330 Final Exam

What are receptors in muscle tendon? Do they provide information about the absolute level of muscle force or changes in muscle force? Why?

- They are golgi receptors that provide information about change in muscle force. It does not provide information about the absolute level of muscles force because of temperature and historesis.

What is phase?

- A position w/in a cycle

List the somatosensory receptors (and their locations) that contribute to the perception of joint positions or their changes?

- In the muscle there is annulospiral which is located in the spindle and golgi which is located in the tendon. For skin there is slow adapting (pacinian and refini), fast adapting and large field

Describe the muscular and neural components and the process that generates an IC for a muscle

- It is called the lambda model.. the components include length-tension relation and neural elements in the stretch reflex. Namely the golgi receptor in the tendon sends a 1B axon to the alpha motor neuron in the vental root of the spinal cord.. The annulospiral receptor in the spindle sends a 1A axon to the alpha motor neuron and the gamma motor neuron.. The alpha motor neuron activates the extrafusal fibers of the muscle and the gamma motor neurons activate the intrafusal fibers inside of the spindle.. When the muscle is stretched the golgi and the spindle respond bt stimulating the alpha which activates the muscles.. A decending signal from the brain to the gamma cause gamme to tune the sensitivity of the spindle.. the spindle in turn determines muscle length at which the spindle responds and begins to activate the muscle.

What is OAC, what problem does it solve and how does it work? How is the other component of motion guided in this theory?

- OAC stands for optical acceleration cancelation and it solves the outfielder problem of trying to catch a fly ball and how to move in order to catch it. OAC works when you move to cancel vertical optical acceleration in order to preserve constant optical vertical velocity. You move to achieve this and keep it constant. When you're not in the plane of motion for the ball the other component of motion, the bearing angle, is guided in this theory. As you move in the direction of the ball you achieve this bearing angle.

What is open loop control? In the pure motor control approach, how were actions hypothesized to be controlled given the assumption that they were controlled mostly open loop? What is the problem of context conditions variability?

- Open loop is an executive contoller that only sends efferent commands to units.. With open loop its not just muscle forces being controlled other foreces contribute to limb movements.. there are other factors besides muscle activation.. The problem of context condition variability is that the commands to units do not uniquely determine movement.

What is the degrees of freedom problem? What are the df in the motor system? If one counts df in terms of joints, then what problem in addition to control mus be addressed and why?

- The df problem is that there are too many things to keep track of.. The dfs in the motor system depends on what youre calling your df (limbs, joints, muscles).. When counting df in terms of joints coordination is a problem in addition to control because not every rotation is done through direct control.. When they can and are able to be controlled together they reduce the responsibility of the brain.

Describe how the lens in the eye is adjusted in accomidation. What is the configuration of the relevant elements when the lens is focused on something close? Something far?

- The elements adjusted in accomidation are the lens, ciliary muscles and zonules. The configurations of relevant objects in the lens when something is close is the lens becomes more curved and fat, the ciliary muscles are contracted and the zonules are relaxed. For when its focused on something far the lens become flat, ciliary mosucles are relaxed, and zonules are tight.

Describe double step targeting experimetns. What is the major result and what did it imply?

- The experiments asked paticipants to touch whatever target was lit up as fast as they could. Once they reached the target and pressed it another targer would light up and they would have to press that one.. The result was the reaches are controlled 'online' or by using feedback control. They found that double step reaches were indistinguishable from the single step reaches

The pendulum in a mechanical pendulum clock is a limit cycle oscillator and is said to be autonomous. Why? What does this mean? How is autonomy demonstrated? How is the autonomy of a limit cycle oscillator relevant to rhythmic human limb movements?

- The pendulum loses energy because of friction and by using a spring it is able to gain that lost energy back.. the spring is connected to something that uses the position of the oscillator itself to determine when to inject energy back.. This is because energy going in and out is controlled by the position of the pendulum itself and not an outside force. The autonomy of a limit cycle oscillator is relevant to rhythmic limb movements because of phase resetting

Hypothetically, if it is assumed that movements are controlled by an executive in the brain, what is the problem of instability for feedback contol of targeted limb movements? What causes instability and why? How could movements be kept stable with such feedback control? Thus, with this analysis, what was concluded regarding the contol of limb movements?

- The problem is that neurotransmission takes time. Errors are random and by the time the error is sent back and corrected there is till ongoing variability occuring which makes the corrected error worse when its sent back.. This creates chatter.. Movements could be kept stable by only correcting smaller portions of error. Regarding the control of limb movements it was concluded that limb motions should only be controlled using open loop.

Describe the problem to be solved by the Reichardt Correlation Detector and the steps via which it solves it. What does it achieve?

