyramidal tract: pathway originates in primary motor cortex in the frontal lobe -> descends down towards the brain stem going to the spine -> CROSSES at the medulla (opp brain sides control opp body sides) -> spinal cord. - This pathway is crucially important and absolutely dominant for voluntary movement. - Some extrapyramidal tracts: - Rubrospinal tract: also for voluntary movement, plays a role in recovery when corticospinal tract is damaged. - Tectospinal tract: head and eye movement. - Vestibulospinal tract: motion balance. - Reticulospinal tract: muscle toning/getting ready for action. Spinal cord injury and dermatome mapping - Different nerves in the spinal cord control different areas of the body. Mapping of these nerves is called a Dermatome. - Plegia -> paralysis of a body region; cannot move at all after a severe injury. - Paresis -> partial paralysis/weakness; a less severe injury. - Quadriplegia -> cannot exert voluntary control over your arms or legs; damage above T1 i.e. C1,2,3,4,5 coz at top of Spinal cord are motor pathways that control entire body) - Paraplegia -> cannot move lower half of body (damage below T1). Unilateral impairment of the corticospinal tract - Spinal cord injury is OFTEN (but not always) bilateral (both sides of the body are impaired); but brain injury can be one-sided only, aka UNILATERAL. Topography of motor cortex -> more space in the motor cortex for a body part = better This study source was downloaded by 100000845920345 from CourseHero.com on 12-08-2023 10:27:37 GMT -06:00 https://www.coursehero.com/file/182603146/B55-LECTURE-7-MOTOR-CONTROLpdf/ - motor control for said parts ⇒ hence face and hands take up so much space. Top black X -> damage there can impact RIGHT trunk, hip, shoulder etc. Hemiplegia -> paralysis of half of the body Hemiparesis -> weakness/partial paralysis of half of the body. Bottom black X -> damage there means you are plegic for the entire RIGHT side of the body => bcuz ALL the motor cortex neural paths ? bundle together at where the X is (internal capsule). Movement is still possible following resection of the spinal cord - Experimenters wanted to see if the brain is required for walking (you don’t need it), they took a cat, put it on a treadmill and it began walking. They then cut the spinal cord at the point where the brain can no longer send information to the hindlimbs, but the cat continued to be able to walk. - They then thought maybe the cat can still walk because it feels the ground moving on the treadmill, so they cut the nerve that sends the touch signal to the spinal cord from the legs but the cat continued to walk. - This anomaly could be explained by neurons in the spinal cord called Central Pattern Generators (CPG) that represent complex movements, since walking is a fairly simple task it seems that these neurons code for alternative movement of the legs and activate the movements needed to walk. The patterned movements are stored in the spine via CPGs, which the brain activates in this situation. - Neurons that contract different muscles in different legs get activated by the central pattern generators. This system of one neuron controlling other neurons is called Hierarchical Control of Movement. The brain controls the central pattern generators. However, this animal can’t walk without the treadmill (its paraplegic), you have to get the animal to start walking through an external influence and then CPG takes over. As long as the CPG is activated, it can still walk even if the brain and spine are now disconnected. - So why is this hard to happen in humans with paraplegia? → this is becoz we are bipedal (use 2 legs to balance and have a huge load bearing posture). In animals, they use 4 legs. After a stroke, if you become paretic, they use a gurney that holds your body weight and you relearn how to walk without the load-bearing posture and then gradually the weight on your legs is added. M1 neurons code the direction of a movement The motor neurons are telling the spinal cord which direction to move the body. Study: measured the neural activity in the primary motor cortex in the frontal lobe of a monkey. They trained the monkey to move a joystick in 4 directions (NEWS) and a combination of those 4 directions. This study source was downloaded by 100000845920345 from CourseHero.com on 12-08-2023 10:27:37 GMT -06:00 https://www.coursehero.com/file/182603146/B55-LECTURE-7-MOTOR-CONTROLpdf/ - - - - Results: these set of neurons i.e M1 neurons are particularly more active when movement is towards the monkey. But how do we know if these M1 neurons are coding for the movement vs where you’re trying to move to (journey or destination)? they changed the endpoint i.e. made the monkey start at a different point to change where the movement ends but not direction. When they did this the endpoint didn’t matter because when the endpoint was changed the activity of the neurons responded the same which meant that M1 neurons code for direction of movement. Specific neurons care most about their specific direction (NEWS) and the further away from that specific direction you move, the lower their neural activity. This is called a Tuning Curve. So, if you move your muscles in a combination of the 4 directions (NE, NW, SE, SW) the neurons that care about the associated primary directions will combine their neural activity to give rise to movement in the combination directions. Movement is caused by a group of neurons coding for different directions; this is called a Population Vector. If you wanna move a little forward but a lot to the right -> the “forward” neurons and the “right” neurons both get activated, the forward one less and the right one more. This allows us to measure activity in the motor cortex before someone moves and predict the direction in which they will move. The experiment proving this had experimenters asking subjects to point in a certain direction and even before they pointed the experimenters saw activity in the motor cortex getting ready to send signals to point in that direction. The role of parietal cortex in spatial planning - Parietal cortex = where the movement lands; involved in the Dorsal