COORDINATION
The dynamics of coordination are strongly dependent on the processing of perceptual information. The flow of afferent feedback through motor neurons is greatly influenced by Renshaw cells each of which are innervated by many motor neurons in synergistic muscle groups (Enoka BOOK )
‘The Seven degrees of freedom’ an approach first coined by Bernstien in 1930’s help the human us to work out the location of the object in the environmental space. These degrees of freedom maybe restricted by being amalgamated together (for example supination/pronation of the forarm, flexion and extension of the arm at the elbow joint.) presumably to allow for more control, we can therefore pick the glass up. It is this muscle joint ‘workout’ which is collectively known as muscle synergy. Coordinating and organising the movements is all a part of the neuromuscular game plan, to be able to control the movements effectively is what is required to allow the glass to be picked up.
Avella et al (2003) state
“The many degrees of freedom of the musculoskeletal apparatus provide great flexibility but make the control problem extremely complex. Muscle synergies—coherent activations, in space or time, of a group of muscles—have been proposed as building blocks that could simplify the construction of motor behaviours”
In terms of our situation where we are going to pick the glass up, and when examining the above opinion this means that from one time until the next there will be variations in posture and muscle synergies.
These linkages (synergies) defined are flexible in nature meaning that the synergies and movements will differ according to the situation essentially from what is within the environment. So from one time to the next the glass may be picked up in a different way according what is presented at the time.
Humans can use several postural strategies to maintain balance, resulting in different responses to the same perturbations. Factors that affect the choice of strategy include prior experience, habituation, expectation, and fear (Torres & Ting 2007)
Important to point out the our ‘central pattern generators’ will help us to initiate many different movements at the same time for example the movement of the eye ball then the head, posture control, arm extension and leg extension/flexion grasping of the glass before we flex at the elbow joint and place the glass gently on the mouth extending the legs.
I am presuming that either the right or the left sided limbs (one -sided) will be dominant in accomplishing the glass pick up task. As we are in the in-phase of ipsilateral co-ordination the limbs will remain stable as we are moving in the same direction. The relative phase standard deviation in this instance will be measured as lower than if we were moving in the opposing directions with the same sided limbs. Suffice to say that we can pick up the glass with ease in a fairly quick time threshold.
CUTANEOUS SENSATION
Sensation on the skin is of vital importance for controlling movement properly. Once the hand comes into contact with the glass, the glass will be sensed, and subsequently fire up the mechanoreceptors of which there are four. In the human hand the sub modalities of touch are sensed by 4 types of mechanoreceptors. Specific tactile sensations occur when distinct types of receptors are activated.
Merkel cells and Ruffini endings both with small receptor fields produce sensations of steady pressure on the skin above the receptor. So we know that these particular cells enable the very initial phase of sensation of hand to the glass. Mahrle & Orfanos (1974) found the significance of the Merkel cells as an important neuro-receptor cell enabled to register and to transform peripheral stimuli into axonal impulses from the dermis, the epidermis and the follicular epithelium as well.
Fast adapting mechanoreceptor fibres will be the first to respond to the contact of the hand as they respond to changes in skin indentation, the pressure of the hand on the glass on the glass. Fast adapting fibres will signal stimulus only for a few seconds when the changes in pressure are taking place. Whereas the slow adapting fibres will respond to the constant pressure of the glass being held in the hand their signals will last for several minutes whilst we maintain the grip on the glass.
Meissner's corpuscles are low threshold phasic receptors many of which are found within the hand aid us to detect friction between the internal ridges of the epidermis indicates they are well situated to detect friction or deformation at the external surface. According to Drew Rugiero F & Wood (2007), there is one single nerve fibre per corpuscle. Any physical deformation of the corpuscle triggers a volley of action potentials that quickly ceases. When the stimulus is removed, the corpuscle regains its shape and while doing so produces another volley of action potentials. Due to their superficial location in the dermis, these corpuscles are particularly sensitive to touch and vibrations, being able to respond to low-frequency vibrations in the range of 20–40 Hz. This means that as we grip the glass Meissner's corpuscles quickly come in to action.
Ruffini endings will signal the vertical gravitational forces applied to the skin as the object is lifted Wing et al (1997) interestingly states that
“…..the size, orientation, and location of an object are not the only features that control the parameters of a grasping movement. To pick up an object successfully, it is not enough to orient the hand and scale the grip appropriately and direct the grasp in the correct direction; the fingers and thumb must also be placed at appropriate opposition points on the object's surface. Computation of these grasp points must take into account the surface boundaries or shape of the object. In fact, even casual observations of grasping movements suggest that the posture of the fingers and hand are remarkably sensitive to object shape.”
Typically our receptors will adapt to the response and we know that when we grip the glass the variability of the strength of the grip applied into the horizontal direction will vary according to whether the glass is slippy or not, obviously our grip strength and force will increase the more slippery the glass is. The load force is the force in the vertical direction that is required to raise the object. The grip force is the force applied to the object in the horizontal direction in order to hold it between the fingers. Sensory receptors measure the load force, the grip force and the vertical motion. Small slips between the object and the skin are measured by accelerations (vibrations) in the object. Pacinian corpuscles are most sensitive to transient mechanical pressures at the start and stop of motion, when the object is lifted off and replaced on the surface.