- The problem to be solved is to detect the speed and movement of the contrast moving over the retina... There are six steps to solve it which involve 2 receptors a given distance apart according to the receptor. 1.) each receptor detects light to dark change in a given time. The output of each receptor is taken and then you take its derivitive (if nothing is happening the derivitive is 0). 2.) Get derivitive of each signal 3.) delay both signals by delta t 4.) Cross correlate the delayed copy of 1 receptor and multiply it by the undelayed copy of the other receptor and vise versa. 5.) subtract one of the multipications from the other and that rules out flicker 6.) if you have a signal remaining then the sin of the signal with tell you if the contrast is moving left or right... This solves direction of optical motion

Joints are moved by torque, but muscles produce muscle forces. What is the relation between joint torque and muscle force and how does this contribute to the problem of context conditioned variability?

- The relation between joint torque and muscle force is lever arm .. This contributes to the problem of context conditioned variability because movement is produced by total torques also lever arm varies with joint position

Describe the molecular force generation mechanisms of skeletal muscle and how it yeilds the length-tension relation.

- There are 2 elements involved which are the actin which is in the form of a helix (ladder) and myosin which has a body and a head that is able to turn. Together they make a slidding fillament model. The myosin head attaches to a rung of the actin ladder then flexes which allows it to pull itself up so that it can release and grab the next rung on the actin ladder. It yeilds the length-tension relation when muscle shortening occurs because myosin molecules start interfering with each other and when this happens myosin cant contact with other actions. When myosin cant contact with actins they stop generating force which makes the total force go down.

Describe the on center/off surround organization in the retina including the various elements involved. What does this organization achieve functionally?

- There are three layers that are involved which include the ganglion cell that send messages to the brain on the inside layer, than the horizontal/amacrine/bipolar cells, and then the last layer towards the back of the eye being the receptors (cones and rods). Center receptors connect to bipolars cells and this activates the ganglion cells which when activated send messgaes to the brain. Surround receptors connect to horizontal cells and inhibit bipolar sounds causing messages to not be sent to the brain. On center/off surround is when the center receptors attach to bipolar cells allowing the ganglion to be activated so that messages can be sent to the brain... If almost all surround cells are activated then horizontal cells are activated therefore inhibiting bipolar cells.. If light hits all center and surround cells then you cant see anything.. This organization achieves contrast detection.

What is the big problem that must be solved to successfully control running over irregular terrain? How was this problem solved in Warren's analysis? Describe the relevant visual information and how the action was controlled so that this information could be used.

- This big problem that need to be solved was distance perception. In warren's analysis this was solved by substitutuing time for space. The relevant info and how the action was controlled was by finding the differences between the potential surfaces of support between taus, this assumes constant horizontal velocity. The percieved distances between the 2 rocks and the differences between taus will tell you how long you need to stay in the air and that information tells you the amount of impulse your leg needs to exert.

Runeson used the polar planimeter as an example to make a couple of different points. What were they?

1.) Depending on the measurement device being used certain measurements can be simple or more complex.. If you measure with a planimeter area is primitive and the length of the lines need to be derived (complex) 2.) The planimeter does not do computations even though it is a complex physical device it itself cannot to math.. Math can be used to explain what it does but it itself does not do computations.

A.) How did Raibert engineer is running robots? B.) Describe his control structure using 3 parts.

A.) He gave them the bouncing ball dynamic which made it a limit cycle oscillator. He made a pneumatic leg that could change stiffness and inject energy in each cycle. The height of the bounce was determined by the amount of energy injected. B.) He used sensors to detect the phase of motion generated by the bouncing ball dynamic.. He used the sensed phase to control different aspects of running and by this he made explicit control parasitic on the underlying dynamics. The 3 parts included were frequency of stepping which he controllled by pneumatically controlled leg stiffness, posture which he controlled by torquing the hip during contact phase and forward speed which he controlled by the leg angle during the flight phase

A.) What does the light travel through in the eye on its way to the receptors? B.) what determines the refractive power of a lens?

A.) Light entering the eye goes through the cornea, aqueous humor, pupil, lens, vitreous humor, and the retina B.) The refractive index and the curvature of the lens determine the refractice power of the lens and the refractive index is determind by relative density and medium.

A.) What is reletive phase? B.) What are the stable reletive phases typically exhibited in human rhythmic limb movements? What happens as frequency of rhythmic finger movements is increased from preferred rates if the fingers are coordinated to move at 180 degrees to start?

A.) Relative position of 2 oscillators moving at the same time B.) 0 degrees and 180 degrees are the stable reletive phases.. as frequency increases 180 switches to 0 spontaneously at around 3 Hz and as speed is increased it becomes increasingly unstable

A.) What is the organization and dynamics of walking? B.) What key figure of running distinguishes it from walking? What is the organization and dynamic of running?

A.) Walking is upright (swing phase) and inverted (stance phase) pendulums whos lengths determine characteristic perferred frequncies. At a perferred rate of walking the muscles are quiet (not activated) except at the transition between the two phases. B.) The dynamic of running is the bouncing ball dynamic which includes projectile motion (flight) and elastic compression and rebound (contact).. The key feature of running that distinguishes it from walking is that the swing leg is folded under as/like a pendulum so it can swing faster.