Reflexes

Question 1

Describe the Stretch reflex?

Answer 1

Found in all muscles.
Follows a sharp tap to the inelastic tendon.
Uses info from muscle spindles which monitor muscle length.
Force from tap is transmitted to muscle fibres which stretch. This stretch activates sensory nerves which then increases the number of APs.

Question 2

What are the 3 types of connection a spindle fibre makes when it divides?

Answer 2

1. directly activate the alpha motoneuron pool to the muscle which was stretched - rapid contraction of agonist. Monosynaptic reflex.
2. Indirectly connect with and influence the antagonist muscle. Agonist contracts = antagonist stretches/relaxes. Reciprocal inhibition.
3. Spindle afferent information also ascends in dorsal columns, connects with somatosensory cortex to tell the brain about length of muscles.

Question 3

Describe the Golgi tendon organ reflex?

Answer 3

Agonist muscle is inhibited so it relaxes.
Antagonist muscle is excited boy interneurones causing it to contract.
Polysynaptic.
It prevents muscles contracting so hard that the tendon insertion is torn away from the bone.
Protective.

Question 4

Describe the Flexor withdrawal reflex?

Answer 4

Withdraw part of the body away from painful stimulus and in towards body - flex.
Increased sensory APs from pain receptors cause an increase in affected flexor muscles via a number of excitatory interneurones. Antagonist extensors are also inhibited.
Polysynaptic
Protective.

Question 5

How do you prevent falling over after a flexor withdrawal reflex?

Answer 5

Contralateral limb extends:

• Several excitatory interneurones which cross the spinal cord excite the contralateral extensors.
• At the same time, via several interneurones, there is inhibition of the contralateral flexors.
• Bears body weight to maintain upright position.
• Sensory information ascends to the brain in the contralateral spinothalamic tract.

Question 6

What does the High activation of y-motoneurones cause?

Answer 6

Causes muscles to become extremely resistant to stretch and muscle is “spastic”.

Question 7

What makes the stretch reflex so specific?

Answer 7

Spindle input is highly localised and affects only  motoneurones of one or two spinal segments.

Question 8

What makes the the withdrawal reflex occur in not just the affected muscle?

Answer 8

Pain fibre input is diffused and spreads through several spinal segments.

Question 9

What is facilitation?

Answer 9

Increases the effect of sensory inputs.
Occurs between similar inputs e.g. many pain stimuli.
Or diverse inputs e.g if burn finger response is exaggerated as whole hand and arm is drawn back.