Lec 10

Question 1

Diff btw GTO’s and Muscle spindles anatomically

Answer 1

GTO
- Lie in series to muscle fibres
- Located at junction between musc and tendon

Spindle
- Lie in parallel to musc fibres
- Located within the musc belly

Question 2

T/F - all muscle fibres are attached to a GTO

Answer 2

False - only need samples, not need every fibre to get idea of tension, just need 1-2 GTO attachements per motor unit so they’re all accounted for. Most fibres don’t pass through GTO

Question 3

What afferent fibre innervates the GTO.
Through what mechanism does this fibre get stimulated?

Answer 3

The 1b afferent innervates.

1b weaves through collagen fibres, when pulled tight, the collagen squeezes against the afferent producing signal.

Question 4

What do GTO’s send info about?

Answer 4

Force and tension mostly from active muscle contractions, but can also be from strong passive stretch

Question 5

Are GTO’s more sensitive when actively or passively stretched?

What benefit does this have.

Does autogenic inhibition have to occur to effect muscles.

Answer 5

More sensitive to active tension when contracted (30-90 millinewtons rather than passive tension when stretched (2 newtons).

This helps fine tune muscle force output during active contractions.

Autogenic inhibtion (GTO reflex) is not the only way GTOs can affact muscles. They also provide ongoingn info to CNS during muscle contraction to regulate muscle contractions.

Question 6

Describe what force to discharge rate of GTO would look like if graphed.

Answer 6

Linear. Means that GTO’s can accurately code for force because it is consistent, proportional, and scaleable.

Question 7

Regarding GTO reflex, explain how info gets from GTO to muscle

Answer 7

GTO pick code for muscle tension when collagen fibres are pulled taught, send code to spinal cord via the 1b afferent. This joins to the inhibitory interneuron which can send IPSP’s if a threshold is reached. IPSP’s sent to the agonist motor neuron via the Alpha motor neuron causing it to stop contracting.

Question 8

True or false - when your muscles are fatigued, GTO’s firing rate goes up.

Answer 8

False, GTO’s measure tension accurately even when your muscles are fatigued

Question 9

What is the role of the inhibitory interneuron in GTO function

Answer 9

• The inhibitory interneuron can turn off motor neurons via IPSP’s.
• If a threshold is reached, then the inhibitory interneuron comes on and inhibits motor neurons (autogenic inhibition). That is the GTO reflex.
• The need of the threshold ensures that as tension increases, you don’t also actively inhibit your muscles at the same time until threshold is reached.

Question 10

What do older textbooks fail to recognize about GTO’s

Answer 10

Fail to recognize the fact that GTO’s are more active with active muscle contraction than passive (although they do still respond if enough passive tension is reached).

Question 11

What do the Ia afferents innervate, what about the Ib afferents?

Answer 11

Ia - muscle spindles

Ib - GTO’s