Introduction to Reflexes

1. REFLEXES
PUBALI KALITA
BPT STUDENT

2. Introduction
 Reflex is an involuntary or automatic action that our body does in response to a
stimulus .
 Reflex activity is the response to a peripheral nervous stimulation that occurs without
our consciousness. It is a type of protective mechanism and it protects the body from
irreparable damages.
 Examples :
1. when hand is placed on a hot object, it is withdrawn immediately.
2. When a bright light is thrown into the eyes, eyelids are closed and pupil is constricted
.

3.  REFLEX ARC :
It is the anatomical nervous pathway for a reflex action. A simple reflex
arc consists of five components ----
1. Receptor
2. Afferent nerve
3. Center
4. Efferent nerve
5. Effector organ

4.  Technique for testing reflexes :
1. The muscle group to be tested must be in a neutral position (i.e. neither stretched nor
contracted).
2. The tendon attached to the muscle(s) which is/are to be tested must be clearly
identified. Place the extremity in a positioned that allows the tendon to be easily
struck with the reflex hammer.
3. To easily locate the tendon, ask the patient to contract the muscle to which it is
attached. When the muscle shortens, therapist should be able to both see and feel the
cord like tendon, confirming its precise location.
4. Strike the tendon with a single, brisk, stroke , which should not elicit pain.
N.B :The Jendrassik maneuver which is particularly useful if the patient is concious ; so to
distract and to function properly the reflex it is done . The patient is asked to clenches the
teeth, flexes both sets of fingers into a hook-like form, and interlocks those sets of fingers
together. Then the reflex is elicited .

5.  GRADING OF REFLEXES :

6.  CLASSIFICATION :
1. Depending upon whether inborn or acquired .
2. Depending upon situation – anatomical classification .
3. Depending upon purpose – physiological classification .
4. Depending upon number of synapse .
5. Depending upon whether visceral or somatic .
6. Depending upon clinical basis .

7.  DEPENDING UPON WHETHER INBORN OR ACQUIRED REFLEXES
1. Inborn Reflexes or Unconditioned Reflexes :
Unconditioned reflexes are the natural reflexes, which are present since the time of
birth, hence the name inborn reflexes. Such reflexes do not require previous learning,
training or conditioning.
2 . Acquired Reflexes or Conditioned Reflexes
Conditioned or acquired reflexes are the reflexes that are developed after conditioning or
training. These reflexes are not inborn but, acquired after birth.

8.  DEPENDING UPON SITUATION – ANATOMICAL CLASSIFICATION
In this method, reflexes are classified depending upon the situation of the center.
1. Cerebellar Reflexes (center in cerebellum)
2. Cortical Reflexes (center in cerebral cortex)
3. Midbrain Reflexes (center in midbrain)
4. Bulbar or Medullary Reflexes (center in medulla oblongata)
5. Spinal Reflexes (center in the spinal cord) . Spinal reflexes are divided into three
groups:
a. Segmental spinal reflexes
b. Intrasegmental spinal reflexes
c. Suprasegmental spinal reflexes.

9.  DEPENDING UPON PURPOSE – PHYSIOLOGICAL CLASSIFICATION
i. Protective Reflexes or Flexor Reflexes
Protective reflexes are the reflexes which protect the body from nociceptic (harmful)
stimuli. These reflexes are also called withdrawal reflexes or flexor reflexes. Protective
reflexes involve flexion at different joints hence the name flexor reflexes.
ii. Antigravity Reflexes or Extensor Reflexes
Antigravity reflexes are the reflexes that protect the body against gravitational force. These
reflexes are also called the extensor reflexes because, the extensor muscles contract during
these reflexes resulting in extension at joints.

10.  DEPENDING UPON THE NUMBER OF SYNAPSE
Depending upon the number of synapse in reflex arc,
reflexes are classified into two types :-
i. Monosynaptic Reflexes (Reflexes having only one
synapse in the reflex arc)
ii. Polysynaptic Reflexes (Reflexes having more than
one synapse in the reflex arc)

12.  DEPENDING UPON WHETHER SOMATIC OR VISCERAL REFLEXES
i. Somatic Reflexes (reflexes for which the reflex arc is formed by somatic nerve fibers )
ii. Visceral or Autonomic Reflexes (reflexes for which at least a part of reflex arc is formed
by autonomic nerve fibers) .

