620 Motor Control Questions

The pyramidal cells of the primary motor cortex are located in which cortical layer?

5

What percentage of pyramidal tract fibers decussate to form the lateral corticospinal tract?

90%

Where are the lower motor neuron cell bodies that innervate the lateral rectus muscle located?

Abducens nucleus

You are watching a movie and having a snack when you accidently drop some of your food, causing you to avert your gaze from the television across the room to your lap. What is one visual response that will occur?

Accommodation of the lens

As a person tries to lift a heavy box, which type of motor unit is recruited first, and which is recruited last, according to the size principle?

According to the size principle, the smallest motor units would be recruited first and the largest motor units that generate the most force would be recruited last. Thus, low-threshold slow motor units are recruited, then FR motor units, and finally FF motor units.

Damage to the medial rectus muscle would lead to dysfunction in which motor response?

Adduction of the eye

How do neurons in the oculomotor nuclei signal amplitude versus direction of an eye movement?

Amplitude of a saccade is correlated with the duration of firing in the lower motor neurons. Direction is based on which eye muscles are activated.

During the patellar reflex, you measure voltage change in the flexor muscle motor neuron cell body in the ventral horn of the spinal cord. After stimulation of the stretch receptors, which of the following would you observe?

An IPSP

While driving, you quickly glance horizontally to the left without moving your head. During that eye movement, which neuronal response is most likely occurring?

An increase in firing rate in lower motor neurons in the left abducens nucleus and right oculomotor nucleus

How are the upper motor neurons in the superior colliculus organized?

As a topographical map of eye movement vectors

Which upper motor neuron syndrome symptom is also present in healthy infants?

Babinski sign

Huntington's disease and Parkinson's disease indicate the importance of which motor system for proper motor functioning?

Basal ganglia

Activation of the left paramedian pontine reticular formation (PPRF) leads to which eye movements?

Both eyes move to the left

Which motor units are resistant to fatigue?

Both slow and fast fatigue-resistant

The area of the brain dedicated to speech production is

Broca's area

Muscles in which region of the body would be expected to have the highest ratio of slow motor units?

Buttocks

Describe central pattern generators in the spinal cord.

Central pattern generators are local circuits in the spinal cord that time and coordinate complex movements of locomotion. synapse on local circuit neurons and/or lower motor neurons.

Ava notices that when she consumes two alcoholic beverages within an hour she has trouble controlling her movements. She stumbles occasionally and may knock over a glass that she intended to pick up. She doesn't have any trouble initiating movement, but all of her movements seem a little "off." Which motor system is most affected by Ava's alcohol consumption?

Cerebellum

Which is not a feature of motor unit plasticity?

Changes in the size and location of motor pools

Which experimental technique has been most helpful in mapping the primary motor cortex?

Cortical stimulation

A patient is having trouble abducting their left eye (moving the eye in a direction away from the nose). What nervous system damage would you expect to find from diagnostic tests?

Damage to the left cranial nerve VI

As motor unit size increases, which property of the α motor neuron decreases?

Excitability

The vestibulospinal tract would play a role in which of the following activities?

Extending your arms to protect yourself after you trip

Which brain region(s) is(are) thought to be most important for vergence eye movements?

Extrastriate occipital regions

Which statement about the transformation from retinotopic coordinates to oculomotor commands is true?

Eye movements are determined by the particular oculomotor neurons that are active and their firing rates.

Compared to the general population, weightlifters would be expected to have a higher ratio of which motor unit(s) in their legs?

FF only

After a few minutes of repeated stimulation, _______ motor units can generate only a fraction of their maximum force, whereas _______ motor units maintain maximum force generation after an hour of repeated stimulation.

FF; S

Upper motor neurons in the cerebral cortex are located in which lobe(s) of the brain?

Frontal

Which part of the lower motor neuron circuit prevents muscles from generating excessive tension and maintains steady muscle tone during muscle fatigue?

Golgi tendon organs

Which neurons coil around the middle of intrafusal fibers?

Group I afferents

Which neurons are responsible for muscle tone?

Group II afferents

Which symptom would you expect to see in a patient with lower motor neuron damage?

Hypoactive deep reflexes

What is meant by the statement that saccades are ballistic?

If the target object moves while a saccade is occurring, the saccade must complete its movement before responding to the subsequent change in target position.

Which symptom is not caused by lower motor neuron syndrome?

Impairment of fine movement only

A patient is experiencing double vision. A medical exam reveals that she can successfully gaze to the left (without head movement), but when asked to gaze forward or to the right, only the right eye moves as directed. Where is the doctor most likely to find neurological damage in this patient?

