Human reflexes Definition: It is involuntary response of an organ to a stimulus. - It is the arrangement of neurons through which the reflex is carried out. - It is usually formed of: Afferent (sensory) neuron. 2) An interneuron (may be absent). 3) nerve center (cell body of the efferent neuron). 4) Efferent (motor) neuron.

1. Human
reflexes
Med_students0

2. HUMAN REFLEXES
 Definition: It is involuntary response of an organ to a stimulus.
 It is the functional unit of the nervous system.
 The Spinal Reflex Pathway : = The Reflex Arc
- It is the arrangement of neurons through which the reflex is carried out.
- It is usually formed of:
1) Afferent (sensory) neuron.
2) An interneuron (may be absent).
3) nerve center (cell body of the efferent neuron).
4) Efferent (motor) neuron.
N.B.: Synapses are present < > different neurons in the reflex arc. All human reflexes are
polysynaptic except the stretch reflex which is monosynaptic as it contains no
interneurons.
Med_students0

3. Med_students0

4. Classification of Human Reflexes
Human
Reflexes
Conditioned
reflexes
- Acquired reflexes.
-seeing, smelling,
hearing or even thinking
of the stimulus in its
absence causes the
response.
-requires intact cortex &
previous training.
Unconditioned
reflexes
Spinal (see later)
Medullary
- Cardiovascular reflexes: HR & ABP.
- Respiratory functions: Herring-Bruer reflex.
- Digestive functions: Swallowing & vomiting.
Midbrain
- Visual reflexes as pupillary light reflex.
- Postural reflexes: righting reactions.
Hypothalamic
- Hunger.
- thirst.
- Regulation of body temperature.
- Inborn reflexes.
- Application of the stimulus
will result in response.
-does not require intact
cortex or previous training.
- Classified according to the
center of the reflex into:
Med_students0

5. Med_students0

7. Pupillary Light Reflex
Med_students0

8. Baroreceptor Reflex

9. Spinal Reflexes
1) Superficial:
- Their receptor are present on the
body surface (skin, cornea,
conjunctiva,….).
- Example:
Planter reflex.
Flexion withdrawal reflex.
Crossed extensor reflex.
Abdominal reflex.
2) Deep:
- Their receptor are present in deep
structures (skeletal muscle, tendons,
……).
- Examples:
Stretch reflex.
3) Visceral:
- Their receptor are present in the
viscera.
- Examples:
Micturition reflex.
Defecation reflex.
Erection reflex.
- Their center is present in
the spinal ventral horn.
- Classified according to the
site of receptor into:

10. 1) In normal subjects , the response consists of plantar flexion of all
the toes .
Planter Reflex
- Scratch of the sole of the foot along its lateral margin, from the heal toward the
toes will result in:
2) Babinski sign is an abnormal response of the plantar reflex, named
after the Polish physician. It consists of dorsiflexion of the big toe and
separation (or fanning out) of the other four toes
Med_students0

11. 2- Pathological causes:
Upper Motor Neuron Lesion (UMNL) which is lesion in higher motor
areas or descending motor tracts.
Babinski sign may be due to:
1- Physiological causes:
 Newly born infants during the first few months of their life, because
during this period the corticospinal tract fibers are not yet completely
myelinated or functioning.
 Normal adults under conditions in which the cerebral cortical
function is considerably depressed, such as during general anesthesia,
coma, or even deep sleep.
N.B.: Center of planter reflex is present in spinal ventral horn of 1st sacral spinal segment
(S1)
Med_students0

12. Med_students0

13. Flexion Withdrawal Reflex Crossed Extensor Reflex
- They are reflexes that move the affected portions of the body away from
a source of painful stimulation.
- When a strong painful stimulus applied to one lower limb, flexion of one
limb is accompanied with extension of the contralateral one.
Mechanism & pathway: see illustration
Importance
1) Withdrawal reflexes are of survival value because they help to
immediately remove the stimulated part of the body away from sources
of painful stimuli that could be harmful to the individual. Thus, it is
prepotent.
2) Crossed extensor are of postural value as it supports the body weight
which is shifted to the other limb. Otherwise, the subject may lose the
equilibrium & fall to the ground.
Med_students0

