Action Flashcards
Substantia nigra
One of the nuclei that form the basal ganglia. Composed of two parts: the pars compacta (the primary source of dopamine) and the pars reticularis
Effector
A part of the body that can move
Alpha motor neurons
Innervate muscle fibers and produce contractions of the fibers
Gamma motor neurons
Part of the proprioceptive system; important for sensing and regulating the length of muscle fibers
Neurotransmitter for alpha motor neurons
Acetylcholine
Muscle spindles
Sensory receptors in the muscles that provide information about how much the muscle is stretched
Spinal interneurons
Neurons in the spinal cord that innervate motor neurons and are innervated by sensory nerves (from the skin, muscles, and joints) as well as descending motor fibers that originate in subcortical and motor cortical structures
Extrapyramidal tracts
Motor pathways (including the vestibular nuclei, substantia nigra, and reticular formation nuclei) in the brain stem that send direct projections down the spinal cord
Vestibulocerebellum
Region of the cerebellum that works with the brainstem vestibular nuclei to control balance and coordinate eye movements with body movements
Spinocerebellum
Medial region of the cerebellum that receives sensory information from the visual and auditory systems as well as proprioceptive information from the spinocerebellar tract
Neocerebellum
The lateral zones of the cerebellar hemispheres which are heavily innervated by descending fibers from regions in the parietal and frontal lobes
Ataxia
Problems with sensory coordination of the distal limb movements; disrupts fine coordination
Basal ganglia
Five nuclei: the caudate nucleus and putamen (together known as the striatum), the globus pallidus, the subthalamic nucleus, and the substantia nigra
Basal ganglia nuclei that receive most of the input
The striatum (caudate and putamen)
Basal ganglia nuclei involved in most output
Internal segment of the globus pallidus and part of the substantia nigra
Corticospinal tract
Axons that exit the cortex and project directly to the spinal cord
Hemiplegia
A result of lesions to the primary motor cortex–characterized by a loss of voluntary movements on the side of the body contralateral to the lesion
Premotor cortex
Lateral aspect of Brodmann Area 6 (anterior to the primary motor cortex). Involved in external sensory-guided actions
Supplementary motor cortex
Medial aspect of Brodmann Area 6 (anterior to the primary motor cortex). Involved in internally guided personal preferences and goals
Apraxia
Condition that affects motor planning; associated with lesions to the secondary motor cortex. Apraxia patients have no motor or sensory impairment but can’t link simple motor gestures into meaningful actions.
Ideomotor apraxia
Type of apraxia in which patients have a rough sense of the desired action but can’t execute it properly
Ideational apraxia
Type of apraxia in which the patient’s knowledge about the intent of an action is disrupted. More often associated with parietal damage than with damage to secondary motor areas
Central pattern generators
Neurons in the spinal cord that can produce an entire sequence of actions without any descending signals or external feedback signals
Endpoint control
A hypothesis concerning how movements are planned in terms of the desired final location. Endpoint control models emphasize that the motor representation is based on the final position required of the limbs to achieve the movement goal
Preferred direction
The tendency for a cell to exhibit greater activation during movements in a particular direction
Population vector
Idea that each neuron can be considered to be contributing a “vote” to the overall activity level, and that the strength of the vote will correspond to how closely the movement matches the cell’s preferred direction. The activity of each neuron can be described as a vector, and the population vector is the sum of all the individual vectors
Direct pathway in the basal ganglia
Involves fast, direct, inhibitory connections from the striatum to the internal segment of the globus pallidus and the pars reticularis of the substantia nigra.
Indirect pathway in the basal ganglia
Takes a slower, roundabout route to the internal segment of the globus pallidus and the pars reticularis of the substantia nigra, first inhibiting the external segment of the globus pallidus, which then inhibits the subthalamic nucleus and internal segment of the globus pallidus.
Dopamine pathway
The projection from the pars compacta of the substantia nigra to the striatum. The substantia nigra excites the direct pathway but inhibits the indirect pathway
Hypokinesia
An absence or reduction in voluntary movement
Bradykinesia
Slow movements (associated with Parkinson’s)
Visuomotor adaptation
A form of sensorimotor adaptation in which the visual field is altered, resulting in a mismatch between proprioception and vision. With practice, the motor system adjusts to compensate for the mismatch
M1 and the cerebellum in adapting to mismatch between the visual and proprioceptive systems
The cerebellum is essential for learning the new mapping, but M1 is important for consolidating new information
Forward model
Refers to the idea that the brain generates predictions of expected events. In motor control, a forward model refers to the prediction of the expected sensory consequences of a movement
Before their activation, neurons in the internal segment of the globus pallidus are
Pre-activated
Before their activation, neurons in the internal segment of the globus pallidus are
Pre-activated
Movements are triggered by
Inhibition of the internal segment of the globus pallidus by the striatum
The striatum inhibits
… only the globus pallidus internal segment neurons controlling the selected movement in the striatum
