Reflexes

Question 1

What is the simplest reflex?

Answer 1

The stretch reflex

Question 2

Where is the stretch reflex found?

Answer 2

In all muscles

Question 3

What are examples of the stretch reflex?

Answer 3

Pattelar tendon

Knee jerk reflex

Question 4

What does the stretch reflex use?

Answer 4

Information from muscle spindles which monitor muscle length

Question 5

What is the stretch reflex?

Answer 5

Follows a sharp tap to an inelastic tendon

Question 6

What is the process of the stretch reflex?

Answer 6

1. Force is transmitted to muscle fibres
2. Stretch activates sensory nerves in muscle spindles
3. Increases the numbers of action potentials in afferent nerves projected through the dorsal horn into the spinal cord

Question 7

What are the three connections that the spindle sensory afferent devides into?

Answer 7

1. Activates alpha motor neurons to the muscle which was stretched (rapid contraction of the agonist muscle)
2. Connects indirectly with and influences the antagonist muscle (agonist muscle relaxes, stretches)
3. Dorsal columns and makes connection in the somatosensory cortex (tells the brain about the length of the muscle)

Question 8

During the stretch reflex, what kind of loop is the activation of the alpha motor neurons to the stretched muscle?

Answer 8

Monosynaptic reflex that is a negative feedback loop

Question 9

During the stretch reflex, why does the antagonist muscle relax when the agonist muscle contracts?

Answer 9

Spindle afferent activates inhibitory interneurons which stop the activation of alpha motor neurons to the antagonist muscle

Question 10

What is the inverse stretch reflex?

Answer 10

Caused by afferent neuron from golgi tendon organs

Muscle contracts and shortens

Pulls on tendon and I_b sensory nerves from the GTO increases firing of APs

Question 11

What is the process of the inverse stretch reflex?

Answer 11

1. Activation of inhibitory interneurons to agonist muscle (decrease in contraction strength)
2. Activation of exitatory interneurons to antagonist muscle
3. Information sent through the dorsal column to somatosensory complex

Question 12

What is the inverse stretch reflex also called?

Answer 12

Clasp knife

Golgi tendon organ reflex

Question 13

What does the inverse stretch reflex prevent?

Answer 13

The inverse stretch reflex prevents the muscle form contracting so hard that the tendon insertion is torn away from the bone

Question 14

What is the flexor (withdrawal) reflex?

Answer 14

Uses information from pain receptors

Withdraws part of the body away from pain stimuli

Question 15

How does the flexor reflex happen?

Answer 15

Increased aciton potentials cause:

1. Increased activity in flexor muscles (excites more neurons)
2. Antagonistic extensors are inhibited at the same time by a number of exitatory and inhibitory reflexors
3. To prevent you falling over extends to the contralateral limbs by excitatory interneurons cross spinal cord excite the contralateral extendors
4. At the same time inhibition of contralateral flexors
5. Sensory information goes to the brain in the contralateral spinothalamic tract

Question 16

What can you say about spinal segments involved in the flexor reflex?

Answer 16

Neurons branch a lot and so activate interneurons in several spinal segments, allowing the control of many muscle groups

Question 17

Is the reaction of the flexor reflex quicker at the source or contralateral limbs?

Answer 17

Slower at the contralateral limbs due to the time taken to travel through so many interneurons

Question 18

How can reflexes be overridden?

Answer 18

Consciously

Question 19

What is an example of consciously stopping a reflex?

Answer 19

If excessive load is placed on a muscle, the GTO reflex is activated causing muscle relaxation and the load to be dropped, but this can be consciously stopped

Question 20

How is it possible to consciously stop a reflex?

Answer 20

A motor neurons recieve more than 10000 synapses

Integration of EPSP and IPSP

Voluntary excitation of alpha motor neurons can overide inhibition from GTO to maintain contraction

Question 21

How can the stretch reflex be overridden?

Answer 21

Decending inhibition hyperpolarises alpha motor neurons

Stretch reflex cannot be evoked

Question 22

What does activation of gamma motor neurons depend on?

Answer 22

Decending pathways

Question 23

What are clinical uses of reflexes?

Answer 23

Assessing spinal cord localisation of a problem (reflex works above but not below the point of damage)

Question 24

What can you say about the spinal segments involved in the stretch reflex?

Answer 24

Stretch reflex is highly localised so only affects alpha motoneurons at one or two spinal segments

Question 25

What can you say about the spinal segments of the withdrawal reflex?

Answer 25

Diffuses and spreads to several spinal segments

Question 26

What is facillitation?

Answer 26

Spreads to many spinal cord segments to allow a quicker response