Flashcards
Motor control 2
Flashcards do conjunto (19)
- 1How do alpha and gamma motor neurons differ during stimulation?
- 2What modulates the gain of the stretch reflex?Gamma Motor Neurons Modulate the Gain of the
Stretch Reflex
- 3Describe the descending somatic motor pathwaysDescending tracts deliver motor instructions from the brain to the spinal cord.
Divided into two groups:
Pyramidal, or corticospinal, tracts.
Indirect pathways—essentially all others.
Motor pathways involve (at least) two neurons .
Upper motor neuron (UMN; e.g. M1 pyramidal cell).
Lower motor neuron (LMN; e.g. alpha motor neuron).
- 4Describe the pyramidal coticospinal pathwayOriginates in the motor cortex.
Layer V pyramidal neurons are the UMNs:
Their axons forms the corticospinal tract.
UMNs synapse in the anterior horn with LMNs:
Some UMNs decussate in pyramids (lateral corticospinal tracts).
Others decussate at other levels of spinal cord (anterior corticospinal tracts).
LMNs (anterior horn motor neurons):
Exit spinal cord via ventral (anterior) root .
Activate skeletal muscles.
Regulates fast and fine (skilled) movements - 5What is the difference between anterior and lateral corticospinal tracts?The corticospinal tract is the primary pathway that carries the motor commands that underlie voluntary movement:
The anterior / ventral corticospinal tract is responsible for the control of the proximal musculature.
The lateral corticospinal tract is responsible for the control of the distal musculature.
- 6What are the pyramids?Most of the corticospinal axons decussate to enter the descending lateral corticospinal tracts.
Those that do not cross over enter the anterior corticospinal tracts
- 7What encompasses the extrapyramidal motor tracts?Includes all motor pathways not part of the pyramidal system.
Upper motor neurons (UMNs) originate in nuclei in brain stem (not in cerebral cortex).
UMNs do not pass through the pyramids.
This system includes:
rubrospinal;
reticulospinal;
vestibulospinal;
tectospinal tracts.
They regulate:
axial muscles that maintain balance and posture;
muscles controlling coarse movements of the proximal portions of limbs;
head, neck, and eye movement. - 8What is the rubrospinal tract?Originates in the Red Nucleus of the midbrain.
The rubrospinal pathway is an alternative by which voluntary motor commands can be sent to the spinal cord.
Although it is a major pathway in many animals, it is relatively minor in humans.
Activation of this tract typically causes excitation of flexor muscles and inhibition of extensor muscles.
- 9Describe the medial extrapyramidal pathwaysThe vestibulospinal tracts originate in the vestibular nuclei, and are involved in posture, and in supporting the body against the force of gravity, mainly targeting extensors.
The tectospinal tracts originate in the superior colliculi and mediate orienting towards visual targets.
The reticulospinal tract originates in the reticular formation—a diffuse collection of neurons in the pons and medulla. It is involved in balance, and provides a major alternative to the corticospinal tract, by which cortical neurons can control motor function via their inputs onto reticular neurons. - 10Describe the mapping of the motor cortexElectrical stimulation of motor cortical areas elicits movements of particular body parts.
Of the three motor cortex areas, stimulation of the primary motor cortex requires the least amount of electrical current to elicit a movement. Low levels of brief stimulation typically elicit simple movements of individual body parts.
Stimulation of premotor cortex or the supplementary motor area requires higher levels of current to elicit movements, and often results in more complex movements than stimulation of primary
The primary motor cortex is somatotopically organized, revealed by microstimulation.
Motor Learning can Reshape the Motor Map - 11Describe neuronal coding in the primary cortexPrimary motor cortex neurons fire 5-100 ms before the onset of a movement. Rather than firing as the result of muscle activity, these neurons are involved in relaying motor commands to the alpha motor neurons.