In the left oculomotor nerve

How do vergence movements differ from other eye movements?

In vergence movements, the eyes move in different directions.

Proper functioning of the lamprey central pattern generator (CPG) is dependent on which input?

Inhibitory interneurons that cross the midline

Which statement about the Babinski sign (or reflex) is false?

It concerns normal versus abnormal flexion of the fingers

How is cranial nerve IV different from other cranial or spinal motor nerves?

It innervates more than one muscle

Which statement about the withdrawal reflex is false?

It results in extensor muscle activation within the stimulated limb.

Which statement about the reticular activating system is true?

It supports transitions between sleep and wakefulness

Which muscle is primarily responsible for abduction of the eye?

Lateral rectus

A woman sustains a spinal cord injury in a car accident and loses the ability to move her fingers and her hand. The injury most likely damaged which region of her spinal cord?

Lateral ventral horn

In which area of the spinal cord can the axons of upper motor neurons that supply lower motor neurons for skilled movements be found?

Lateral white matter

A patient is asked to perform a sequence of eye movements without moving his head. He successfully looks to the right, but when asked to look forward or to the left, only the right eye moves in the correct direction. The left eye remains looking toward the left, and the patient complains of diplopia. The patient most likely has neurological damage to which nerve?

Left abducens nerve

A patient is diagnosed with a tumor located in the right internal capsule. Which motor dysfunction would you expect to see in this patient?

Left side paralysis (or severe weakness) of the lower face

Which of the following body areas listed has the greatest area of motor cortex devoted to it?

Lips

Which neurons receive converging inputs from several different sources before they relay signals to the muscles in the flexor reflex?

Local circuit neurons

Why are lower motor neurons referred to as the "final common pathway" for movements? Are the motor neurons that innervate head muscles upper or lower motor neurons?

Lower motor neurons are referred to as the "final common pathway" because commands for both voluntary and reflexive movement use this pathway to initiate movement in skeletal muscles. The motor neurons that innervate head muscles are lower motor neurons.

_______ neurons in the _______ reticular formation modulate forebrain activity.

Magnocellular; rostral

Upper motor neurons involved in the control of axial muscles would most likely project to the spinal cord in which pattern?

Medial gray matter over many spinal segments

Medial versus lateral spinal cord interneurons differ in location and pattern of connections. Describe how these anatomical distinctions correspond to functional differences.

Medial interneurons are located in the medial region of the intermediate zone of the spinal cord gray matter, and they synapse on lower motor neurons in the medial ventral horn that maintain posture, balance, and locomotion. Lateral interneurons are located in the lateral regions of the intermediate zone where they synapse on lower motor neurons in the lateral ventral horn that dictate skilled movements in distal limb muscles.

Which area of the brain is important for initiating movements from memory without external cues?

Medial premotor cortex

At which level of the nervous system does pyramidal decussation occur?

Medulla

An experimental animal undergoes a surgical lesion, and testing after recovery reveals that the animal has lost the ability to perform smooth pursuit movements. In which structure is the lesion most likely located?

Middle temporal area

What is the name of the neurons that fire when an animal observes and performs a goal-oriented task?

Mirror motor neurons

How would mirror motor neurons help someone learn new skills in a gymnastics class?

Mirror motor neurons would fire as a person watched a classmate or instructor perform a new skill and while attempting to perform the new skill. These neurons would help the person learn the motor movements from the experience of observation.

What is the basis for muscle tone?

Muscle tone is the resting level of tension in muscle, and it is dependent on the resting level of discharge of α motor neurons. This discharge is regulated by the γ efferent system in muscle spindle afferents.

Which sensory modalities can elicit eye movements?

Neurons in the superior colliculus respond to visual, auditory, and somatosensory stimuli.

Do neurons in the cerebellum and basal ganglia synapse on a motor neurons?

No, neurons from the cerebellum and basal ganglia synapse on upper motor neurons, not a motor neurons, which are lower motor neurons

Which observation would a researcher expect to make after chronically stimulating a cat's leg muscle over a month-long period?

Phenotypic change of FF motor units to S motor units

Local circuit neurons that run the entire length of the spinal cord and connect the medial parts of the spinal cord gray matter are primarily involved in which type of movement?

Postural control

Which motor area of the brain receives extensive multisensory input from the parietal and frontal lobe?

Premotor cortex

Which of the following is not one of the five basic types of eye movements?

Ptosis

A patient complains of inability to move his right eye toward his nose and a drooping right eyelid. What other symptom would you expect to find upon examination?

