1. ON CONTROL OF OCTOPUS ARMS
G. Sumbre et al (Hebrew University Jerusalem, IL) discuss octopus
arm control. The octopus arm can move in any direction, using a
virtually infinite number of degrees of freedom. This high
maneuverability results from the fact that the octopus arm is
almost entirely constructed of densely packed muscle fibers along
its transverse, longitudinal, and oblique axes. The flexible arms
are controlled by an elaborate peripheral nervous system
containing approximately 5 x 10^(7) neurons distributed along
each arm. Only approximately 4 x 10^(5) of these neurons are the
motor neurons which innervate the intrinsic muscles of the arm
and locally control muscle action. This peripheral nervous system
is organized as an axial nerve cord composed of approximately 300
interconnected clusters of nerve cell bodies (ganglia) and two
cerebrobrachial axonal tracts of approximately 30,000 nerve
fibers running dorsally to the ganglia. The axons in the tracts
carry sensory and motor information to and from the highly
developed centralized brain. The authors demonstrate that octopus
arm extensions can be evoked mechanically or electrically in arms
whose connection with the brain has been severed. These
extensions exhibit kinematic features that are almost identical
to normal behavior, which suggests that the basic motor program
for voluntary movement is embedded within the neural circuitry of
the arm itself. The authors suggest that such peripheral motor
programs represent considerable simplification in the motor
control of this highly redundant appendage.
http://scienceweek.com/2001/sw011130.htm
Contents of this Issue (Full reports in Section 2):
1. On Control of Octopus Arms
2. Evolution, Viruses, and Cell-Surface Receptors
3. On Aquaporin Water Channels in Membranes
4. On the Microbiome
5. On Self-Organization of Motors and Microtubules
6. Ecology and Social Network Analysis
7. A Sperm Ion Channel Required for Sperm Motility
8. On Catastrophic Shifts in Ecosystems
9. Problems in NMR Spectroscopy of Biological Macromolecules
10. Behavior of Water in Thin Films
11. On the Moons of Jupiter
12. Plasma Jets in Active Galactic Nuclei
13. PostDoctoral Fellowships Profile: Laboratory of Sampath
Parthasarathy at Emory University, US
14. In Focus: On Russian Science and Bioterrorism
15. From PRAXIS: Bt Corn: Current Risk Assessment
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