The location of MCs between the are highly active during the initial period of contact as grasp force increases; these receptors also fire when a second burst when the grip is released. Merkel disk receptors are also stimulated during the initial grip, but they continue to fire as the object is lifted, signalling grip force; they cease firing when the grip is released. .Firing of all 4 receptors produces the sensation of contact with an object. Selective activation of Merkel cells and Ruffini endings produces sensations of steady pressure on the skin above the receptor. When the same patterns occur only in Meissner's and Pacinian corpuscles, the tingling sensation of vibration is perceived.
References
Bridgeman B (2007) Efference copy and its limitations Computers in Biology and Medicine Vol 37(7), Pages 924-929 Vision and Movement in Man and Machines
Säfström D and Edin B B. In Humans Task Requirements Influence Sensory Integration During Grasping Learning and. Memory 2004 11: 356-363
Tubaldi F, Ansuini, C; Luisa Dematte, Roberto Tirindelli3 and Umberto Castiello C Effects of Olfactory Stimuli on Arm-Reaching Duration. Chemical Senses Advance Access published March 15, 2008
Neuromechanics of Human Movement. Enoka RA.
Mahrle G, Orfanos CE(1974) Merkel cells as human cutaneous neuroreceptor cells Archives of Dermatological Research, Volume 251, Number 1 / March, 1974
Drew LJ a, Rugiero F aand Wood (2007) JRaTouch Current Topics in MembranesVolume 59, 2007, Pages 425-465http://en.wikipedia.org/wiki/Efference_copy
Andrea d'Avella1, 2, Philippe Saltiel1 & Emilio Bizzi1Nature Neuroscience 6, 300 - 308 (2003) Published online: 3 February 2003; doi:10.1038/nn1010 Combinations of muscle synergies in the construction of a natural motor behaviour
Simon C. Gandevia1, Janette L. Smith1, Matthew Crawford2, Uwe Proske3 and Janet L. Taylor1
J Physiol Volume 571, Number 3, 703-710, March 15, 2006 DOI: 10.1113/jphysiol.2005.103093
Rapid report - Motor commands contribute to human position sense
Alan M. Wing, Patrick Haggard and J. Randall Flanagan The Hand in Action Hand and Brain The Neurophysiology and Psychology of Hand Movements 1996, Pages 1-3
(Tresilian, 1999)
Fitts PM, Posner MI (1967) Human Performance. Belmont, CA: Brooks/Cole.
The dynamics of coordination are strongly dependent on the processing of perceptual information. The flow of afferent feedback through motor neurons is greatly influenced by Renshaw cells each of which are innervated by many motor neurons in synergistic muscle groups (Enoka BOOK )
‘The Seven degrees of freedom’ an approach first coined by Bernstien in 1930’s help the human us to work out the location of the object in the environmental space. These degrees of freedom maybe restricted by being amalgamated together (for example supination/pronation of the forarm, flexion and extension of the arm at the elbow joint.) presumably to allow for more control, we can therefore pick the glass up. It is this muscle joint ‘workout’ which is collectively known as muscle synergy. Coordinating and organising the movements is all a part of the neuromuscular game plan, to be able to control the movements effectively is what is required to allow the glass to be picked up.
Avella et al (2003) state
“The many degrees of freedom of the musculoskeletal apparatus provide great flexibility but make the control problem extremely complex. Muscle synergies—coherent activations, in space or time, of a group of muscles—have been proposed as building blocks that could simplify the construction of motor behaviours”
In terms of our situation where we are going to pick the glass up, and when examining the above opinion this means that from one time until the next there will be variations in posture and muscle synergies.
These linkages (synergies) defined are flexible in nature meaning that the synergies and movements will differ according to the situation essentially from what is within the environment. So from one time to the next the glass may be picked up in a different way according what is presented at the time.
Humans can use several postural strategies to maintain balance, resulting in different responses to the same perturbations. Factors that affect the choice of strategy include prior experience, habituation, expectation, and fear (Torres & Ting 2007)
Important to point out the our ‘central pattern generators’ will help us to initiate many different movements at the same time for example the movement of the eye ball then the head, posture control, arm extension and leg extension/flexion grasping of the glass before we flex at the elbow joint and place the glass gently on the mouth extending the legs.
I am presuming that either the right or the left sided limbs (one -sided) will be dominant in accomplishing the glass pick up task. As we are in the in-phase of ipsilateral co-ordination the limbs will remain stable as we are moving in the same direction. The relative phase standard deviation in this instance will be measured as lower than if we were moving in the opposing directions with the same sided limbs. Suffice to say that we can pick up the glass with ease in a fairly quick time threshold.
CUTANEOUS SENSATION
Sensation on the skin is of vital importance for controlling movement properly. Once the hand comes into contact with the glass, the glass will be sensed, and subsequently fire up the mechanoreceptors of which there are four. In the human hand the sub modalities of touch are sensed by 4 types of mechanoreceptors. Specific tactile sensations occur when distinct types of receptors are activated.
