Muscle Tone

Question 1

What is tone?

Answer 1

The amount of resistance to passive stretch in a resting muscle.

Question 2

What are the two components of tone?

Answer 2

Mechanical

Neural

Question 3

Mechanical component of tone is?

Answer 3

The inherent/intrinsic physical properties of the tissues that make up the muscle.

Question 4

Neural component of tone is?

Answer 4

The number of active motor units at a given time.

-The number of active motor units can be altered by the brain/brainstem to adjust to the environment.

Question 5

Fact of Tone are?

Answer 5

-Always have tone even at rest.

Question 6

What is the Gamma (Y) Loop?

Answer 6

Not a reflex but one means of many of adjusting muscle tone.

Question 7

The gamma motor neuron is?

Answer 7

The motor neuron innervating the contractile component of the muscle spine.

Question 8

What happens with hypotonicity?

Answer 8

Completely atonic - flaccid

Typically due to damage to lower motor neuron innervating skeletal muscle in either the CNS (soma) or in the PNS (axon).

-Fewer motor units able to contract

Question 9

Hypotonicity is associated with?

Answer 9

An acute injury

• Nervous system shock
• Persists with a chronic upper motor neuron injury.

Question 10

Hypotonicity without an AP reaching the axon terminal to release ACh at the?

Answer 10

Neuromuscular junction the motor unit cannot contract.

• Cannot contract voluntarily
• Cannot contract involuntarily

Question 11

Hypotonicity - Fewer weak actin-myosin bonds are associated with?

Answer 11

• Reduced or lost deep tendon reflex
• -Disruption of the reflex arc
• Paresis/paralysis
• -Loss of innervation to the muscle fibers

Question 12

Hypertonicity is?

Answer 12

Upper motor neuron damage

-Injuries in the brainstem and spinal cord

Question 13

Hypertonicity is often accompanied by?

Answer 13

An exaggerated deep tendon reflex and presence of a tonic stretch reflex (hyperreflexia)

Question 14

What is spasticity - Velocity Dependent - Myoplastic changes are?

Answer 14

• Contracure

- Increased weak actin-myosin bonds

Question 15

What is spasticity - Velocity Dependent - Neural changes are?

Answer 15

Neuromuscular overactivity causing too many active motor units

Chronic upper motor neuron injuries

Question 16

Spasticity - Possible neural mechanisms are?

Answer 16

• Loss of cortical inhibition of excitatory brainstem upper motor neuron tracts = overactivity of lower motor neurons and abnormal muscle systems
• Decreased activation threshold of lower motor neuron = enhanced excitability of lower motor neurons

Question 17

Spasticity - Possible neural mechanisms are - Underactivity of?

Answer 17

inhibitory upper motor neuron on stretch reflexes

-Disinhibition of interneurons and reflex arc (hyperreflexia)

Question 18

Spasticity - Possible neural mechanisms are - Decreased activation threshold of?

Answer 18

Lower motor neuron = enhanced excitability of lower motor neuron

Question 19

Spasticity - Possible neural mechanisms are - other theorized contributors are?

Answer 19

Impaired reciprocal inhibition

• Abnormal co-contraction
• Injury to immature nervous system
• Loss of fractionation in mature system

Question 20

Hypertonicity - Rigidity is?

Answer 20

Velocity independent

-Basal nuclei (ganglia) disorder (ex: Parkinson disease)

Question 21

Hypertonicity - Decerebrate posture - Caudal midbrain injury is?

Answer 21

-Extension of limbs and trunk with upper extremity internal rotation and ankle plantarflexion

Question 22

Hypertonicity - Decorticate posture - Injury rostral midbrain or bilateral injuries superior to midbrain is?

Answer 22

Extension of lower extremity and trunk with upper extremity flexion at elbow and wrist, and ankle plantarflexion