Stream which helps us formulate spatial perception which goes hand in hand with movement to navigate the world (aka the “WHERE”). - E.g. the Parietal reach region (PPR) = reaching for something movement - Lateral intraparietal area (area LIP) = eye movements - Anterior intraparietal area (area AIP) = grasping things - All these areas care about the destination of the movement, This study source was downloaded by 100000845920345 from CourseHero.com on 12-08-2023 10:27:37 GMT -06:00 https://www.coursehero.com/file/182603146/B55-LECTURE-7-MOTOR-CONTROLpdf/ and the frontal lobe tells u where to stop. Experiment: Reach memory-guided task: - Trained monkeys to move their hand to a laser pointer. They would start at at point with the monkey’s hand and laser being in the same spot (hold phase), then they would move the laser around while them monkey’s hand is still in the same old spot (target phase), then the monkey will have to remember where they have to move their hand (memory phase) and then the monkey will move its hand (go signal). - They inactivated the PRR to show that it would be important to perform this task. Doesn’t matter which side of space, if the right PRR is disabled you can’t reach the right side. Disruption of PRR = couldn't reach for things. Saccade memory-guided task: Experimenters trained monkeys to move their eyes to a laser pointer being moved elsewhere. - Damage to PRR didn’t affect them cuz that’s not the region that’s for eye movements. TMS to aIPS impairs online adjustment of goal-directed grasping Adjustment of goal directed grasping => it helps you detect movement of things in the external environment and help you adjust to that so you can interact with it. Ex: Walking and giving someone a high five but that someone is also walking toward you as well. - - When you TMS this area, ppl struggle to interact with the moving objects because they can’t adjust their movement. They did a TMS on the aIPS in an experiment where the Jenga block rotates and then stops. In the control condition, it stops in the exact same position, so you don’t need to change your hand position to grasp it. In the other condition, it stops in a different position from its first which requires you to use aIPS to adjust your hand to grasp it. Monkey and human premotor cortex (PMC) Area in the frontal lobe before the motor cortex. It has mirror neurons that get activated when you perform an action, but also when someone else performs an action. It helps us perceive the actions of others by imagining ourselves doing This study source was downloaded by 100000845920345 from CourseHero.com on 12-08-2023 10:27:37 GMT -06:00 https://www.coursehero.com/file/182603146/B55-LECTURE-7-MOTOR-CONTROLpdf/ that action. (lack of mirror neurons in autism can result in lack of empathy) - Mirror neurons also get activated due to the sound of an action Ex: watching/thinking about a paper rip or hearing a paper rip activates the mirror neurons in the same magnitude. - Peripersonal space is the space around which you can reach and grab things. Anything beyond peri-personal space is extrapersonal space. - There are neurons that care about action (hearing or seeing them) in the peri-personal space only (25%), while other neurons care about action in the extra-personal space (25%) and some care about both (50%). - Extra-personal space neurons are important for interacting with the world ex: getting things outside your peripersonal space. - Peripersonal space neurons are important for a threat regulation ex: to be able to reach for things you might need in danger or otherwise. - There are some extra-personal neurons that get more and more active the further the action moves away from you. Likewise, there are some peri-personal neurons that get more and more active the closer the action comes to you. Memory-guided actions and the supplementary motor area (SMA) - Located above the premotor cortex and is important for performing a sequence of actions to perform a task, ex: doing a secret handshake. - Monkey experiment: taught them a 3-pattern movement: turn, push and pull and monitored brain activity. - They found that the SMA is the most (or only?) active for the start of the sequence, after it had learned the whole pattern. - The SMA is active right before you are about to perform the sequence of actions and once you start doing the first action it gets turned off while the other action follows. So, the SMA prepares you for a complicated task. - There is a pre SMA that operates like the PMC. The pre SMA is concerned with learning new actions, once you learn the new actions well, they transfer from the pre SMA to the SMA. Motor imagery engages the SMA This study source was downloaded by 100000845920345 from CourseHero.com on 12-08-2023 10:27:37 GMT -06:00 https://www.coursehero.com/file/182603146/B55-LECTURE-7-MOTOR-CONTROLpdf/ - Just imagining about doing something (that you know the movements to i.e swinging a baseball bat) can also trigger SMA. This therefore can suggest that just visualizing doing something better and better actually helps you DO it better and better. Cerebellum The cerebellum has a huge number of densely packed neurons (more than the cortex). One of the many functions of the cerebellum is motor coordination i.e. making motor functions smooth. - Alcohol interacts with GABA and it depresses cerebellum activity which makes motor coordination difficult (sloppy talking and walking). Possible effects of cerebellar lesions Cerebellar Ataxia -> difficulty in voluntary motor coordination due to damage/lesion in the cerebellum. - Ppl with this usually have cerebellar gait which makes them walk differently also, they tend to spread their legs under normal circumstances to lower their center of gravity gain balance. Dysmetria -> difficulty reaching for things properly. Dysarthria -> speech impediment (slurring of speech) due to lack of coordination of the mouth and tongue. You do KNOW what to say. This study source was downloaded by 100000845920345 from CourseHero.com on 12-08-2023 10:27:37 GMT -06:00 https://www.coursehero.com/file/182603146/B55-LECTURE-7-MOTOR-CONTROLpdf/ Powered by TCPDF (www.tcpdf.org)