Muscle S18

Question 1

muscle cramps

Answer 1

characterized by a sudden onset of painful, involuntary squeezing or contraction of muscle.

Question 2

muscle cramps offen involve..

Answer 2

lower-limbs

Question 3

nocturnal leg cramps

Answer 3

common for elderly; closely associated with cold temperature

Question 4

nocturnal leg cramps

Answer 4

common for elderly; closely associated with cold temperature

Question 5

What can speed relief of a muscle cramp?

Answer 5

stretching the muscle or contraction of its antagonist muscle

Question 6

triggering factors for muscle cramp

Answer 6

sweat losses leading to dehydration, electrolyte disturbance, and thermal strain during exercise.

Question 7

Cramps may result in persistent soreness, swelling, and elevated serum…

Answer 7

creatine kinase

Question 8

Evidence suggest cramps arise from SPONTANEOUS discharges of the motor nerves rather than within the muscle itself, BUT…

Answer 8

monitoring the duration of muscle cramp using EMG reveals APs for the involuntary firing of motor unit are at HIGH FREQUENCY, not a representation of spontaneous muscle activity.

Question 9

EMG data strongly suggest that muscle twitch (involuntary muscle contraction and relaxation) during cramps are of ..

Answer 9

peripheral nerve origin

Question 10

Susceptibility to exercise-associated muscle cramps have a…

Answer 10

neurogenic basis

Question 11

leg cramps in pregnancy

Answer 11

• common in third trimester
• could be secondary effect to physical distortion of neuromuscular junction as a byproduct of fluid retention and joint laxity that accompanies later stages of pregnancy.

Question 12

disorders associated with cramps

Answer 12

• thyroid disease and hypoadrenalism (endocrine diseases)
• liver disease
• cirrhosis

Question 13

how are frequency of cramps decreased in cirrhotic patients?

Answer 13

infusion of human albumin

Question 14

threshold

Answer 14

minimum frequency of electrical stimulation to induce cramp

Question 15

idiopathic cramp

Answer 15

unknown cause; motor units fire at unusually RAPID rates

Question 16

chronic partial denervation

Answer 16

motor units fire at unusually rapid rates

Question 17

Motor unit firing during cramp … after initial burst.

Answer 17

decreases

Question 18

Cramps are abolished by nerve block but may still be induced by repetitive nerve stimulation DISTAL to the anesthetic block, therefore…

Answer 18

Likely that cramps usually have a PERIPHERAL neurogenic origin

Question 19

muscle spindles

Answer 19

stretch receptors that can be found in the capsules of extrafusal muscle fibres and contain intramural fibres

Question 20

alpha motor neuron

Answer 20

innervates extrafusal muscle fibres

Question 21

gamma motor neurons

Answer 21

innervates and control contraction in intrafusal fibres

Question 22

sensory neurons

Answer 22

send info to spinal cord and synapses directly on alpha motor neurons

Question 23

muscle spindles at rest

Answer 23

• extrafusal muscle fibers at resting length
• sensory neuron is tonically active
• spinal cord integrates function
• alpha motor neurons to extrafusal fibers receive tonic input from muscle spindles
• extrafusal fibres maintain certain level of tension

Question 24

muscle spindles when stretched

Answer 24

• stretching of extrafusal muscle will also stretch muscle spindles
• increased afferent signals to spinal cord thru sensory neuron (muscle is stretched)
• increased efferent output thru alpha motor neurons
• firing rate of afferent sensory neuron decreases (muscle returns to initial length)

Question 25

stretch reflec

Answer 25

to prevent damage from overstitching

Question 26

muscle spindles in absence of gamma motor neurons activation (alpha activation alone)

Answer 26

- alpha motor neuron fires - muscle contracts - less stretch on centre of intramural fibres - firing rate of spindle sensory neuron DECREASES

Question 27

cramps provokes by peripheral electrical stimulation in a BLOCKE motor nerve vs those evoked by stimulating a physiologically normal nerve

Answer 27

- cramp threshold is higher when nerve is blocked (difficult to induce cramp) - cramp duration and signal amplitude and motor unit firing rate is always HIGHER when nerve is intact