Muscle mechanics and neural control
Youlian Hong, Roger Bartlett in Routledge Handbook of Biomechanics and Human Movement Science, 2008
Motor circuits in the spinal cord are not only relevant to execute stretch and withdrawal reflexes but also to enable natural locomotion. Animal studies provide strong evidence that the spinal cord contains the basic circuitry to produce locomotion. As early as 1911, Graham-Brown observed in the cat that coordinated flexor-extensor alternating movements could be generated in the absence of descending or afferent input to the spinal cord (Graham-Brown, 1911). The neural network in the spinal cord which has the capacity to produce this basic locomotor rhythm is called central pattern generator (CPG). The original half-centre model proposed by Graham-Brown consists of a flexor and an extensor half centre that individually possess no rhythmogenic ability, but which produce rhythmic output when reciprocally coupled. However, based on this model it is difficult to explain the diverse patterns which can be generated by spinal CPGs (Stein et al., 1998; Burke et al., 2001). To overcome this problem, it was proposed that multiple oscillators are flexibly coupled to create different patterns (Grillner, 1981). According to this model, spinal CPGs are able to realize many different motor behaviours like walking, swimming, hopping, flying and scratching. The basic pattern produced by a CPG is influenced by signals from other parts of the CNS and sensory information arising from peripheral receptors. This sensory feedback can help to increase the drive to the active motoneurons and is also needed for corrective responses which may be reflectively or voluntarily performed.
The Central Nervous System Organization of Behavior
Rolland S. Parker in Concussive Brain Trauma, 2016
A basic mechanism is central pattern generators (CPGs), which in humans provide rhythmic motor patterns for walking, breathing, chewing, swimming, micturition, and sexual reflexes. The CPG is sited within the lumbosacral spinal cord, but is modified by supraspinal control and peripheral sensory information (mechanoreceptors and cutaneous receptors). It creates oscillatory motor output without any oscillatory input. Control of walking is generated by assemblies of CPGs (spinal interneurons), which are interlinked by propriospinal fibers to facilitate interlimb coordination (Thompson, 2004). By spinal automaticity, it is meant the concept of ability to carry out complex but routine tasks without “conscious thought” (walking across a room; shorter steps taken by the inside limb when walking in an arc; enhancing flexion of the ipsilateral leg when stepping over an object versus enhancing extension in the contrelateral limb, etc.). Proprioception is interpreted by the spinal cord analogously to the manner in which the visual system processes information. Based upon peripheral information (proprioceptive, cutaneous), the CPG receives, interprets, and predicts the appropriate sequences of action for the step cycle. The corticospinal tract, based upon animal study, seems to make fine adjustments rather than generating the basic locomotor pattern, while executing standing and stepping, as well as adapting to varying loads, speeds of stepping, turning, and stepping over objects (Edgerton et al., 2004).
Medical aspects of automatism
John Rumbold in Automatism as a Defence in Criminal Law, 2018
One of the chief features of sleepwalking appears to be that the frontal lobe (neocortex) is not active, but the limbic system is. This is a typical functional impairment that is compatible with medicolegal automatism – the executive centres are impaired, but the central pattern generators or some other source of motor activity are still functioning (Tassinari et al., 2006). Central pattern generators are located in various parts of the brain, and are responsible for various activity such as walking, chewing and more complicated actions involved with flight or fight. The stereotyped behaviours of medical automatism arise from the central pattern generators. The central pattern generators may also be the source of the typical behaviour observed during parasomnias. This would explain the complex motor behaviour triggered by an emotional response but freed from the constraints of the executive centres (and so lack planning and intention). In a nutshell, the capacity for particular motor actions is decoupled from the capacity for moral reasoning, and so it follows that criminal responsibility should not be inferred
Control strategy for intraspinal microstimulation based on central pattern generator
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2023
Xiongjie Lou, Yan Wu, Song Lu, Xiaoyan Shen
The central pattern generator (CPG) is a motor neuronal network located in the spinal cord that can generate rhythmic control output to stimulate muscle movement and control the rhythmic movement of hindlimbs (Rybak et al. 2006; Asadi and Erfanian 2011). Therefore, by electrically stimulating the site of CPG on the spinal cord, we can use a small number of electrodes to restore the movement of the paralyzed lower limbs in a way that is closer to the physiological state. Previous studies have demonstrated that the polarity reversal of stimulation signals reverses the alternating motor pattern in the spinal cord CPG site (Shen et al. 2022). The positive pulse stimulates this CPG site to induce forward and backward movements of the left and right hindlimbs, respectively. Once the polarity of the stimulation signal is reversed, negative pulse stimulation is used to induce backward and forward movements of the left and right hindlimbs, respectively. Therefore, we can realise a complete alternating movement of the rat hindlimbs by combining the two pulse signals with opposite polarities in a certain time sequence.
