Spinal Reflexes

Question 1

Where is the stretch reflex found?

Answer 1

in all muscles using information from muscle spindles

Question 2

When does the stretch reflex occur?

Answer 2

following a sharp tap to the inelastic tendon

Question 3

Is the stretch reflex by which the alpha motor neurone is activated, monosynaptic or include interneurones?

Answer 3

monosynaptic

Question 4

Where is the force from the tendon transmitted to?

Answer 4

muscle fibres which are more elastic than tendons and are able to stretch to activate the spindle

Question 5

What happens after activation of the muscle spindle?

Answer 5

there is an increased number of action potentials that enter the spinal cord in afferent neurones through the dorsal horn

Question 6

What are the 3 outcomes of activation of the muscle spindle in the stretch reflex?

Answer 6

1. alpha motor neurone of the muscle that was stretched is activated (monosynaptic) - is the agonist and causes contraction
2. the antagonist muscle relaxes (stretches) by reciprocal inhibition
3. spindle afferent information ascends in dorsal columns to brain

Question 7

What is reciprocal inhibition?

Answer 7

• spindle afferents activate inhibitory interneurones

- interneurones inhibit activation of alpha motor neurones to the antagonist which then relaxes

Question 8

What is the other name given to the Golgi-tendon organ reflex?

Answer 8

inverse stretch reflex

Question 9

What do the Golgi Tendon Organs monitor?

Answer 9

muscle tension

Question 10

What is the purpose of the GTO reflex mechanism?

Answer 10

to prevent the muscle contracting so hard that the tendon insertion is torn from the bone

Question 11

Does the GTO reflex mechanism work monosynaptically or polysynaptically?

Answer 11

involves lots of interneurones

Question 12

What effect does the GTO reflex have on the agonist muscle when it contracts?

Answer 12

• muscle contracting pulls on tendons and sensory nerves from GTO, sending APs
• synapses with an inhibitory interneurone
• ultimately leads to decrease in contractile strength

Question 13

What effect does the GTO reflex have on the antagonist muscle?

Answer 13

• muscle contracting pulls on tendons and sensory nerves from GTO, sending APs
• synapses with excitatory interneurones to antagonist muscles which may contract a little

Question 14

Where does the information from the GTO ascend to?

Answer 14

once the information from the GTO reaches the spinal column, as well as there being a reflex action, the information also ascends in the dorsal columns to the somatosensory cortex in the brain to provide info about muscle tension

Question 15

What causes GTO discharge?

Answer 15

muscle contraction

Question 16

Flexor reflexes (withdrawal reflexes) use information from where?

Answer 16

pain receptors (nocireceptors) in skin, muscle and joints

Question 17

What do flexor reflexes do?

Answer 17

withdraw part of the body from a painful stimulus by flexing the affected part

Question 18

How does the flexor reflex result in the withdrawal of the limb?

Answer 18

• increased sensory APs from the pain receptors
• flexor muscles are activated via excitatory interneurones
• extensor muscles are inhibited via excitatory and inhibitory interneurones

Question 19

In what tract does the information from the flexor reflex ascend?

Answer 19

contralateral spino-thalamic tract

Question 20

How does the flexor reflex pass information so that contralateral limbs can act with the affected limb?

Answer 20

• several excitatory interneurones cross the spinal cord to excite the contalateral extensors
• at the same time, via a number of interneurones the contralateral limb flexors are inhibited

Question 21

What will inhibit the GTOs from preventing contraction if it is important that the contraction is maintained?

Answer 21

descending facillitatory and inhibitory inputs to the alpha motor neurones

Question 22

What can prevent a stretch reflex from being evoked?

Answer 22

strong descending IPSPs to alpha motorneurones

Question 23

What pathways do the gamma motorneurones depend on for their activity?

Answer 23

descending pathways

Question 24

What would happen to the muscle if discharge to the muscle from the gamma motroneurone was increased?

Answer 24

muscle become resistant to stretch and said to be ‘spastic’

Question 25

What is the relationship between the magnitude of the pain stimulus and the spinal spread?

Answer 25

the greater the pain stimulus, the greater the spinal spread and the larger the response

Question 26

What does the facilitation do?

Answer 26

increases the effects of sensory inputs

Question 27

How does facilitation work?

Answer 27

when motor neurones from a particular input are stimulated they can (if multiple inputs are being stimulated) cause the depolarisation and firing of another area of motor neurones