13.8 Reflexes

Question 1

Reflex arc

Answer 1

Stimulus
Receptor
Sensory neurone
Relay neurone
Motor neurone

Question 2

Knee jerk reflex

Answer 2

Leg tapped just below patella
Stretches patellar tendon - acts as a stimulus and initiates reflex arc
Causes extensor muscle to contract
At the same time, relay neurone inhibits motor neurone of the flexor muscle - causing relaxation
Contraction coordinated with the relaxation of the antagonistic flexor hamstring muscle causes the leg to kick

Question 3

Why is the knee jerk reflex required?

Answer 3

Used by body to maintain posture and balance
Allows you to stay balanced with little effort or conscious thought

Question 4

What type of reflex is the blinking reflex?

Answer 4

Cranial reflex - occurs in the brain, not the spinal cord

Question 5

What happens in the blinking reflex?

Answer 5

When cornea is irritated by a foreign object, stimulus triggers an impulse along the sensory neurone
Impulse passes through a relay neurone in the lower brain stem
Impulse is sent along branches of the motor neurone to initiate response to close the eyelids
Reflex causes a consensual response - both eyes are closed in response to stimulus

Question 6

When is blinking reflex tested?

Answer 6

When examining unconscious patients. If reflex is present, lower brain stem is functioning. Tests if patient is brain dead or not

Question 7

Why are reflexes essential for survival?

Answer 7

Involuntary responses - decision making part of brain is not involved
Don’t need to be learnt - present at birth and give immediate protection
Extremely fast - short reflex arc and only one or two synapses