14. Med_students0

15. Micturition Reflex
- Distention of urinary bladder with urine will result in reflex evacuation of the
bladder (Micturition).
Mechanism & pathway:
 Receptors: stretch (receptor) in the wall of bladder.
 Center: sacral segments 2, 3 & 4.
 Afferent & efferent: pelvic nerve.
 Response:
Contraction of detrusor muscle (body).
 Relaxation of internal sphincter of urethra.
Relaxation of external urethral sphincter via the pudendal nerve which
is somatic nerve originating from AHC of sacral segment 2, 3, & 4.
N.B.: This reflex is automatic in infants below 2 years BUT in adults it is under voluntary
control.
Med_students0

16. Infants Adults

17. Definition:
Tapping of the tendon of a skeletal muscle (using a medical hammer) results in
brief contraction followed by rapid relaxation.
Mechanism:
Tendon Jerk
Receptor: Nuclear bag.
Afferent: 1ry endings.
Center: α-MNs of the stretched skeletal muscle
Efferent: Thick myelinated type Aα nerve fiber
Response: brief contraction followed by rapid relaxation.
Med_students0

19. Med_students0

21. Efferent (Motor) Innervation:
- Supplies the peripheral contractile parts on the intrafusal muscle fibers.
- Their cell bodies are located in gamma motor neurons (-MNs) which are
the small AHCs (30% of AHCs).
- Stimulation of -MNs -----> afferent impulses along -afferent fibers ----->
contraction of the peripheral contractile parts of the intrafusal muscle
fibers stretch of the central (receptor) part ------> depolarization of the
central part -----> action potential & impulse discharge along 1ry & 2ry
endings ----> stimulation of α-MNs innervating the stretched muscle ----->
muscle contraction (stretch reflex).

23. Examples of Tendon Jerks:
Tapping of Contraction of Movement Center
The Knee Jerk
The Ankle Jerk
The Biceps Jerk
The Triceps Jerk
patellar tendon
tendo-achilles
biceps tendon
triceps tendon
quadriceps femoris
gastrocnemius & soleus
biceps muscle
triceps muscle
Extension of the knee
plantar flexion of the
foot
flexion of the arm at
the elbow joint
extension of the arm
at the elbow joint
L 2,3,4
S 1,2
C 5,6
C 6,7

24. Clinical Significance of the Tendon Jerks:
a) Assess the Integrity of Reflex Pathways of the Tendon Jerks:
Absent tendon jerk indicates damage of any part of the reflex pathway
which may be:
- Lesion of the afferent as in Tabes dorsalis.
- Lesion in the nerve center as in poliomyelitis.
- Lesion in the efferent as in trauma.
b) Localize the level of the lesion in the nervous system.

25. c) Examine the State of the Supraspinal Centers:
- Exaggerated tendon jerks indicate damage of Supraspinal inhibitory
centers.
- Inhibited tendon jerks indicate damage of Supraspinal facilitatory
centers.
Hyperactive Tendon Jerks
(Exaggerated)
Hypoactive Tendon Jerks
(Inhibited)
i.e., TJ becomes faster and stronger than
normal.
 It is due to ↑supraspinal facilitation of -
MNs, ----> ↑sensitivity of muscle spindles
to the stretch.
 May be:
a) physiological: anxiety & nerotic persons.
b) Pathological: tetany, lesions in any of the
supraspinal inhibitory centers.
i.e., TJ becomes delayed and weaker than
normal.
 It is due to ↓ supraspinal facilitation of -
MNs, ----> ↓ sensitivity of muscle spindles to
the stretch
 May be:
a) physiological: sleep, anaethesia
b) Pathological: coma, lesions in any of the
supraspinal facilitatory centers.

