Robotic Simulation of the Musculo-Skeletal System - Research Paper Example

Robotic Simulation of the Musculo-Skeletal System Although, the muscles in the body are divided into three categories viz. the skeletal, smooth and the cardiac muscle, it is only the skeletal muscle that is under voluntary and conscious control of any mammalian species. The smooth muscles like those of the intestines, the uterus, blood vessels and bladder, as well as the cardiac muscles, are controlled automatically through the actions of neurotransmitters and are therefore collectively referred to as involuntary. The skeletal muscles are also called voluntary or striated muscles which possess peculiar anatomical and physiological characteristics to enable them to control locomotion in conjunction with the skeletal structures, under the influence of neural signals from the brain. They do so by alternately contracting and relaxing in response to the stimuli provided by the righting reflex as well as gravity. Bones serve as points of attachment to the skeletal muscles and multiple sets of muscles work in conjunction with each other and emulate various types of levers to bring about movement for different life activities. To emulate the movements of the skeletal system in a robot or a prosthetic limb therefore requires understanding of the neural control of skeletal muscles as well as how the various lever systems function. Anatomy of the Skeletal Muscle A typical skeletal muscle although composed of similar type of cells is functionally divided into three parts: 1. Origin: The point where the muscle is firmly attached to the bone. 2. Body: The major muscular tissue. 3. Insertion: The farther extremity of the muscle which is transformed into a glistening white tendon. The body of the muscle is made up of hundreds of cylindrical fibers running all the way from the origin to insertion. These cylindrical fibers are composed of an array of a specialized category of cells which collectively form the myofibrils. Each muscle fiber develops from the fusion of many cells called myoblasts. Muscles contract by the action of Acetyl Choline (A Ch), a neurotransmitter secreted from the nerve ending supplying the muscle. Action of A Ch causes a change in the action potential at the neuromuscular synapse leading to binding of Actin and Myosin molecules which results in a contraction. Muscle Movements The human skeleton is made up of 206 bones and covered all over by skeletal muscles which keep it together as well as allow various types of coordinated locomotor functions. Each bone is connected to the other in an intricate pattern of joints which may exhibit different levels of mobility. The movements which are possible in joints can be divided into four types: gliding and angular movements, circumduction, and rotation (Grey’s Anatomy). These movements, however, do not take place exclusively and occur in form of combinations in various joints, so as to produce an infinite variety. Various types of movement possible through the joint actions of the muscles and bones include Flexion/Extension, Abduction/Adduction, Lateral/Medial Rotation, Circumduction, Elevation/Depression, Retraction, Rotation, Dorsiflexion/Plantar Flexion, Eversion/Inversion, Abduction/Adduction, Opposition and Pronation/Supination (Bruenger et al, 1994). Muscle movement takes place in conjunction with the bones to which they are attached following the basic principles of the three types of levers. Usually for each type of movement carried out by a particular muscle, there is a reciprocal muscle to reverse the action of the original muscle and such muscles are known as antagonistic muscles. The main pairs of antagonistic muscles present in the human body and their respective movements are described as under (Bruenger et al, 1994): 1. Biceps-Triceps: The upper end of the biceps or its origin is from the triangular bone at the back of the shoulder called scapula and its other end or insertion is on the Radius (inner) bone of the forearm. Contraction of biceps brings about flexion or rising of the forearm and this muscle is therefore a flexor muscle. The opposite or the antagonistic muscle is the Triceps which relaxes at the time the Biceps contracts. Triceps is located behind the upper arm and its origin is from the Scapula as well as the Humerus bone in the upper arm, and its point of insertion is at the Olecranon process of the Ulna (the exterior bone in the forearm). Contraction of Triceps straightens the arm and hence this muscle is known as an extensor muscle. 2. Anterior Tibialis and Gastrocnemius muscles: These muscles form the pair which is responsible for the movement of the lower leg. The two muscles are used when a person rocks forwards and backwards on the feet. The Anterior Tibialis contracts when one rocks forward while the Gastrocnemius relaxes and the opposite takes place when the person rocks backwards. 3. Scapula: The triangular bone at the back of the shoulders and its muscles play antagonistic roles when one hunches forwards, the muscles contract and when the shoulders are squared, they retract. This type of antagonistic muscles movement is known as Protraction-Retraction. The Deltoid muscle originates from the Clavicle (Collar bone) and the Scapula and inserts on the Humerus (Main bone of the upper arm). The Deltoid is composed of 3 muscles. The Anterior Deltoid is responsible for flexion, internal rotation and stabilization while the Medial Deltoid abducts the shoulder. 4. Wrist Extension/Flexion: The major Extensors of the wrist are the two muscles called the ‘Extensor Carpi Radialis Longus’ and the ‘Extensor Carpi Ulnaris’. This origin of this muscle group is from the Humerus and the insertion is on the metacarpal bones in the body of the hand. These muscles come into action when the wrist is extended. The flexor muscles of the wrist include the ‘Flexor Carpi Radialis’ and ‘Flexor Carpi Ulnaris’ muscles. Both these muscles have their origin at the Humerus and insertion on the Metacarpals. 5. Latissimus Dorsi and the Teres Major muscles: The ‘Latissimus Dorsi’ is the largest muscle of the back and is a paired muscle on both sides of the back. Its origin lies along the lower thoracic/lumbar vertebrae, the Pelvis and Sacrum bones, and its insertion point is the Humerus bone in the upper arm. The Latissimus Dorsi works synergistically with Teres Major to extend, adduct and internally rotate the arm at the shoulder. 6. Gluteus Medius and Gluteus Minimus: Gluteus Medius and Gluteus Minimus are the hip abductor muscles. They originate from the external surface of the Ileum and attach to the Femur or the thigh bone. These two muscles are responsible for stabilization of the body posture and assist in the external rotation of the Hip Joint. Emulation of the skeletal movements in robotic structures is an overwhelming task as it involves development of intricate electronic control units for each movement which have to be synchronized with each other. Emulation of the signals originating from the brain which coordinate skeletal movement is the most difficult task and it has to be coordinated with mechanical structures designed to mimic human skeletal movement. The general hierarchical structure of the humanoid locomotion controller and the robot with virtual muscles involves emulation of the signals originating from the brain stem, cerebellum, basal ganglia and the cerebrum (Shan & Nagashima, undated). Activities of the cycle locomotion behavior are generated through rhythmic neuronal activities originating in the spine and Central Pattern Generators (CPGs) operate at the level of motoneurons (MNs). MNs are the area from where virtual muscles can be stimulated through electronic control commands for movement of the robotic joint. Current robotics development is focused around the control of MNs through electronic stimulation to emulate human skeletal movements in prosthetic structures. References Bruenger, J., Fischer, T., Chapman, C. et al (1994). Hypermuscle: Muscles in Action, Retrieved Dec. 18, 2010 from: http://www.med.umich.edu/lrc/Hypermuscle/ Shan, J. & Nagashima, F. (undated). Biologically Inspired Spinal locomotion Controller for Humanoid Robot, Retrieved Dec. 18, 2010 from: http://192.240.0.102/downloads/GLOBAL/labs/papers/hoap2.pdf The Kind of Movement Admitted in Joints, Gray's Anatomy, Retrieved Dec. 18, 2010 from: http://www.bartleby.com/107/71.html Read More