C13 - Reflex arc

Question 1

What is the simplest type of nervous response to a stimulus?

Answer 1

• REFLEX ARC

Question 2

What is a reflex arc?

Answer 2

A REFLEX ARC

is the neural pathway taken by the nervous impulse

of a reflex action.

e.g. A withdrawl reflex…Pulling your hand away from a flame.

Question 3

What is a REFLEX ACTION?

Answer 3

A REFLEX ACTION IS A…

• Rapid,
• Automatic response
• Resulting from nervous impulses
• Which have been initiated by a stimulus.

The decision making parts of the brain are not involved in this process as it is involuntary

E.G. Move your hand away from a flame.

Note: Reflex actions are normally protective…

Question 4

Additional Slide - Drawing Page 252

What are the 8 stages of the Nervous Control Mechanism?

Answer 4

1. Stimulus
2. Sensory receptor
3. Sensory neurone pathway
4. Central nervous system - Neurones connecting sensory and motor pathways
5. Motor pathway
6. Effector
7. Response
8. Feedback

Question 5

Additional slide (Table Pg 252)

What are the 6 STAGES of the REFLEX ARC?

Answer 5

1. Stimulus ⇒
2. Sensory Receptor ⇒
3. Sensory Neurone ⇒
4. Central Nervous System ⇒
5. Motor Neurone ⇒
6. Response

Question 6

Additional Slide (Table Pg 252)

What are the 6 stages of a WITHDRAWL REFLEX?

Answer 6

Withdrawl reflex

1. Heat stimulus
2. Temperature & pain (sensory receptors) in the skin
3. Sends impulse ⇒ Up arm ⇒ Spinal cord via (Sensory Neurone)
4. A relay neurone in the spinal cord transmits an impulse from the sensory neurone to a motor neurone
5. The motor neurone sends an impulse to an effector, in this case muscle
6. The muscle contracts & moves hand away from the heat stimulus

Question 7

Additional Slide (Table Pg 252)

What are the 6 stages of a pupil reflex

Jamie note - If its a pupil reflex, the part of the CNS involved is the Brain NOT THE SPINAL CORD

Which is different to the withdrawl reflex…

Answer 7

1. Light stimulus
2. Picked up by the Photosensitive cells in retina (Sensory receptors)
3. Which transmit impulse up Optic nerve (Sensory neurone)
4. To the Brain (CNS)
5. Which sends an impulse to the muscles of the iris (Motor Neurone)
6. Muscles of the contract or relax, altering the diameter of the pupil (Response)

A relay neuronein the spinal cordtransmits an impulse from the sensory neuroneto a motor neurone

The motor neuronesends an impulseto an effector, in this case muscle

The muscle contracts & moves hand away from theheat stimulus

Question 8

Additional slide (Drawing Pg 252)

• What are the 11 features of the transverse section of a spinal cord

Answer 8

The reflex arc element

• Sensory neurone (dorsal root)
• Cell body of sensory neurone in dorsal root ganglion
• Relay Neurone
• Motor Neurone (ventral root)

Other features

• Spinal nerve
• Dorsal root
• Ventral root
• Dorsal root ganglion
• White matter
• Grey matter (H shape)
• Central Canal

Question 9

Study point

Answer 9

the reflex arcs of some reflex actions do not have a relay neurone e.g. the knee-jerk reflex

The sensory neurone synapses directly with the motor neurone

Question 10

Study point 2

Answer 10

The cell bodies of sensory neurones all lie together and appear as a swelling called a ganglion