Motor Units, Muscle Spindles, Golgi Tendon Organs and Joint Receptors

Question 1

a-MN

Answer 1

Innervate the bulk of fibres within a muscle that generate force.

Question 2

y-MN

Answer 2

Innervate sensory organ (muscle spindle) within muscle

Question 3

How many pairs of mixed spinal nerves

Answer 3

30 pairs
C8
T12
L5
S5

Question 4

Motor Unit

Answer 4

a-MN and all the skeletal muscle fibres that it innervates

Question 5

Motor Neurone Pool

Answer 5

Collection of a-MNs that innervate a single muscle

Question 6

Three input sources to a-MN to regulate its activity

Answer 6

UMNs in motor cortex and brain stem
Spinal interneurones
Central terminals of dorsal root ganglion cells whose axons innervate muscle spindles

Question 7

Muscle strength depends on

Answer 7

Firing rates of LMNs involved
Number of LMNs that innervate muscle (ie. number of motor units)
Coordination of movement
Fibre size (hypertrophy)
Fibre phenotype (fast twitch/slow twitch)

Question 8

Slow-Oxidative (Type I) fibres

Answer 8

ATP derived from oxidative phosphorylation
Slow contraction an relaxation
Fatigue resistant
Red fibres (dark) due to high myoglobin content

Question 9

Fast (Type IIa) fibres

Answer 9

ATP derived from oxidative phosphorylation
Fast contraction and relaxation
Fatigue resistant
Red and reasonably well vascularised

Question 10

Fast (Type IIx) fibres

Answer 10

ATP derived from glycolysis.
Fast contraction
Not fatigue resistant
Pale in colour and poorly vascularisedd

Question 11

Increase in force due to

Answer 11

Temporal summation (first)
Recruitment of more motor units via different threshold a-MNs (second). - recruitment of a-MN by size allows the fine and graded development of muscle force.

Question 12

Golgi Tendon Organs

Answer 12

Located at junction of muscle and tendon
Monitor changes in muscle tension
Innervated by group Ib sensory afferents (myelinated, slightly slower than Ia)
Regulate muscle tension to protect muscle from overload and generally regulate muscle tension to optimum range.

Question 13

Joint proprioception

Answer 13

Free nerve endings - capsule and connective tissue, most numerous, high threshold, slowly adapting, nociceptive function

Golgi-type endings - ligaments, high threshold, slowly adapting, protective role

Paciniform endings - periosteum near articular attachments and fibrous part of joint capsule, low threshold, slowly adapting, acceleration detectors

Ruffini endings - joint capsule, low threshold, slowly adapting, static position and speed of movement