5.5.7: Reflex actions Flashcards
What are reflex actions?
Responses to changes in the environment that do not involve any processing in the brain to coordinate the movement.
Why is the nervous pathway as short as possible in a reflex action?
-So that the reflex is rapid.
What do most reflex pathways consist of?
-Just three neurones:
Sensory neurone→relay neurone→motor neurone
What is the brain’s role in a reflex action?
-The brain may be informed that the reflex has happened, but is not involved in coordinating the response.
What is the survival value of a reflex action?
-A reflex may be used to get out of danger, to avoid damage to part of the body, or it may be used to maintain balance.
What are two examples of reflex actions?
- Blinking
- Knee jerk reflex
What does the blinking reflex cause?
Temporary closure of the eyelids to protect the eyes from damage.
The nervous pathway for the blinking reflex passes through part of the brain. What type of reflex is this?
- A cranial reflex.
- However, the pathway is a direct pathway that does not involve any thought processes in the higher parts of the brain.
Why is the blinking reflex a reflex arc?
The receptor and effector are in the same place.
Blinking may be stimulated by sudden changes in the environment such as:
- A foreign object touching the eye (the corneal reflex)
- Sudden bright light (optical reflex)
- Loud sounds
- Sudden movements close to the eye.
Describe the steps in the corneal reflex.
- The reflex is mediated by a sensory neurone from the cornea, which enters the pons.
- A synapse connects the sensory neurone to a relay neurone, which passes the ap to the motor neurone.
- The motor neurone passes back out of the brain to the facial muscles, causing the eyelid to blink.
Why is the corneal reflex very rapid (0.1 seconds)?
It is a short and very direct pathway.
How do the sensory neurones involved in the corneal reflex allow the reflex to be overridden by conscious control?
- sensory neurone also passes the ap to myelinated neurones in the pons.
- These carry the ap to the sensory region in the cerebral cortex,
- informs the higher centres of the brain that the stimulus has occurred.
- The higher parts of the brain (cerebral cortex) can send inhibitory signals to the motor centre in the pons.
- myelinated neurones carrying impulses to and from the cerebral cortex transmit aps faster than the non-myelinated relay neurones in the pons.
- Therefore, the inhibitory aps can prevent the formation of an ap in the motor neurone.
What is the benefit of the optical reflex?
-This protects the light-sensitive cells of the retina from damage.
How does the opical reflex happen?
- The stiulus is detected by the retina and the reflex is mediated by the optical centre in the cerebral cortex.
- It is a little slower than the corneal reflex.