13.  DEPENDING UPON CLINICAL BASIS
Depending upon the clinical basis, reflexes are classified into four types:
i. Superficial reflexes (Superficial reflexes are the reflexes, which are elicited from the
surface of the body)
ii. Deep reflexes (Deep reflexes are elicited from deeper structures beneath the skin like
tendon).
iii. Visceral reflexes (Visceral reflexes are the reflexes arising from pupil and visceral
organs)
iv. Pathological reflexes (Pathological reflexes are the reflexes that are elicited only in
pathological conditions. Well-known pathological reflexes are: 1. Babinski sign , 2. Clonus ,
3. Pendular movements)

14. Superficial mucous membrane reflexes

15. Superficial cutaneous reflexes

16. Deep reflexes

17.  Following are the visceral reflexes:
1. Pupillary reflexes : Pupillary reflexes are:
i. Light reflex
ii. Accommodation reflex
iii. Ciliospinal reflex.
2. Oculocardiac reflex
3. Carotid sinus reflex.

18.  PATHOLOGICAL REFLEXES
 In normal plantar reflex, a gentle scratch over the outer edge of the sole
of foot causes plantar flexion and adduction of all toes. But in Babinski
sign, there is dorsiflexion of great toe and fanning of other toes.When
Babinski reflex is present, the condition is commonly called Babinski
positive sign and when it is negative, the condition is called Babinski
negative sign .
 Clonus is a series of rapid and repeated involuntary jerky movements,
which occur while eliciting a deep reflex . Clonus occurs when the deep
reflexes are exaggerated due to hypertonicity of muscles in pyramidal
tract lesion. Clonus is well seen in calf muscles producing ankle clonus
and quadriceps producing patella clonus.

19.  Pendular movements are the slow oscillatory movements (instead of brisk
movements) that are developed while eliciting a tendon jerk. Unlike clonus, pendular
movements occur because of hypotonicity of muscles. Pendular movements are very
common while eliciting the knee jerk or patellar tendon reflex in the patients
affected by cerebellar lesion.

20. 1. ONE WAY CONDUCTION : In any reflex activity, impulses are transmitted in only one
direction through the reflex arc as per Bell-Magendie law ; means the impulses pass from
receptors to center and then from center to effector organ. This is also known as Bell-
Magendie law .
2. REACTION TIME : It is the time interval between application of stimulus and the onset of
reflex. It basically depends upon the length of afferent and efferent nerve fibers, velocity of
impulses and central delay (the delay at the synapse) .
3. SPATIAL & TEMPORAL SUMMATION : When two afferent nerve fibers supplying a muscle are
are stimulated separately with subliminal stimulus, there is no response. But the muscle
contracts when both the nerve fibers are stimulated together with same strength of stimulus.
It is called spatial summation.
When one nerve fiber is stimulated repeatedly with subliminal stimuli, these stimuli are
summed up to give response in the muscle. It is called temporal summation .
Properties Of Reflexes

22. 4 . OCCLUSION : It is demonstrated in a flexor reflex involving a muscle, which is innervated by
two motor nerves. These nerves can be called A and B. When both the nerves, A and B, are
stimulated simultaneously, the tension developed by the muscle is less than the sum of the
tension developed when each nerve is stimulated separately.

23. 5 . SUBLIMINAL FRINGE : In some reflexes involving the muscle with two nerve fibers, the
tension developed by simultaneous stimulation of two nerves is greater than the sum of
tension produced by the stimulation of these nerves separately.
6 . RECRUITMENT : Recruitment is defined as the successive activation of additional motor
units with progressive increase in force of muscular contraction.
7 . AFTER DISCHARGE : After discharge is the persistence or continuation of response for
some time even after cessation of stimulus.

24. 8. REBOUND PHENOMENON : Reflex activities can be forcefully inhibited for sometime.
But, when the inhibition is suddenly removed, the reflex activity becomes more forceful
than before inhibition. It is called rebound phenomenon .
9. FATIGUE : When a reflex activity is continuously elicited for a long time, the response is
reduced slowly and at one stage, the response does not occur. This type of failure to give
response to the stimulus is called fatigue.

25. N.B :-
REFLEXES IN MOTOR NEURON LESION :
 UPPER MOTOR NEURON LESION
During upper motor neuron lesion, all the superficial reflexes are lost. Deep reflexes are
exaggerated and the Babinski sign is positive .
 LOWER MOTOR NEURON LESION
During lower motor lesion, all the superficial and deep reflexes are lost .