Pupillary dilation in right eye

Which function does the reticular formation contribute to?

Relaxation of muscles during restful periods

Which motor tract, important for controlling arms or forepaws, is prominent in animals but nonexistent in humans?

Rubrospinal tract

According to the size principle, in which order are motor units recruited in response to increasing synaptic input?

S, FR, FF

What are the five kinds of stereotyped eye movements? Are they voluntary or reflexive?

Saccades: both voluntary and reflexive. Smooth pursuit: voluntary. Vergence: reflexive. Vestibulo-ocular: reflexive. Optokinetic: reflexive.

During a medical exam, a patient presents with eye movement task dysfunctions. Specifically, smooth pursuit movements are jerky, with more errors and irregularities than average. During a free-viewing test, visual sampling of a scene is less robust than average, viewing only a small portion of the image. Finally, the patient has difficulty remaining fixated on a target object. What disorder might these test results indicate?

Schizophrenia

Which cognitive disorder is correctly paired with its eye movement dysfunction?

Schizophrenia—impairment in smooth pursuit movements

Damage to the dorsal visual stream in the parietal lobe would affect which type of eye movement?

Smooth pursuit

What is spinal shock?

Spinal shock is the lack of reflexive activity after a spinal cord injury. It is usually most noticeable in the arms and legs and is usually transient, with function often returning after several days.

Which activity would recruit all three types of motor units?

Sprinting

The flexion-crossed extension reflex would occur in response to which activity?

Stepping on a sharp object

Which statement about the directional control of saccadic eye movements is true?

Stimulation of particular upper motor neurons in the superior colliculus always produces a movement of the same magnitude and direction.

Which brain region is important for controlling axial musculature in the neck?

Superior colliculus

What the Golgi tendon organ reflex, and how does it function?

The Golgi tendon organ, located at the junction of a muscle and tendon, is arranged in series with extrafusal muscles. Thus, as a muscle contacts, the Golgi tendon organ increases its output to the Ib afferents. These afferent neurons connect with inhibitory interneurons to inhibit the muscle that is contracted. This negative feedback is the body's way of protecting the muscle from extensive tension and helping to maintain a steady level of tone during muscle fatigue.

Which statement about sensorimotor integration in the superior colliculus (SC) is false?

The activation of neurons in the upper layers of the SC results in offset activation of lower-SC layers, producing a checkerboard pattern of upper-to-lower layer signaling.

Which statement about stabilized retinal images is false?

The fading of retinal images serves mainly to protect neurons in LGN and area 17 from photodamage.

Which statement about the organization of muscles and motor neurons is false?

The fastest, strongest muscle fibers can produce the most sustained force output.

Which statement about primary motor cortex neurons is false?

The firing of primary motor cortical neurons occurs precisely at the onset of a muscle contraction.

Which evidence suggests that upper motor neurons in the primary cortex have a preferred direction?

The firing rate of a particular upper motor neuron is highest when the hand moves from left to right.

Where are the horizontal and vertical gaze centers? How do they help the superior colliculus translate motor goals into eye movements?

The gaze centers are located in the reticular formation. The gaze centers simplify the circuits needed to move the eyes in any direction. The superior colliculus can integrate sensory information and then innervate the two gaze centers instead of innervating a unique set of individual motor neurons to each eye muscle for each eye movement.

What is unique about the monosynaptic reflex arc in reciprocal innervation?

The monosynaptic reflex arc is unique because most sensory neurons from the periphery do not synapse directly on lower motor neurons. Most sensory neurons exert their effects through local circuit neurons instead.

What comprises a motor unit?

The motor unit is an α motor neuron and all the muscle fibers it innervates.

Anterograde tracers are used to visualize downstream neural connections. If you were to inject an anterograde tracer into a site in the superior colliculus that was known to move the eye directly to the left, where would you expect to see labeled neurons (where would the superior colliculus innervate), according to the proposed models?

The paramedian pontine reticular formation (PPRF)

Contrast the roles of the primary motor cortex and premotor cortex.

The primary motor cortex is responsible for initiating movement, while the premotor cortex encodes intention for movement. Both areas use the corticospinal tract, but upper motor neurons from the primary motor cortex have more monosynaptic connections to α motor neurons. Additionally, the primary motor cortex encodes action goals within personal space, whereas the premotor cortex encodes action goals for extra- personal space.

Does the pyramidal tract originate only from the motor cortex? Does it terminate only in the spinal cord?

The pyramidal tract originates from the primary motor cortex and the premotor cortex. It terminates on the cranial nerve nuclei, reticular formation, red nucleus, and the spinal cord.

