Reflex actions 5.5.10

Question 1

What are reflex actions?

Answer 1

Involuntary responses to certain stimuli

Question 2

What is the purpose of reflex actions?

Answer 2

Protective purpose or survival value

Question 3

Give 5 examples of reflex actions

Answer 3

• Yawning
• Knee jerk
• Blinking (corneal reflex)
• Pupil reflex (constricting the muscles of the iris in response to bright light)
• Pulling a part of the body away from a source of pain (withdrawal reflex)

Question 4

Give an example of a reflex action that can be carried out on purpose

Answer 4

Blinking

Question 5

What is the sequence involved in a reflex action?

Answer 5

Stimulus
|
Receptor
|
Coordinator
|
Effector
|
Response

Question 6

Explain the reflex action sequence

Answer 6

Reflex actions require detection, involving a stimulus and being detected by a receptor cell
The nerve impulses sent by receptor cells travel to a coordinator in the CNS
In most reflexes the cooridnator is the spinal cord, however some reflexes may involve unconcious parts of the brain
From the coordinator the impulse is conducted to the specific effector that will produce the appropriate response

Question 7

What is the knee jerk reflex?

Answer 7

Often used by doctors to assess whether the nervous system of a patient is working properly
Doctors use a specialised hammer to hit a ligament between the klnee cap and the tibia, and they leg of the patient will involuntary straighten in a small kicking motion

Question 8

State the sequence of the knee jerk reflex

Answer 8

• Stimulus = stretching of the quadriceps caused by pressure on the ligament, from the hammer
• Receptor = stretch receptors in the quadriceps muscle, send impulses down a sensory neurone which connects directly to a motor neurone (synapse) in the spinal cord
• Coordinator = the spinal cord
• Effector = quadriceps muscle
• Response = contraction of the quadriceps muscle, causing the leg to straighten

Question 9

Why are there no relay neurones in the knee jerk reflexes?

Answer 9

As the coordinator is not the brain, which is where most relay neurones are located

Question 10

Why are reflex actions so fast and automatic?

Answer 10

As the brain has no chance to make a decision, due to the impulse travelling through sensory and motor neurones (not relay), and the coordinator is the spinal cord

Question 11

What information will be sent to the brain in the knee jerk reflex?

Answer 11

Connections from the spinal cord to the brain will still allow information about the stimulus (pressure caused by the hammer) to be sent to the brain but by the time it receives and processes this information, the response will have already occurred.

Question 12

Describe the nervous pathway of the blinking reflex

Answer 12

• Irritation or drying of the cornea sends impulses down the trigeminal sensory nerve to the medulla of the brain, where it connects with other neurones to transmit the signal to effector molecules
• Relay neurones are involved in the transmission of impulses to the effectors in the lower eyelid
• The effectors for the blinking reflex include the superior levator palpebrae muscle, which lowers the upper eyelid, and the orbicular oculi muscle, which pulls the eyelids inwards and helps to close them