5.5.7 reflex actions

Question 1

what are reflex actions

Answer 1

responses to changes in the environment that don’t involved any processing in the brain to coordinate the movement

Question 2

reflex pathway

Answer 2

sensory neurone —> relay neurone —> motor neurone

Question 3

survival value of reflex actions

Answer 3

• get out of danger
• avoid damage to part of the body
• used to maintain balance

Question 4

why type of reflex is the knee jerk reflex

Answer 4

spinal reflex (nervous pathway passes through spinal cord rather than brain)

Question 5

what is the knee jerk reflex involved in

Answer 5

coordinated movement & balance

Question 6

describe the knee jerk reflex

Answer 6

• quadricep contracts to straighten leg
• quadricep attached to lower leg via patella tendon
• patella tendon connects patella to lower leg bones at front of the knee
• when quadriceps are stretched, muscle spindles detect the increase in length of the muscle
• if stretching is unexpected, reflex action causes contraction of same muscle

Question 7

which mechanism is the knee jerk reflex part of

Answer 7

mechanism which enables us to balance on 2 legs

Question 8

nervous pathway of knee jerk reflex

Answer 8

sensory neurone —> motor neurone

Question 9

what does inhibition of movement rely on & why can the brain not inhibit the knee jerk reflex

Answer 9

• relies on rapid myelinated neurones carrying inhibitory action potential to the synapse before the motor neurone is stimulated
• no relay neurone in the knee jerk reflex, so insufficient delay to enable inhibition

Question 10

how is the knee jerk reflex stopped when we are walking/running

Answer 10

• knee bends & stimulates muscle spindles
• complex pattern of nervous impulses from cerebellum is able to inhibit the reflex contractions
• as action potentials are sent to hamstrings, stimulating it to contract, inhibitory action potentials are sent to the synapse in the reflex arc
• this prevents reflex contraction of opposing muscle