Merkel cells and Ruffini endings both with small receptor fields produce sensations of steady pressure on the skin above the receptor. So we know that these particular cells enable the very initial phase of sensation of hand to the glass. Mahrle & Orfanos (1974) found the significance of the Merkel cells as an important neuro-receptor cell enabled to register and to transform peripheral stimuli into axonal impulses from the dermis, the epidermis and the follicular epithelium as well.
Fast adapting mechanoreceptor fibres will be the first to respond to the contact of the hand as they respond to changes in skin indentation, the pressure of the hand on the glass on the glass. Fast adapting fibres will signal stimulus only for a few seconds when the changes in pressure are taking place. Whereas the slow adapting fibres will respond to the constant pressure of the glass being held in the hand their signals will last for several minutes whilst we maintain the grip on the glass.
Meissner's corpuscles are low threshold phasic receptors many of which are found within the hand aid us to detect friction between the internal ridges of the epidermis indicates they are well situated to detect friction or deformation at the external surface. According to Drew Rugiero F & Wood (2007), there is one single nerve fibre per corpuscle. Any physical deformation of the corpuscle triggers a volley of action potentials that quickly ceases. When the stimulus is removed, the corpuscle regains its shape and while doing so produces another volley of action potentials. Due to their superficial location in the dermis, these corpuscles are particularly sensitive to touch and vibrations, being able to respond to low-frequency vibrations in the range of 20–40 Hz. This means that as we grip the glass Meissner's corpuscles quickly come in to action.
Ruffini endings will signal the vertical gravitational forces applied to the skin as the object is lifted Wing et al (1997) interestingly states that
“…..the size, orientation, and location of an object are not the only features that control the parameters of a grasping movement. To pick up an object successfully, it is not enough to orient the hand and scale the grip appropriately and direct the grasp in the correct direction; the fingers and thumb must also be placed at appropriate opposition points on the object's surface. Computation of these grasp points must take into account the surface boundaries or shape of the object. In fact, even casual observations of grasping movements suggest that the posture of the fingers and hand are remarkably sensitive to object shape.”
Typically our receptors will adapt to the response and we know that when we grip the glass the variability of the strength of the grip applied into the horizontal direction will vary according to whether the glass is slippy or not, obviously our grip strength and force will increase the more slippery the glass is. The load force is the force in the vertical direction that is required to raise the object. The grip force is the force applied to the object in the horizontal direction in order to hold it between the fingers. Sensory receptors measure the load force, the grip force and the vertical motion. Small slips between the object and the skin are measured by accelerations (vibrations) in the object. Pacinian corpuscles are most sensitive to transient mechanical pressures at the start and stop of motion, when the object is lifted off and replaced on the surface.
The location of MCs between the are highly active during the initial period of contact as grasp force increases; these receptors also fire when a second burst when the grip is released. Merkel disk receptors are also stimulated during the initial grip, but they continue to fire as the object is lifted, signalling grip force; they cease firing when the grip is released. .Firing of all 4 receptors produces the sensation of contact with an object. Selective activation of Merkel cells and Ruffini endings produces sensations of steady pressure on the skin above the receptor. When the same patterns occur only in Meissner's and Pacinian corpuscles, the tingling sensation of vibration is perceived.
References
Bridgeman B (2007) Efference copy and its limitations Computers in Biology and Medicine Vol 37(7), Pages 924-929 Vision and Movement in Man and Machines
Säfström D and Edin B B. In Humans Task Requirements Influence Sensory Integration During Grasping Learning and. Memory 2004 11: 356-363
Tubaldi F, Ansuini, C; Luisa Dematte, Roberto Tirindelli3 and Umberto Castiello C Effects of Olfactory Stimuli on Arm-Reaching Duration. Chemical Senses Advance Access published March 15, 2008
Neuromechanics of Human Movement. Enoka RA.
Mahrle G, Orfanos CE(1974) Merkel cells as human cutaneous neuroreceptor cells Archives of Dermatological Research, Volume 251, Number 1 / March, 1974
Drew LJ a, Rugiero F aand Wood (2007) JRaTouch Current Topics in MembranesVolume 59, 2007, Pages 425-465http://en.wikipedia.org/wiki/Efference_copy
Andrea d'Avella1, 2, Philippe Saltiel1 & Emilio Bizzi1Nature Neuroscience 6, 300 - 308 (2003) Published online: 3 February 2003; doi:10.1038/nn1010 Combinations of muscle synergies in the construction of a natural motor behaviour
Simon C. Gandevia1, Janette L. Smith1, Matthew Crawford2, Uwe Proske3 and Janet L. Taylor1
J Physiol Volume 571, Number 3, 703-710, March 15, 2006 DOI: 10.1113/jphysiol.2005.103093
Rapid report - Motor commands contribute to human position sense
Alan M. Wing, Patrick Haggard and J. Randall Flanagan The Hand in Action Hand and Brain The Neurophysiology and Psychology of Hand Movements 1996, Pages 1-3
(Tresilian, 1999)
Fitts PM, Posner MI (1967) Human Performance. Belmont, CA: Brooks/Cole.
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