13.8 Reflexes

Question 1

Definition of a reflex

Answer 1

An involuntary response to a sensory stimulus

Question 2

What is the pathway of neurones involved in a reflex action?

Answer 2

stimulus, receptor, sensory neurones, relay neurones, motor neurones, effector, response

Question 3

What is the role of the relay neurone?

Answer 3

Connect the sensory neurone to the motor neurone within the spinal cord or brain (CNS)

Question 4

What is the role of motor neurone within a reflex arc?

Answer 4

Carries impulse to the effector to carry out the appropriate response

Question 5

What is the role of sensory neurones within a reflex arc?

Answer 5

Carries impulse to spinal cord

Question 6

Explain the process involved in the reflex arc when your touch a hot candle

Answer 6

1. Stimulus is the heat of the candle
2. Thermoreceptors in skin detects heat
3. Sensory neurones pass nerve impulse to spinal cord
4. Relay neurones passes impulse across the spinal cord
5. Motor neurones passes the impulse to the effector (muscle)
6. Effector contracts
7. Response is to move the hand quickly away from the flame

Question 7

What is the acronym to remember the order of a reflex arc?

Answer 7

Silly
Rodger
Says
Rabbits
May
Evolve
Rapidly

Question 8

Label the diagram of an eye

Answer 8

Question 9

How does the blinking reflex work?

Answer 9

-Sensory nerve endings in the cornea are stimulated by touch
-A nerve impulse is sent along sensory neurones to a relay neurone in the CNS
-Impulse is then passed to motor neurones
-Motor neurones send impulses to the effectors (the orbicularis oculi muscles) that contract to cause the eyelids to close and prevent damage to the eye

Question 10

How does the knee-jerk reflex work?

Answer 10

-Stretch reflex in the quadriceps muscle detect that the muscle is being stretched
-Nerve impulse passed along sensory neurones, which communicated directly with motor neurones in the spinal cord, no relay neurone is involved
-The motor neurone carries the nerve impulse to the effector (the quadriceps muscle) causing it to contract so the lower leg moves forward quickly

Question 11

What does the knee-jerk reflex help to do?

Answer 11

Maintain posture and balance

Question 12

How can the blinking reflex be used to determine the brain activity of a unconscious patient?

Answer 12

-If the reflex is present, it indicated the lower brain stem is still functioning, the patient cannot be diagnosed as brain-dead

Question 13

How do reflexes increase your chance of survival?

Answer 13

-Being involuntary responses, preventing the brain from being overloaded with situations
-Not having to be learnt, provide immediate protection as present at birth
-Extremely fast, only involves one or two synapses
-Many reflexes are what we consider everyday actions