Chapter 8: Action

Question 1

Akinesia

Answer 1

The absence of voluntary movement.

Question 2

Alpha motor neurons

Answer 2

The neurons that terminate on muscle fibers, causing contractions that produce movements.

Question 3

Apraxia

Answer 3

A neurological syndrome characterized by loss of skilled or purposeful movement that cannot be attributed to weakness or an inability to innervate the muscles.

Apraxia results from lesions of the cerebral cortex, usually in the left hemisphere.

Question 4

Ataxia

Answer 4

A movement disorder associated with lesions or atrophy of the cerebellum. Ataxic movements are clumsy and erratic, even though muscle strength is normal.

Question 5

Basal ganglia

Answer 5

A collection of five subcortical nuclei:
1. The caudate
2. The putamen
3. The globus pallidus
4. The subthalamic nucleus
5. The substantia nigra
The basal ganglia are involved in motor control and learning.

Reciprocal neuronal loops project from cortical areas to the basal ganglia and back to the cortex.

The two prominent basal ganglia disorders are Parkinson’s disease and Huntington’s disease.

Question 6

Bradykinesia

Answer 6

Slowness in the initiation and execution of movements. Bradykinesia is a prominent symptom in Parkinson’s disease.

Question 7

Brain-machine interfaces (BMIs)

Answer 7

A device that uses the interpretation of neuronal signals to perform desired operations with a mechanical device outside the body.

For instance, signals recorded from neurons or EEG can be used to move a prosthetic arm.

Question 8

Central pattern generators

Answer 8

A neural network limited to the spinal cord that produces patterned motor outputs without descending commands from the cerebral cortex or sensory feedback.

Question 9

Cerebellum

Answer 9

Literally, “small cerebrum” or “little brain”.

A large, highly convoluted (infolded) structure located dorsal to the brainstem at the level of the pons.

The cerebellum maintains (directly or indirectly) interconnectivity with widespread cortical, subcortical, brainstem, and spinal cord structures, and plays a role in various aspects of coordination ranging from locomotion to skilled, volitional movement.

Question 10

Corticomotoneurons (CM neurons)

Answer 10

Specialized corticospinal neurons with axons that terminate directly on spinal motor neurons. Most are located in the primary motor cortex.

Question 11

Corticospinal tract (CST)

Answer 11

Also called pyramidal tract. A bundle of axons that originate in the cortex and terminate monosynaptically on alpha motor neurons and spinal interneurons in the spinal cord.

Many of these fibers originate in the primary motor cortex, although some come from secondary motor areas.

The corticospinal tract is important for the control of voluntary movements.

Question 12

Deep brain stimulation (DBS)

Answer 12

The electrical stimulation of brain structures via an implanted electrode.

Stimulation of the subthalamic nucleus, one of the nuclei in the basal ganglia, is used as a treatment for Parkinson’s disease.

Question 13

Effector

Answer 13

Any part of the body that can move, such as an arm, finger, or leg.

Question 14

Endpoint control

Answer 14

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.

Question 15

Extrapyramidal tracts

Answer 15

A collection of motor tracts that originate in various subcortical structures, including the vestibular nucleus and the red nucleus. These tracts are especially important for maintaining posture and balance.

Question 16

Forward model

Answer 16

The idea that the brain generated predictions of expected events. In motor control, the prediction of the expected sensory consequences of a movement.

Question 17

Hemiplegia

Answer 17

A neurological condition characterized by the loss of voluntary movements on one side of the body.

Hemiplegia typically results from damage to the corticospinal tract, either from lesions to the motor cortex or from white matter lesions that destroy the descending fibers.

Question 18

Hyperdirect pathway

Answer 18

Direct connections from the motor cortex to the subthalamic nucleus (STN) that bypass the striatum and convey excitatory input directly to the STN and pallidum.

Question 19

Huntington’s disease

Answer 19

A genetic degenerative disorder in which the primary pathology, at least in early stages of the disease, is observed in the striatum (caudate and putamen) of the basal ganglia. Prominent symptoms include clumsiness and involuntary movements of the head and trunk. Cognitive impairments are also seen and become pronounced over time.

