Muscle spindles, Golgi tendon organs and spinal reflexes

Question 1

What categories can intrafusal fibres be subdivided into on the basis of morphology and function?

Answer 1

Nuclear bag fibres (dynamic or static)

Chain fibres

Question 2

What are dynamic nuclear bag fibres?

Answer 2

Sensitive to the rate of change of muscle length, innervated by dynamic, but not static y-MNs

Question 3

What are static nuclear bag fibres?

Answer 3

More sensitive to the absolute length of the muscle. innervated by static y-MNs

Question 4

What are chain fibres?

Answer 4

Sensitive to the absolute length of the muscle. innervated by static y-MNs.

Question 5

Which two types of afferent fibres innervate the intrafusal fibres?

Answer 5

Ia (Aa) and II (AB)

Question 6

Describe Ia fibres?

Answer 6

Form a primary annulospiral nerve ending winding around the centre of all intrafusal fibres

Question 7

Describe II fibres?

Answer 7

More slowly conducting, form flower spray endings on all intrafusal fibres except the bag 1 dynamic type

Question 8

In activities in which muscle length changes slowly and predictably only ______ ______ are active

Answer 8

In activities in which muscle length changes slowly and predictably only static y-MNs are active

Question 9

_______ ______ are active during behaviours in which muscle length changes rapidly and unpredictably.

Answer 9

Dynamic y-MNs are active during behaviours in which muscle length changes rapidly and unpredictably.

Question 10

Where are Golgi tendon organs located?

Answer 10

At the junction of muscle and tendon

Question 11

What do Golgi tendon organs do?

Answer 11

Monitor changes in muscle tendon, they are in series with, rather than parallel to extrafusal fibres

Question 12

What innervates Golgi tendon organs?

Answer 12

Group Ib sensory afferents (myelinated, slightly slower than Ia fibres)

Question 13

What is the role of Golgi tendon organs?

Answer 13

Regulate muscle tension

• protect muscle from overload (weight lifting)
• regulate muscle tension to an optimal range

Question 14

Group Ib afferents enter the spinal cord and synapse upon _________ ____________ which, in turn, synapse upon the ______ _______ neurones of the ___________ muscle forming the basis of the reverse myotactic reflex

Answer 14

Group Ib afferents enter the spinal cord and synapse upon inhibitory interneurones which, in turn, synapse upon the alpha motor neurones of the homonymous muscle forming the basis of the reverse myotactic reflex

Question 15

Why is the reverse myotactic reflex important?

Answer 15

Proprioceptive feedback is thought to be important for the proper execution of fine motor acts

Question 16

Proprioceptive axons are present in connective tissue of joints e.g.

Answer 16

Joint capsules and ligaments

Question 17

Proprioceptive axons respond to changes in _____, ______ and ________ of movement of a joint. Also prevent excessive _______ or ________

Answer 17

Proprioceptive axons respond to changes in angle, direction and velocity of movement of a joint. Also prevent excessive flexion or extension

Question 18

Mixture of ____ adapting and _______ adapting units that have either a ____ ________ or ___ ________ for activation (thus information concerning movement and the static, or resting position of a joint is transmitted to the CNS.)

Answer 18

Mixture of fast adapting and slowly adapting units that have either a high threshold or low threshold for activation (thus information concerning movement and the static, or resting position of a joint is transmitted to the CNS.)

Question 19

Nocicepitve free nerve endings are found in capsule and connective tissue, __ and __ are most numerous

Answer 19

Nocicepitve free nerve endings are found in capsule and connective tissue, HT and SA are most numerous

Question 20

Golgi-type endings are found only in _______ and __, __ are the most numerous

Answer 20

Golgi-type endings are found only in ligaments and HT, SA are the most numerous

Question 21

Paciniform endings are found where and what is their function

Answer 21

Found in periosteum near the articular attachments and the fibrous part of the joint capsule

LT and SA acceleration detectors

Question 22

Ruffini endings are found mainly where and what is their function

Answer 22

Found in joint capsule

LT and SA to detect static position and speed of movements

Question 23

Proprioceptive information arises from (3)?

Answer 23

• muscle spindles
• Golgi tendon organs
• joint receptors

Question 24

Spinal interneurones receive input from (4)

Answer 24

1. primary sensory axons (Ia and Ib)
2. Descending axons from the brain
3. collaterals (branches) of LMNs
4. other interneurones

Question 25

Input to spinal interneurones may be _______ or _______. interneurones integrate incoming information to generate an _______

Answer 25

Input to spinal interneurones may be excitatory or inhibitory. interneurones integrate incoming information to generate an output

Question 26

Inhibitory interneurones mediate (2)?

Answer 26

1. inverse myotactic reflex

2. reciprocal inhibition between extensor and flexor muscles

Question 27

At a joint voluntary contraction of an _______ will stretch an antagonist flexor, initiating the _______ reflex. However, _______ pathways that activate the a-MN controlling the extensor muscles also via ______ _________, inhibit the a-MNs supplying the antagonist muscles, in this case allowing extension.

Answer 27

At a joint voluntary contraction of an extensor will stretch an antagonist flexor, initiating the myotactic reflex. However, descending pathways that activate the a-MN controlling the extensor muscles also via inhibitory interneurones, inhibit the a-MNs supplying the antagonist muscles, in this case allowing extension.

Question 28

Excitatory interneurones mediate (2)

Answer 28

The flexor reflex

The crossed extensor reflex

Question 29

What is the crossed extensor reflex

Answer 29

Noxious stimulus cause slump to extend by;

• contraction of extensor muscles via excitatory interneurones
• relaxation of flexor muscles via excitatory and inibitory interneurones

Question 30

Why is the crossed extensor reflex important?

Answer 30

Enhances postural support during withdrawal of a foot from a painful stimulus

Question 31

What is the flexor reflex

Answer 31

Noxious stimulus cause limb to flex by;

• contraction of flexor muscles via excitatory interneurones
• relaxation of extensor muscle via excitatory and inhibitory interneurones