What is the importance of the rapid eye movements (saccades) when examining an image?

The saccades align important aspects of the scene with the fovea.

List the three sources of direct synaptic input to a motor neurons. Which one is the major input?

The sources of direct synaptic input to a motor neurons include the motor cortex, the mesencephalic locomotor region, and local circuit neurons. The motor cortex is the major source of input.

The primary motor cortex "controls movements, not individual muscles." What does statement mean, and what evidence supports this concept?

The spike-triggered averaging method showed that a single upper motor neuron directly facilitates the movement of multiple muscles that work together to perform a specific movement. These muscles are known as the muscle field of the upper motor neuron. Thus, a motor unit controls movement, not individual muscles.

Which structure is not involved in the generation of smooth pursuit eye movements?

The superior colliculus,PPRF,frontal eye fields, and Area MT

You are about to drink some coffee when an insect lands on the rim of your cup. What three reflexive visual responses do you make?

The three visual reflexes are convergence, accommodation of the lens, and pupillary constriction. These are also known as the near reflex triad.

Which statement about the motor functions of the superior colliculus (SC) is false?

The uppermost layer of the SC is a somatotopic map that enables us to look at different locations on our body

Usually, you do not see the shadows of blood vessels in your retina. Why not?

The vascular shadows are normally invisible because they create a stabilized retinal image and activate only one set of photoreceptors. The photoreceptors undergo retinal adaptation after a short period of time, which interferes with perception of the shadows

Which statement about directional tuning and population coding by primary motor cortical neurons is true?

The vector summation of population responses of primary motor cortical neurons is important for directional control of motor movements.

Which statement about "mirror" motor neurons is false?

They fire in response to a specific motor act, irrespective of there being a behavioral goal associated with the act.

What is the function of tiny saccades and drift during visual perception?

To change retinal stimulus during fixation, preventing retinal adaptation

Which statement provides evidence that locomotion is organized by central pattern generators in the spinal cord?

Transection of the spinal cord does not prevent coordinated limb movements

Which is not a function of the reticular formation?

Transmission of spinal nociceptive and tactile sensory signals to the cerebellum

Which nucleus innervates the superior oblique muscle?

Trochlear nucleus

Motor neurons with cell bodies in the cerebral cortex or the brainstem are part of which motor system?

Upper motor neurons

Which statement regarding neurons in the superior colliculus is most accurate?

Visual neurons respond to a specific region of visual space and synapse on motor neurons that move the eye to that same region.

What happens to activity levels in muscle spindle afferents versus Golgi tendon organ afferents when a muscle contracts? When a muscle is passively stretched?

When a muscle contracts, afferent activity increases in a Golgi tendon organ and decreases in an intrafusal muscle fiber. When a muscle is stretched, afferent activity decreases in a Golgi tendon organ and increases in an intrafusal muscle fiber. These responses lead to the muscle spindle maintaining muscle length while the Golgi tendon organ maintains muscle force.

Explain how the antagonist muscle is inhibited in reciprocal innervation.

When muscle spindles are stretched, activity in the group Ia afferents in increases. These Ia afferents directly excite the α motor neurons of the stretched muscle, but inhibit the α motor neurons of the antagonist muscle via reciprocal-Ia-inhibitory interneurons.

The lateral corticospinal tract innervates α motor neurons that are important for which task?

Writing

The patellar tendon (knee-jerk) reflex is

a monosynaptic reflex arc mediated by Ia afferents

The condition called "fused tetanus" refers to

a sustained maximal contraction due to intense motor unit firing

A motor pool (as opposed to a motor unit) consists of...?

all of the motor neurons that project to a given muscle

Damage to the vergence centers in the brainstem would lead to dysfunction in all eye alterations except

anti-saccades

Saccadic eye movements

are preceded by activity in the superior colliculus and the frontal eye fields

The local circuits in the spinal cord that are fully capable of controlling the timing and coordination of complex locomotion are called?

central pattern generators

Cortical areas that plan and initiate motor sequences

comprise several functionally distinct but highly interconnected regions

Vergence eye movements

depend on binocular disparity measurements made in neocortex, are performed in conjunction with saccadic eye movements, depend on vergence centers in the midbrain, and are driven by bursts of action potentials that drive either converging or diverging movements.

Spinal interneurons that project ipsilaterally between the lumbar and cervical enlargements are most likely involved with

ensuring coordination of the forelimbs and hindlimbs.

