The tapping of the patella tendon from the quadricep muscles produces an automatic involuntary extension of the leg that is not generally under the control of your thoughts.
Here is how the patella reflex works. When you tap the quadricep muscle tendon (patella tendon) at the knee, nerve endings in the quadricep muscle send an impulse (message) via sensory nerves to the spinal cord. Note that sensory nerves receive information from the body and the outside world and send such messages to the spinal cord and/or brain. This sensory message enters the back (dorsal) portion of the spinal cord and is picked up by another nerve cell (neuron) called the interneuron. The interneuron communicates the messages to a third nerve (neuron) at the front (anterior) portion of the spinal cord, which is a motor neuron. Motor neurons connect to muscles, and when impulses are transmitted to such muscles from the motor neuron, there is muscle contraction. In the patella reflex situation, the motor neuron connects with the quadricep muscle, which causes an automatic contraction of the quadricep muscle, resulting in the movement of the leg.
| Image # 9 – Patella Reflex (“Tail” behavior) |
This movement occurs within a second after the patella is tapped by a neurological hammer and is a good measure of the speed at which nerve impulses move through the nervous system. This kind of behavior is simple, without thought, one track, and stereotypical, meaning you will get the same response depending on how hard the knee is hit. This reflex does not really perform a function, but it is part of a broader path in the nervous system, which allows us to move in a balanced and coordinated manner when integrated with higher “head” functions. The interneuron, i.e., the second order of neurons in the three neuronal response, is connected to the higher “head” center through a system of motor nerve cells called upper motor neurons. These neurons connect to higher centers in the cerebral cortex. The connecting track to the brain is referred to as the corticospinal tract. The fascinating way we gain control at the lower levels of the motor system of our limbs comes from some interneurons that excite or stimulate muscle contraction and others that inhibit and shut down motor activities. Input from the corticospinal tracks from higher centers that connect to stimulatory interneurons promotes increased muscle activities, and input from the corticospinal tract that inhibits interneurons inhibits or reduces muscle activity or contractions. When there is damage to the higher centers such as in a TBI or concussion or a stroke, messages from the higher centers are reduced or eliminated, and the local system in the spinal cord takes over.
The corticospinal and reticulospinal tracts, when stimulated, help dampen the patella reflex by eliminating some of the nerve impulses going through. If there is a disconnection between the upper motor neurons and the lower motor neurons, then the patella reflex is not dampened, and the reflex is exaggerated. This is the major influence that the higher centers “head” have on the lower “tail.” In this case, neurologists use the patella reflex to indicate injury at higher centers. So, in the case of a stroke or brain injury where the higher centers are affected, there is limited input passed through the corticospinal tracks. This results in the patella reflex working without inhibition and, thus, causing increased or exaggerated patellar reflex. Other than in patients who are anxious, increased reflexes can mean there is some malfunction in the higher centers, starting from where the corticospinal tract connects at the level in the spinal cord and extending up into the highest centers of the brain – the cerebral cortex.
Another practical example of tail behavior is the vaso-vagal response occurring in Mario’s case when his heart automatically became bradycardic due to increased ICP. This is a kind of stereotypical response that occurs involuntarily.
By contrast, the “head” symbolically, structurally, and physiologically represents the crown of our human existence. “Head behavior” involves the most sophisticated and complex behaviors that make us human and represents what is referred to as the higher cortical functions in neuroscience. These “head behavior” functions include reasoning skills, memory, attention, perception, decision making, and emotions among other sophisticated behaviors.
The BHET method is based on our understanding of the anatomic and physiologic structure of the central and peripheral nervous system and how this structure translates into functional activities and expressions. Notably, the central nervous system comprises the brain and spinal cord. The peripheral nervous system comprises all of the nerve connections that connect the body and the outside world to the central nervous system.
| Image # 10 – Central and peripheral nervous system |
As you go from the “tail to head,” it is evident that the organization and behavior of the nervous system becomes more functionally complex and involves a greater array of nerve cells as they relate to each other.
From Head to Tail is about a hierarchically organized messaging system at various levels with an “input” from the peripheral nervous system (sensory system) to the spinal cord and brain, “output” from the brain and spinal cord to the peripheral nervous system (motor and autonomic system), and “central processing core” that is the brain and spinal cord (central nervous system). As an analogy, the computer was designed based on how the human nervous system works. The peripheral nerves represent the keyboard and connecting wires (input). The brain and spinal cord represent the computer’s central processing unit (CPU) with varying levels of sophistication and organization. The motor output system represents the printer and monitor.
| Image # 11 – Input, process and output – computers and humans |
The BHET method is heavily evaluation based, and attempts are generally being made to first classify each concussion and/or TBI based on what level of hierarchical disruption has occurred in the structural anatomy, physiological functioning, psychosocial relationships, and neuropsychological and neurobehavioral functioning from the “head to tail.”
QUESTIONS RELATED TO the complexity of brain development, organization, and disruption following an injury have haunted me throughout my career. I began exploring these concepts using information from a biology class I took at Andrews University called “The Evolution of Behavior.” Dr. Stout, an animal behaviorist, helped us understand the development of the nervous system from lower forms that perform simple stereotypical functions to a more complex brain that allows us to perform elaborate behaviors that make us truly human, over the many years of evolution. The term used in science for this type of evolution is called phylogeny. Another class in embryology and genetics, under a different professor also provided me the basis to understand human growth and development, starting from the sperm and the egg uniting to develop into a sophisticated well-organized nervous system. This nervous system’s embryological development with the noted anatomical, structural, and physiologic functioning linked to behavioral development is the concept of ontogeny.
It was then that I understood that the human nervous system was hierarchically organized, having evolved over time to perform very complex and sophisticated functions. I was moved by this issue and applied the concepts of phylogeny and ontogeny to help shape the BHET Method.
Ironically,