Applied Muscle Physiology

Question 1

Components of neuromuscular unit

Answer 1

ventral horn cells

peripheral spinal nerve innervating muscle

neuromuscular junction

muscle itself

Question 2

PEx findings for an UMN disorder.

Answer 2

muscle tone is spastic (muscles are stiff and difficult to move)

DTRs are increased

plantar reflex (Babinski) is positive (big toe moves up and other toes fan out with firm stroke, normally disappears in infancy)

Question 3

PEx findings for a LMN disorder.

Answer 3

muscle tone is hypotonic

DTRs are decreased

plantar reflex (Babinski) is normal (big toe does not move when plantar firmly stroked)

Question 4

Multiple sclerosis mechanism

Answer 4

demyelination on odliodendrocytes in the CNS

Question 5

Guillain-Barre mechanism

Answer 5

demyelination of Schwann cells in the PNS

Question 6

Tetanus mechanism

Answer 6

enters skin through wound, travels up axons to Renshaw Cells in the spinal cord - these inhibitory interneurons normally limit muscle contraction via creating feedback loop

Question 7

Curare - drug

Answer 7

a-bungarotoxin from cobra venom - paralytic antagonist of nAChR

Question 8

Myasthenia Gravis mechanism

Answer 8

autoimmune disorder in which immune system destroys nAChRs, making neurotransmission less effective

Question 9

Duchenne and Becker’s muscular dystrophies mechanism

Answer 9

Muscle protein disorders due to X-linked mutation in dystrophin gene - leads to improper alignment of the sarcomere/interaction with cytoskeleton/lack of force or transmission

Question 10

Metabolic muscle disorders

Answer 10

disorders that inhibits muscle from getting sufficient ATP - glycogen storage diseases (e.g., McArdle’s disease), lipid storage diseases,
mitochondrial myopathies.

Question 11

Inflammatory muscle disorders

Answer 11

polymyositis, dermatomyositis - chronic conditions that lead to muscle weakness and extreme pain

Question 12

Malignant hyperthermia

Answer 12

inherited mutation in RyR receptors that causes overly high sarcoplasmic Ca2+ sin response to inhaled anesthetics causing increased muscle contraction, depletion of ATP, and heat production.

Question 13

Hyperkalemia/hypokalemic periodic paralysis

Answer 13

transient paralysis/muscle weakness due to mutations in sodium channel gene, which causes the sodium channels to be either stuck open or stuck closed

Question 14

Rhabdomyolysis

Answer 14

disorder that leads to the breakdown of muscle tissue and increased plasma myoglobin

Question 15

Myotonia congenita (Thomsen or Becker’s)

Answer 15

mutations in ClC-1 channel (calcium channel that haps to repolarize and relax the muscle fiber) leading to prolonged muscle contraction and muscle hypertrophy