B. Neuromuscluar Anatomy and Physiology

Question 1

Motor Unit

Answer 1

• A motor neuron and the muscle fibers that it innervates (typically several hundred muscle fibers in a single motor unit)

Question 2

Neuromuscular Junction

Answer 2

The junction between a motor neuron and the muscle fibers it innervates

Question 3

Type I Muscle Fiber

Answer 3

• Slow Twitch
• Efficient, fatigue resistant, high aerobic energy supply
• limited rapid force development, low myosin ATPase activity, low anaerobic power

Question 4

Type II Muscle Fiber

Answer 4

• Fast Twitch
• Inefficient, Fatiguable, Low Aerobic Power
• Rapid Force Development, High Myosin ATPase activity, high anaerobic power

Question 5

Type II(a) vs. Type II(x) Muscle Fibers

Answer 5

Type II(a) - greater capacity for aerobic metabolism and more capillaries surrounding fibers

Type II(x) - lower capacity for aerobic metabolism and less capillaries surrounding fibers

Question 6

Proprioceptors

Answer 6

• specialized sensory receptors located within joints, muscles, and tendons
• relay information concerning muscle dynamics to the conscious and subconscious parts of the central nervous system

Question 7

Muscle Spindle

Answer 7

• Proprioceptors that consists of several modified muscle fibers enclosed in a sheath of connective tissue
• provide info about muscle length and rate of change in length

Question 8

What happens to spindles when a muscle lengthens?

Answer 8

• The spindle stretches and sends the information to the spinal cord, which synapses with motor neurons
• This activates the motor neurons that innervate the same muscle

Ex) knee jerk reflex

Question 9

Golgi Tendon Organ

Answer 9

• Proprioceptors located in tendons near the myotendinous junction and are attached end to end with extrafusal muscle fibers

Question 10

How is a Golgi Tendon Organ activated?

Answer 10

• Activated when the tendon is stretched. When tension in muscle increases, GTOs discharge increases. Sensory neurons then synapse with an inhibitory interneuron which activates the same muscle

Question 11

What is the result of the Golgi Tendon Organ synapse?

Answer 11

• Reduction in tension within the muscle and tendon

Question 12

Activation of GTOs

Answer 12

Minimal - with low forces placed on the muscle

Maximal - with extremely heavy loads (causes reflexive inhibition causing the muscle to relax)

Question 13

Motor Recruitment Patterns (2)

Answer 13

1. Variation in Frequency

2. Recruitment of more Motor Units

Question 14

1. Variation in Frequency

Answer 14

• If motor unit is activated once, the twitch that arises does not produce great deal of force
• If frequency of activation is increased so that forces of the twitches begin to overlap (summate), resulting force developed by motor unit is much greater
• important in smaller muscles (hand muscles)

Question 15

2. Recruitment of more Motor Units

Answer 15

• an increase in force through varying the number of motor units activated
• large muscle (quads), motor units activated at high rate, increase in force output are achieved through recruitment of additional motor neurons

Question 16

Summation

Answer 16

• Increase in tension that results when a muscle fiber is unable to relax between twitches.
• Individual twitches overlap and produce a continuous smooth contraction of increasing strength