- Slides: 49
Abstract Octopus vulgaris has been studied for more than 50 years, but it has proven to be a very complicated creature. The research group focus is understanding the way the octopus moves, so this knowledge will be used, for example, in the field of robotics. It has been discovered that the octopus has a stereotypical reaching movement. The goal was to understand the mechanisms that generate those movements and create a dynamic computer model.
Octopus Belongs to the Cephalopoda. The only one with a brain. An octopus is composed mainly of muscles. Arms uses: sensing, chemotaxis, movement, catching pray … There is no preferred arm. Special abilities: change color, change body texture, jet propulsion, ink ejection, regenerate. Octopus is muscular hydrostat.
Degrees of freedom Degree of freedom - The relative movement between two parts that can be describes with one parameter. Skeleton imposes a constraint on the number of degrees of freedom. The human hand has 7 degrees of freedom. The octopus has a virtually infinite number of degrees of freedom. e=mc^2? How can a movement be calculated? !? !
Reaching movement It was found (Guetfruind et al. 1996) that the octopus has a stereotypical active reaching movement (not whip like). b. Bend propogation a. Bend formation It can be described as such: a. A bend is formed somewhere along the arm (suckers towards target). b. The bend propagates from the base part of the arm to it’s tip. The part of the arm proximal to the bend remains extended. (Gutfreund et al. 1996)
Reaching movement The bend of a normal reaching movement advances in a slightly curved manner in a single linear plane. (Gutfreund et al. 1996)
Velocity profile Tangential velocity- bend advance in x, y, z axis (in 3 D). The velocity profile of the octopus has bell shaped characteristics: Velocity stats: (Gutfreund et al. 1996) min 16 cm/sc max 61 cm/sc mean 35 cm/sc sd 9. 5 cm/sc
Embedded Reaching movement • • • The total number of neurons in an octopus is In the arms, there are neurons. There are motor neurons in each arm. • This information led to the assumption that the reaching movement of the octopus is embedded in the arm itself. .
Evoked Reaching movement Arm extensions can be elicited in denervated arms by electrical stimulation of the arm axial nerve cord or by tactile stimulation of the skin or suckers, suggesting that a major part of this voluntary movement is controlled by a motor program that is confined to the arm’s neuromuscular system. (Sumbre et al. 2001) a. Arm cross section: b. Axial nerve cord: (Sumbre et al. 2001)
The Reaching Model Our group has devised a dynamic computer model to simulate the reaching movement of the octopus in 2 D (3 D is now the goal). The model has a similar velocity profile like the normal reaching movement. There are several parameters that can be changed: gravity, friction in water (drag), activation force …
OOW Movement Goals 1. Analyze differences In Water and OOW environments for the octopus, and its implications. 2. Characterizing the bend point position in space, velocity profile, duration. 3. Understand the mechanism behind the reaching movement in general. 4. Comparison to the Reaching Dynamic Model.
OOW- Methods The octopus’s movements were videotaped on two cameras. For each experiment a calibration body was used, in order to integrate the data from the two cameras into three dimensions. During the OOW experiment, one of the octopus’s arms was held by the experimenter.
OOW Environment In OOW environment some parameters are not the same as in water: No drag force OOW. 2. No buoyancy. Buoyancy force = (Density) (Volume) 3. Gravitation force. 4. OOW movement is probably energetically costly. 1.
OOW – Bend pos. in Space The bend position in space in normal reaching movement is in a single linear plane, with slightly curved path. The bend position in OOW reaching movement is in three dimension. Movement 6_1
OOW – Velocity profile for normal reaching was calculated using Tangential velocity formula. BUT, The nonlinear nature of the OOW reaching movement makes this formula inadequate. Another was used: (which I term Euclidian velocity) Reaching movement Velocity profile table: Normal Mean peak vel. (cm/sec) num of movements Upwards OOW 1 OOW 2 35. 24± 9. 55 28. 1± 10. 74 7. 88± 2. 59 15. 94± 5. 5 83 17 23 13
OOW – movement duration Reaching movement duration table: Normal Mean dur. (sec) num of movements Upwards OOW 1 OOW 2 1. 02± 0. 42 1. 11± 0. 38 0. 97± 0. 4 1. 03± 0. 34 83 17 23 13
Correction of arm base during OOW reaching movement- two mechanisms 90° view of the bend point as a function of time base Tan vel. Euc vel. The advance of the bend point is independant of the base correction
Bell shaped velocity profile? • When using the Euclidian velocity profile on normal reaching movements, the first phase was gone. • This implies that this phase is due to a correction of the base of the arm. Euc vel profile (Tan-Euc) vel profile
OOW – The Model The parameters of the model were modified: 1. The octopus’s arm base is directed upwards. 2. The Drag force is eliminated. 3. No buoyancy OOW. The activation forces were modified on need.
Fetch movement • It is interesting to see another kind of movement-the fetch movement, and understand how this movement can be generated.
In water reach (no gravity) OOW reach (gravity) In water OOW Movement dur. 0. 8 sec 0. 72 sec
Circadian Rhythms Amit Shabtay 2004
The Clock in our Lives • In 1729, De. Marain described a daily rhythmic opening and closing of the leaves of a heliotrope plant. • What was very interesting, is that this rhythm persisted, even in the absence of light. • Since then it has been discovered that this “clock” is present in almost all eukaryotic life. • Another kind of clock was found- a timer, on which we will not elaborate.
Definitions • Free run- only darkness conditions. • Circadian time- the inner cycle of the animal, which is usualy != 24 hours cycle. • Solar time- 24 hours cycle of the sun. • Citegeber time- artificial cycle given to the animal. • All these cycles are normalized to 24 hours cycle.
Experimental Data Solar time Free run
Reseting the Clock What about blind people?
There are Many “Clocks” • The signal from the SCN travels to the entire body, and affects many functions of it.
Phase Response Curve Next night will be earlier Next night will be postponed There is a delay in the response of the clock
Two oscillating proteins
A few Words about Skeletal muscles A skeletal muscle is a muscle that is connected to the skeleton (as opposed to the heart muscle or smooth muscle) Always work in maximum tension
Length-Tension curves The skeletal muscle has two kinds of forces- passive force and active force
The Importance of Closed circle Control Mission 1 a neurons Calc firing rate Check Sit. Spindle Activate muscle α Motoneurons
Adding Load is added, Spindle is stretched α Motoneurons cause the muscle to contract. Spindle is relaxed Spindle is stretched again.
Two Variable Equation Firing motoneurons as a function of muscle length Muscle length as a function of firing motoneurons
Two Variable Equation Matching axes Firing motoneurons as a function of muscle length Muscle length as a function of firing motoneurons
Two Variable Equation Joining graphs Working point
Correcting Errors Correction Error
Correcting Errors Time of error
Correcting Errors When the amplification is too high, oscillations can occur
Stable Feedback System • The feedback system will always be stable if these three conditions are met: 1. Amplification < 1 2. Short delays 3. Slow response to changes Response Firing rate of mn α Delay Muscle length time
Returning to Working Point Short delays, Fast response
Returning to Working Point Short delays, Slow response