Your instructor will show you how to take measurements for latent period and magnitude of the knee jerk in class. For each of the following exercises, you will examine two basic features of the reflex: maximum rotation and latent period.
Consult the following figure below to make your maximum rotation and latent period measurements. Figure 4: Making the measurements for Latent period. Measure the time in seconds it takes for the reflex to begin by starting where the trace levels off the trace moves up the y axis when the mallet is hit to the time when the trace goes down. Magnitude measured in degrees is measure as the dip in the trace as indicated on the graph.
Each group will do parts A-E. Record the data as you perform the experiments, then enter the data into the excel spreadsheet on the instructor's computer when you have collected all of your trials. The data will be pooled from all the lab sections and posted on e-mailed to you or posted on Blackboard.
Voluntary knee movement: Obtain data from three voluntary knee jerks from one subject. The subject should again look away but this time voluntarily jerk the knee after hearing the hammer tap on a soft surface.
The tester should minimize the effect of anticipation by not being predictable about when the hammer is tapped. Involuntary patellar with mental distraction: Prepare several addition problems consisting of ten three-digit numbers. One lab member should read these problems one at a time to the subject and the subject should try to solve the addition problems in their head with no paper or pencil mental math.
Obtain data from three knee jerks of this type from one subject. Involuntary patellar with muscle-straining: Obtain data from three knee-jerks while the subject grasps their hands in front of them and strains to pull them apart.
Involuntary patellar with iced quadriceps muscle: After completing A-D, unstrap the subject and ice the right quadriceps muscle for 20 minutes. Restrap towards the end of "icing" then retest the involuntary reflex. Winter, Sharon. National Association of Biology Teachers, www. Columbus Ohio Local Outreach team. Jensen, Murray. Human Reflex lab. It relies on interactions across complex networks of neurons distributed throughout the peripheral and central nervous systems.
Researchers can use imaging techniques, such as functional magnetic resonance imaging and electroencephalography , to see what areas of the nervous system are active during different thought processes, and how information flows through the nervous system.
Many scientists consider the best proxy measure of the speed or efficiency of thought processes to be reaction time — the time from the onset of a specific signal to the moment an action is initiated. Indeed, researchers interested in assessing how fast information travels through the nervous system have used reaction time since the mids.
This approach makes sense because thoughts are ultimately expressed through overt actions. Reaction time provides an index of how efficiently someone receives and interprets sensory information, decides what to do based on that information, and plans and initiates an action based on that decision.
The time it takes for all thoughts to occur is ultimately shaped by the characteristics of the neurons and the networks involved. Many things influence the speed at which information flows through the system, but three key factors are:.
Distance — The farther signals need to travel, the longer the reaction time is going to be. Reaction times for movements of the foot are longer than for movements of the hand, in large part because the signals traveling to and from the brain have a longer distance to cover.
Instead, ions travel through what are called gap junctions and transfer an electrical charge to the next neuron. These gap junctions may actually be better understood in other areas of the body, as they are not unique to neurons. There are other cells, like in the heart, that also have gap junctions that transmit electrical signals. On the other hand, at chemical synapses, the electrical signal within neurons, called an action potential, is translated into a chemical signal that can travel across the synapse to the next neuron in the circuit.
This is done through the release of chemicals called neurotransmitters, which are released in packets called vesicles upon arrival of an action potential at the synapse. When the neurotransmitter reaches the next neuron in the chain, the chemical signal is transformed back into an action potential that travels down that neuron to the next synapse, and so on. Memory may also involve the creation of new synapses. Slow reaction times may come with consequences. Reaction time is a measure of the quickness an organism responds to some sort of stimulus.
You also have "reflexes" too. Reflexes and reactions, while seeming similar, are quite different. Reflexes are involuntary, used to protect the body, and are faster than a reaction. Reflexes are usually a negative feedback loop and act to help return the body to its normal functioning stability, or homeostasis. The classic example of a reflex is one you have seen at your doctor's office: the patellar reflex.
This reflex is called a stretch reflex and is initiated by tapping the tendon below the patella, or kneecap. In their original papers Erb referred to the reflex as the "Patellarsehnenreflex" while Westphal denoted it as the "Unterschenkelphanomen". Thankfully, we now refer to it as the patellar reflex.
This reflex is also known as a "reflex arc". It is a negative feedback circuit that is comprised of three main components:. The knee reflex arc is a spinal reflex, and the circuit is drawn above. This picture shows how the sensory afferent neuron sends information through the dorsal root ganglion into the spinal cord; where the signal splits into two different paths. The first is the motor neuron efferent leading back to the quadriceps.
When your quad muscle's motor neuron receives the information it fires and causes your lower leg to spring forward up in the air. The second signal from the sensory neuron travels to an interneuron which sends a signal to the motor neuron efferent leading to the hamstring. This signal tells your hamstring to relax so there is no negative force acting on the quadriceps muscle when it contracts.
Both signals work together and all of this happens in the spinal cord without going to the brain.
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