Biomechanics and control of the octopus arm Yoram Yekutieli, Hadassah Academic College and Weizmann Institute of Science

Transcription

1 Biomechanics and control of the octopus arm Yoram Yekutieli, Hadassah Academic College and Weizmann Institute of Science Ultrafest V, Haskins Laboratories, March 2010

2

3 Searching Cleaning Swimming Prying open an oyster Gathering stones

4 The octopus arm

5 The octopus arm musculature Oblique muscle fibers Transverse muscle fibers Longitudinal muscle fibers

6 The octopus arm is a muscular hydrostat Antagonistic muscle groups Oblique muscle fibers Transverse muscle fibers Longitudinal muscle fibers

7 Highly localized control: ~0.01 x 1 mm muscle cell Electrically compact Uncoupled 3.8 x 10 5 motor neurons/arm Motor unit size ~3300 muscle cells / neuron ~0.2 mm 3 Localized mechanoreceptors

8

9 Stereotypic movements as clues to the existence of control strategies

10

11 J. Neuroscience, 1996, 16(22):

12

13 J. Neuroscience, 1998, 18(15):

14

15 The final trajectory depends on the initial posture of the arm

16 The reaching movement and its initiation may compensate for the lack of position and shape information: 1. The initiation may take an arm from an arbitrary posture to a standard one, where the arm is ready to reach again. 2. The reaching movement strategy uses a simple geometry to point and reach to the targets: a straight arm whose orientation is based on two angles.

17 What is the mechanism that produces the Extension movement? How does the bend moves? By a specific pattern that differentially activate the dorsal and the ventral muscles and moves along the arm, or by a uniform wave of muscle contraction that travels along the arm and stiffens the arm?

18 J. Neurophysiology 94: , 2005.

19 J. Neurophysiology 94: , 2005.

20

21 A 0m s B 200ms 400ms 600ms C 800ms 1000ms

22 Checking the model in different conditions Passive pendulum

23 Gutfreund et al. 1998

24 Longitudinal muscles relaxed length Transverse muscles Constant area normalized force normalized muscle length Longitudinal muscles Transverse muscles Constant area

25 This biomechanical organizational principle may be seen as a way to simplify control; irrespective of the current shape of the organ, equal and concurrent activations of all muscle groups shape the organ to a standard shape with a degree of stiffness that is dependent on the level of activation. This standard shape is the shape in which all muscle forces are balanced, and its actual dimensions depend on the relative number of muscle fibers in each orientation and their contractile properties. Transverse muscles Longitudinal muscles Constant area normalized force normalized muscle length Longitudinal muscles Transverse muscles Constant area

26 Stimulating the nerve cord using high amplitude and high frequency signal opens the loop of the arm in a movement that is different from the extension movement. Sumbre et al. 2001

27 A 0ms B 60ms Using a fast and strong activation signal in the simulation results in a similar movement 120ms 180ms 240ms 300ms

28

29 The fetch movement involves an articulated-like structure 0 ms 1160 ms 800 ms 1360 ms 1040 ms 1640 ms

30

31 The articulated structure is formed by two waves of muscle contraction, propagating in opposite directions 10 A B C Normalized delay Normalized delay D L2 L3 Pull L1 L2 L3 > > = > < <

32 1.5 1 A The integrated EMG correlates with the length of the articulated structure Standarized length 1.5 B EMG Standarized length Time (sec)

33 The octopus motor system couples together degrees of freedom in different ways but both the reaching movement and the fetching movement can be described by a small number of control variables.

34 J. Neurophysiology 98: , 2007

35

36

37

38

39

40 Journal of Neuroscience Methods 182 (2009)

41

42

43

44 Elongation - squid (by W.M. Kier)

45 Elongation octopus Shlomi Hanassy, Hebrew University of Jerusalem. unpublished

46

47

48

49

50

51

52

53

54

55 Weizmann Institute: Prof. Tamar Flash Dr. Ido Zelman Trayambaka Nath Karra Hebrew University: Prof. Benny Hochner Dr. Yoram Gutfreund Dr. German Sumbre Henri Matzner Rea Mitelman Shlomi Hanassy Dr. Letizia Zullo Thank you

56