Effect of Tapping Bout Duration During Freely Chosen and Passive Finger Tapping on Rate Enhancement
Published in Journal of Motor Behavior, 2021
Anders Emanuelsen, Michael Voigt, Pascal Madeleine, Ernst Albin Hansen
The capacity to perform voluntary stereotyped rhythmic movements is of great importance for humans to function well. Examples of such movements include walking, running, pedaling, and finger tapping. Improved understanding of the control and behavior of such rhythmic movements can in a long-term perspective contribute to the improvement of motor treatment, rehabilitation, function, and performance of injured and healthy humans. Our current understanding of human voluntary stereotyped rhythmic movements is that such movements are considered to be controlled by spinal neural networks, termed central pattern generators (CPGs), assisted by tonic supraspinal input, and afferent feedback (Grillner, 2009; MacKay-Lyons, 2002; Prochazka & Ellaway, 2012; Zehr et al., 2004; Zehr & Duysens, 2004). Briefly, it has been argued that CPGs act as a component for the generation and modulation of rhythmic movements in humans (Burke et al., 2001, Zehr et al., 2004, Zehr, 2005). Besides, it has been described that sensory signals play an important role for the nervous system’s generation and modulation of rhythmic movement (Grillner, 2009, Frigon, 2017).
Spinal cord injury and diaphragm neuromotor control
Published in Expert Review of Respiratory Medicine, 2020
Matthew J. Fogarty, Gary C. Sieck
There is considerable regenerative neuroplastic capacity in the neural inputs onto phrenic motor neurons following spinal cord injury. These involve inputs from contralateral bulbospinal projections, local segment interneurons and ascending projections from more caudal regions of the spinal cord [52,99,101–104,109,111,117–119]. In cases where ventilatory behaviors are impaired, such as in the cervical spinal hemisection model, synaptic stripping occurs for the axotomized inputs, with a marked reduction in the number of excitatory glutamatergic pre-synaptic terminals remaining on phrenic motor neurons [120]. In a preliminary study from our group, we found that following unilateral cervical spinal hemisection, the extent of loss of glutamatergic presynaptic terminals (synaptic stripping) is much greater on smaller phrenic motor neurons. This observation confirms that descending inspiratory presynaptic drive for ventilatory behaviors is primarily ipsilateral [49–55] and further suggests this drive is distributed disproportionately to smaller phrenic motor neurons. It is possible that a significant proportion of presynaptic drive for expulsive/straining behaviors does not emanate from a supraspinal origin. In limb locomotor control, the central pattern generator and presynaptic neurons are located segmentally in the spinal cord [1]. This may also be the case for expulsive/straining behaviors of the diaphragm [11,13,17–19,68], particularly those that involve co-activation of chest wall and abdominal muscles (Figure 3).
Related Knowledge Centers
- Brainstem
- Lamprey
- Neural Oscillation
- Neuromodulation
- Proprioception
- Ventral Nerve Cord
- Spinal Cord
- Neural Circuit
- Swallowing
- Hypoglossal Nucleus