- Components and driving paths
- Afferent and efferent pathway
- Physiology
- Exploration
- Clinical findings
- Absence
- References
The triceps reflex is an independent motor response of the will elicited by a mechanical stimulus at the level of the triceps tendon. It belongs to the group of so-called tendon reflexes, the reflexes that have their origin by stimulation of the neuromuscular spindle by stretching at the height of the fibers of the muscle belly.
The muscle and tendon only function as transmitters of tension; that is, the reflex depends on the nerve to be explored. Studying this reflex is very important in the routine neurological examination of any patient requiring a complete physical examination, as it provides information on the state of the conduction pathways of the nervous system.
The study of tendon reflexes is very useful in the differential diagnosis of syndromes such as upper and lower motor neuron.
Components and driving paths
- Receiver.
- Afferent pathways, corresponding to axons of the sensory neurons located in the spinal ganglia.
- Interneuron.
- Nervous center, located in the spinal cord, which in turn is composed of a sensory neuron, an interneuron and a motor neuron at the C7 level.
- Efferent pathways, made up of motor neuron axons.
The nervous communication pathways -which together form the reflex arc- is formed by a receptor, afferent pathway, central integration, efferent pathway and, finally, the effector organ
Afferent and efferent pathway
The afferent pathway in the tricipital reflex is represented by neurons that are located in the spinal ganglia of the posterior horn of the spinal cord.
For its part, the efferent pathway is made up of the efferent, motor fibers of the anterior horn of the spinal cord.
Physiology
The main characteristic of the triceps reflex is that it is a monosynaptic reflex, since it belongs to the group of ROTs (tendon reflexes), which implies that only one synapse is made between the afferent and efferent neurons.
The receptor that is activated in the triceps reflex is called the muscle spindle. When stretched or elongated, this spindle generates a nerve impulse that travels to the spinal cord in the spinal column through fibers called afferents.
Once in the spinal cord, these fibers synapse with an alpha motor neuron; by feedback, this motor neuron generates an excitatory signal that is transmitted to the muscle to perform the contraction.
The receptor in this type of reflex is within the muscle itself, which means that it is one of the few examples where the receptor and the organ that will carry out the involuntary movement are in the same place. This series of events together is called a reflex arc.
Exploration
In the case of exploration of this reflex, general considerations common to the examination of all tendon reflexes should be taken.
The patient must be in complete muscle relaxation; This relaxation is achieved through different ways, among which are:
- Use the Jendrassik maneuver, by which the patient is asked to contract a muscle group distant from the muscle group to be explored.
- Divert the patient's attention. You can talk to her or ask her to look away.
Once the patient is relaxed, the reflex exploration procedure is carried out as follows: with one hand the patient's forearm is grasped at the elbow and the forearm is dropped, seeking to generate a right angle.
The triceps tendon is percussed; as a result, extension of the forearm over the arm is achieved.
Clinical findings
The degree of reflex contraction should be the same in both limbs -that is, in the right upper limb and in the left upper limb-, since an asymmetry could suggest some alteration in the anatomical, neurological or homeostatic areas.
From the clinical examination of the triceps reflex, one of the following results could be obtained:
- A reflection of normal characteristics; that is, extension of the forearm over the arm.
- Features increased in mirroring; that is, hyperextension of the forearm over the arm (hyperreflexia).
- A reflection of diminished characteristics; that is, hypoextension of the forearm over the arm (hyporeflexia).
- Absence of the tricipital reflex.
In the clinical history, the results described above are represented as follows:
- 0: Areflexia.
- - +: Contraction without displacement.
- ++: Normal.
- +++: Hyperreflexia.
- ++++: Clonus (repeated muscle contractions and relaxations).
Absence
The decrease or total disappearance of this reflex usually reveals some type of arch interruption or a muscular defect; thus, the problem may be in the sensory afferent pathway, receptors, motor neuron, interneuron, effector apparatus, or efferent pathway.
Other processes through which hyporeflexia or areflexia can be generated are general anesthesia, spinal shock, deep coma, electrolyte disturbances and hypothyroidism, among others.
Exaggeration of tendon reflexes is considered evidence of upper motor neuron injury due to alterations in supraspinal control of anterior horn cells, which become unduly excitable.
In this case, the motor neurons are stimulated by fibers such as the reticulospinal and vestibulospinal fibers.
Other causes of hyperreflexia include anxiety, hyperthyroidism, electrolyte disturbances, tetany, tetanus, among others.
References
- Impaired coordination and reflexes. (2017). Recovered from: semiologíaclínica.com
- Osteotendinous reflexes. Department of Physiological Sciences (2000). Recovered from: med.javeriana.edu.co
- González, Nancy. (2007). The Clinical History and Semiology of Medical Propedeutics. University of Zulia, Maracaibo, Venezuela.
- Snell RS Clinical Neuroanatomy. 4th edition. Editorial Médica Panamericana. Madrid (1998)
- Kandell ER, Schwartz JH and Jessel TM Principles of Neuroscience. McGraw-Hill / Interamericana. Madrid (2001)