Question 20

Hyperkinesia

Answer 20

A movement disorder characterized by excessive movement. Hyperkinesia is a prominent symptom of Huntington’s disease.

Question 21

Hypokinesia

Answer 21

A movement disorder characterized by the absence of movement or a reduction in the production of movement. Hypokinesia is a prominent symptom of Parkinson’s disease.

Question 22

Mirror neuron network

Answer 22

A distributed network of neurons that respond not only to one’s own actions but also to perceived actions.

Question 23

Mirror neurons (MNs)

Answer 23

A neuron that shows similar responses when an animal is either performing an action or observing that action produced by another organism.

For instance, a mirror neuron responds when you pick up a pencil and when you watch someone else pick up a pencil.

Mirror neurons are hypothesized to provide a strong link between perception and action, perhaps providing an important basis for the development of conceptual knowledge.

Question 24

Optic ataxia

Answer 24

A neurological syndrome in which the patient has great difficulty using visual information to guide her actions, even though she is unimpaired in her ability to recognize objects.

Optic ataxia is associated with lesions of the parietal lobe.

Question 25

Parkinson’s disease

Answer 25

A degenerative disorder of the basal ganglia in which the pathology results from the loss of dopaminergic cells in the substantia nigra. Primary symptoms include difficulty in initiating movement, slowness of movement, poorly articulated speech, and, in some cases, resting tremor.

Question 26

Population vector

Answer 26

The sum of the preferred directions of individual neurons within a group that represents the activity across that group.

Population vectors reflect the aggregate activity across the cells, providing a better correlation with behavior that obtained from the analysis of individual neurons.

For example, the population vector calculated from neurons in the motor cortex can predict the direction of a limb movement.

Question 27

Preferred direction

Answer 27

A property of cells in the motor pathway, referring to the direction of movement that results in the highest firing rate of the neuron.

Voxels have also neem shown to have preferred directions in fMRI studies, indicating that such preferences can even be measured at the cell population level of analyses.

Question 28

Premotor cortex

Answer 28

A secondary motor area that includes the lateral aspect of Brodmann area 6, just anterior to the primary motor cortex.

Although some neurons in the premotor cortex project to the corticospinal tract, many terminate on neurons in the primary motor cortex and help shape the forthcoming of movement.

Question 29

Primary motor cortex (M1)

Answer 29

A region of the cerebral cortex that lies along the anterior bank of the central sulcus and precentral gyrus, forming Brodmann area 4.

Some axons originating in the primary motor cortex from the majority of the corticospinal tract; others project to cortical and subcortical regions involved in motor control.

The primary motor cortex contains a prominent somatotopic representation of the body.

Question 30

Prosthetic devices

Answer 30

Also called prosthesis. An artificial device that functions as a replacement for a missing body part.

Question 31

Sensorimotor adaptation

Answer 31

A form of motor learning in which a learned skill is modified because of a change in the environment or agent.

For example, a soccer player who adjusts her shot to compensate for a strong crosswind is exhibiting a form of motor adaptation.

Question 32

Sensorimotor learning

Answer 32

The improvement, through practice, in the performance of sensory-guided motor behavior.

Question 33

Spinal interneurons

Answer 33

Neurons found in the spinal cord.

Many descending axons from the pyramidal and extrapyramidal tracts synapse on interneurons, which, in turn, synapse on other interneurons or alpha motor neurons.

Question 34

Substantia nigra

Answer 34

One of the nuclei that form the basal ganglia.

The substantia nigra is composed of two parts:
1. The axons of the substantia nigra pars compacta provide the primary source of the neurotransmitter dopamine and terminate in the striatum (caudate and putamen).
2. The substantia nigra pars reticularis is one of the output nuclei from the basal ganglia.

Question 35

Supplementary motor area (SMA)

Answer 35

A secondary motor area that includes the medial aspect of Brodmann area 6, just anterior to the primary motor cortex.

The SMA plays an important role in the production of sequential movements, especially those that have been well learned.