Muscle Function: Analysis and Demonstration

Question 1

Agonist

Answer 1

Primary mover; responsible for the initiation and execution of a specific action at a joint

Question 2

Antagonist

Answer 2

Opposes or reverses the action of the prime mover

Question 3

Synergist

Answer 3

Assists the prime mover in its actions

Question 4

Reciprocal inhibition

Answer 4

Skeletal muscles function in pairs; one of the muscles works as the agonist muscle and the other the antagonist

Question 5

Electromyography

Answer 5

Analysis of motor unit action potentials (MUAP) and assessment of baseline electrical signal at rest

Recorded using a surface or needle electrode

Can be used to monitor a muscle’s activity during a certain action and to assess integrity of the muscle and nerves supplying it

Question 6

What is a motor unit?

Answer 6

All the muscle fibers innervated by one nerve

Question 7

Innervation ratio

Answer 7

The number of muscle fibers innervated by a single axon/motor neuron

• Varies widely between muscle
• Low for fine motor (extra ocular muscles)
• High for gross motor (soles)

Question 8

What are some of the different kinds of muscle action potentials?

Answer 8

Motor unit action potential
Sensory nerve action potential
Compound muscle action potential

Question 9

What is the size principle?

Answer 9

Motor units are recruited from smallest to largest size.

Question 10

How can electromyography be used to diagnose disease?

Answer 10

Tests skeletal muscle fibers

Standard needle electromyography mostly tests type I muscle fibers

Question 11

How can Nerve conduction studies be used to diagnose disease?

Answer 11

Tests motor, sensory and mixed nerves

Question 12

What are the three types of contraction?

Answer 12

Isometric
Concentric
Eccentric

Question 13

Concentric contraction

Answer 13

Limb is shortening

Question 14

Eccentric contraction

Answer 14

Limb is lengthening

Question 15

Isometric contraction

Answer 15

No movement but still contracting

Question 16

When you walk are there more eccentric or concentric contractions?

Answer 16

Eccentric

Question 17

Name some agonists of wrist flexion.

Answer 17

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

Question 18

Name some antagonists of wrist flexion.

Answer 18

Extensor carpi radialis longus and brevis
Extensor ulnaris
Extensor digitorum

Question 19

Name some agonists of hip flexion.

Answer 19

Iliopsoas
Rectus femoris
Add long/brev
Pectineus
Gracilis
Sartorius
Tensor fasciae latae

Question 20

Name some antagonists of hip flexion.

Answer 20

Biceps femoris
Semitendinosus 
Semimembranosus
Gluteus maximus 
Adductor magnus

Question 21

What is upper motor neuron syndrome?

Answer 21

Lesion of upper motor neuron in the CNS
Overactivity – hyperreflexia, spasticity
Underactivity – weakness
No inherent muscle atrophy

Question 22

What is spasticity?

Answer 22

Velocity-dependent increase in tonic stretch reflex (muscle tone)

Question 23

What can be used to reduce focal muscle overactivity?

Answer 23

Botulinum neurotoxin
Effects intrafusal and extrafusal muscle
May affect nociceptor pathways via C and A delta fibers and substance P
Can also be used to block salivary and sweat gland

Question 24

Botulinum toxin mechanism of action

Answer 24

Heavy chain targets presynaptic membrane
Light chain goes in, gets endocytosed and cleaves SNAP-25
Local, temporary cholinergic chemodenervation