Download Conduction Velocity and Patellar Reflex Blah A. Blah Partner B

Conduction Velocity and Patellar Reflex
Blah A. Blah
Partner B. Partner, Partner A. Partner, and Partner C. Partner
Biol 203 Section 501
November 15, 2012
Introduction
The purpose of this experiment is to find changes in the conduction velocity
based on the patellar reflex as the subject is put through three different conditions:
the Jendrassik’s maneuver, mental distraction, and fatigue.
The main function of the stretch reflex is to maintain the muscle at a constant
length, which the brain sets via the motor neurons. This experiment will focus on
the knee-jerk reflex that allows us to stand upright and prevents our knees from
buckling. There are various steps involved in this reflex and research by Marieb
and Hoehn (2011) supports that. First, tapping the knee ligament excites the
muscle spindles, which then activates the afferent pathway, allowing sensory
neurons to transmit impulses to the spinal cord, causing a spinal reflex. Second, the
signal is transformed into a response in the spinal cord that travels down the
efferent or exit pathway via motor neurons to the effectors, which are, in this case,
the quadriceps. The signal causes the quadriceps to contract and, thus, extend the
knee. Lastly, the interneurons not only connect the afferent pathway (sensory) to
the efferent pathway (motor) in the spinal cord, but in the spinal cord they also
activate the inhibitory synapses of the neurons of ventral horns to inhibit the
hamstrings, the antagonist muscles, from contracting, so the quadriceps can
contract without opposing resistance. Stretch reflexes are considered to be
ipsilateral, which means the motor neuron activity occurs on the same side as of
the motor synapse. The stretch reflex is also monosynaptic, meaning the reflex
only uses a single synapse.
This experiment will measure the conduction velocity of the patellar reflex
and how it changes with respect to the baseline as a result of Jendrassik’s maneuver,
mental distraction, and fatigue. Conduction velocity is the speed at which the
electrical messages are being transmitted through a nerve, which for this
experiment, is the femoral nerve.
The brain is able to modulate the reflexes, so it can inhibit, facilitate or adapt
based on the reflex activity. This experiment will show whether the speed of the
reflex can be affected when the person is prevented from consciously changing his
or her neural response.
First, it is hypothesized that the conduction velocity of the patellar reflex will
increase compared to the baseline as a result of simultaneous muscular activity
(Jendrassik’s maneuver). It is believed that when the person is pulling their hands
hard enough, the task will prevent them from anticipating a knee jerk because they
will be distracted with the activity, which will result in an increase in the firing of
neurons.
Second, it is hypothesized that the conduction velocity of the patellar reflex
will increase compared to baseline as a result of mental distraction. This hypothesis
is based on the belief that when a person is reading a book, the neurons in the brain
are sending descending messages to the arm muscles. The descending messages to
the arm muscle will reduce the input to inhibit patellar reflex, which will then
heighten the knee jerk causing an increase in the conduction velocity.
Lastly, it is hypothesized that the conduction velocity of the patellar reflex
will decrease compared to the baseline as a result of fatigue. This hypothesis is
based on the belief that when a person is tired, the muscles are fatigued and they
are might not contract as effectively. This might lead to the decrease of patellar
reflex because the reflex will appear to be reduced because of the fatigued muscle.
Procedures
Please refer to the Anatomy and Physiology Lab Manual, Lab 3, Activity.
Reflex Conduction Velocity (m/s)
Data
115
110
105
100
95
90
85
80
Baseline
Jendrassik's
Mental
Maneuver
Distraction
Conditions
Patellar Reflex
Discussion
In this experiment, the patellar reflex was used to study the conduction
velocity. The independent variable was conduction velocity; whereas the dependent
variables were Jendrassik’s maneuver, mental distraction, and fatigue.
First, we hypothesized that the conduction velocity of the patellar reflex will
increase compared to baseline as a result of simultaneous muscular activity
(Jendrassik’s maneuver). In this case, our hypothesis was supported, as we see an
increase in conduction velocity when compared to the baseline. One reason that our
hypothesis is supported might be because the participant was actually pulling the
hands enough to provide them with a source of distraction.
Second, we hypothesized that the conduction velocity of the patellar reflex
will increase compared to baseline as a result of mental distraction. In this case, our
hypothesis was not supported, as we see a decrease in conduction velocity when
compared to baseline. This might have resulted because the participant was not
actually reading the material that was provided to them, the book might have been
too boring for them to continue studying. The activity might not have distracted the
participant enough, which resulted in the decrease in conduction velocity.
Lastly, we hypothesized that the conduction velocity of the patellar reflex will
decrease compared to baseline as a result of fatigue. In this case, our hypothesis was
not supported, as we see an increase in conduction velocity when compared to
baseline. One reasonable explanation could be because when the participant was
doing sit ups, his muscle were not tired enough due to the fact that the person is a
great athlete.
Based on the results above, the conduction velocity informs us about the rate
at which the neurons are firing and getting excited at the spinal cord. As the
difficulty of task increase, the increase in gamma motor output makes the spindle
muscles more sensitive, increasing the knee reflex. The stretch reflex pathway is a
tool that guides the movement of our muscles and efferent and afferent pathways
are players that have an active role in controlling those movements.
The findings from this study should be read with several limitations in mind.
It is important to mention that the total sample size is only 1, which is very small for
a sample size. Also, it is the first time for the group to use the LabScribe application;
this was a first trial for us as a group. Lastly, the lab groups cell phone might not
have been completely turned off, which might have led to the discrepancy in data.
Conclusion
In this experiment, the results supported the hypothesis that conduction
velocity changes in response to the activities performed with the knee jerk. The data
did provide a sufficient interaction to show that Jendrassik’s maneuver increases
the conduction velocity when compared to baseline. Similarly, fatigue showed the
same increase in conduction velocity from baseline. However, the mental distraction
showed a negative interaction, where the activity led to a decrease in conduction
velocity. Based on the task performed, the receptors detected the stimulus when the
knee jerk was performed. The sensory neuron is a messenger that carries that
information towards the brain or spinal cord. The brain then processes that
information and connects the sensory neuron with a motor neuron via
interneurons. The motor neuron carries the message from the brain to the effector
and the muscle contracts.
In healthcare field, when doing a physical examination, doctors often starts
out by checking the patellar reflex. This type of reflex is necessary to keep your
balance and when doctors perform this task, they are checking if your nervous
system is functioning well (Dowshen, 2012). According to Marieb and Hoenhn
(2011), patients with injuries to ventral horn, chronic diabetes, and neurosyphillis
tend to have a missing stretch reflex, which explains the lag in response when the
knee jerk is performed.
Work Cited
Dowshen, S. (2010, September). kidshealth.org. Retrieved from
http://kidshealth.org/kid/talk/qa/reflexes.html
Marieb, E. N., & Hoehn, K. (2011). Human anatomy and physiology. (9th ed., pp. 513519). Boston: Pearson.
Nerve conduction velocity (ncv). (2011). Retrieved from
http://www.hopkinsmedicine.org/healthlibrary/test_procedures/neurological/nerve_condu
ction_velocity_ncv_92,P07657/