Triceps reflex
Encyclopedia
The triceps reflex, a deep tendon reflex, is a reflex as it elicits involuntary
Involuntary
Involuntary is the antonym of voluntary. An involuntary action is one that occurs without volition or will; see volition and will . Involuntary may also refer to:*Involuntary , a 2008 Swedish film by Ruben Östlund...

 contraction of the triceps brachii muscle
Triceps brachii muscle
The triceps brachii muscle is the large muscle on the back of the upper limb of many vertebrates. It is the muscle principally responsible for extension of the elbow joint .-Terminology:...

. It is initiated by the Cervical (of the neck region) spinal nerve
Spinal nerve
The term spinal nerve generally refers to a mixed spinal nerve, which carries motor, sensory, and autonomic signals between the spinal cord and the body...

 7
Cervical spinal nerve 7
The cervical spinal nerve 7 is a spinal nerve of the cervical segment..It originates from the spinal column from above the cervical vertebra 7 ....

 nerve root (the small segment of the nerve that emerges from the spinal cord). The reflex is tested as part of the neurological examination
Neurological examination
A neurological examination is the assessment of sensory neuron and motor responses, especially reflexes, to determine whether the nervous system is impaired...

 to assess the sensory
Sensory neuron
Sensory neurons are typically classified as the neurons responsible for converting external stimuli from the environment into internal stimuli. They are activated by sensory input , and send projections into the central nervous system that convey sensory information to the brain or spinal cord...

 and motor
Motor neuron
In vertebrates, the term motor neuron classically applies to neurons located in the central nervous system that project their axons outside the CNS and directly or indirectly control muscles...

 pathways within the C7 and C8 spinal nerves.

Testing

The test is performed by tapping the triceps tendon
Tendon
A tendon is a tough band of fibrous connective tissue that usually connects muscle to bone and is capable of withstanding tension. Tendons are similar to ligaments and fasciae as they are all made of collagen except that ligaments join one bone to another bone, and fasciae connect muscles to other...

A tendon is a strip or sheet of connective tissue
Connective tissue
"Connective tissue" is a fibrous tissue. It is one of the four traditional classes of tissues . Connective Tissue is found throughout the body.In fact the whole framework of the skeleton and the different specialized connective tissues from the crown of the head to the toes determine the form of...

 that transmits the force generated by the contraction of muscle to the bone by attaching with it. Thus, in simple words, a tendon attaches a muscle to a bone
with the sharp end of a reflex hammer
Reflex hammer
A reflex hammer is a medical instrument used by physicians to test deep tendon reflexes. Testing for reflexes is an important part of the neurological physical examination in order to detect abnormalities in the central or peripheral nervous system....

 while the forearm
Forearm
-See also:*Forearm flexors*Forearm muscles...

 is hanging loose at a right angle to the arm. A sudden contraction of the triceps muscle causes extension,A straightening at the elbow joint) of the forearm and indicates a normal reflex.

Reflex arc

The arc involves the stretch receptors in the triceps tendon, from where the information travels through the C7 nerve root to the spinal cord, and the motor signal for contraction returns through the radial nerve
Radial nerve
The radial nerve is a nerve in the human body that supplies the upper limb. It supplies the medial and lateral heads of the triceps brachii muscle of the arm, as well as all 12 muscles in the posterior osteofascial compartment of the forearm and the associated joints and overlying skin.It...

.A reflex arc is the path in the nervous system through which the sensory information (stimulation—sudden stretching of the triceps tendon in this case) travels to the spinal cord in form of an action potential
Action potential
In physiology, an action potential is a short-lasting event in which the electrical membrane potential of a cell rapidly rises and falls, following a consistent trajectory. Action potentials occur in several types of animal cells, called excitable cells, which include neurons, muscle cells, and...

 through a sensory neuron
Sensory neuron
Sensory neurons are typically classified as the neurons responsible for converting external stimuli from the environment into internal stimuli. They are activated by sensory input , and send projections into the central nervous system that convey sensory information to the brain or spinal cord...

, and comes in contact with a motor neuron
Motor neuron
In vertebrates, the term motor neuron classically applies to neurons located in the central nervous system that project their axons outside the CNS and directly or indirectly control muscles...

 at a synapse
Chemical synapse
Chemical synapses are specialized junctions through which neurons signal to each other and to non-neuronal cells such as those in muscles or glands. Chemical synapses allow neurons to form circuits within the central nervous system. They are crucial to the biological computations that underlie...

, which also carries an action potential back to the muscle of origin and results in its (triceps's) contraction. Note that the contact between the sensory and motor neurons does not require immediate involvement of the brain making it involuntary, though the sensation of stretch (as the hammer hits the skin and tendon beneath) and contraction of the muscle are both sent to the brain making the subject aware of the entire testing procedure.

Test indicators

  • Absence of a reflex (areflexia): If no reflex is elicited then it is essential to try again with reinforcement, with the patient clenching his or her teeth just as the reflex hammer strikes.
  • Hyper-reflexia (a response far larger than considered normal): Indicates a potential upper motor neurone lesion.

Absence of reflex

An absence of reflex can be an indicator of several medical conditions: Myopathy
Myopathy
In medicine, a myopathy is a muscular disease in which the muscle fibers do not function for any one of many reasons, resulting in muscular weakness. "Myopathy" simply means muscle disease...

, neuropathy, spondylosis
Spondylosis
Spondylosis is a term referring to degenerative osteoarthritis of the joints between the centra of the spinal vertebrae and/or neural foraminae. If this condition occurs in the zygapophysial joints, it can be considered facet syndrome...

, sensory nerve disease, neuritis, potential lower motor neurone lesion
Lesion
A lesion is any abnormality in the tissue of an organism , usually caused by disease or trauma. Lesion is derived from the Latin word laesio which means injury.- Types :...

, or poliomyelitis
Poliomyelitis
Poliomyelitis, often called polio or infantile paralysis, is an acute viral infectious disease spread from person to person, primarily via the fecal-oral route...

.

Other medical problems that may cause irregular reflexes include Hyperthyroidism
Hyperthyroidism
Hyperthyroidism is the term for overactive tissue within the thyroid gland causing an overproduction of thyroid hormones . Hyperthyroidism is thus a cause of thyrotoxicosis, the clinical condition of increased thyroid hormones in the blood. Hyperthyroidism and thyrotoxicosis are not synonymous...

.

External links

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