During the flexion-crossed extension reflex, stimulation would lead to _______ of ipsilateral flexor muscles and _______ contralateral flexor muscles.

excitation; inhibition of

A specialized motor unit, with an average size of three muscle fibers, controls

eye muscles

In an anticipatory postural response of a standing person about to tug on a handle, the early response of leg muscles (such as the gastrocnemius) that precedes the actual tug is an example of

feedforward motor control

The lamprey central pattern generator (CPG)

generates an alternating left-right bending pattern by means of crossed inhibitory fibers

While helping a friend move, you hold out your arms to take a box from your friend. To ensure that you do not drop the box, your _______ neurons send a signal to your _______ neurons to contract your biceps and relax your triceps.

group Ia afferent; α motor

In regulating lateral rectus muscle activity, abducens motor neurons fire

in bursts during lateral eye movements and at somewhat lower firing rates during lateral displacements

As a person squats, the quadriceps muscles contract. At the same time, the respective Golgi tendon organs _______ their firing rate, and the intrafusal muscle fibers _______ their firing rate.

increase; decrease

Although the phenomenon is not well understood, the increased muscle tone and spasticity that develop after an upper motor neuron injury appears to be due, at least in part, to

increased responsiveness of motor neurons to Ia afferent inputs

"Spike-triggered averaging"

is a means of correlating upper motor neuron activity with muscle activation

A "muscle field"

is the group of muscles whose activity is directly facilitated by a given upper motor neuron

Neurons from the _______ are responsible for regaining balance and posture via projections to the proximal muscles of the limbs.

lateral vestibulospinal tract

When visually examining an object such as a painting of a face, a person will usually

make many rapid eye movements, in different directions, acquiring information primarily during brief pauses at different locations on the object

Lower motor neurons responsible for posture and locomotion are found in the _______ and primarily receive input from upper motor neurons in the _______.

medial ventral horn; brainstem

Local circuit neurons that supply input to _______ lower motor neurons are located in the medial _______.

medial; intermediate zone

The rubrospinal pathway

might not exist in humans

The peripheral muscle group that an upper motor neuron projects to is the

muscle field

Golgi tendon organs are most sensitive to

muscle tension

A drooping eyelid can be expected as result of damage to the _______ nerve.

oculomotor

A woman is rushed to the hospital after a serious car accident. When she enters the emergency room on a stretcher, a resident notices that her arms and legs are extended and her neck is retracted. The resident suspects the woman has sustained damage to her _______, causing decerebrate rigidity.

pons

The "indirect pathway" from cortex to spinal cord does not play a role in

post-injury recovery of fine motor functions such as using two fingers to pick up food

Asynchronous firing of motor neurons

provides a means by which a population of motor neurons can maintain constant force over a finite time interval.

A man is rushed to the hospital after he has had a stroke involving his left middle cerebral artery. The man will likely lose his ability to

raise the right corner of his mouth

Damage to the medial longitudinal fasciculus would affect communication between the

right abducens nucleus and the left oculomotor nucleus

The right paramedian pontine reticular formation (PPRF) innervates the

right abducens nucleus directly and the left oculomotor nucleus indirectly

In a muscle with a high gain, a _______ stretch of a muscle would lead to _______ increase in extrafusal muscle tension.

small; a large

The motor neurons innervating the medial gastrocnemius muscle of the cat are found...?

spanning several segments of lateral lumbar and sacral spinal cord

The frontal eye fields influence horizontal eye movement by innervating the

superior colliculus and the paramedian pontine reticular formation (PPRF)

Corticospinal axons mostly

synapse onto spinal local circuit neurons

The part of the motor system that acts as a servomechanism to minimize motor error is...?

the cerebellum

If fixation of an eye is controlled, such that the eye remains fixated at a single point on a projected image

the image fades rapidly

The acute phase of upper motor neuron syndrome is characterized by

the passive dropping of an affected limb that has been elevated and then released

When shaking one's head back and forth while looking straight ahead at a stationary object, the mechanism that maintains the focal image at a roughly constant location on the retina is called

the vestibulo-ocular reflex

One candidate hypothesis for the selective degeneration of lower and upper motor neurons in ALS is that

their very long axons make them more vulnerable to defects in axonal transport

Lesions of the left frontal eye field result in

transient deviation of the eye to the left, plus a transient contralateral saccade deficit

A person with damage to the direct motor pathway but an intact indirect motor pathway, would have the most difficulty

tying shoes

The type of eye movement that is used to focus vision at different distances is called

vergence

Velocity of a vergence movement is coded by frequency of action potentials in neurons located in the

vergence centers in the brainstem

_______ innervate striated muscle fibers, and _______ innervate specialized fibers called _______.

α motor neurons; γ motor neurons; muscle spindles