Question 1

The phasic Ia stretch reflex:&#10;A)Has a polysynaptic reflex arc.&#10;B)Acts to maintain a constant level of tension in the muscle.&#10;C)Is initiated by a receptor that lies in series with the extrafusal fibers.&#10;D)Has its sensitivity controlled by the gamma motor neuron system.

Accepted Answer

The phasic Ia stretch reflex is a monosynaptic reflex arc initiated by muscle spindles, which are parallel to extrafusal fibers. The sensitivity of the muscle spindle, and thus the reflex, is controlled by the gamma motor neuron system.

Question 2

According to the size principle:&#10;A)Large &#945; motor neurons are recruited before small ones.&#10;B)Large and small &#945; motor neurons are recruited simultaneously.&#10;C)&#945; and $\gamma$ motor neurons are activated simultaneously during a movement.&#10;D)&#945; motor neurons are activated before $\gamma$ motor neurons during a movement.&#10;E)Small motor neurons are more excitable than are large motor neurons.

Accepted Answer

The size principle states that smaller motor neurons, which innervate fewer muscle fibers and thus produce smaller forces, are recruited before larger motor neurons during the gradual increase of force in a muscle. This is because smaller motor neurons have a lower threshold for activation, making them more excitable than larger motor neurons.

Question 3

A stimulus applied to the surface of the cerebellar cortex activates a beam of parallel fibers.This produces:&#10;A)A wave of inhibited Purkinje cells in line with the parallel fiber beam.&#10;B)Waves of excited Purkinje cells that flank the parallel fiber beam.&#10;C)A wave of excited basket and stellate cells in line with the parallel fiber beam.&#10;D)Waves of excited basket and stellate cells that flank the parallel fiber beam.&#10;E)Complex spikes in Purkinje cells in line with the parallel fiber beam.

Accepted Answer

A stimulus applied to the surface of the cerebellar cortex activates parallel fibers, which in turn excite both basket and stellate cells in line with the parallel fiber beam. These interneurons modulate the activity of Purkinje cells, which are the primary output neurons of the cerebellar cortex.

Question 4

Upper motor neuron (or pyramidal tract)syndrome is:&#10;A)Characterized by the permanent loss of the stretch reflexes.&#10;B)Fully expressed when only the corticospinal tract is interrupted.&#10;C)Characterized by a lasting decrease in muscle tone.&#10;D)Characterized by Babinski's sign and the appearance of other pathological reflexes.&#10;E)Fully expressed after damage to the vestibular nuclei.

Accepted Answer

Upper motor neuron syndrome is characterized by Babinski's sign and the appearance of other pathological reflexes. It is caused by damage to the corticospinal tract, which leads to spasticity and hypertonia, rather than a decrease in muscle tone. It does not necessarily result in the permanent loss of stretch reflexes. Damage to the vestibular nuclei would not result in the full expression of upper motor neuron syndrome.

Question 5

With a person standing upright,head rotation to the right causes:&#10;A)Activation of hair cells in the left horizontal canal and right abducens nucleus.&#10;B)Activation of hair cells in the right horizontal canal and right abducens nucleus.&#10;C)Activation of hair cells in the left horizontal canal and left abducens nucleus.&#10;D)Activation of hair cells in the right horizontal canal and left abducens nucleus.&#10;E)A vertical nystagmus

Accepted Answer

When the head rotates to the right, the right horizontal semicircular canal is activated, which in turn activates the left abducens nucleus to coordinate eye movement to the left, maintaining gaze stability.

Question 6

Damage to which structure would produce an extensor rigidity that would not be significantly altered by section of the dorsal roots?&#10;A)Lateral vestibular nucleus.&#10;B)Anterior vermal region of the cerebellar cortex.&#10;C)Medullary reticular formation (nucleus gigantocellularis).&#10;D)Cortical afferent pathways to the pontine and medullary reticular formation.&#10;E)Cortex of the cerebellar hemisphere.

Accepted Answer

The answer of Damage to which structure would produce an...

Question 7

A monkey makes arm movements while you record the activity of a cell in primary motor cortex in a cortical column related to arm muscles.What is probably true about the cell's activity?&#10;A)It is linearly related to movement direction and thus can predict the direction of the upcoming movement.&#10;B)It does not vary with movement direction.&#10;C)It always increases during the movement.&#10;D)It is nonlinearly related to movement direction and does not predict the specific direction of the upcoming movement.

Accepted Answer

The answer of A monkey makes arm movements while you...

Question 8

In the motor map of the primary motor cortex:&#10;A)Each muscle is represented by a single cortical column.&#10;B)Each muscle is represented by multiple columns within a single continuous region.&#10;C)The number of cortical columns representing a muscle is proportional to the mass of the muscle.&#10;D)The amount of territory representing a muscle is correlated with the degree of fine control over movements made using that muscle.&#10;E)Columns controlling different muscles are randomly intermixed.

Accepted Answer

The primary motor cortex allocates more cortical territory to muscles that require fine motor control, such as those in the hands and face, rather than based on muscle mass.

Question 9

Dopamine's action in the caudate and putamen will _____ activity in the globus pallidus internal (GPi)as a result of _______.&#10;A)Decrease; activation of the direct pathway and inhibition of the indirect pathway&#10;B)Decrease; inhibition of the direct pathway and activation of the indirect pathway&#10;C)Increase; activation of the direct pathway and inhibition of the indirect pathway&#10;D)Increase; inhibition of the direct pathway and activation of the indirect pathway&#10;E)Decrease; inhibition of both direct and indirect pathways

Accepted Answer

Dopamine's action in the caudate and putamen will activate the direct pathway and inhibit the indirect pathway. This will result in a decrease in activity in the globus pallidus internal (GPi). With less activity in the GPi, there will be less inhibition of the thalamus, allowing for more excitation of the cortex and increased movement.

Question 10

Intrafusal muscle fibers but not extrafusal fibers:&#10;A)Receive only sensory innervation.&#10;B)Are innervated by only one motor neuron.&#10;C)Contain an equatorial region with little to no contractile protein.&#10;D)Run the length of the muscle.

Accepted Answer

Intrafusal muscle fibers, unlike extrafusal fibers, have a central region (equatorial region) that is characterized by a lack of or significantly reduced amount of contractile proteins. This region is primarily involved in sensory detection, particularly in the stretch reflex mechanism, rather than contraction.

Deck 9: Organization of Motor Function