26. Clonus
- It is regular rhythmic contractions of a muscle.
- It is a sign of increased supraspinal facilitation.
- It is produced by applying a sudden maintained stretch on the tendon of a
muscle -----> regular rhythmic contractions that continue as long as the
stretch is applied. - Clinically, clonus has 2 types:
a) Patellar Clonus:
- initiated by grasping the patella inbetween the examiner’s fingers, then
applying a sudden maintained downward pull.
- This causes clonic contractions of the quadriceps muscle, producing
rhythmic oscillation of the patella.
- initiated by applying a sudden maintained dorsi-flexion of the foot.
- This causes clonic contractions of the calf muscles causing regular
rhythmic plantar flexions of the foot.
b) Ankle Clonus:

27. The Reflex Hammer
You will need to use a reflex hammer when performing this aspect
of the exam. A number of the most commonly used models are
pictured below. Regardless of the hammer type, proper technique is
critical. The larger hammers have weighted heads, such that if you
raise them approximately 10 cm from the target and then release,
they will swing into the tendon with adequate force. The smaller
hammers should be swung loosely between thumb and forefinger.
Med_students0

28. Medical
Hammer
Med_students0

29.  The muscle group to be tested must be in a neutral position (i.e.
neither stretched nor contracted) (= semiflexed & in dependent position).
 The muscle group to be tested must be exposed.
 The tendon attached to the muscle(s) which is/are to be tested must be
clearly identified. If you are having trouble locating the tendon, ask the
patient to contract the muscle to which it is attached. When the muscle
shortens, you should be able to both see and feel the cord like tendon,
confirming its precise location.
Technique
 Strike the tendon with a single, brisk, stroke. While this is done
firmly, it should not elicit pain. Occasionally, due to other medical
problems (e.g. severe arthritis), you will not be able to position the
patient's arm in such a way that you are able to strike the tendon. If this
occurs, do not cause the patient discomfort. Simply move on to another
aspect of the exam.

30. The vigor of contraction is graded on the following scale:
0 No evidence of contraction.
1+ Decreased, but still present (hypo-reflexic)
2+ Normal
3+ Super-normal (hyper-reflexic)
4+ Clonus: Repetitive shortening of the muscle after a single
stimulation

31. If you are unable to elicit a reflex, stop and consider the following:
1) Are you striking in the correct place? Confirm the location of the
tendon by observing and palpating the appropriate region while asking
the patient to perform an activity that causes the muscle to shorten,
making the attached tendon more apparent.
2) Make sure that your hammer strike is falling directly on the
appropriate tendon. If there is a lot of surrounding soft tissue that could
dampen the force of the strike, place a finger firmly on the correct tendon
and use that as your target.
3) Make sure that the muscle is uncovered so that you can see any
contraction (occasionally the force of the reflex will not be sufficient to
cause the limb to move).

32. 4) Reinforcement is accomplished by asking the patient to clench their
teeth, or if testing lower extremity reflexes, have the patient hook
together their flexed fingers and pull apart. This is known as the
Jendrassik maneuver.

33. Sometimes the patient is unable to relax, which can inhibit the reflex even
when all is neurologically intact. If this occurs during your assessment of
lower extremity reflexes, ask the patient to interlock their hands and
direct them to pull, while you simultaneously strike the tendon. This
sometimes provides enough distraction so that the reflex arc is no longer
inhibited.
Occasionally, it will not be possible to elicit reflexes, even when no
neurological disease exists. This is most commonly due to a patient's
inability to relax. In these settings, the absence of reflexes are of no clinical
consequence. This assumes that you were thorough in your history taking,
used appropriate examination techniques.

34. AnkleJerk

35. KneeJerk

36. BicepsJerk

37. TricepsJerk
Med_students0