Deck 10: The Motor System: Motor Neurons

Question 1

Which of the following contributes to the spinal control of walking?

A)Afferent input from muscle spindles and GTOs
B)Adaptable networks of interneurons that modulate lower motor neuron firing patterns
C)Reciprocal signals crossing the dorsal columns and commissure of the spinal cord
D)All of the above

Answer 1

D
Explanation: Stepping pattern generators (SPGs)contribute the spinal control of walking.SPGs are adaptable networks of interneurons that receive input from muscle spindles and GTOs and modulate lower motor neuron firing.The cycles of left and right SPGs are coordinated by signals that cross in the anterior commissure,so that the right lower limb hip and knee flex while the left hip and knee extend.

Question 2

What is the mechanism by which onabotulinumtoxinA (BOTOX)decreases muscle activation?

A)Blocks the binding of acetylcholine (ACh)to the motor end plate.
B)Inhibits the binding of myosin to active sites on actin.
C)Blocks the release of Ca⁺² from the sarcoplasmic reticulum.
D)Inhibits the release of ACh from the presynaptic terminal.
E)None of the above occurs.

Answer 2

D
Explanation: Botox decreases muscle activation by inhibiting the release of ACh from the presynaptic terminal.With decreased transmitter release from the alpha motor neuron,the muscle membrane does not get the signal to initiate muscle contraction.

Question 3

Decorticate rigidity occurs with which of the following?

A)Lesions of the medulla
B)Vascular lesions of the anterior choroidal artery
C)Lesions superior to the midbrain
D)Lesions to the cerebellar lobes
E)All of the above

Answer 3

C
Explanation: In decorticate rigidity,the entire brainstem is intact and the lesion is superior to the midbrain.

Question 4

After lower neuron motor denervation caused by poliomyelitis,how does recovery of some muscle strength occur?

A)Cell division of surviving motor neurons produces new motor neurons.
B)Loss of interneuronal inhibition causes hyperreflexia.
C)Axonal sprouting of surviving neurons innervates muscle fibers.
D)Both A and B
E)A,B,and C

Question 5

Abnormal cutaneous reflexes that occur after an upper motor neuron lesion include which of the following?

A)Emergence of Babinski's sign
B)Muscle spasms in response to normally innocuous stimuli
C)Paresthesias
D)Both A and B
E)A,B,and C

Question 6

Clonus is characterized by which one of the following?

A)Involuntary,repetitive,and rhythmic muscle contractions in response to muscle stretch
B)Decrease in resistance to passive stretch of a hypertonic muscle
C)Excessive resistance to both passive and active muscle stretch
D)Prolonged contraction of antigravity muscles
E)Brief,involuntary contraction of a single muscle fiber

Question 7

Myoclonus is:

A)Severe and painful muscle spasms
B)Quick twitches of a single motor unit
C)Brief involuntary contractions of a muscle or group of muscles
D)Persistent muscle twitching after spinal or cerebral shock
E)None of the above

Question 8

Which one of the following proteins is NOT involved in the active process of muscle contraction?

A)Myosin
B)Actin
C)Tropomyosin
D)Troponin
E)Titin

Question 9

If the lower motor neurons to a muscle are destroyed,which of the following signs affects the denervated muscles?

A)Loss of reflexes
B)Atrophy
C)Muscle hyperstiffness
D)Both A and B
E)A,B,and C

Question 10

In an individual with paraparesis secondary to an incomplete spinal cord lesion,the increase in Achilles tendon tension during gait coincides with the stretch of the triceps surae during passive dorsiflexion of the foot in the stance phase.The increase in Achilles tendon tension is not correlated with an increase in EMG.What causes the abnormal muscle resistance to stretch?

A)Spasticity
B)Contracture
C)Cocontraction
D)Hyperreflexia
E)Atrophy

Question 11

Which of the following is true about the Golgi tendon organ (GTO)?

A)Maximum GTO activation occurs before maximum voluntary contraction.
B)GTO inhibition of the agonist alpha motor neuron causes immediate muscle relaxation via the GTO reflex.
C)Effectiveness of the contract-relax technique for stretching is dependent on GTO input.
D)GTO conveys information via a type IIa afferent to the spinal cord.
E)All of the above are true statements.

Question 12

Reciprocal inhibition produces inhibition of the alpha motor neurons to which of the following?

A)Agonist muscle
B)Agonist muscle and its synergists
C)Antagonist muscle
D)Agonist muscle,its synergists,and its antagonists
E)Homologous muscles in the opposite limb

Question 13

Which one of the following produces weak actin-myosin bonding?

A)Active muscle contraction
B)Muscle immobility
C)Physiologic contracture
D)Active contraction in lengthened muscles
E)Reflexive muscle contraction

Question 14

The term phasic stretch reflex is synonymous with which of the following?

A)Myotatic reflex
B)Muscle stretch reflex
C)Deep tendon reflex
D)Both A and B
E)A,B,and C

Question 15

Which one of the following major factors limits movement in individuals who have had a stroke?

A)Paresis caused by decreased agonist activation
B)Loss of ability to fractionate movement
C)Abnormal timing of muscle activation
D)Both A and B
E)A,B,and C

Question 16

What is the purpose of alpha-gamma coactivation?

A)Prevents simultaneous activation of fast twitch and slow twitch muscles.
B)Coordinates reciprocal reflex innervation.
C)Coordinates the actions of the basal ganglia and cerebellum.
D)Maintain muscle spindle sensitivity when extrafusal muscle fibers contract.
E)Prevents contraction of an antagonist muscle when the agonist is contracting.

Question 17

Which one of the following involuntary muscle contractions is always abnormal?

A)Muscle spasms
B)Cramps
C)Fasciculations
D)Fibrillations
E)All of the above

Question 18

Myoplasticity results from which of the following?

A)Contracture
B)Increased weak actin-myosin binding
C)Spasticity
D)Both A and B
E)A,B,and C

Question 19

Which of the following statements about fast twitch muscle fibers is true?

A)The neuron innervating the muscle determines twitch characteristics.
B)Alpha motor neurons having large-diameter axons innervate fast twitch muscle fibers.
C)Using a long train of repetitive contractions identifies twitch characteristics.
D)Both A and B
E)A,B,and C

Question 20

Continuous prolonged immobilization of skeletal muscle in a shortened position results in which of the following?

A)Increased muscle tone from hyperactive reflexes
B)Contracture from loss of sarcomeres
C)Increased tensile strength from the addition of titin
D)Both A and B
E)A,B,and C