Muscle Function: Analysis and Clinical Demonstration

Question 1

Define an agonist

Answer 1

• “Primary mover”
• Often considered as functional muscle group
• Responsible for the initiation and execution of a specific action at a joint

Question 2

What is an antagonist?

Answer 2

A muscle that opposes or reverses the action of the prime mover

Question 3

What are synergists?

Answer 3

Muslces that assist the prime mover in its actions

Question 4

What is reciprocal inhibition

Answer 4

Skeletal muscle functions usually include pairs of muscles

Depending on the muscle function, one of the paired muscles works as the agonist muscle and the other the antagonist muscle

Question 5

How does reciprocal inhibition leads to maximal muscle efficiency

Answer 5

• Increased tone in preparation for full activation
• The antagonist muscle prepares to slow down/stop the intended function
• The muscle pair need to coordinate their contractions to avoid muscle injury

Question 6

What type of inhibition contributes to antagonist suppression during movement?

Answer 6

Group Ia-mediated reciprocal inhibition

Question 7

Depolarization of all the fibers in a motor unit creates an electrical potential called…

Answer 7

A motor unit action potential (MUAP)

Question 8

How are MUAPs used in electromyography

Answer 8

MUAPs generated by contraction of an individual muscle can be recorded by using a surface or needle electrode

Question 9

What is the innervation ratio?

Answer 9

Number of muscle fibers innervated by a single axon/motor neuron

Question 10

Which types of muscles have a high innervation ratio? Which have a low innervation ratio?

Answer 10

High for gross motor (soleus)

Low for fine motor (extraocular muscles)

Question 11

What is the size principle?

Answer 11

Smaller fibers are recruited first in a movement and progressively larger fibers are then recruited as needed

Question 12

Difference between nerve conduction studies and electromyography

Answer 12

Nerve conduction studies test motor, sensory and mixed nerves

Electromyography tests skeletal muscle fibers - most test type I fibers

Question 13

Types of contraction

Answer 13

Isometric

Concentric

Eccentric

Question 14

In a normal gait, are their more eccentric or concentric contractions?

Answer 14

Eccentric

Question 15

Wrist flexion agonists

Answer 15

• Flexor carpi radialis
• Flexor carpi ulnaris
• Flexor digit profundus
• Flexor digit sublimis

Question 16

Wrist flexion antagonists

Answer 16

• Extensor carpi radialis longus and brevis
• Extensor ulnaris
• Extensor digitorum

Question 17

Hip flexion agonists

Answer 17

• Iliopsoas
• Rectus Femoris
• Adductor longus and brevis
• Pectineus
• Gracilis
• Sartorius
• Tensor fasciae latae

Question 18

Hip flexion antagonists

Answer 18

• Biceps femoris
• Semitendinosis
• Semimebranosis
• Gluteus maximus
• Adductor magnus

Question 19

What is upper motor neuron syndrome?

Answer 19

Lesion of the uppor motor nueron in the central nervous system (brain or spinal cord)

Question 20

UMN syndrome

Positive signs:

Negative signs:

Answer 20

Positive signs (overactivity): Hyperreflexia; spasticity

Negative signs (underactivity): Weakness

Question 21

What is spasticity?

Answer 21

• Velocity dependent increase in tonic stretch reflex (muscle tone)
• Hyperexcitability of the stretch reflex
• One component of the upper motor neuron syndrome

Question 22

Uses of botulinum neurotoxin

Answer 22

• Injections can be used to reduce focal muscle overactivity
  
  • Affects both intrafusal and extrafusal muscle
• Can be used to block salivary and sweat glands
• Used to treat numerous disorders: dystonia, spasticity, opthalmologic, GI/GU, dermatologic and pain

Question 23

Botulinum toxin can affect nociceptor pathways via…

Answer 23

C and A delta fibers and substance P

Question 24

Types of Electromyography

Answer 24

• Surface EMG
• Needle EMG
  
  • Tests type I fibers