Reflexes-A No Brainer

 Reflexes aren’t just useful in evolutionary terms, protecting the body from danger; they also have clinical significance in diagnosing neurological disorders. As the reflex arc (the pathway of a nerve impulse from the sensory receptors along a motor neurone to the spinal cord and to a muscles along a motor neurone) involves all the parts of the peripheral nervous system, reflexes can quickly test how well all these nerves are working.

the Knee Jerk Reflex Arc

  One of the most commonly tested reflexes is the knee-jerk response. The reflex has evolved to keep the body in a standing position. As the knees buckle due to the weigh of the body the tendons in the knee stretch and activate stretch receptors in your thigh. This sets of a reflex that activates the thigh muscles to straighten the leg and stop you falling over. This happens many times a minutes without you noticing. In a clinical setting the reflex can be activated by tapping the patella tendon with a rubber hammer and the knee should extend. It is strongly recommended that you don’t stand in front of the patient when doing this. If the reflex is not present it can be a sign of an injury to the spinal cord.

  Another set of reflexes commonly used to diagnose is the pupillary and blink reflexes. The pupillary reflex is the dilation of the pupils to a bright light. Normally both pupils will dilate even if the light is only shone into one eye. If for instance the right pupil dilates when a light is shone into it but the left remains undilated then this could suggest damage to the motor nerve to the left eye. If both pupils dilate when a light is shone into the left eye but no response from either pupil if the light is shone in the right eye then this suggests a sensory problem in the right eye such as retina damage or damage to the right optic nerve. No response at all from either eye could suggest damage to the sensory nerves or brain stem or could be a sign of drug abuse.

An Abnormal Pupillary Reflex Response

    The blink reflex evolved to protect the eye from object coming towards it. It’s particularly useful because it can be conditioned out by the brain (for example by any one like me who wears contact lenses and so has to move object towards their eye). A good way of testing it is by tapping some one lightly on the forehead repeatedly (Try this one at home, I found it quite entertaining). For the first few taps they will blink fully but after that they won’t or only twitch their eyelids slightly. This is because the cerebellum begins to tune down the reflex when the brain realises there is no apparent danger. An absence of this response could suggest damage to the cerebellum. 

  Another interesting set of reflexes is the primitive or infantile reflexes. These are reflexes that are present at birth but slowly disappear. They have mostly evolved to protect or aid the baby such as the sucking reflex that aids breastfeeding and the swimming reflex where the baby attempts to paddle if its face is placed into water giving its mother longer to save it (don’t try this at home however tempting). A common reflex is the Moro reflex (after the Austrian paediatrician Ernst Moro). When startled or experiencing falling the baby will fling its arms to the side, look shocked and then start crying. This probably evolved to help the baby cling to its mother when being carried. It usually disappears around 3-4 months after birth. If it persists it could suggest a birth injury or neurological problems.

A- The Babinski Response
B- Normal adult response

 Another infantile reflex is the Babinski or plantar reflex (after Joseph Jules Francois Felix Babinski a French neurologist with a very long name). If the sole of the foot is stroked from the heel to near the big toe with a probe adults curl the toes downwards. Infants show the Babinski response which is when the toes curling upwards. If adults show the Babinski response or other infantile reflexes such as the Moro reflex this could mean the patient has dementia or has suffered a stroke.