The document discusses the H-reflex, which is a monosynaptic reflex elicited by electrically stimulating sensory neurons that monitor muscle stretch. Specifically: - The H-reflex was discovered in 1918 and involves stimulating Ia fibers that monitor muscle stretch rate, which triggers a reflex response through the spinal cord and back to the same muscle. - It is consistently obtained by stimulating the tibial nerve below the knee and recording from the gastrocnemius-soleus muscle, but can also be recorded in the median nerve and femoral nerve. - To record the H-reflex, active and reference electrodes are placed on the calf muscles and ground electrode is placed between the stimulating and active electrodes.

1. BY: Syed Irshad Murtaza
Trainee Technologist
Neurophysiology Dept
The Aga Khan University Karachi
Date: 22-08-2012

3.  The H-reflex is the electrical equivalent of the
monosynaptic stretch reflex and is normally
obtained in only a few muscles.
 The H (Hoffmann's) reflex, named after
German neurologist Johann Hoffmann
 who first evoked the response in 1918.

4. G3
G1
G2
G3
G2

5.  The H-reflex (or Hoffmann's reflex) is a reflectory
reaction of muscles after electrical stimulation of
type Ia sensory fibers (Primary Afferent Fibers
which constantly monitor how fast a muscle
stretch changes) in their innervating nerves. The H-
wave, is the expression of a monosynaptic reflex,
which runs in afferents from the muscle and back
again through efferents of the same muscle.
 OR

6. It is elicited by selectively
stimulating the sensory Ia fibres
(Primary Afferent Fibers which
constantly monitor how fast a
muscle stretch changes) of the
posterior tibial or median nerve.

7.  The stimulus travels along the Ia fibers,
through the dorsal root ganglion, and is
transmitted across the central synapse to
the anterior horn cell which fires it down
along the alpha (large lower motor
neurons of the brainstem and spinal cord)
motor axon to the muscle.

8. 

9.  The H-Reflex which is monosynaptic reflex
consistently obtained in normal adults only, by
stimulating the tibial nerve sub-maximally,
generally in the popliteal fossa, while recording
from the gastrocnemius-soleus muscle, similar to
the clinically elicited Achilles reflex.
 The H.Reflex can also be recorded in median nerve
recording from the FCR muscle and stimulating in
elbow, and from femoral nerve recording from
quadriceps muscles (VM, RF, VL, VI)

10.  To record the H-Reflex,
 G1 (active recording electrode) is placed 2-3
fingerbreadths distal to the soleus over the two
bellies of the gastrocnemius muscle and
 G2 (Reference Electrode) is placed over the
Achilles tendon (usually 14cm distal to G1).
 Ground electrode is generally placed between G1
and Stimulating electrode (stimulator cathode)