Muscle Function Review - Ketchum

Question 1

Distinguish between a muscle agonist and synergist.

Answer 1

Synergists are “secondary movers”, and serve to assist the agonist in its actions.

Question 2

What is the function and physiologic basis of reciprocal inhibition?

Answer 2

Functions to coordinate contraction for smooth activation and stopping, and to avoid muscle injury.

Antagonizing muscles are reciprocally inhibited by group Ia fibers.

Question 3

What does electromyograpy assess?

Answer 3

Assess muscle function and nerve signaling (MUAPs & conduction).

Question 4

What is the size principle?

Answer 4

In muscle contractions, the smallest motor units (slow-twitch) are recruited first.

Question 5

What are the three types of contraction?

Answer 5

Isometric (no change in length, eg pushing a static object)

Concentric (shortening of muscle fiber length)

Eccentric (contraction under lengthening)

Question 6

Recall the agonists and antagonists involved in wrist flexion.

Answer 6

Agonists: FCR(L/B), FCU, FDP, FDS.

Antagonists: ECR(L/B), Extensor ulnaris, extensor digitorum.

Question 7

Recall the agonists and antagonists involved in hip flexion.

Answer 7

Agonists: Iliopsoas, rectus femoris, S/G/T, TFL, adductors longus/brevis.

Antagonists: Semitendinosus, Semimembranosus, Biceps femoris, Gluteus maximus, Adductor magnus.

Question 8

Recall the clinical signs of an upper motor neuron lesion.

Answer 8

Hyperreflexivity, spasticity (positive signs)

Weakness (negative signs) *without atrophy

Question 9

How does botulinum toxin impede muscle contraction?

Answer 9

Its heavy chain cleaves synaptobrevin, resulting in loss of ACh presynaptic release at the NMJ.