5.5.10 Reflex Actions

Question 1

What are reflex actions?

Answer 1

• Very fast
• Involuntary response
• To survive

Question 2

What are some reflex actions?

Answer 2

• Yawning
• Saliva production
• Swallowing
• Withdrawal reflex
• Blinking
• Constricting muscles of iris in response to bright light

Question 3

What is the sequence of components in a reflex action?

Answer 3

1. Stimulus
2. Receptor
3. Coordinator (spinal cord, or unconscious parts of brain like medulla)
4. Effector
5. Response

Question 4

What is the knee-jerk reflex?

Answer 4

• Used by doctors to see if nervous system is working
• Hammer hits ligament between kneecap and tibia
• Patient involuntarily straightens leg
• NO RELAY NEURONE

Stimulus - Hammer
Receptor - Stretch receptors in quads
Coordinator - Spinal cord
Effector - Quads
Response - Contraction of quads

Question 5

Why are involuntary responses faster than voluntary ones?

Answer 5

• Nerve impulses delayed by synapses
• If travelling to brain, impulses have to travel across many synapses
• Which is slower

Question 6

What is the blinking effect?

Answer 6

• Something travelling towards eye
• Causes us to blink
• Impulses go via brain but not through decision making areas, so numbers of synapse crossed is still minimal

Pathway :
- Irritation
- Impulses sent down trigeminal sensory nerve
- To medulla
- Signal to effector muscles
- Superior levator palpebrae muscle lowers upper eyelid
- Orbicularis oculi muscle pulls eyelid inwards and helps them to close