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biol 125 homework 5
Part 1: Multiple choice
1. Upper motor neurons
A. Control the upper half of the torso
B. synapse on muscles in the eye, neck, and head
C. synapse on local circuit neurons and/or lower motor neurons <–––
D. affect motor patterns only indirectly via their inputs to the basal ganglia.
E. None of the above
2. A motor pool (as opposed to a motor unit) consists of
A. all of the motor neurons that project to a given muscle <–––
B. all of the motor neurons within a single segment of spinal cord
C. all of the motor neurons that project to a given limb
D. a single motor neuron and all of the muscles it innervates
E. a single motor neuron and all of its afferent interneurons
3. Which of the following statements about the organization of muscles and motor neurons is false?
A. Red muscle fibers contract slowly and produce the smallest amount of force
B. Large motor neurons are recruited only at higher levels of stimulus intensity
C. The fastest, strongest muscle fibers can produce the most sustained force output <–––
D. Successive stimulation of muscles can produce force levels that build up over time
E. Individual muscles can be used in a variety of different locomotor patterns or gaits
4. The patellar tendon (knee-jerk) reflex is
A. mediated by Golgi tendon organs
B. a monosynaptic reflex arc mediated by Ia afferents <–––
C. a polysynaptic reflex arc that integrates the input from groups Ia, Ib, and II afferents
D. mediated by collaterals of somatosensory afferents
E. a volitional response to the impending impact of an object (i.e., the physician’s rubber hammer) directed toward the knee
5. Golgi tendon organs are most sensitive to
A. muscle tension
B. muscle stretch
C. absolute joint position
D. muscle contraction frequency <–––
E. They are equally sensitive to all of the above
6. One candidate hypothesis for the selective degeneration of lower and upper motor neurons in ALS is that
A. these neurons share distinct sets of G-protein-coupled receptors
B. these neurons exhibit high resting firing levels
C. motor neurons are used far more intensively than other CNS cell types
D. these cells are exposed to infectious agents via their peripheral projections
E. their relatively long axons, as compared to many other neurons with cell bodies in the CNS, make them more vulnerable
<–––
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biol 125 homework 5
7. Upper motor neurons involved with the control of axial muscles would most likely project to the spinal cord in which of the
following patterns?
A. Lateral gray matter over many spinal segments
B. Lateral gray matter over just a few spinal segments
C. Medial gray matter over many spinal segments <–––
D. Medial gray matter over just a few spinal segments
E. In equal proportions to both lateral and medial gray matter
8. Corticospinal axons mostly
A. send ipsilateral axons into the lateral corticospinal tract
B. send contralateral axons into the ventral (anterior) corticospinal tract.
C. synapse onto spinal α motor neurons
D. synapse onto spinal local circuit neurons <–––
E. synapse onto spinal γ motor neurons
9. Which of the following statements about primary motor cortex (PMC) neurons is false?
A. The firing of PMC neurons occurs precisely at the onset of a muscle contraction <–––
B. PMC neurons can be directionally selective
C. The firing rate of a PMC neuron codes for or contributes to the force of a movement
D. The directional control of a movement is coded by the activity of a population of PMC neurons
E. The directional responses of PMC pyramidal cells tend to be broadly tuned in that they respond over a somewhat broad
range of movement directions
10. Which of the following statements about “mirror” motor neurons is false?
A. They are found in the ventrolateral portion of premotor cortex
B. They fire in response to a specific motor act, irrespective of there being a behavioral goal associated with the act. <–––
C. They fire in response to observation of a particular motor act being performed by others
D. They fire most strongly in response to an observed motor act that corresponds to the act that would activate the neuron
during self-initiated movements
E. All of the above are true, none is false
11. 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
A. feed-forward motor control <–––
B. feed-back motor control
C. equilibrium-point motor control
D. a “winner take all” motor coding strategy
E. sparse population coding
12. Which of the following is not a function of the reticular formation?
A. Modulation of cortical functions via serotonergic, noradrenergic and cholinergic transmitter systems
B. Modulation of cortico-striatal interactions
C. Descending modulation of spinal reflexes
D. Coordination of gaze centers and branchiomotor functions
E. Transmission of spinal nociceptive and tactile sensory signals to the cerebellum <–––
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biol 125 homework 5
13. Which of the following statements about the Babinski sign (or reflex) is false?
A. It involves the corticospinal tract
B. It changes “sign” between infancy and later development
C. It is considered an upper motor neuron deficit
D. It concerns normal versus abnormal flexion of the fingers <–––
E. It can be affected by stroke, trauma, and other neurological problems
Part 2: Short answers
1. 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?
The first is the slow motor units and the last are the fast fatigable motor units.
2. What happens to activity levels in muscle spindle afferents versus Golgi tendon organ afferents when a muscle contracts?
When a muscle is passively stretched? Is this consistent with the proposal that muscle spindle and Golgi tendon organ
feedback systems monitor and maintain muscle length and force, respectively?
Contracts- Muscle spindle is more quiet or no change, golgi tendon organ more active. Stretched- Spindle more active, Golgi
unaffected. Yes
3. How would mirror motor neurons help you learn new skills in a gymnastics class?
Mirror neurons fire when watching a movement and also when performing a movement. The idea is that they can help
prepare for a particular sequence of events.
Part 3: Short answers
Doctors visits- give the injury location, genetic defect, or environmental injury that could lead to the following symptoms.
1. A woman has a droopy lower left face, but the rest of the face is normal.
Defect in face areas of right primary motor cortex.
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biol 125 homework 5
2. A Man comes in with loss of reflexes and a loss of muscle tone in distal but not proximal muscles.
Defect in primary motor cortex or degeneration in ventral-lateral spinal cord
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