L4 - Proprioception and Spinal Reflexes

Question 1

What does fusiform mean?

Answer 1

Tapered at both ends/spindle shaped

Question 2

A 1a sensory axon would refer to what?

Answer 2

The afferent axon to the CNS.

Question 3

What is the difference between intrafusal and extrafusal muscle fibre?

Answer 3

Intrafusal muscle is embedded in muscle spindle, while extrafusal isn’t. Extrafusal is the fibre that does the work in contracting, etc.

Question 4

What information does the muscle spindle send to the CNS?

Answer 4

Sends information about muscle length and rate of change (of length)

Question 5

Describe the monosynaptic reflex arc when the tendon below your knee is tapped.

Answer 5

• muscle spindle stretches when tapped, pulling intra-fusal and extrafusal muscle fibre.
• 1a afferent fibre fires, sending a signal into the spinal cord.
• This 1a afferent is connected to alpha motor neurons, which are activated by the 1a afferent signal.
• Muscle contracts to oppose the stretching

Question 6

How do muscle spindles signal the length and rate of change in length of the muscle?

Answer 6

• Bag fibres

- Chain fibres

Question 7

What are the two types of bag fibres?

Answer 7

Bag 1 and bag 2

Question 8

In muscle spindle, what signals information about length and what signals information about rate of change in length?

Answer 8

Bag 1 is called the dynamic bag - sends information about rate of change.
Bag 2 and chain fibres sends static information about absolute length.

Question 9

In what ways can gamma motor neurons tune muscle sensitivity?

Answer 9

• The sensitivity of the muscle spindles can change by pulling them together
• The type of information sent from the spindles can be influenced by pulling on one type of fibre more than another.

Question 10

What is spasticity and what is it caused by?

Answer 10

Pathologically increased muscle tone (rigidity) because of excessive stretch reflex. Caused by overactive muscle spindle.

Question 11

What are the functions of gamma motor neurons?

Answer 11

• alter the length of intrafusal muscle fibres
• can bias spindle towards dynamic or static sensitivity.
• regulates sensitivity during voluntary contraction
• important in the regulation of muscle tone

Question 12

What do Golgi tendon organs detect?

Answer 12

Tension in a tendon or muscle

Question 13

Where are Golgi tendon organs located?

Answer 13

Between the muscle spindle and tendon.

Question 14

How can Golgi tendon organs be activated?

Answer 14

Passive stretch or active muscle contraction

Question 15

What does GTO stand for?

Answer 15

Golgi tendon organ

Question 16

1b afferents refer to what?

Answer 16

Signals from the Golgi tendon organ

Question 17

What action do Golgi tendon organs take and how do they do it?

Answer 17

They control muscle tension by inhibiting alpha motor neurons using inhibitory interneurons.

Question 18

What is the purpose of the actions of Golgi tendon organs?

Answer 18

They are protective mechanisms - preventing muscles from having sustained levels of high tension, which could be dangerous for the muscle.

Question 19

What does CPG stand for?

Answer 19

Central pattern generators

Question 20

What might the CPG be responsible for?

Answer 20

Regulating limb and inter-limb movements, such as the ones required for walking, running, etc.

Question 21

If you don’t have proprioception - what might happen if you don’t have it?

Answer 21

Won’t be able to co-ordinate limbs properly.

Question 22

What is the time delay in the monosynaptic reflex arc?

Answer 22

40 milliseconds.

Question 23

What is an elemental action?

Answer 23

A motor action in which the goal outcome is achieved by executing just one goal-directed action

Question 24

Typically, what type of actions are elemental actions?

Answer 24

Discrete actions

Question 25

What are discrete actions?

Answer 25

A motor action whose execution has clearly identifiable start and end points.

Question 26

What is the sensorimotor principle?

Answer 26

Sensory perception is necessary for goal directedness

Question 27

What is the role of joint receptors in proprioception?

Answer 27

Free endings are located in tissue surrounding the joints, but only signal extreme joint angles.

Question 28

Muscle spindles are known as what?

Answer 28

1a afferents (afferent axon to the CNS)

Question 29

What are extrafusal muscle fibres innervated by?

Answer 29

Alpha motor neurons

Question 30

What is the function of muscle spindles?

Answer 30

To detect muscle stretch

Question 31

What is reciprocal innervation?

Answer 31

The inhibition of alpha neurons for antagonistic muscles, through inhibitory interneurons, to keep it relaxed. This allows the main muscle to contract.

Question 32

Describe the di-synaptic reflex arc.

Answer 32

• The GTO signals muscle tension along the 1b afferent, into the spinal cord.
• The first synapse is with an inhbitiory interneuron and the second is with a motor neuron.
• This allows regulation of muscle tension.

Question 33

Describe the two circumstances in which the GTO would control tension.

Answer 33

• detects and corrects small changes in tension.

- overcomes drive to/inhibits muscles when very large tension changes are required.

Question 34

Which stat about feedback in muscles indicates how much we use sensory information when performing tasks?

Answer 34

There’s a 50/50 split between afferent and efferent nerves into and out of muscles.

Question 35

What are bag 1 muscle fibres activated by?

Answer 35

Gamma motorneurons.