Reflexes pt 2

Question 1

What is the knee-jerk reflex?

Answer 1

• a reflex commonly tested by doctors
• it is a spinal reflex
  
  • this means that the neural circuit only goes up to the spinal cord, not the brain
• cranial reflex
  
  • occurs in the brain

Question 2

How does the knee-jerk reflex work?

Answer 2

• when the leg is tapped just below the patella, it stretches the patellar tendon and acts as a stimuluis
• the stimulus initiaites a reflex arc that causes the extensor muscle on top of the thigh to contract
• at the same time, a relay neurone inhibits the motor neurone of the flex muscle, causing it to relax
• this contaction, coordinated with the relaxation of the the antagonistic flexor hamstring muscle, causes the leg to kick

Question 3

What do unusual knee-jerk responses suggest?

Answer 3

• ansemce of reflex
  
  • indicate nervous problems
• multiple oscillation
  
  • may be a sign of cerebellar disease

Question 4

What is the knee-jerk reflex used for?

Answer 4

help the body maintain posutre and balance, allowing you to remain balanced with little effort or conscious thought

Question 5

What is the blinking reflex and when does it occur?

Answer 5

• involuntary blinking of the eyelids
• occurs when the cornea is stimulated
  
  • e.g. by being touched

Question 6

What is the purpose of the blinking reflex?

Answer 6

• keep the cornea safe from damage due to foreign bodies such as dust or flying insects entering the eye
  
  • also occurs when sounds greater than 40-60dB are hearf

Question 7

What is the difference between the corneal reflex and the optical reflex?

Answer 7

• corneal reflex
  
  • keep the cornea safe from damage due to foreign bodies
• optical reflex
  
  • protect the lens and retina due, e.g. due to light

Question 8

How is the blinking reflex coordinated?

Answer 8

• when the cornea of the eye is irritated by a foreign body, the stimulus triggers an impulse along a sensory neurone
• the impulose then passes through a relay neurone in the lower brain stem
• impulses are then sent along branches of the motor neurone to initieate a motor response to close the eyelids
• the reflexinitiates a consensual response
  
  • both eyes are closed

Question 9

What is the blinking reflex used for?

Answer 9

indicate whether the patient is brain-dead as it indicates that the lower brain stem is functioning

if the corneal reflex is present the person cannot be diagnosed as brain dead