Reflexes

Question 1

Describe the stretch reflex

Answer 1

This reflex is elicited by a sharp tap to the tendons, which are inelastic, and so the force is transferred to the muscle fibres which stretch and stimulate the spindles. This activates the alpha motoneurones and the agonist muscle contracts. This is the only known example of a monosynaptic reflex.

Since muscles work in pairs, the antagonist muscle must also relax during this reflex because the spindle afferents activate inhibitory interneurons which decrease alpha motorneurone transmission to the antagonist.

Question 2

Describe the reflex mediated by the golgi tendon organ

Answer 2

Known as the inverse stretch or clasp-knife reflex, this depends entirely on Golgi tendon organs to produce an effect.
As the muscle contracts, it pulls on the tendons and the Golgi tendon bodies increase their discharge. This activates inhibitory interneurons to the agonist muscle and decreases the contraction strength, while also activating excitatory interneurons to the antagonistic muscle.
This reflex is polysynaptic and protective. It prevents over contraction and prevents the muscle from tearing the tendon insertion points away from the bones.

Question 3

Describe the flexor-withdrawal reflex

Answer 3

These reflexes use information from the nociceptors in skin, muscles and joints. They are polysynaptic and withdraw the affected part of the body away from the stimulus and towards the body.
Sensory stimulus causes an increase in activity of flexor muscles via a number of excitatory interneurons, while inhibitory neurones work on the antagonistic extensors. If this happens in our legs, we need the other leg to extend to keep us upright. Therefore, the excitatory interneurons which cross the spinal column cause the extensor muscles to contract while other interneurons inhibit the contralateral flexors.

Question 4

Describe the role of interneurones

Answer 4

Involved in reciprocal inhibition and GTO reflexes

Question 5

Describe ipsilateral and contralateral reflexes

Answer 5

Ipsilateral reflexes - a reflex in which the response occurs on the side of the body that is stimulated

Contralateral reflexes – a reflex in which the response occurs on the opposite side of the body, often in coordination with ipsilateral reflexes to prevent falling over etc.

Question 6

Define a reflex

Answer 6

A reflex action, differently known as a reflex, is an involuntary and nearly instantaneous movement in response to a stimulus. Scientific use of the term “reflex” refers to a behavior that is mediated via the reflex arc

Question 7

Define a reflex arc

Answer 7

A reflex arc is the nerve pathway of a reflex, including in its simplest form a sensory nerve and a motor neurone with a synapse between.

Question 8

Describe facilitation

Answer 8

Facilitation - the enhancement of the response of a neuron to a stimulus following prior or nearby stimulation.