This article details how to turn your SI-H muscle research system into
one that records the action potentials from the stretch receptors at the
same time that the length and tension of the muscle are recorded.
Stretch receptors are specialized fibers that are in parallel to the
fibers in muscle. The receptors stretch as the muscle is lengthened, and
they generate action potentials. The frequency of these action
potentials is proportional to the length of muscle stretch and the
position of the muscle. Through sensory nerve fibers from the stretch
receptors, the action potentials and their frequency provide feedback to
the central nervous system that will modulate reflex responses and
motor control of the muscle.
For these studies, the whole muscle and the nerve that innervates it
are isolated from the organism. A muscle and its nerve, like the Soleus,
is isolated and placed in the cuvette of an SI-MT or SI-MKB muscle
research system. The muscle is positioned so that the myoneural junction
(the place where the nerve innervates the muscle) is on the top side of
the muscle. The ends of the muscle are attached to a transducer and a
motor through the tissue holders, and the end of the nerve is in the
bath solution in the cuvette.
Making Recordings - Suction Electrode
Recordings are made from the nerve as the muscle is stretched and
relaxed using a device known as a suction electrode. Suction electrodes
are specialized extracellular electrodes designed to hold onto the ends
or sides of nerves and record the action potentials passing through
those nerves. The tip of the suction electrode is a short, glass
microcapillary pipette with an internal diameter that matches the
diameter of the nerve. The conductors in a suction electrode are
positioned so that the nerve can be kept alive in the bath solution and
the action potentials can be recorded at the same time. The signals
recorded by the suction electrode are amplified through a simple,
extracellular amplifier and recorded on the same data acquisition unit
as the muscle length and the muscle tension.
Materials Needed to Modify an SI-H System
To add this feature to an SI-MT or SI-MKB system, the following items are needed:
(1) Micromanipulator or micropositioner. The unit should be no larger
than the KITE or the M3301. The M325 is ideal. The control should be
right-handed, because the unit will be to the right of the microscope
(1) Micromanipulator rod. Since the base of the SI-MT and SI-MKB is
non-ferrous, the micromanipulator needs to be mounted on a rod screwed
into the base of the system in a position that allows the electrode to
reach the center of the cuvette.
(1) Extracellular amplifier with an electrode adapter. The DAM50,
DAM80 or the ISO-80 are the amplifiers to consider. The model you select
depends on the inherent noisiness of the lab room.
(1) Suction electrode. Suction electrodes are delicate and are best
constructed by the user. They need to be made of fine wire so that
electrode can flex when the muscle is stretched. See Constructing an Extracellular Suction Electrode.