This region does not generally control individual muscles directly, but rather appears to control individual movements or sequences of movements that require the activity of multiple muscle groups. - 12What do primary motor cortex neurons encode?Primary motor cortex neurons can encode:
The force of a movement: Neurons in primary motor cortex encode the amount of force that is necessary to make a movement, not (usually) the force of contraction of an individual muscle. Alpha motor neurons, in turn, translate the commands of the motor cortex neurons and control the amount of force generated by individual muscles to accomplish that movement.
The direction of movement. Many neurons in the primary motor cortex are selective for a particular direction of movement. For example, one cell may fire strongly when the hand is moved to the left, whereas it will be inhibited when the hand is moved to the right.
The extent of movement: The firing of some neurons is correlated with the distance of a movement.
The speed of movement. - 13Describe M1 neuronsConvergent and Divergent Connectivity between M1 and Motor Neuron Pools
M1 Neurons can Encode the Direction of a Movement
M1 Neurons can Encode the Force of a Movement - 14describe two other motor cortical areas that aid the primary motor cortexhe premotor cortex (PM) appears to be involved in motor planning: selecting motor programs based on visual stimuli or on abstract associations.
The supplementary motor area (SMA) is involved in programming complex sequences of movements and coordinating bilateral movements, as well as selecting movements based on remembered sequences of movements. - 15What is the function of premotor neurons and the premotor cortex?Premotor Neurons can Signal an Intention to Move
Premotor cortex is sensitive to the behavioural context of a particular movement.
Premotor cortex neurons are sensitive to the intentions behind a movement, not just the movement itself.
Some Premotor Neurons Code for a Specific Type of Grip
Mirror Neurons in the Premotor Cortex allow an individual to learn a movement by viewing it - 16Describe the supplementary motor areaSMA responds to sequences of movements and to mental rehearsal of sequences of movements:
When movements are simple, such as a repetitive movement of a single digit, the contralateral primary motor cortex and the primary somatosensory cortex are activated.
When a subject is asked to perform a complex sequence of finger movements, the SMA is activated bilaterally, in addition to the contralateral primary motor and somatosensory cortex activation.
Finally, when the subject is asked to remain still but to mentally rehearse the complex sequence of activity, the SMA is still active, even though the primary motor and somatosensory cortex areas are silent. - 17How do PM and SMA neurons respond to different types of cues?To obtain a reward, a monkey must press three keys in the correct sequence.
The sequence is indicated either by the keys lighting up one by one (visual) or must be remembered after training sessions (internal).
PMs fired in response to visual cues and SMA fired in response to visual cues but more so to internal cues - 18What areas are involved in reaching and graspingReaching and grasping are controlled by distinct but interconnected networks involving visual, parietal, and premotor areas.
Reaching and grasping require the transformation of visual information into a pattern of motor command, and involves connections between visual, parietal, and premotor areas.
Reaching is mediated by a dorsal pathway running from the posterior occipital cortex to the mediodorsal parietal cortex, and on to the dorsal premotor cortex.
Grasping an object is mediated by a more ventral pathway running from the dorsal extrastriate cortex to the AIP (anterior intraparietal area), and on to the ventral premotor cortex. - 19Describe parietal neural interfacesRegions of the parietal cortex involved in reaching and grasping offer potential targets for brain-machine interfaces.
Neurons in these regions code provide a population code for the direction of a reaching movement.
This code is more closely related to the intention / planning of the movement, rather than the coding of the movement itself (cf. primary motor cortex).
The population code can be ‘read’ and converted into movement commands executed by, for example, a robotic arm.
This technology has been tested in primates (e.g. Revechkis et al. 2014 Journal of Neural Engineering), and more recently in humans with spinal cord injury.
Informações
- Descrição
- Sensory and motor neuroscience FlashCards sobre Motor control 2, criado por Megan MacLeod em 30-04-2019.
- Criado por
- Megan MacLeod
- Visualizações
- 1
- Avaliação
Mais sobre Motor Cortex and Voluntary Movement