Reflex

Question 1

What is a reflex action and the general reflex arc?

Answer 1

Reflex action: an involuntary response to a sensory stimulation

• Faster responses, minimises damage to body

General Reflex Arc

1. Receptor detects stimulus and crates action potential in sensory neurones
2. Sensory neurone carries impulse to spinal cord
3. Relay neurone connects sensory neurone to motor neurone within spinal cord or brain
4. Motor neurone carries impulse to effector for response

Question 2

Describe the Knee-Jerk reflex

Answer 2

• A spinal reflex – meaning the neural circuit only goes to the spinal cord and not the brain

1. The leg is tapped just below the patella (kneecap), stretching the patellar tendon acting as a stimulus
2. Stimulus initiates a reflex arc, causing the extensor muscle on top of the thigh to contract
   
   1. Simultaneously, the relay neurone inhibits the flexor muscle (antagonist to extensor muscle) neurone, causing it to relax
3. After the tap the knee extends once and then rests

Absence of this reflex indicates neuronal complications, the constant oscillation of this reflex indicates cerebellar disease

Question 3

Describe the blinking reflex

Answer 3

Involuntary blinking of the eyelids

• Stimulated by cornea – e.g. if it is touched – it is to protect from damage such as dust or foreign bodies
  
  • Known as corneal reflex
• A blink reflex is if there are sounds greater than 40-60dB or a bright light (protects lens and retina) – it’s a cranial reflex (occurs in the brain not spinal cord)

1. Cornea of eye is irritated by foreign body stimulates impulse along sensory neurone (5^th cranial nerve)
2. Impulse passes through a relay neurone in lower brain stem
3. Impulse sent to motor neurone (7^th cranial nerve) to initiate motor response to close eyelids
4. This reflex initiates a consensual response – both eyes are closed in response

Doctors examine the blinking reflex in unconscious patients – if reflex is present, indicates lower brain stem is working, if there is on reflex, the patient may be brain dead

Question 4

What is the spinal cord?

Answer 4

Spinal cord is a column of nervous tissue running up ones back, surrounded by the spine for protection.

Neurones appear at intervals along the vertical of the spinal cord

Question 5

What is the survival importance of reflex actions?

Answer 5

• Being involuntary – decision-making region of brain not needed, brain can deal with complex responses and are not overloaded with situations that have the same responses every time
• Don’t need to be learnt – present at birth and give protection since
• Extremely fast – reflex arc is short – involves one or 2 synapses (they are the slowest part of transmission)
• They support daily function keeping people upright